Altering The Timestamp In Perseus IQ .WAV Files

Three or four years ago I got into SDR receivers. I don't own a Perseus, but I do own and use an Airspy HF+ Discovery, an SDRPlay RSP1a, and an SDRPlay RSPdx.

Perseus IQ .WAV files can be found on the internet or compatible ones can be created by several SDR receiver programs. One of those programs is the HDSDR program. Even if you don't own a Perseus receiver (the hardware), you can use the free Perseus demo (version 5) to play the .WAV files.

Perseus V5 demo from MicroTelecom

These IQ files are fairly typical .WAV riff files. Within the file header is a special field which specifies the date/time of the recording. The Perseus receiver software picks this up and uses it in its display of the recording.

Occasionally someone has the need to change the time of the recording, possibly because their computer clock was off when the recording was made. This can be easily done if you don't mind some byte twiddling in a hex editor.

Altering The Timestamp (2 ways)

Both methods require a manual procedure, one easy and one a little more detailed. I've tested both and they work.

The starting date/time timestamp field is contained within the Perseus .WAV file header. It's found at hexadecimal location x34 and is 4 bytes long. It is the Epoch time for the start date/time. Epoch time is the number of seconds since January 1, 1970 at midnight AM: 00:00:00 GMT. No ending timestamp seems to be used, rather they use the actual length of the audio file to calculate the end time.

We must change this 4 byte starting timestamp field at location x34. That would be bytes 34, 35, 36, and 37.

There are two methods to change this timestamp. Follow along, looking at the screenshot below.

Method 1, the easier method. You need:

1. The freeware hex editor program HxD. HxD is a nice freeware one for Windows that I use.

https://mh-nexus.de/en/hxd/

Start your hex editor HxD and open the Perseus .WAV file. With your mouse, select the 4 bytes starting at hex location x34 (34,35,36,37). In the lower right panel look for the item named "time_t (32 bit)". You will see that HxD has converted the 4 byte value at hex x34 and displayed the date/time conversion in plain text right there.

Each of the items in the right panel can be modified. Here's how to modify the date/time item:

Only after selecting the 4 bytes starting at hex location x34, make your changes to the date/time in the "time_t (32 bit)" item, then press ENTER. HxD will calculate the 32 bit Epoch time value and replace the one at location x34.

Save the file. HxD will also save a backup of the old file for backup purposes.

You are done except for renaming the file, see below after Method 2.

Method 2, the harder geek method. You need:

1. The freeware hex editor program HxD. HxD is a nice freeware one for Windows that I use.

https://mh-nexus.de/en/hxd/

2. Access to an Epoch timestamp converter (available online).

https://www.epochconverter.com

3. Access to a decimal to hexadecimal converter or a programmer's decimal-hexadecimal calculator.

https://www.rapidtables.com/convert/number/decimal-to-hex.html

Start your hex editor HxD and open the Perseus .WAV file. With your mouse, select the 4 bytes starting at hex location x34 (34,35,36,37). In the lower right panel look for the item named "time_t (32 bit)". You will see that HxD has converted the 4 byte value at hex x34 and displayed the date/time conversion in plain text right there.

Write down your new start date and time. Go to the Epoch timestamp converter site (or another if you prefer) and enter the date/time you have chosen. Convert that date/time to the new Epoch time. You will get a big number. For example, for 11-21-2024 0450 GMT (NOV 21, 2024 @ 04:50:00 GMT), the Epoch time is 1732164600.

Again, one Epoch time converter site is: https://www.epochconverter.com

Now, we must convert this number to a 4 byte (8 digit) hexadecimal value.

Go to the hexadecimal converter site and in the decimal field type the Epoch time number. In our example it was "1732164600" for 11-21-2024 0450 GMT.

Using our example, you will get the hexadecimal value: 673EBBF8

The Perseus .WAV file requires this value to be in what programmers call "little-endian format", that is, low value to high value. The value above is in "big-endian format", or high to low value.

We simply need to mirror the hexadecimal number we have. Mirror 673EBBF8, getting F8BB3E67.

We now need to plug in our example number F8BB3E67 into the .WAV file at hex location x34.

Back in your hex editor HxD, set your cursor at hex location x34 (left click just to the left of the location x34 byte itself) and type the new value, F8BB3E67, into the main hex display replacing the 4 bytes starting at hex location x34.

Save the file. HxD will also save a backup of the old file for backup purposes.

Renaming The File

It's not necessary for the Perseus SDR receiver software, but to maintain clarity, rename the .WAV file to the new start time. And since you know the length of the file in minutes, also add the new end time too.

If you have multiple .WAV files, i.e., when a time period is longer than 15 minutes, be sure to change the start time in each file (_001, _002, _003, etc).

That's it. If I get some time at some point, I'll code up a little program to do all this automatically.

Modding Experiments With The YouLoop

The Outstanding Passive Loop Antenna by Airspy

Airspy, the maker of the HF+ Discovery SDR receiver, also makes the YouLoop, the passive, so-called "2-turn" mobius loop sold for use especially with Airspy's SDR receiver lineup.

I bought a YouLoop three or so years ago when I bought my Discovery, tried it for a short time, and put it away, not fully realizing its potential. Sometimes, as in real life, there's more just under the surface than what meets the eye at first. If you don't give a second look, you might miss it. For starters, you have to get your mindset pointed in the right direction, that is, towards ultra-low noise floors and signal-to-noise ratio improvement. Don't stay focused on S-meter readings and brute signal strength. The YouLoop is perfectly matched to present an ultra-low noise floor with maximized signal pickup, and particularly for the mediumwave band.

Factory stock YouLoop

From the factory, the YouLoop has a circumference of 2 meters, comprised of two, one meter sections joined at both the top and bottom, presenting a diameter of 0.64 meters, or 25.2 inches. The top ends are joined through a simple crossover network, interchanging the coax shield with the inner conductor. At the bottom we have a tiny voltage balun to match the loop's low impedance and provide additional noise suppression and isolation. A low noise, highly sensitive receiver is required to get the best out of the YouLoop, to wit, the HF+ Discovery, which has a noise floor on the order of -142 dBm and a minimum discernable signal (MDS) sensitivity of -140 dBm (0.02 uV / 50 ohms at 15 MHz). That is an extremely faint signal. The YouLoop will work minimally with the SDRPlay RSP series of receivers, but they lack the low noise floor and sensitivity to get full value from it. A preamp might help there, mounted right at the loop itself.

In the mediumwave band, the stock YouLoop's sensitivity falls off gradually below 1000 KHz. It was evident that a slightly larger loop might help with this. In attempts to correct this I've done experiments by adding to the length of the YouLoop, first adding two short 1/2 meter lengths of RG-402 (one per side), then two 1 meter lengths in a similar fashion. The 1/2 meter lengths increase the total circumference to 3 meters, the 1 meter lengths increase it to 4 meters. In order to add to the existing YouLoop coax, you will need to purchase two coax pigtails of the same type (RG-402) and two female SMA unions, both readily available from Amazon.

SMA unions and RG-402 pigtails

Let's Do Some Testing

Testing was performed with both extension modifications, comparing each to the stock 2 meter loop while noting the signal strength and the signal-to-noise ratio differences. The standard 6 ft. coax feeder was used between the SDR and the YouLoop and the SDR was connected to the computer through a 15 ft, high quality shielded USB cable to get it as far away from digital hash as possible.

Two distant stations were used as reference and checked during mid-daytime hours, CHLO-530 KHz, Brampton, Ontario (1 KW) at 195 km distance and WWKB-1520 KHz, Buffalo, NY (50 KW) at 111 km distance. Both put in readable but not overly strong signals at these distances.

Results were very interesting, and somewhat surprising, indeed. See the table just below. SNR values are measured to include the carrier + the sidebands.

Freq     Stock 2-meter YouLoop         3-meter YouLoop                4-meter YouLoop   

-----------------------------------------------------------------------------------------------------------------------

 530     -84dB (snr=30, nf=-114)    -76dB (snr=30, nf=-106)     -68dB (snr=31, nf=-99) 

1520    -85dB (snr=37, nf=-122)    -85dB (snr=38, nf=-123)     -83dB (snr=39, nf=-122) 

        *signal strength values in dBFS (dB Full Scale)

        *snr = signal-to-noise ratio, in dB

        *nf = background noise floor, in dBFS

Signal strengths at 530 KHz improved by about 8 dB when the loop circumference was extended from 2 to 3 meters. A 16 dB improvement (530 KHz again) was seen when the loop was extended to 4 meters. To my surprise, signal strengths at the high end of the band (1520 KHz) remained essentially the same for all three loops, rising only about 3 dB (half an S-unit) with the 4 meter loop. The 2 and 3 meter loops produced identical signal strengths at 1520 KHz.

Perhaps more surprising, the SNR, or signal-to-noise ratio of both stations did not vary more than 1-3 dB across all three loop lengths at each frequency. At 530 KHz, all three loops realized an SNR of 30-31 dB. At 1520 KHz, the SNR hovered between 37-39 dB. The relatively unchanging SNR is significant and will allow us to choose the best length loop for our receiving purposes.

The last phase of the testing was null depth. Null depth did not change across all three loops. Differences were undetectable from the original product. I am able to get 23-26 dB null differential across the MW band on semi-local, low angle (60 miles distant) groundwave signals.

So which loop would be the best choice for mediumwave?

The 4 meter loop had only a small gain change over the original 2 meter version at the high end of the band, some 3 dB, but realized about 16 dB gain at the low end. The 4 meter loop seems the logical choice. However, our noise floor at 530 KHz rises from -114 dBm (original YouLoop) to -99 dBm, an increase of 15 dB too! The new -99 dBm noise floor is the equivalent of S-5 on the S-meter. The original YouLoop's noise floor at -114 dBm is about S-2 and much quieter, and with the same SNR and same copyability.

3 meter YouLoop with added pigtails

The 3 meter loop had virtually no gain change over the original 2 meter version at the high end of the band but showed about 8 dB gain at the low end. This time our noise floor at 530 KHz rises from -114 dBm (original YouLoop) to -106 dBm, an increase of 8 dB too! The new -106 dBm noise floor is the equivalent of S-3.5. The original YouLoop, still at -114 dBm (S-2) and still quieter, has the same SNR and same copyability.

The 3 meter loop, the one with the two 1/2 meter extensions, may be the best compromise here. We get signal gain, as it raises signal levels at the low end of the band by about 8 dB. Our noise floor is kept in check at the low end as well, rising only to -106 dB, near a one microvolt signal. The larger 4 meter loop sets the noise floor too high at -99 dB, possibly masking very weak signals at the microvolt level (-107 dBm).

The YouLoop at 3 meters circumference starts to become a little unwieldy indoors, but can be arranged in a vertical oval so that it can be rotated a little easier and not hit other objects in a room. Arrange it in a 24 inch wide by 48 inch tall configuration. Little difference was seen in its nulling ability or signal degradation when configured in this shape.

Conclusions

Extending our original YouLoop to 3 and 4 meters increased our signal levels, but the background noise levels increased by the same amount. Kicking in the preamp on SDR# would accomplish the same thing, amplifying the signal and noise the same amount. The HF+ Discovery has a 15 dB preamp.

The HF+ Discovery's published sensitivity is -110 dBm for 6 dB signal-to-noise ratio. That is a signal some 6 dB, or one "S" unit above the noise. You're going to have to do a bit better than that, however, in that you need a better SNR than 6 dB to extract meaningful audio out of a signal. 9-10 dB might give results, 12-15 dB even better. The signal must be modulated adequately too - low modulation levels will require a higher SNR to make sense of. We can hear a 1 microvolt signal (-107 dBm) if our background noise is enough below that, our bandwidth just right, and our signal is modulated properly.

You need to get the signal strengths up there, closing in on the -107 dBm level to copy audio from signals. In that signal range, it would be best to have a base noise level of not much more than about -115 dBm actual measured noise level.

Note again, we also have the preamp at our disposal. A low noise preamp can make up the difference we need in signal strength. Remember, though, generally the background noise will be amplified equally with the signal. Not to worry if it brings our signal up to a listenable level. Example: Rising out of a -120 dBm noise floor we have a -110 dBm signal we are struggling to get copyable audio out of. Kick in the preamp and we raise that -110 dBm signal to -95 dBm, even though our noise floor is also raised to -105 dBm. The signal is now copyable.

Bonus Test

While I was at it, I put together a tiny 1 meter circumference loop using the two 1/2 meter pigtails. It is the size of a pie plate. One would think this would be so small a loop as to be totally ineffective. Not so.

Here are the test results for that YouLoop configuration as compared to the factory YouLoop:

Freq     Stock 2-meter YouLoop     tiny 1-meter YouLoop !!

------------------------------------------------------------------------------------

 530     -84dB (snr=30, nf=-114)    -97dB (snr=27, nf=-124)

1520    -85dB (snr=37, nf=-122)    -89dB (snr=35, nf=-124)

Signals were lower but adequate, and signal-to-noise levels were in the same ballpark of the other loops. Surprising, even a tiny YouLoop is effective!

Some Low Noise And Signal Improvement Tips

1. Position the YouLoop as far away from your computer and monitor as possible. Monitors in particular are terrible electrical hash generators.

2. Position the SDR itself as far away as possible from your computer for the same reasons.

3. To keep the SDR as far away as possible from your computer, you will need a long USB cable. The USB 2.0 standard allows for cable lengths of up to about 15 ft. You MUST use a good quality, properly shielded USB cable. Stay away from the latest rage, the cotton-covered USB cable. The ones I've tried have inadequate shielding and let all kinds of trash in. I've had great luck with the Monoprice line of cables, available on Amazon. If you attempt to run farther than 15 ft., be aware that you may incur data transmission loss. Your SDR will suddenly drop out of "Play" and into "stop" mode. It may not even start. Trust me, I've tried it. They do make USB amplifiers. I haven't tried them or know if they'd even work.

4. The YouLoop works best when the connecting coax to your SDR is the shortest length possible. Operated passively (without a preamp), you will not get good results or maybe even any results by feeding it with 50 ft. of coax and placing it out in the yard. Try to keep the coax feed under 12 ft. Three to six ft. of coax is optimum. SDRs, like the HF+ Discovery, can also be directly connected to the YouLoop feed point for outstanding results.

5. Used indoors, place the YouLoop next to a window for maximum signal pickup. This really does make a difference.

6. Don't be sloppy with the circle or oval you form. Make a wooden form in the shape of a cross if you like, and fasten the loop to it, ensuring the coax lies in a flat plane. This will maximize the loop's balance and nulling abilities on mediumwave. A child's plastic Hula Hoop also makes a wonderful circular form and can be used in pairs for bigger loop sizes.

RDMW 2024 Mediumwave Pattern Reference

North American Broadcast Mapping Tool & Database

We are proud to announce the launch of the latest edition RDMW-2024 Medium Wave Pattern Reference.

The Radio Data Medium Wave (RDMW) mapping reference is the definitive and most up to date tool for visualizing the broadcasting coverage of radio stations in North America.

Latest features:

• The latest callsign and technical data for all US and Canadian MW stations
• Late summer database cutoff date of August 7, 2024
• Seasonal ionospheric variations included in calculations, targeting October 20, 2024
• Smoothed sunspot predictions included, targeting October 20, 2024
• Current Mexico and selected Bahamas, Bermuda and Caribbean map pins
• Coverage of 490kHz & 518kHz Navtex stations
• Updated skywave formulas producing more accurate nighttime maps
• Real-time night/day terminator (greyline)
• “Click+Save” setting of your receiver location
• Easy tuning control on control bar
• Easy daypart selector on control bar
• Ray tracing control available on a per station basis
• Distance tooltips to all stations
• In-screen “Help” button

Included is a complete set of GoogleMap-based, HTML-driven maps which show the most current pattern plots of all licensed US and Canadian mediumwave broadcast stations from 530 - 1700 KHz. Due to unavailability of Mexican technical data, Mexican stations are represented by pins only this year. Lastly, also included are a sample of Caribbean stations, and the coastal marine NAVTEX 490 Khz and 518 KHz stations. The set includes all frequencies for the indicated services: Unlimited, Daytime, Nighttime, and Critical Hours. Individual maps are grouped by channel frequency x10 kHz: 540, 550, 560, .. 1700 KHz, etc. Data for the plots in this offering is based on the current FCC and Industry Canada databases available at the time of its creation (August 7, 2024). In calculating signal strengths, seasonal ionospheric variations are accounted for as well as smoothed sunspot predictions, targeting October 20, 2024.

Bonus: When you get your copy of RDMW24 you will also receive a copy of William Scott’s interactive greyline mapping tool which overlays on Google Maps. Enjoy!

Click image for the bigger picture.

Daytime pattern example for WAQI-710

Ordering (follow the instructions on this page) https://mwcircle.org/radio-data-mw-rdmw-2024/

Europe's premier medium wave DX club, The Medium Wave Circle will be hosting the download. The Medium Wave Circle is an international club for radio enthusiasts. It brings together people all over the world with a similar interest in medium wave radio (MW, AM or BCB) and related topics.

A small fee will be charged to cover bandwidth costs, less than a price of a coffee. Paid membership in the club is not required. Payment is through a PayPal gateway and is safe and secure. You do not need a PayPal account to use this facility.

Click the link just below and get your copy today.

RDMW 2024 Medium Wave Pattern Reference – Medium Wave Circle (mwcircle.org)

https://mwcircle.org/radio-data-mw-rdmw-2024/

Consider supporting The Medium Wave Circle by joining. Its membership fee is a modest amount for a great return. You will also get access to the group's monthly newsletter, The Medium Wave News, published since 1954, and over 500 past copies of MWN available exclusively to members. This is a 70-90 page newsletter which comes out every month. You will also get access to the Circle archives and pre-publication discounts on the essential reference book the World Radio TV Handbook. Last but not least, you will have access to a great forum of friendly and helpful people on groups.io.

RDMW-24 LAUNCH DATE: 6th SEPTEMBER, 12:00 UTC

User help & FAQ: https://mwcircle.org/RDMW-24-user-guide/

Why MW radio patterns matter to DXers: https://mwcircle.org/north-american-mw-coverage-maps/

We hope you will enjoy this latest version of the Radio Data Medium Wave Pattern Reference. A few hundred hours have been spent this year enhancing the pattern generating program and curating the data. Best of DX!

Checking Signal-to-Noise Ratio The Correct Way

Many of you may be familiar with the HF+ Discovery, Airspy's excellent, highly sensitive, high dynamic range, software-defined radio. I acquired one about three years ago to compare with my SDRPlay RSP1a. There is no competition there, the Discovery wins hands down in virtually all categories.

SDR Sharp, known as SDR#, is Airspy's SDR software made for their product line of receivers, including the HF+ Discovery. It is an outstanding piece of tech and includes many frills like the innovative Co-Channel Canceller which can effectively cancel or null one signal amongst several others on the same channel. I use SDR# exclusively here for reception of mediumwave and shortwave.

Herein we will describe a tip on how to accurately check signal-to-noise ratio using Airspy's SDR# receiving program. More Airspy SDR# receiving tips may appear in this blog, so check back often. I have several of them in mind.

In all the talk about signal strength and signal-to-noise ratio (SNR) lately, the community is finally coming around to realizing that SNR is what makes the difference between copying a station or not. Surprisingly signal strength, usually measured as the strength of the received carrier, may have little to do with it.

Noise floors on today's receivers are high, though there are ways to mitigate this using low-noise antennas and other sundry items in our toolkit. The goal is to set up an antenna and feed system environment with a low noise floor and capture enough signal to rise above that. Don't focus on S-meter readings and brute signal strength. The oft-held directive usually heard is, "Allow the antenna to set the noise floor". Translation: We want enough antenna to capture the signal, but not too much antenna to raise the background noise floor to unacceptable levels.

Signal-to-Noise Measurements

So first, how do we measure SNR? And second, how much signal-to-noise difference do we need? We are not talking about tedious lab measurements here, but simply, "How far above the noise is this signal I'm receiving?". Casual measuring of signal-to-noise ratio while receiving on an SDR is often not done correctly, and sometimes SDR software itself does not report it correctly. It's a value that's interesting to know, and tells us a lot about the signal, our background noise level, and the recoverability of the audio we might be hearing.

To get a sensible reading we must set our bandwidth properly and position it correctly in relation to the signal's carrier. The SNR reported will be the signal power contained within the currently set bandpass compared to the average noise floor also within that bandpass. The measurement problem arises when the station's carrier is contained within the filter bandpass. As we will soon see, the carrier does not convey intelligible information, but its presence may add as much as 20 dB or more to our SNR reading!

So therein lies the mistake: Don't center the bandpass on the carrier! In fact, keep the carrier outside of the bandpass altogether.

dBm Talk, And How We Measure Signal Strength

dBm is the common scale used to quantify received signal power. The dB part, or the decibel, is a logarithmic ratio of one value to another. The 'm' part means relative to a milliwatt, or decibels below (can also be above) one milliwatt expended power into 50 ohms. Let's be clear here about dBm and signal measuring. Most SDR receiving software, and SDR# is one of them, does not have calibrated spectrum scales in dBm. The scale shown is in dBFS, or dB relative to Full Scale. Full Scale is where the SDR's analog-to-digital converter overloads. The meat of our testing here will refer to relative values in dB when comparing loops to each other. That is the important thing to note in the discussion which follows.

Let's talk about the makeup of an AM modulated signal, that which we usually receive on our SDR.

The AM Modulated Carrier

The total AM modulated signal consists of the lower sideband (LSB), the carrier, and the upper sideband (USB). They occupy bandwidth on the RF spectrum. Any time information is impressed upon a carrier it occupies bandwidth. The carrier itself is very narrow, and may only occupy 100 cycles (Hz), maybe even less, depending on how pure it is. All three are easily seen on an SDR spectrum display if we zoom in on the signal a little. Find a signal on your SDR and expand your bandwidth out to about +/-5 KHz either side of the carrier peak and you will see the sidebands fluttering up and down. The audio intelligibility is contained in the sidebands, not the carrier, and can be extracted in total from either sideband. Also note the lower and upper sidebands are mirror images of each other.

AM modulation showing sidebands

If the carrier is fully modulated, called "100% modulation", the carrier (the spike in the middle) will contain 50% of the station's power, and each sideband will contain 25% of the power. If there is no audio signal modulating the carrier, then there will be no power in the sidebands.

To properly measure the signal-to-noise ratio of the signal we're trying to hear, we need to measure how far above the noise the entirety of one of the sidebands is. Thus, we must isolate one of the sidebands in the bandpass.

Here's how, using SDR#:

1. Be sure to use "snap to center" tuning, that is, when you click on the spectrum, the tuning point is always centered in the spectrum window.

2. It's always good to be in DSB (double sideband) tuning mode.

3. Take a look at the zoomed in signal and note how wide the modulation is from the carrier peak to the general edge of the audio variations on either side.

4. With your mouse, grab one of the edges of the bandpass and drag it to reduce the total bandwidth to this edge. It may approach 10 KHz, or +/-5 KHz.

5. Note the bandpass width and roughly divide it in half. Example: If 10 KHz, use the mouse to narrow it further to 5 KHz. We want the width of one of the sidebands. Important! Stay away from encroaching splatter from adjacent channels.

6. Retune the receiver, offsetting the main tuning either positively (for an upper sideband check), or negatively (for a lower sideband check), so that the bandpass contains only the sideband. Important! Make sure the carrier peak is just outside the bandwidth stripe. Try to keep a margin of at least 100 cycles (Hz). It's imperative to not include the carrier in the SNR test. It conveys no intelligible information and greatly inflates the SNR reading to a meaningless value for our purposes.

7. Last, hover your mouse within the bandwidth stripe on the spectrum display. Let the SNR reading settle in for a few seconds. You will see several values. The SNR value will be your signal-to-noise value for the set bandpass width. The Floor value will be the noise floor.

Let's try some examples.

In the example, we see WPIE-1160 in Trumansburg, NY, a 5 KW station at 94 km distance. Our real signal-to-noise ratio is 17.1 dB with a noise floor of -116.6 dBFS. We have 17.1 dB of signal poking its head above the noise. That's plenty, but not overly strong. Our original screenshot of us hovering over WPIE's carrier with the bandpass centered would have us believing our SNR was 44.1 dB. That would be considered an exceptionally strong SNR. But it includes the power in the carrier. Remember, the carrier itself carries no audio information.

Click image for larger version.

WPIE-1160

One more example, WSKO-1260 in Syracuse, NY a 5 KW station at 121 km distance. WSKO is extremely weak, and marginally copyable just out of the noise.  Our real signal-to-noise ratio is only 8.2 dB with an extremely low noise floor of -126.4 dBFS. That is minimal and about the weakest signal which we are able to extract copyable audio. Our original screenshot of us hovering over WSKO's carrier with the bandpass centered would have us believing our SNR was 29.6 dB, under normal circumstances a very comfortable listening level.

Click image for larger version.

WSKO-1260

You will find that signal-to-noise ratios of 9-10 dB to be about minimum for extracting audio intelligibility from a signal. 15 dB becomes comfortable, 25 dB armchair copy.

Remember, centering our carrier in the bandpass is our mistake in measuring SNR. A carrier with no audio modulation or one which is weakly modulated may show an SNR of 40 dB. It's a meaningless value unless you wish to know the SNR of the carrier itself to the noise.

Try this method of checking signal-to-noise ratio. It will give a much more accurate representation of the receiving condition.

Updated Portable Greyline Map v1.9.1 2024

The Portable Greyline Map has been updated to version 1.9.1 2024.

Look for the download at the upper right of this page.

Knowing where there is daylight and darkness over the earth at any given time is somewhat of a necessity when DXing shortwave or mediumwave. There are online maps, sure. But what if you had your own personal daylight/darkness map you could save to your computer and click on any time you wish?

The Daylight/Darkness Greyline Reference Map is produced by my Radio Data MW program.

Included is a GoogleMap-based, HTML-driven map which shows the current daylight/darkness state over the earth. Being a Google-based map, it is zoomable and scrollable. You may choose map view or satellite view. If desired, a home location may set by scrolling the map and clicking "<<Set Home". This will allow you to return to the same reference point as long as the current map page remains open. Depending on your browser, latitude and longitude may be saved across map restarts.

Draw tracks, check distances and bearings to points, all displayed in the marker tooltip

You must have an internet connection to view the map.

The file download is at the upper right of this page. It's a small 19 KB. For more details on usage, be sure to read the greyline_readme.txt file contained in the download.

Portable Greyline Map v1.9.1 2024

Eliminating Noise With The 1:1 Voltage Balun

This little gadget might save your DXing career, the 1:1 isolation voltage balun. Follow along as we talk about bothersome electrical noise, weak signals, and how we might use this balun to dramatically lessen your noise problem.

The 1:1 Isolation Voltage Balun

I've been fighting electrical and digitally generated noise here for a few years now. It's been a tough go. New battles rise up often. Most recently, the next door neighbor bought a new appliance which is throwing even more hash across the AM broadcast and shortwave broadcast bands. What to do? Give up radio? I entertained that idea for awhile.

Over these years, I've tried it all - impedance matching, ferrite sleeves, choke baluns, taping up coils of coax, strategic-positioning of antennas, probably more. Moderate success in noise elimination was sometimes gained but total success has eluded me. 

Noise levels here, even with on-ground antennas, can run as high as S9 or more on a traditional signal strength meter. Welcome to the modern era, dear radio DXer. S9 is your new "atmospheric" noise floor in a manner of speaking. If your desired signal isn't a little or a lot above that level (we'll call that the signal-to-noise ratio, SNR), you're not going to copy anything intelligible from it. If below S9, forget it. You will hear nothing because the signal is buried in the noise.

Most modern receivers, and that includes SDRs, will produce meaningful, copyable intelligence from a 1 microvolt signal if the noise floor is low enough. A 1 microvolt signal will show S3 on our strength meter. That's pretty low, but common when dialing across the bands. In order to hear that signal our noise floor must be lower than that.

Let's calculate this out. The 1 microvolt signal coming into our receiver is -107 dBm on the power scale (-107 dB less than 1 milliwatt into 50 ohms). Let me illustrate how infinitesimal a signal that is. The decibel or dB scale is a logarithmic scale. Every increase (or decrease) of 10 dB multiplies (or divides) our signal's power by a factor of x10. In ratio form, our 1 microvolt signal at S3 is only 0.000398 the voltage strength of our S9 signal we talked about earlier.

Depending on the signal and the receiver, many receivers can produce intelligence from a signal if it's at least 10 dB stronger than the background noise. Thusly, to receive our 1 microvolt signal our noise floor must be at least -10 dB below, or not more than -117 dBm. With the proper receiver, hardware, antenna, and some luck, we might be able to accomplish this.

One of the tricks of lessening noise pickup is to get your antenna as far as you can from any noise source. Whether on-ground or in the air, put it out in the far corner of the yard as far away as possible. I've found results usually start to improve at about the 100 ft. distance. In the extreme out on the farm, I've run the coax feeder out to on-ground wire antennas which were 200 ft. away. Great results in noise-abatement can be had at that distance. Don't worry about long runs of coax. In the bands we are concerned with, attenuation is still borderline microscopic with RG-6 common cable coax. RG-6 is available and cheap, at 75 ohms, which makes nary a difference when receiving at MW and SW frequencies.

Seriously consider the on-ground antenna, that is, an antenna which lies on the ground. Yes, it goes against common sense, doesn't it. Old hams and SWLers pre-1980s are of a mindset to hoist as much wire into the air, as high as possible. Today, often what you get is S9++ noise on your receiver. I've experimented with many on-ground antenna types, among them the LoG (loop-on-ground), the DoG (dipole-on-ground), and what I'll call the VDoG (vee-shaped dipole-on-ground). After a lot of experimentation, I became a convert to the on-ground antenna school of thought. You must start thinking in SNR (signal-to-noise ratio), not brute S-meter readings.

My current antenna is what I call a VDoG, the vee-shaped dipole-on-ground. It's positioned as far out in the yard as I'm able to get it. It's fed with 80 ft. of RG-6 coax up to a second-floor window. The antenna itself is two sections of 22 ft. #18 stranded insulated wire fed at the middle, arranged to form an angle of about 80 degrees with the open end facing south. It shows a little gain towards the open end, about unity gain on the sides, and a bit of a null at the back, or north. From here in western New York, it's good for mediumwave DXing, southerly along the eastern seaboard all the way to Cuba.

Even with this low-noise antenna, in my eco-system this antenna hears a lot of noise due to all the electrical buzz flying around, amounting to about a steady S9+ across the AM broadcast band. The noise is essentially electrical hash coming from mine and the two adjacent houses, the power lines which transit across the back edge of the yard, and the ones feeding the properties.

The VDoG, the LoG, and the DoG are balanced antennas. If you want to lower your noise problem, stick with a balanced antenna. Avoid end-fed wires, even if layed on the ground.

Common noise-abatement thinking would be to place a choke balun at the antenna feed point and then perhaps clip a few ferrite snap cores to the coax end coming through the window, just before it connects to the receiver. I installed an MFJ-911H 4:1 current balun I had at the feed point and snapped some cores on at a strategic point. It produced little improvement, helping a little more at the higher end of the MW band than the lower.

The 1:1 Voltage Balun

A single item I accidentally stumbled upon about a year ago was what killed the noise dead in its tracks. That was the 1:1 voltage balun, which will isolate the entire feed system, including the coax shield, from the receiver. These are sometimes called galvanic baluns.

Of course, this type of balun can be home-constructed, and in the past, I've wound these myself on ferrite cores and used them with varying success. On larger cores they become an unwieldy mess, and the connecting wires are a noise magnet. Size matters. The extra exposure of a larger object to RF hash matters. Searching eBay one day I found compact, miniature versions of these from China already constructed on a very small circuit board, complete with SMA connector on each end. The entire board is only about an inch long. They are 1:1 ratio, 50 ohm impedance in/out. More importantly, they have no physical connection between input and output, and no grounding. The board uses a Chinese clone of the Mini Circuits 1:1 balun and costs about $8 apiece with a little shipping added to that. I ordered one. It worked so well I ordered two more.

The 1:1 Balun in use with the HF+ Discovery

Positioned correctly in the coax feed to the receiver, the resulting reduction in noise was miraculous. Positioning is important. Inserted right at the receiver input (SDR here) using a double-ended male union produced the best results. Looking at the schematic diagram this little balun should be bi-directional, meaning either connector should be able to be used for input or output. It didn't seem the case. Connecting it one way resulted in a little better noise reduction than when reversed.

Here are graphics of the results, the before balun and after. Graphic shots were taken with an Airspy HF+ Discovery tuned to 860 KHz at 4 AM local time, lots of skywave arriving, showing the MW band span from 500 KHz to 1000 KHz. The noise floor goes from an unmanageable average -70 to -80 dBm (~S9) to an astoundingly low -110 dBm (S2) across the band and holds close to that figure across the shortwave bands to 30 MHz too! Look particularly at the frequency range 500 - 620 KHz. The crazy electrical hash bubble there has even been completely removed.

Before application of 1:1 isolation balun

After application of 1:1 isolation balun

Most signals run 25-35 dB above the -110 dBm noise floor, peaking in the -70 to -80 dBm range, equivalent to S8-S9 strength. But S8-S9 means something here, as our noise floor is at S2! Signals are strong and well out of the noise. DXing is possible again.

I won't suggest that the 1:1 voltage balun will work for total noise abatement in all cases. It works for me in my environment, as you can see. If you have severe noise problems, consider trying a low-noise antenna and this low-cost, miniature isolation balun.

Here is the eBay link to the 1:1 isolation balun:

https://www.ebay.com/itm/166955230066

If the eBay link is dead, try searching eBay for "0.1M-550M 1:1 Isolation Transformer High Frequency Transformer SMA Connector".

I hope this article helps with your noise abatement.

Using The SDR Sharp Co-Channel Canceler

Another major update to this post on August 14, 2024! Be sure to reread as there are some important new tips in the discussion section.

Here at RADIO-TIMETRAVELLER I have two SDR radios in use. They are the SDRPlay RSPdx and the Airspy HF+ Discovery. The Airspy is by far the more sensitive and the one with the lowest noise floor. I use it both for mediumwave DXing and shortwave DXing. Antennas currently are a 44 ft. vee dipole on ground (a VDoG?) and a passive loop. The loop is the YouLoop, also by Airspy. It is a remarkable antenna when used with Airspy's HF+ Discovery on the medium waves.

Airspy HF+ Discovery

Recently I've gotten into the also remarkable Co-Channel Canceller offered in the SDR# (SDR Sharp) software. This is becoming a very necessary tool to have in the DXing toolchest. It is particularly useful if using a wire antenna which is generally non-directional versus the YouLoop. Used with the YouLoop or other nulling loop, results can be even more dramatic.

The idea behind the Co-Channel Canceller is to minimize the effect of one station over another, the two (or more) carriers and their associated modulation information that might occupy the same channel. We are not simply talking about "notching" a carrier here but removing the chosen carrier and the modulated spectrum associated with that carrier, leaving everything else beneath it intact.

The key here is we need to know the exact frequency offset of that carrier down to the fraction of a Hertz (Hz) of all the carriers on the channel. There may be two, three, or many on channel.

The Micro Tuner

Enter the Micro Tuner, a neat and necessary little gadget also available as standard in SDR#. Bringing up the Micro Tuner plugin will show a spectrum display 10-30 Hertz wide surrounding the tuned frequency. It takes some time to settle in, but after a couple of minutes, each carrier peak surrounding the tuned frequency will be displayed. Here we are tuned to WHCU in Ithaca, New York on 870 KHz.

The Micro Tuner

WHCU, the strongest spike you see, is 8.469 Hz low in frequency, or a negative -8.469 offset. At least three other weaker carriers are present just above "0" (exactly 870 KHz), as well as several noise spikes at about -3 Hz below 870 KHz.

Now, please understand that the Micro Tuner plugin is a separate plugin from the Co-Channel Canceller and can be used in different ways outside of the Co-Channel Canceller experience. In its elemental form, it can be enabled to allow micro-tuning of a signal, that is, positioning the tuned frequency on the exact carrier intended down to a fraction of a cycle. One must only enable it (just tick the checkbox), then click on a desired carrier peak in the graph. Apart from Co-Channel Cancelling, try experimenting with the Micro Tuner sometime when in SSB mode (either USB or LSB), or in DSB mode (double sideband).

In conjunction with the Co-Channel Canceller, we will use the Micro Tuner to identify the exact carrier frequency offsets on the channel we are tuned to. After all settings are made, we can simply click on carrier peaks in the Micro Tuner window to test the cancel process for each.

Let's get right into it.

The Co-Channel Canceller

I'm using SDR# v.1920, the latest software version as of this writing. The Co-Channel Canceller works best using this latest version.

The SDR# Co-Channel Canceller

It is important to first invoke the Micro Tuner to see exactly where the offensive station (and its carrier) is in relation to dead center "0", which is your tuned frequency.

The following tips and process are initial settings derived from DX Central's Loyd Van Horn's excellent video describing how to use the Co-Channel Canceller. Be sure to check out his video.

https://www.youtube.com/watch?v=Rk_0LMFAquk

After we go through these, I'll describe further tips on enhancing its performance.

The process:

1. To start, be sure you're using the DSB (double sideband) demodulation method. *important!* The Co-Channel Canceller will not work in LSB or USB mode, or in AM mode.

2. Widen your receiver bandwidth out to something around 8000 Hz (8 KHz). You generally will get better results with a little wider audio bandwidth than the normal 4-6 KHz.

3. In the Radio tab, ensure "Lock Carrier" is checked.

I recommend turning AGC ON at first.

Tune to the frequency where you wish to engage the cancel feature. Example: I've been chasing a Cuban station on 670 KHz at sunrise lately. I typically have a rough time nulling WSCR 670 in Chicago, WSCR being the much stronger station. I tune to exactly 670.000 KHz.

Start the Micro Tuner and let it settle in. Drag the Micro Tuner's window width out fairly wide so you can see the detail better. Give it a couple of minutes to stabilize.

Enable the Micro Tuner by checking its box. *important!*

You probably will see several carriers. The strongest is likely the one you wish to remove.

Open the Co-Channel Canceller (AM) plugin. Start with the Canceller OFF. Do the following in its settings:

1. Check Remove carrier.

2. Uncheck Auto Tune. *important!*

3. Set Carrier Offset to 0.000

4. Allow bandwidth to settle at 8 KHz.

5. Set IF Offset to 0.000

6. Set Correction to mid-range.

Now to the cancelling process.

1. Locate the strong signal peak in the Micro Tuner. *works best when one peak is well above the others*

2. Click on the peak at its exact center.

3. Enable the Co-Channel Canceller.

4. Fine adjust the Correction slider for best results. Mid-range or a little less usually does it.

Done! WSCR in my example is gone.

Auto Tune attempts to guess at the right peak to cancel, but results are usually less than desirable this way versus manually clicking a chosen peak in the Micro Tuner.

Once everything has settled in with the Co-Channel Canceller enabled, you can experiment with AGC off and controlling attenuation/gain manually. I've had mixed results turning AGC off. I am in a high signal area, and I get better results with the canceller using AGC ON.

Experiment with the FFT filters. You may see slightly better results with the various filters.

Discussion & New Tips

Demodulation modes. DSB, or double sideband has been stated to be the only mode that works for the Co-Channel Canceller. RAW mode works as well, and sometimes even better. Depending on bandpass centering, RAW may produce a more or less binaural or stereo effect which can enhance the audio clarity and intelligibility. The binaural effect is quite evident when the bandpass width is equally centered on the carrier, less so when the bandpass is skewed off to one side of the carrier. If you start the IF Spectrum plugin making sure the Asymmetric Filter box is checked, using the mouse you can drag the filter extents independently, left and right. This is how the much-desired AM Sync is accomplished in SDR#. The AM Sync process is accomplished as such: Tune to an AM signal in DSB mode. Make sure Lock Carrier is checked. Start the IF Spectrum plugin making sure the Asymmetric Filter box is checked. Using the mouse, you can drag the filter extents independently, left and right to encompass the correct sideband, USB or LSB.

The "Order" setting in the Radio plugin. Lately, this seems to be set at a default of 1000. Leave it there, or at least between 500-1000. The greater the value, the steeper the slope of your bandpass filter setting. At a value of 10, for example, filter slopes will be very gradual and broad. With the Co-Channel Canceller we want sharp, vertical edges to our filters.

The Micro Tuner span. My Micro Tuner spans +/- 30 Hz. Some have reported that theirs only spans +/- 10 Hz. Check your version of SDR# to make sure you are running v.1920. Also make sure you have the latest firmware for the HF+ Discovery installed.

Auto Tune. Checking Auto Tune will attempt to find the "'right" carrier to cancel. Be sure Auto Tune is off. If you enable it, you will never know which carrier peak Auto Tune settles on. Generally, Auto Tune searches for the strongest one, but many times the carriers are very close in strength. The Co-Channel Canceller works best when you have one defined signal peak which is somewhat stronger than the rest.

Pros and cons of Lock Carrier. Checking Lock Carrier here with the Co-Channel Canceller engaged does not always produce positive results, often making the signal worse or even recognizable. I almost always leave it off. Lock Carrier is really the old AM sync function, in this case stabilizing the sync between the clicked carrier in the Micro Tuner and the Co-Channel Canceller's frequency (frequency the algorithm is processing). Unchecked, you may possibly get some signal buffeting and degraded cancelling. Under good atmospheric conditions and if you are dead-on center of the carrier peak in the Micro Tuner, you may not need Lock Carrier. Experiment with this setting and see which works best for you.

Receiver bandwidth. I've had great success widening the receiver bandwidth out even further than 8000 KHz, the bandwidth suggested by Loyd at DX Central, and even sometimes narrowing it down to as little as 3 KHz. Choosing the right bandwidth and bandwidth centering is critical in the cancelling process. Follow along as this is going to get a little complicated.

This is what I do, which usually produces wonderful results:

1. Be sure you are using "snap to center" tuning, that is, when you click on the spectrum, the tuning point is always centered in the spectrum window.

2. Using the Zoom slider, zoom in on the spectrum so that the 10 KHz adjacent channels are at the extreme left and right sides of the display, showing about 20 KHz of spectrum with the tuned frequency in the center.

3. Look at the modulation extent of the adjacent channels, left and right. One or even both channels might be strong enough to be encroaching on the center frequency. On the left side you will be viewing the upper sideband of the lower adjacent channel. On the right side, you will be viewing the lower sideband of the higher adjacent channel. Most stations cut their audio bandpass to about 5 KHz, the halfway distance to the next adjacent channel. A few run at a conservative 4 KHz, but there are a fair number pushing the limit at 6 or even 7 KHz above and below their carrier. We want to avoid this encroahment.

4. In the spectrum window using the mouse, drag the bandpass narrower and away from the modulation effects of the adjacent channels. Use the widest bandpass right up to the encroachment points. Co-Channel Canceller works by analyzing the sidebands surrounding the clicked peak in the Micro Tuner. It works best when the lower and upper sideband of the bandpass are "pure" and devoid of outside splatter from adjacent channels. We want our sidebands surrounding the clicked peak in the Micro Tuner to be perfect mirror images of each other, if possible, and without side splatter or other encroaching noise. You may be lucky and settle in on a 10 KHz bandpass (+/- 5 KHz). You will find the bandpass can be usable way down to 5.6 KHz (+/- 2.8 KHz) or so.

5. If the adjacent channel encroachment is closer on one side than the other, we can remedy that problem too. Start the IF Spectrum plugin making sure the Asymmetric Filter box is checked. Using the mouse, drag the filter extents independently, left and right until you remove the encroachment properly on both sides.

Remove Carrier does indeed work. You can prove it very easily. With Co-Channel Canceller engaged and running, start the FFT: IF Spectrum plugin. Toggle the Remove Carrier checkbox and observe the carrier at the center of the window. The carrier will disappear when the Remove Carrier checkbox is checked. It is important to note that the actual carrier removed is NOT at the receiver's displayed tuned frequency, but at the Carrier Offset to the signal peak you clicked in the Micro Tuner. 

Remember, in tuning we are dealing with fractions of a Hertz here with the Micro Tuner and Co-Channel Canceller. Remove Carrier may not be effective in many receive situations. Actual received carriers are not infinitely narrow, there may be several carriers very close to the clicked peak on the Micro Tuner, and Remove Carrier may remove more than what you desire. Experiment with this setting under different receive situations and see which works best for you.

Correct IQ. Correct IQ can be used to our advantage when using the Co-Channel Canceller. This control is still present in the latest HF+ Discovery firmware. Its original intent is to remove the small, annoying center peak artifact in the spectrum display, present with certain dongles. Lucky for us, it will also remove a carrier at the receiver's tuned frequency, independent of the Carrier Offset and the Micro Tuner. With the Co-Channeler engaged, try checking Correct IQ to remove the narrow bandwidth surrounding the tuned carrier.

Correction slider. Finally, once you are satisfied with all your settings, play with the Correction slider. The Correction slider is not a "center" based control (plus or minus), but rather applies a linear amount of co-channel correction to the cancel operation. Setting it all the way to the right applies the maximum correction to the algorithm. You will find its best setting to be somewhere near mid-range or just below mid-range. Stronger stations require a little more to the right. Use the smallest setting possible which remove the unwanted station.

Carrier Offset. The limit to Carrier Offset looks to be one-half the receiver bandwidth, so if your receiver bandwidth is 8000 KHz, the max Carrier Offset you can have is +/- 4000. Varying Carrier Offset a little up or down fine tunes the "click point" in the Micro Tuner. Allow 2-4 seconds if you make changes like this, other changes too, for the Co-Channel Canceller to settle in and do its work. The response is not immediate. I sometimes also turn the canceller off and then back on if it seems to be jammed up. Sometimes it seems to lock up in a weird configuration. Just start over in that case. You may even need to restart SDR#.

IF Offset. Changing the IF Offset value can occasionally help. If the wanted signal is to the left of the removed carrier, move the IF Offset negative. Change to positive if the wanted signal is to the right of the removed carrier. You can add quite a bit of offset to this box. Remember this box shows values in cycles (Hz), not KHz, so does the Carrier Offset box. Type 100 and it will display 100.000 (100 cycles, or Hz).

Side splatter. Co-Channel Canceller has difficulty on channels having a lot of "side" splatter. Example: Received at night in the Rochester, NY area we have WGY 810, Schenectady severely splattered by CKLW 800, Windsor, Ontario. Trying the Co-Channel Canceller on 810 KHz had mixed results due to the 800 KHz splatter. Results will vary under these situations. See my tips on setting receiver bandwidth (above) to help eliminate this kind of problem.

Eliminating channel splits. The DX Central video shows how one might eliminate a TA (trans Atlantic) channel split. Example: trying to pull out Algeria 891 KHz when a strong American station is on 890. He sets Carrier Offset to -1000.000 Hz (-1 KHz) in the Co-Channel Canceller box, then clicks dead-center on the Algerian carrier in the Micro Tuner.

Finally, think about this. Used with a rotatable loop antenna having good nulling properties, you have the option to remove two offending stations. First use the loop to null one station. Then, use the Co-Channel Canceller to remove a second station.

There you have it, a short course on how to use the SDR# Co-Channel Canceller.

List of Stations in Path of Totality, 2024 Eclipse

Using my pattern mapping program Radio Data MW which has extensive area search capability, I've compiled a list of all U.S. and Canadian stations that fall within the 2024 Solar Eclipse path of ~100% totality. There are 456 stations. Results are drawn from the March 20 FCC LMS database and Industry Canada database.

If you would like this list, download from this link.

https://www.mediafire.com/file/125ih5yrmw4puib/2024-eclipse-stations-by-longitude.zip/file

Across the U.S. and Canada, from its entry at Texas to its exit through NE Canada and into the Atlantic Ocean, the totality path width varies from a maximum of 199 km at U.S. entry to about 160 km at the Atlantic exit off Newfoundland, or 123 to 99 miles.

456 stations are found in this eclipse path. I purposely set the path width to 210 km from start to finish. This gives a few km slop on both sides of the 100% totality path for good measure.

Unzip the downloaded .ZIP file, where you will find 3 files. The stations in each file are sorted by longitude, from west to east. This gives us the progression of the eclipse path, with the eclipse starting at the first station in the list and ending with the last station.

File #1 is a simple text file.

File #2 is in .CSV format. You can easily input it to an Excel file.

File #3 is in .HTML format. It includes links to each station's Google Map latitude-longitude coordinates for the satellite view of the transmitter tower array. Another link takes you to the FCC AM Query link for that station.

I hope these files are beneficial. There should be many propagation path possibilities outside of this list as well.

2024 Solar Eclipse DXing

DXing the mediumwaves promises to be an exciting event on April 8 during the 2024 total solar eclipse.

I've been mulling over the DX possibilities a lot lately and have come to some conclusions. I think it boils down to three promising DX scenarios.

Scenario 1. For those who live within or very near the path of totality, I believe best chances of DX would be first to listen to your southwest, along the path where totality is approaching. Darkness will already have happened in that direction, and a certain amount of residual de-ionization of the ionosphere will still remain. After the point of totality passes your location, I would swing my attention to the northeast.

Scenario 2. For those living within about 800 km (or about 500 miles) of the path of totality I believe best chance would be a perpendicular path across the totality path to a point roughly equidistant on the other side. This puts the signal reflection point right at the center of the totality path, or the deepest point of darkness.

Scenario 3. For those living more than about 800 km from the path of totality I believe best chance would be along a line from your receiving site to a perpendicular intersection to the totality path. This should define the greatest shaded path.

I think scenarios #1 and #2 have the best possibility for DX.

Across the U.S. and Canada, from its entry at Texas to its exit through NE Canada and into the Atlantic Ocean, the totality path width varies from a maximum of 199 km at U.S. entry to about 160 km at Atlantic exit, or 123 to 99 miles.

Important to keep in mind - skywave signal strength analysis is based almost entirely on the condition of the ionosphere at the reflection point, not at the receiving site. For single hop propagation, normally the reflection point is at the halfway point to the station along the great circle route.

Note: the 800 km distance from the totality center stated for scenarios #2 and #3 I wouldn't hold as gospel. I'm throwing that figure out as a point where scenario #2 may start to transition to scenario #3.

Timing is of the essence for DXing. The shadow velocity exceeds 1000 mph, increasing from 1587 miles per hour at Eagle Pass, Texas to 3176 mph at Houlton, Maine. You may have only minutes to DX.

I'll be in Rochester, NY at the time of totality, and we are right at dead center. I'll be scenario #1. My plan is to listen to my southwest initially, where totality is approaching. I'll be listening particularly for WLW-800 in Cincinatti, OH, WHAS-840 in Lexington, KY, and others along or near that path.

Scenario #2 possibly holds the most promise. Calculate your distance to the path center line and look for stations on a direct line across the totality path and at an equal distance on the opposite side of the path from you. One such scenario might be WSB-750, Atlanta to a reception point in northwestern Illinois, central Iowa, or southern Wisconsin or southern Minnesota. Many possibilities on cross-paths exist here. I feel best results would be with a signal path that crosses the path of totality closest to 90 degrees.

A question was raised about the possibility of DX from Spokane, Washington, an extreme distance from the path of totality. That particular scenario would be scenario #3, more than 800 km to the path of totality. Maximum obscurity should be when northeast Texas (let's say the Dallas area) is experiencing full totality, as the great circle line to the totality path intersects at approximately 90 degrees to the line at that point. This would be at about 1848 UTC. I would listen for any signals along a great circle path between Spokane to anywhere from the Dallas area and northward.

Obviously, Spokane to Dallas is an extremely long one hop path, at about 2450 km. At that distance, the reflection point is near Denver, which will have a solar obscuration of 65.1 percent at maximum.

A Dallas area reception would be next to impossible I would think, but there are many more stations along that great circle path one could try for. Closer stations will obviously move the reflection point closer and start to reduce the solar obscurity. I did a scan along that path and there are some 340 stations within 200 km either side of the line of the great circle path between Spokane and Dallas.

A presumed Scenario #4.

Another scenario was suggested by Nick Hall-Patch, that of reception parallel to the path of totality and outside the 100% totality band. The 2017 solar eclipse across the northern part of the U.S. was DXed extensively and produced some interesting results. It is well documented. Check their document repository here:

http://dxer.ca/images/stories/2019/irca-reprint-index.pdf

Nick reports: The receptions of KSL-1160 described in the report showed the results of 3 DXers listening across the path of the eclipse (Scenario #1), but the fourth, Dave Aichelman, was monitoring KSL from a location parallel to the eclipse path (Scenario #2) and got very good enhancement as well. 

We might name this "Scenario #4".

I checked out that document on the KSL reception from the solar eclipse of 2017. It looks like the Dave Aichelman (at Grants Pass, OR) reception of KSL had a mid-path reflection point of about 95% solar obscurity. The distance was 971 km (602 miles). Graphing KSL, I see it has a nice fat low angle takeoff and impressive skywave strength at 900 km, some 1.3 mV/m for that distance.

Better yet, the article indicated Aichelman also received XEPE-1700 across the Mexican border from San Diego too. That was a mid-point reflection obscurity of only about 83% as far as I can deduct from the maps. The distance was 1238 km (769 miles). The mid-path reflection point there was in the neighborhood of 700 km from the central path of totality.

So, DX is indeed possible where both the station and the receiver are off center from the totality path. It's looking like anything from at least 80% obscurity at mid-path reflection may have some real possibilities, particularly if you are at the end nearest the path of totality. Lower obscurities, perhaps down to 50% or so may even produce results.

Check out these links.

https://nationaleclipse.com/cities_partial.html

https://eclipse.gsfc.nasa.gov/SEpath/SEpath2001/SE2024Apr08Tpath.html

https://eclipse2024.org/eclipse_cities/statemap.html

Click image for full size.

C.Crane Twin Coil Ferrite Signal Booster DISCONTINUED!

It's always been in my head to try an actual C.Crane Twin Coil Ferrite Signal Booster. I've used tuned Q-stick devices before with a lot of success. They have sharp nulls and lots of inductive gain. The Crane unit promised more of the same with its 8-inch twin coil ferrite rod.

https://ccrane.com/twin-coil-ferrite-am-antenna-signal-booster

Checking the Crane website the other day, I was shocked to find that they have discontinued it. Now, if I want to give it a try, I'll have to find one elsewhere - maybe eBay. I see there are a few of them out there yet. I'd advise you to pick up one of these fabulous goodies before they are gone forever.

U.S. Broadcast Station Counts 1922-2022

100 years of AM broadcast in the U.S.

Shown below on the graph are the counts of licensed stations in the FCC's AM broadcast service for the years 1922-2022. You will see a steady rise in counts from 1922 to 1990.

I remember listening as a kid in Philadelphia in the very early 1960s. The band was literally alive with stations every night from as far away as St. Louis (KMOX), San Antonio (WOAI), New Orleans (WWL), Minneapolis (WCCO), and many others. Even the Mexican border blasters with the likes of Wolfman Jack were a normal catch every night.

We are in slow decline over the past thirty years and gaining more downward speed in the last ten. When will it end? What decade was the heyday of AM broadcasting? You decide.