Monday, October 25, 2021

RDMW 2022 Mediumwave Pattern Reference

North American Broadcast Mapping Tool & Database

We are proud to announce the launch of the latest edition RDMW-2022 Medium Wave Pattern Reference. Now in its 9th year, RDMW comes with many new features and updated station data ready for 2022.

Radio Data Medium Wave (RDMW) allows you to see and map the coverage area of all medium wave (AM/MW) broadcast stations in North America.

Included is a complete set of Google Map-based, HTML-driven maps which show the most current pattern plots of all licensed US and Canadian mediumwave broadcast stations from 530 - 1700 KHz. Through careful curating, virtually 99% of all licensed Mexican stations are also included, the vast majority with plots. 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. Data for the plots is based on the current FCC and Industry Canada databases available at creation (October 19, 2021).

870 KHz - skywave at night to the UK

If you've ever wondered why a radio listener would be interested in the coverage patterns or maps of radio stations then you can find out at Medium Wave Circle.

New developments for 2022 include:

  • The latest callsign and technical data for all US and Canadian MW stations
  • Expansion to cover Mexico, Bahamas and the Caribbean for the first time
  • Expansion to cover 490kHz – 1700kHz; now includes MW Navtex stations
  • Addition of real-time night/day terminator (greyline)
  • “Click+Save” setting of your receiver location
  • Easy tuning control added to control bar
  • Easy daypart selector added to control bar
  • Ray tracing control added on a per station basis.
  • In-screen “Help” button

Knowledge drawn from RDMW has been fundamental in helping DXers further their craft and enjoy their hobby. It can help you plan your listening and help you target stations broadcasting from particular areas. Intelligence displayed by RDMW has helped U.S. & European DXers plan and hear US stations over great distances – including so-called “daytimer DX” and transpolar propagation. The RDMW maps will also help you determine which stations you might hear on a particular channel, and which might be rather more elusive.

Drawing on the latest data from official sources, club sources and topped off with many days of extensive data checking and validation RDMW probably has the most comprehensive and up to date dataset for AM/MW broadcasting stations in North America. This data is combined with complex geophysical data and propagation modelling to provide you with extremely detailed coverage maps for both daytime groundwave and nighttime skywave coverage for around 5000 radio stations.

RDMW 2022 has been developed and tested by Bill Scott and Steve Whitt and is exclusively available from the Medium Wave Circle DXing club.

This year marks a sea change in how the map sets will be delivered to you, the end user. 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 2022 Medium Wave Pattern Reference – Medium Wave Circle (

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. 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

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

Tuesday, October 5, 2021

Magnetic Longwire Balun : The Original by RF Systems

 An oldie but a goodie. Remember this?

Magnetic Longwire Balun

Years ago (almost 40) when I was quite active in my ham career and shortwave DXing I purchased one of these for about $40. An expensive little device. But I was curious about the claims.

It was advertised as a magnetic balun, low noise, matching almost anything below 40 MHz. Receive only of course. You can search on "RF Systems Magnetic Balun" and find many sites, blogs and forums where the merits of this device have been discussed.

The RF Systems Magnetic Balun is basically an 18:1 impedance matching transformer. "Balun" means balanced-to-unbalanced transformation - a transformer device which takes a balanced impedance (like the center feed point off a dipole) and transforms it to an unbalanced impedance (like coaxial cable). The RF Systems Magnetic Balun is really not a balun but what is known as an Un-un. In this case, an 18:1 impedance transformer, transforming an unbalanced input to an unbalanced output. One such example might be to match the unbalanced end-fed longwire to a 50 ohm coaxial cable, which is also unbalanced.

In more recent times, I've had very good luck with mine using it with both a "longwire" and a 25 ft., ground-mounted, but ungrounded vertical. Longwire in this case, means anything of 25 to 100 ft. in length, which is not really long in the traditional sense.

In personal experience over the years, the low noise claim gave minimal results. Low noise might be gained by positioning your longwire a ways away from any noise source and feeding the receiver with a long run of coax. But that's just common sense. Grounding the coax's shield at the entry point to the house can help too.

Presented at the bottom of this post are good quality .JPG images of the original document which came with the RF Systems Magnetic Balun. catalog item for the RF Systems Magnetic Balun

Other Matching Options

Good or even better results can sometimes be had with other matching devices like an antenna tuner which will also do the matching like a balun would. MFJ Enterprises has quite a few which can be used for simply tuning odd lengths of wire. Google will produce many results for antenna tuners. They can be made pretty simply with a variable capacitor and some hand wound coils.

For AM broadcast DXing I prefer inductive coupling right into the radio's own ferrite antenna. Matching is pretty well taken care of then and good signal transfer is also accomplished, and often without the overloading that can occur when directly connected.

A circuit example of a similar, but 9:1 impedance transformation "magnetic balun" can be found at M0UKD.

This is another "un-un", as it transforms between unbalanced input (the longwire) to unbalanced output (the coax input of the radio). This circuit is actually the same circuit as the RF Systems balun I have. It takes a high impedance (the longwire) and transforms it by a 9:1 ratio down to a lower impedance (usually the radio's input connector). Note that radios with external longwire posts like a CCRadio SW may already be set up for high impedance input. It depends on the input circuitry used in the radio.

Be careful directly connecting wire to any of these DSP radios. Modern chip electronics is not so forgiving as the old tube stuff from my generation. I have fried several radios with static discharge.

Inductive coupling to a radio's ferrite loop can easily be done.

Find an old piece of ferrite bar or rod and close-wind 15-20 turns of insulated wire on it. Ground one end to the earth and connect the other end to the longwire. Then couple the ferrite bar/rod to your radio's ferrite antenna. You can even run it through a length of coaxial cable, though better results will be obtained by using the RF Systems balun or 9:1 balun where the longwire connects to the end of the coax (outside).

My 25 ft. vertical is set up that way. Picture the vertical as a simple end fed longwire (fed at the bottom and insulated from the ground). It is attached there to the RF Systems balun and through the balun to the coaxial cable. The 50 ft. coax cable runs to the inside of the house where the center and shield of the coax is connected to the 15-20 turn winding around that spare piece of ferrite bar/rod.

Sensitivity can then be adjusted by the closeness of the coupling to the radio.

Be aware, most of these radios are easily overloaded by excessive signal. It shouldn't take much of a longwire to do that.

The old-fashioned Pi type tuners work quite well for longwires. This involves two variable capacitors with a coil between them. I used to have a homemade one which I used for years on the ham bands for both transmit and receive. That style can match about anything.

The Grove TUN-4 Antenna Tuner

Grove Electronics, now out of business, (they also published the Monitoring Times magazine years ago) used to sell quite a few receive tuners. I still have the TUN-4 which is quite nice and will tune from below the AM band to 30 MHz. It also has a preamplifier. You can often find these and the others on eBay. The American Radio History web site has many old radio catalogs which you can peruse. Here is an old Grove catalog, dating back to 1989.

Grove Catalog, 1989

The Grove TUN-4 Antenna Tuner

Why impedance matching?

Maximum signal is transferred (and I might add with minimum distortion) if the impedance is matched between input and output of a circuit. To give a simple example, in the old days of Hi-Fi the audio enthusiast always made sure his speakers were matched to the stereo's speaker output. If the stereo had an 8 ohm speaker connection, you made sure you used 8 ohm speakers, not 16 or 32 ohm speakers. Maximum signal would be transferred to an 8 ohm speaker, and also as important, minimum distortion would result.

The same is with radio and antennas. Typical longwire antennas might have an inherent impedance in the neighborhood of 450 ohms, or more. Old radios which had a single antenna post for a longwire usually made sure that the input was designed around 450 ohms. The coax inputs or mini-jack inputs of most receivers are usually designed around an input impedance of about 50 ohms. If we connect a longwire to one of these inputs we are creating a series circuit of 450+50 or 500 ohms at the input with our "tap" at the 50 ohm point above ground. Ohm's law tells us that we are only getting 50/500 or one-tenth the signal available from the longwire. This is remedied by the impedance matching transformer or by the antenna tuner. Properly matched, we get the full signal off the longwire.

In the ham radio world, good matching is even more important when transmitting to an antenna. A poor match results in the antenna reflecting some or most of the power right back at the transmitter. These reflections also exist on receiving antennas when mis-matched.

Some radios seem to be a little more tolerant of antenna mismatch, some not. I have the SDRPlay RSP1a SDR receiver here and I find it not tolerant at all of antenna mis-match. Another, the Yaesu FRG-7, dating back to the late 1970s, is particularly sensitive to proper impedance matching. This is a very sensitive radio, but you must match the antenna to it to get maximum results, and particularly on mediumwave. Many radios, however, will respond favorably by hooking up any sort of wire to them.

For receive purposes, feeding the radio using 75 ohm coax instead of 50 ohm won't matter much. I've used 75 ohm TV cable for years for receiving on the HF bands - 30 MHz and below. Transmitting or VHF/UHF work would be a different story. The 75 ohm to 50 ohm mis-match is a 1.5:1 mis-match, which coincidentally is also a 1.5:1 SWR (Standing Wave Ratio) in the ham radio transmitting world. That's usually about at the edge of acceptability for transmitting in the HF range.

The impedance transformation of 450 to 50 ohms is a 9:1 ratio of course. It is based on the windings ratio and is equivalent to the square of the windings ratio. If the input side (the 450 ohm side) has 3 times the number of turns than the output side (the 50 ohm side), then the turns (windings) ratio is 3. 3 squared = 9, so the impedance transformation is 9:1. The RF Systems balun, at 18:1, presents a turns ration of about 4.25, the square root of 18.

For 75 ohms, you'd need an impedance transformation ratio of 6:1 (450/75). The square root of 6 is approximately 2.5, so you'd need a turns ratio of 2.5 from input to output. 10 turns to 4 turns would do it.

Understand that the 450 ohm figure for the longwire may vary greatly above or below this figure depending on the frequency you are receiving. In other words, the impedance presented at the end of the wire is frequency dependent. The original concept of a longwire was a wire of several wavelengths. Casually, someone throws an odd length of wire out a window and calls it a longwire. If your end-fed "longwire" is anywhere near one-quarter wavelength of the frequency being received, you probably are looking at an impedance of 20-75 ohms, not 450 ohms. An end-fed halfwave length of wire might present itself around 1000-2000 ohms. The point I'm trying to make here is that the 9:1 or 18:1 balun is there just to get you in the ballpark for this higher impedance, matching-wise.

And now, the RF Systems Magnetic Balun. Click on each image for the full resolution.

Sunday, September 26, 2021

Greyline Propagation

Let's talk about greyline propagation.

Greyline propagation, or propagation along the earth's sunrise/sunset terminator, is very noticeable on the 160, 80, and 40 meter ham bands and lower shortwave bands. Mediumwave signals can and do travel that path as well.

What does the greyline look like on a map?

There's a great solar clock map I've found which I use called Simon's World Map. You can start it and leave it on your desktop.

Simon's World Map

It's freeware. The creator (Simon) is the guy involved in the HF+ Discovery SDR project, competitors to the SDRPlay and SDRUno, and others.

A screenshot of mine in use right now:

The night/day overlay over the world map shows the width of the earth's terminator and its transition from total darkness to the sunrise and sunset edge. The actual sunrise or sunset point is the edge where the overlay disappears. The lightest band of the overlay is civil twilight, where the sun is just below the horizon to a point 6 degrees below the horizon. The next darkest band is nautical twilight, where the sun is between 6 degrees and 12 degrees below the horizon. The next darkest band is astronomical twilight, where the sun is between 12 degrees and 18 degrees below the horizon. The darkest area is where total darkness exists, where the sun's position is greater than 18 degrees below the horizon. Medium wave and other signals in the lower shortwave bands, as described above, can propagate along the terminator at greatly reduced signal attenuation - often received at astonishing distances. 

Space Weather Specialists define it this way on their Real-Time Maximum MUF page, found here:

Space Weather Specialists

Their definition puts the greyline stripe exactly between the rising or setting sun and the 12 degree point of darkness below the horizon, also known as the Nautical Twilight point. However, they seem to ignore any greyline existence on the daylight side of SR/SS.

Civil twilight is halfway to Nautical Twilight, or 6 degrees below the horizon.

Published sunrise/sunset times in newspapers and charts almost always base their times on "Official" sunrise/sunset which is 90 degrees 50 minutes, or 90.833333 degrees from solar zenith, making their times several minutes different from actual SR/SS. Actual SR/SS is based on 90 degrees from solar zenith.

I would argue that greyline conditions of course exist for a time past sunrise and before sunset, straddling the actual SR/SS. How much? I would tend to split it at about 6-9 degrees on either side of SR/SS, but it depends on the frequency too. 6 degrees rotation of the earth is 24 minutes of clock time.

12 degrees below the horizon seems a bit much to me. 12 degrees of earth curvature is 828 miles or 48 minutes of sun travel which is quite a departure from actual sunrise and sunset. Again, I would tend to split it at 6-9 degrees on either side of SR/SS. 7.5 degrees is 30 minutes, which seems about right.

VOACAP has a nice calculator which gives their representation of greyline start and end times by location and date:

VOACAP Calculator

VOACAP uses the 6 degree below the horizon (darkness side) and 3 degree above the horizon (daylight side) points for their greyline calculations.

Their greyline notes can be read here.

My mediumwave broadcast pattern map set  for 2022 is almost ready for publication, coming mid-October. This year it will be available exclusively on The Medium Wave Circle. Many changes and updates have been implemented over the last 18 months. One is a greyline day/night overlay, similar to Simon's World Map. Coming soon!

Greyline is a good topic for discussion. Maybe others have thoughts.


Friday, August 27, 2021

A Radio Story

I had a conversation recently with a fellow who was interested in starting into the radio hobby, and I thought the conversation might be of interest to anyone who has ideas of radio DXing. I'll reproduce the gist of the conversation here.

Nice to meet you. Glad to see people are still getting involved in our "archaic" hobby!!

I'm 74 years old this year and have been involved since about 1960, some 60 years. I got my first ham license in 1963. Before that I used to listen on my grandfather's old Sears Silvertone wooden console as a young boy. Shortwave was fun in the days back then and in the 1970s, all during the Cold War. Fascinating and scary stuff.

Sears Silvertone 7067, about 1942

I sort of quit the ham activity in the late 1990s after some 30 years, though I've hung on to that license. My ham and radio interest was always more of a technical one, though I made a lot of contacts all over the world via my preferred CW (code) mode over the years. Since about 2008 I've been doing a lot of mediumwave DXing mostly, but recently got back into shortwave listening too over the last couple of years.

International shortwave is only a fraction of what it was years ago. Most stations have moved on to the internet or don't exist at all. But don't be discouraged as there is still a lot of stuff out there to hear. It's just a little more difficult than the big booming signals of the old days.

I'm glad you decided to look for something beyond the Tecsun PL-380. It's 12 year old technology at this point and has been much improved since 2008 or so, even for those radios that are using the same radio chip. Silicon Labs makes the radio chips, though the Chinese have cloned them now and they produce their own too.

C Crane, a US company, also makes some nice radios, and sensitive too. Their original CC Skywave is actually sort of a "super" PL-380, but at about $80. The Chinese then cloned it with the RadiWow R-108, and in my opinion, did a better job for half the price. Understand, this is a tiny radio, it will fit in the palm of your hand. It is sensitive, and has corrected many of the original consumer gripes we had for the PL-380.

I have a Tecsun PL-880. They are good radios with nice sound. It's more paperback book sized, where the PL-380 and R-108 are cigarette pack sized. On medium wave it's more sensitive with the longer ferrite antenna. Shortwave is a bit better too, and of course it can receive single sideband SSB as well. FM is superb of course. The only gripe I have with mine is the frequency readout is 2 KHz off on the AM band. An alignment problem I'm sure, but I don't think it's correctable at this point.

I also have a Sangean ATS-909X, a newer model to the old '909. There is also an even newer model just out, the ATS-909X2, available on Amazon. All the 909's are beautiful looking radios. I love mine and actually prefer it to the PL-880, though it performs about equally. I find that radios you buy have a certain "feel" about them, independent of their performance. I call it "fun factor". The 909X has greater fun factor for me for some reason.

On the PL-660 and PL-880 comparison. I don't have a '660 but always wished I'd tried one. I do have an older Tecsun PL-600, sort of the predecessor to the '660. They are analog radios, superhetrodyne design. They are good radios, and the '660 is probably equally able as the '880. However, the '880 will have better bandwidth options since it uses the DSP chip, which is very nice to have. I suspect the speaker sound is better in the '880 too. Sensitivity may be about equal. Tuning may be preferable on the '880 as well, especially for SSB.

On shortwave, all of these radios will improve with a little wire clipped to their telescoping whip antennas. Just a word of advice - be careful when connecting outside long wires to them. Static discharge can destroy them in a hurry. I have ruined two - an old Sony ICF-2010 years ago, and the Sangean '909 I have. I was able to send the '909 in for repairs under warranty and it came back in perfect shape, luckily.

In these modern times we are plagued with RFI - radio frequency noise from all kinds of devices. Try listening outside away from your house if you have problems. Or even go to a park.

Three different web entities produce up-to-date shortwave schedules. They are:




I find EIBI and NDXC rather good. You can download them for free. Once unzipped you will find text files that you can look at.

China has a huge presence on shortwave, and I find listening to them rather fun, especially their music. Radio Romania has a nice signal into the US. Also Turkey and Greece, and I love their music as well. I often listen to Radio New Zealand at night. Sadly, Australia is not on any more. BBC still has a presence, mainly out of their Ascension Island relay, Asia and the Middle East. Also Voice of America. Lots of signals coming out of Africa. There are many others.

For best results, learn to listen at the right times. After dark and at sunrise/sunset times, check the 4-10 MHz bands. During the daytime and at sunrise/sunset times, check the 10-21 MHz bands, particularly 11500-12100 KHz, 13500-14000 KHz, and 15000-15800 KHz. Best times are actually the hours right around sunrise and sunset. Where you are on the west coast, check for Europe late in the afternoon through the evening. Asia will be dominant during sunrise hours. Listen for long path propagation, a weak, warbly signal with an echo, indicating reception from both directions. It is indeed possible and happens all the time, but you need a good antenna usually. Consult those shortwave schedules frequently. Find yourself a nice world map clock off the web, showing a world map with the light and dark areas of the world for the current time. "Simon's World Map" is a great little clock-map that is free and you can install it on Windows. It's by the guy behind the HF+Discovery SDR radio I think.

The last five years or so I've gotten into SDR radios, software defined radios. I have an SDRPlay RSP1A (Ham Radio Outlet has them) and an HF+Discovery. Either is about $120. They would have been the equivalent of a $3000 military grade radio back in 1970. They are cigarette pack sized and plug into your USB slot. You tune and use them through software on your computer. They have spectrum displays and lots of bells and whistles that you'd never find on a portable. If you get deep enough into the hobby you might want to try one of these as the entry price is certainly very reasonable. They require an outside antenna for shortwave, or a loop can be used very effectively for the medium wave band.

Hope this has been helpful and has given you some ideas. Let me know how it goes. Have fun.