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.

In fact, later on I discovered that the SMA connections were labeled P1 and P2. It turns out that the P1 connection is the balun input and the P2 connection is the balun output. Be sure to connect the balun in this way, using P1 as the input (the antenna side), feeding P2 to your receiver. It really does matter.

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.