Carrier Sleuthing, Using Proppy to Check Propagation
Proppy, by James A. Watson, is a web-based application to perform HF Circuit analysis. It supports on-demand HF propagation predictions for Point-to-Point (P2P) and Area coverage in addition to monitoring conditions in real time. In P2P mode, it will show basic circuit reliability (BCR), expected signal-to-noise ratio (SNR), or predicted signal strength (PR) over a predetermined transmitter --> receiver path.
In addition to prediction capabilities, the Proppy site also provides tools to help assess current conditions by monitoring NCDXF/IARU Beacons and current space weather conditions.
Proppy is my Go-To for checking propagation when Carrier Sleuthing. It's also very easy to use. Note again that Proppy is for the HF frequencies, shortwave only. Let's dive in.
The main Proppy site is found here. https://soundbytes.asia/proppy/
For Carrier Sleuthing and other DXing activities, I've found the Point-to-Point, or P2P function to be the most helpful. Let's go there:
Point-to-Point https://soundbytes.asia/proppy/p2p
Let's use an example, one of my favorites to watch, the Voice of Vietnam on 7435 kHz. Much of my monitoring is done between 0300 AM - 0900 AM local time each day, which are the three hours before and after my sunrise this time of year. Presently in late summer, August, it coincides nicely with the approach of Asian sunset occurring at nearly the same time. Mainland Vietnam in the Hanoi area experiences sunset at 1135 UTC in early August, or 0735 AM local time here in western New York. We can start monitoring 7435 kHz at about 0530 local time (2 hours before their local sunset, and throughout our sunrise period) and watch to see if their signal appears and strengthens.
Using Proppy, let's see what we might expect in signal strengths and signal-to-noise ratios, and more importantly, when or if they might peak.
Example for Voice of Vietnam 7435 kHz
On Proppy's P2P Point-to-Point page, we must first establish the location of our receiver and transmitter. We can easily do this. Using the mouse, move the the Tx (transmitter) and Rx (receiver) pins to their correct locations. The Rx pin will be at your receive location, obviously, and the Tx pin will be at Son Tay, Vietnam, just west of Hanoi. Zoom in the map to place the pins accurately.
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| Voice of Vietnam. Short and long path. |
We will now prepare to run a prediction. First we need to set some of the input parameters under the "System" block, "Tx. Site" block, and "Rx Site" block.
Under System:
Set the Date, actually the month for the prediction. This is normally the current month of course. I like to round my months up. For instance, at the very end of July, I am using the month of August for my prediction runs.
Set Traffic to User Defined.
Set Bandwidth to the filter bandwidth you are using on your receiver. I am using a bandwidth of 1000 Hz, and tuning the carrier at 500 Hz below its frequency in USB mode, 7434.500 kHz. This places the carrier squarely in the center of the bandpass.
Set SNR, or Signal-to-Noise Ratio. This figure only matters for the Basic Circuit Reliability prediction. I set my SNR (dB) to -30, our arbitrary threshold for signal detectability. This, for the sake of the argument, is 30 dB below the noise. Now, there are those who will argue that any signal specified as "below the noise" cannot be detected and they are technically correct. However the phrase, "below the noise" is actually a misnomer, in that the signal is immersed "in the noise", not below it. And thus, down to a certain level (modern techniques prove at least -30 dB below), it can be detected.
Keep SSN Source at Standard Curves.
Set Power (W) to 100000. This is the power at which Voice of Vietnam transmits, 100 KW. Set accordingly for the station you are predicting.
Set Man Made Noise to Quiet. This of course will depend on your receiving environment and antenna. I almost always use a passive loop antenna, which maintains a very quiet noise floor.
Set Path to Short Path, initially. We will check the most direct and shortest path from the transmitter to us. Later we will check the long path and may get surprising results!
Under Tx Site:
Latitude and Longitude should already be set when you moved the Tx pin on the map. These can also be set by entering the values directly, as can any of the other inputs.
Keep Antenna at Isotropic.
Keep Ant(enna) Gain at 2.16 dBi. We don't know the transmitter antenna gain, and often don't know the antenna target direction which also affects the gain directed at us. We will keep the gain at 2.16 dBi, which is dipole antenna gain above an isotropic (point source) antenna.
Under Rx Site:
Latitude and Longitude should already be set when you moved the Rx pin on the map. Otherwise, enter your home location.
Keep Antenna at Isotropic.
Set Ant(enna) Gain. This will depend on your antenna, but a simple estimate will do nicely. My one turn passive loop I usually set at about -15 dBi. A dipole up in the air, oriented correctly, should be set at 2.16 dBi. For a moderately-sized outside Loop-on-Ground (LoG), somewhere between -10 and -20 dBi. The same for a moderately-sized Dipole-on-Ground (DoG), between -10 and -20 dBi.
Running and Analyzing the Prediction
We are ready to run the propagation prediction. Let's get right to it.
Short Path
Click the Run Prediction button to run the short path analysis.
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| Basic Circuit Reliability. V of Vietnam 7435 kHz. |
Click the BCR tag on the display to check Basic Circuit Reliability. This is presented in a tooltip appearing under the mouse cursor as a percentage, 0-100%.
Hover over the graphic so the frequency range of interest (7 MHz) appears in the tooltip. Read the BCR off the tooltip as you move the mouse along the timeline from about 0800 UTC to 1400 UTC. For carrier sleuthing, anything above 0% may be detectable. We see nothing that rises above 0%. Remember, this is the short path between Vietnam and our receiver site.
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| Circuit SNR. V of Vietnam 7435 kHz. |
Click the SNR tag on the display to get the signal-to-noise analysis graphic (in dB referenced to the noise floor).
Hover over the graphic so the frequency range of interest (7 MHz) appears in the tooltip. Read the SNR off the tooltip as you move the mouse along the timeline from about 0800 UTC to 1400 UTC. For carrier sleuthing, anything exceeding about -30 dB should be detectable. The SNR does not rise above -30 dB.
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| Signal Strength. V of Vietnam 7435 kHz. |
Click the PR tag to get the signal strength analysis graphic (in dBm).
Hover over the graphic so the frequency range of interest (7 MHz) appears in the tooltip. Read the PR off the tooltip as you move the mouse along the timeline from about 0800 UTC to 1400 UTC. For carrier sleuthing, anything exceeding about -135 to -130 dBm should be detectable. The PR, or signal strength, does not rise above -135 dBm.
Long Path
Let's check the long path to Vietnam. We have a surprise coming.
Under System choose Long Path. Leave all other settings the same.
Click the Run Prediction button to run the long path analysis.
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| Basic Circuit Reliability. V of Vietnam 7435 kHz. |
The Basic Circuit Reliability shows a distinct peak for the long path at 1100 UTC. Running our mouse across the timeline for 7 MHz we find we have a BCR of some 95% exactly at 1100 UTC. This is relative to our choice of System SNR of -30 dB, meaning that V of Vietnam's signal will rise above -30 dB for 95% of the time around the 1100 UTC hour.
In actual receiving using our passive loop, our SDRPlay RSP1B SDR receiver, our one turn passive loop, and the Spectrum Lab software, we see evidence of a signal starting as early as 0930 UTC, building as we approach 1000 UTC and peaking right at the 1100 UTC time. Evidence of signal remains until we are well past the 1200 UTC hour.
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| Circuit SNR. V of Vietnam 7435 kHz. |
Going further, our Proppy SNR figure at 7 MHz rises to -11.5 dB at 1100 UTC, perfectly viewable in Spectrum Lab and well above the minimum -30 dB required.
Finally below, Proppy's PR, or signal strength figure at 7 MHz rises to a nice, viewable -109.7 dBm at 1100 UTC.
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| Signal Strength. V of Vietnam 7435 kHz. |
For a period of a couple of hours, 1000 - 1200 UTC, Spectrum Lab (and our other spectrum analysis software) can "see" evidence of Voice of Vietnam's signal via the long path. Proppy predicts a sharp peak at 1100 UTC.
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| V of Vietnam 7435 kHz starts to appear at about 0930 UTC. |
At about 0930 UTC, the Voice of Vietnam starts to appear (above) on the spectrum analyzer waterfall, rising up out of the noise. We are tuned in USB mode at 507 Hz lower than the carrier frequency on the SDRPlay RSP1B. The extra 7 Hz is cranked in to compensate for oscillator inaccuracy on the RSP1B. V of Vietnam, correctly shown, is actually about 3 cycles high in frequency.
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| V of Vietnam 7435 kHz temporarily ending at 1024 UTC. |
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| V of Vietnam 7435 kHz on the SDRPlay RSP1B |
Note the signal levels on the RSP1B receiver (above). We are on the one turn passive loop. Tuned to 7435.507 kHz which will center 7435 kHz in the bandpass, V of Vietnam is just a hair above the RSP1B's minimum discernible signal (MDS) level, showing a carrier peak of -138 dBm. The aggregate noise in the 1000 Hz bandpass reads -118 dBm on the S-meter. This is an extremely faint signal showing no audio whatsoever in the headphones but is clearly discernible on the spectrum analyzer.
Proppy is fun to experiment with. Its calculations are based in part on the current, predicted smoothed sunspot number for the month of interest. Its SNR and PR (signal strength) tools allow us to predict exact times of day when signals will peak or rise above the detection threshold. Using its Date tool, we can check propagation forward (approximately one year) or backward (several years) in time. It is a valuable tool which can be used for Carrier Sleuthing or general DXing to nail down the right time to be looking for stations anywhere in the world.
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