Using GB3VHF

Propagation monitoring

The beacon can be used for determining if propagation conditions are enhanced or have deteriorated over a period of time. Careful monitoring of the beacon can give a useful indication that conditions are likely to improve, and as such give rise to an early alert of an opening.

The beacon can be monitored using JT65B as shown on the Receiving GB3VHF page, and using the decoding software the beacons signal strength can be monitored over a period of time, even when inaudible in a conventional receiver bandwidth.

Another method is to use your receiver S meter reading to determine relative signal strength again over a period of time and the data can be logged using software. The software can then be used to display either in real time or historically, a graph showing any changes to conditions.

An interesting account from Dave G8TTI of propagation conditions on the 21st of November 2011

Here is a recording that I made on the morning of the 21st of November of the signal strength of the GB3VHF beacon which is located in Kent JO01EH, as received here near Chippenham IO81WM. The beacon's signal strength usually hovers around S6-7, but there was a clear enhancement in the morning. Doubtless more distant repeaters and stations than normal were heard on FM. The line on the graph is the signal strength of the beacon (-60dBm is S9+10db approx), with time shown right to left. The recording starts at 1140z and ends at 1211z. Weather at first was fog, with rain arriving at approximately 1145z and then becoming more persistent. I consider that the deterioration of propagation conditions is very apparent.

Towards the end of the recording the signal strength is bumping along at S5-6 (-90dBm) and it's also a lot less stable than earlier. The regular dips in the trace at the beginning are the WSJT tones sent by the beacon which produce a slightly lower average S meter reading. The receiving hardware was a homebrew 144 MHz SDR that uses SDR-Radio by Simon Brown HB9DRV. In the 420 to 0 sec section of the chart I did make some small adjustments to the receive filter which will account for the two deep dips seen.

I thought it was interesting to see how the signal tailed off as rain approached and started falling here. Simon Brown's SDR-Radio now has a very useful S meter history feature. On Monday morning (21/11/11) the beacon was very strong here so I just left the receiver running while I was away for a few hours and returned to see the graph recorded. The drop in signal pretty much coincided with the arrival of rain. It had been dry earlier but foggy, so when it started to rain it was a horrible day indeed. I made no local note of atmospheric pressure but the data for the pressure and rainfall for the day is shown below, together with the Hepburn data.

Two days later on the 23/11/2011 you can see by comparison with the recording of the 21/11/2011, that the beacon is being received under more normal propagation conditions with frequent peaks and troughs of QSB.

An interesting account of how Bill GM3PMB uses the beacon's JT65B mode to monitor propagation over a period of time

During March 2012, Bill GM3PMB located in IO74QJ monitored the beacon for several hours and found a large variation in signal strength. Although the beacon is at the limit of Bill's range of reception using conventional CW, the use of JT65B enables propagation changes to be monitored. Bill said "Over a period of about 90 minutes it never missed a decode. During that period the signal strength went from -2 dB to -20dB so there was a substantial propagation swing. You will see much evidence of aircraft multipath and enhancement but that does not seem to completely explain the deep QSB".

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