Receiving GB3VHF

Monitoring the beacon using WSJT JT65B mode

The use of JT65B enables the beacon to be received and monitored at extreme ranges, even when inaudible in a conventional receiver bandwidth. The use of JT65B will ensure that the user at long distances from the beacon can see if there is any enhancement to propagation, or if propagation conditions have deteriorated. It thus also allows automatic monitoring of the beacon over a period of time.

Software to decode the JT65B is easily obtainable on the Internet at the WSJT website www.physics.princeton.edu/pulsar/K1JT/

To decode the JT65B, tune the carrier to obtain a tone of 1500Hz with the receiver set to USB, and the dial frequency reading 144.4285. The JT65 will then be tuned in correctly.

GB3VHF as received on JT65B by Paul G4DCV

New JT65B and A1A beacon weaker than the old FSK one ??

The new beacon is running at 30 watts output compared to the 40 watts output of the old unit. This difference of only -1.2 db should make no perceptible difference under the same propagation conditions. However, if you think that the new beacon is weaker than the old unit then Andy G4JNT explains……

The claims of it being considerably weaker are almost certainly a psychological effect of only receiving the tone for a little over one minute out of two. If they are happily listening to CW and a steady tone at their preferred frequency, the ears are operating at an effective bandwidth of 10 - 50Hz. After making some S/N measurements, I measured my ear/bio-DSP combination at around 20 - 40Hz, but only over a very small preferred tonal range - for me that is around 600Hz. If there is any change in tone frequency away from the optimum, apparent S/N plummets.

And that's what it is like listening to a weak GB3VHF signal. By putting 20 - 25dB of attenuation in the antenna feed for an average received signal strength, I can reduce the received signal from quite CW-readable to something that takes several WSJT averages to give the message and is not audible. Given the right tuning point, time of day, lighting, background noise, alcohol intake etc etc, the tone is detectable by ear at 15dB attenuation, although I haven't a hope of copying CW at that S/N. So, as soon as the JT65 signalling starts, the audio appears to fail completely. Such a drop would easily be interpreted as a much weaker signal than before, and even when it reappeared, 49 seconds later, the psychological effect of its going will dominate. I wonder if there are any psychologists / audio experts who are interested in weak signal listening and low S/N auditory phenomena, who could take this idea further and devise some real experiment.

Andy G4JNT

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How to configure WSJT to receive GB3VHF using deep search mode

Thanks to Bernd DF2ZC for the following text.

Hello All,

Though it is a little off topic it might still be interesting to many...

As some of us have already learned the well-known 144 MHz beacon GB3VHF (JO01EH) is now the first - at least to my knowledge - beacon which also transmits in JT65B mode. Every even minute (corresponding to having ticked "tx First" in the WSJT JT65B subroutine window) the beacon transmits "GB3VHF JO01EH". In the odd minutes it transmits the same message in plain old A1A.

This gives a wonderful opportunity to monitor the beacon signal even if one is not in shack: By tuning in on 144.42860 MHz in SSB mode (CW carrier is on144.430 MHz in CW mode), untick the "tx First" in the WSJT program, press "F3" for Mute and then let the software run and decode the beacon signal.

Since the message text "GB3VHF JO01EH" does not match the message conventions for the deep search mode in JT65B the additional dBs sensitivity are wasted. This is particularly unfortunate for hams wanting to do some long distance beacon monitoring, not just 500 km like from here.

However, there is a way out to force the software to use the deep search decoder, because one could also regard JO01EH also as a callsign:

(1) Set your own callsign to GB3VHF in WSJT options

(2) Set "JO01EH" as TO-Callsign (you can even use JO01EH als as JO01EH's locator)

(3) Store this unusual callsign JO01EH from JO01EH in calls3.txt

The turn your antenna to the beacon location and start running muted tx 2nd. It will work.

Good luck in beacon monitoring. And have fun with the statistic work and graphic display later.

Thank you to the team at GB3VHF! Details of the beacon are at

www.gb3vhf.co.uk

vy 73 Bernd DF2ZC (JO30RN)

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

Website: www.df2zc.de

Just for your information below please find an example. I can copy GB3VHF nearly 100% of the time with my 4 x 18 ele M2 at 20 m AGL and 380 m ASL at signal strengths between s1 and s7 in CW. Sometimes the QSB is quite astonishing as you can see from the example at 1644Z where only a decode with the deep search mode was possible.

73 Bernd DF2ZC

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

135600 15 -2 0.1 22 1 * GB3VHF JO01EH 1 10

135800 12 -7 0.1 22 4 * GB3VHF JO01EH 1 10

140000 6 -9 0.1 22 3 * GB3VHF JO01EH 1 10

140200 4 -7 0.1 24 1 * GB3VHF JO01EH 1 10

140400 8 -4 0.1 24 3 * GB3VHF JO01EH 1 10

140600 10 -4 0.1 24 2 * GB3VHF JO01EH 1 10

140800 6 -9 0.1 24 3 * GB3VHF JO01EH 1 10

141000 7 -7 0.1 24 2 * GB3VHF JO01EH 1 10

141200 9 -7 0.1 24 4 * GB3VHF JO01EH 1 10

141400 8 -7 0.1 22 5 * GB3VHF JO01EH 1 10

141600 14 -5 0.1 22 3 * GB3VHF JO01EH 1 10

141800 8 -9 0.1 22 4 * GB3VHF JO01EH 1 10

142000 7 -7 0.1 24 4 * GB3VHF JO01EH 1 10

142200 10 -5 0.1 24 0 * GB3VHF JO01EH 1 10

142400 7 -6 0.1 24 1 * GB3VHF JO01EH 1 10

142600 6 -4 0.1 24 2 * GB3VHF JO01EH 1 10

142800 11 -5 0.1 24 4 * GB3VHF JO01EH 1 10

143000 10 -6 0.1 22 3 * GB3VHF JO01EH 1 10

143200 11 -8 0.1 19 5 * GB3VHF JO01EH 1 10

143400 6 -6 0.1 24 4 * GB3VHF JO01EH 1 10

143600 12 -4 0.1 24 2 * GB3VHF JO01EH 1 10

143800 7 -6 0.1 24 1 * GB3VHF JO01EH 1 10

144000 5 -5 0.1 24 2 * GB3VHF JO01EH 1 10

144200 5 -6 0.1 22 5 * GB3VHF JO01EH 1 10

144400 5 -7 0.0 22 5 * GB3VHF JO01EH 1 10

144600 10 -6 0.0 22 1 * GB3VHF JO01EH 1 10

144800 6 -8 0.0 22 5 * GB3VHF JO01EH 1 10

145000 6 -7 0.2 24 3 * GB3VHF JO01EH 1 10

145200 5 -4 0.2 24 4 * GB3VHF JO01EH 1 10

145400 11 -9 0.1 24 3 * GB3VHF JO01EH 1 10

145600 5 -8 0.2 24 3 * GB3VHF JO01EH 1 10

145800 5 -7 0.2 24 1 * GB3VHF JO01EH 1 10

150000 8 -4 0.2 22 1 * GB3VHF JO01EH 1 10

150200 8 -6 0.2 19 3 * GB3VHF JO01EH 1 10

150400 5 -8 0.2 19 6 * GB3VHF JO01EH 1 10

150600 6 -6 0.2 22 3 * GB3VHF JO01EH 1 10

150800 10 -3 0.2 24 3 * GB3VHF JO01EH 1 10

151000 4 -5 0.2 24 4 * GB3VHF JO01EH 1 10

151200 8 -3 0.2 24 1 * GB3VHF JO01EH 1 10

151400 7 -6 0.2 24 4 * GB3VHF JO01EH 1 10

151600 6 -6 0.2 22 2 * GB3VHF JO01EH 1 10

151800 7 -7 0.2 22 5 * GB3VHF JO01EH 1 10

152000 6 -5 0.2 19 5 * GB3VHF JO01EH 1 10

152200 4 -8 0.2 22 4 * GB3VHF JO01EH 1 10

152400 5 -4 0.2 22 4 * GB3VHF JO01EH 1 10

152600 5 -7 0.2 24 3 * GB3VHF JO01EH 1 10

152800 10 -5 0.2 22 3 * GB3VHF JO01EH 1 10

153000 5 -8 0.2 22 4 * GB3VHF JO01EH 1 10

153200 6 -6 0.2 22 2 * GB3VHF JO01EH 1 10

153400 5 -9 0.1 19 3 * GB3VHF JO01EH 1 10

153600 8 -6 0.2 22 5 * GB3VHF JO01EH 1 10

153800 9 -5 0.2 24 4 * GB3VHF JO01EH 1 10

154000 8 -6 0.2 24 4 * GB3VHF JO01EH 1 10

154200 6 -7 0.1 22 4 * GB3VHF JO01EH 1 10

154400 1 -5 0.1 24 4 * GB3VHF JO01EH 1 10

154600 6 -7 0.1 22 0 * GB3VHF JO01EH 1 10

154800 8 -3 0.1 22 0 * GB3VHF JO01EH 1 10

155000 12 -8 0.1 19 5 * GB3VHF JO01EH 1 10

155200 11 -8 0.1 22 3 * GB3VHF JO01EH 1 10

155400 6 -11 0.1 22 3 * GB3VHF JO01EH 1 10

155600 9 -10 0.1 24 4 * GB3VHF JO01EH 1 10

155800 12 -7 0.1 22 5 * GB3VHF JO01EH 1 10

160000 8 -5 0.1 24 5 * GB3VHF JO01EH 1 10

160200 14 -4 0.1 22 3 * GB3VHF JO01EH 1 10

160400 6 -6 0.1 22 4 * GB3VHF JO01EH 1 10

160600 5 -5 0.1 19 3 * GB3VHF JO01EH 1 10

160800 7 -6 0.1 22 3 * GB3VHF JO01EH 1 10

161000 1 -9 0.1 24 5 * GB3VHF JO01EH 1 10

161200 7 -14 0.1 24 5 * GB3VHF JO01EH 1 10

161400 6 -8 0.1 22 5 * GB3VHF JO01EH 1 10

161600 7 -9 0.1 22 5 * GB3VHF JO01EH 1 10

161800 10 -5 0.1 22 4 * GB3VHF JO01EH 1 10

162000 7 -8 0.1 19 5 * GB3VHF JO01EH 1 10

162200 4 -6 0.1 19 2 * GB3VHF JO01EH 1 10

162400 17 0 0.1 22 3 * GB3VHF JO01EH 1 10

162600 6 -9 0.1 22 2 * GB3VHF JO01EH 1 10

162800 7 -14 0.1 22 7 * GB3VHF JO01EH 1 10

163000 7 -5 0.1 22 1 * GB3VHF JO01EH 1 10

163200 8 -3 0.1 22 3 * GB3VHF JO01EH 1 10

163400 6 -10 0.1 22 5 * GB3VHF JO01EH 1 10

163600 9 -6 0.1 22 6 * GB3VHF JO01EH 1 10

163800 5 -10 0.1 19 4 * GB3VHF JO01EH 1 10

164000 0 -7 0.1 22 2 * GB3VHF JO01EH 1 10

164200 7 -13 0.1 22 4 * GB3VHF JO01EH 1 10

164400 0 -28 0.1 24 4 * GB3VHF JO01EH JO01 0 10

164600 1 -9 0.1 22 3 * GB3VHF JO01EH 1 10

164800 1 -13 0.1 22 3 * GB3VHF JO01EH 1 10

165000 7 -7 0.1 22 3 * GB3VHF JO01EH 1 10

165200 7 -6 0.1 22 1 * GB3VHF JO01EH 1 10

165400 3 -6 0.1 19 3 * GB3VHF JO01EH 1 10

165600 6 -4 0.1 19 1 * GB3VHF JO01EH 1 10

165800 5 -11 0.1 22 2 * GB3VHF JO01EH 1 10

170000 7 -2 0.1 22 1 * GB3VHF JO01EH 1 10

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