My ERP on 137.766kHz is.......

Thanks to G4FEV, I've just realised that I made a fundamental mistake measuring my field strength, forgetting to turn off the AGC when taking the measurements of my signal relative to DCF39. Whereas my initial measurements indicated the ERP was in the low mW region, in reality my signal is much, much weaker. For example, G4FEV reckons my signal is some 70-80dB weaker than DCF39 where he is, if not more! So, tomorrow I shall have to try the test again and see if I can get a sensible figure with AGC turned OFF.

G3XDV's screenshot of my QRSS3 LF signal this afternoon.

Mike G3XDV (61km) has just sent me a very comprehensive report with 178 screenshots of my QRPp signal over the last 30 hours. Copy was remarkably good considering everything. Again, I am amazed how well this works.

More results on 137kHz and a better ERP calculation

Today I managed, I believe, for the first time to accurately measure the ERP of my QRPp system on 137kHz. This is the method used:

• Using the E-field probe, FT817 (AGC off, gain backed off as far as possible and a 10dB pad between the EFP and the FT817) and Spectran I went to my usual test site 1.5km away from the QTH, 45 degrees off the main lobe of the TX loop/earth electrode antenna.
• Measured the signal level of DCF39 on 138.83kHz
• Measured the signal level of G3XBM on 137.675kHz
• Repeated this three times to reduce errors.
• Noted the difference in FS level.

Difference in signal level = 44dB . I feel pretty confident this is an accurate figure now and not effected by AGC and overload. Assuming DCF39 is 1mV/m here (info from Alan Melia)  then my FS at the test site is 6.4uV/m.  Using the formula ERP = (E*d)^2/49 where E = 6.4*10E-6 and d=1.5*10E3 gives an ERP = 1.9uW giving an antenna efficiency of -63dB using the earth electrode antenna with the elevated feed and 4W from the PA. 

The test site is about 45 degrees off the main line of fire of the antenna, so in the best direction it could be 10dB (?) stronger, i.e. 20uW ERP giving an antenna efficiency of -53dB in the best directions. Frankly I'm amazed that anyone can copy this signal at any distance, so full marks to G3XIZ (48km) and G3XDV (62km).

Mike G3XDV sent me another screenshot of my signals this morning during the tests. if you look carefully you can just make out "G3X..." in QRSS3.

62km with QRPp and earth electrodes on 137.675kHz

Today I ran an earth electrode transmission test with Mike G3XDV in Welwyn Garden City 62km away. I put my QRSS3 8-10uW ERP beacon on and Mike took regular screen shots through the day until mid afternoon. Although unable to copy the message in QRSS3, when using QRSS30 speed for reception the start and end of the message sequences (9 mins 7 seconds apart) could clearly be seen. He was able to precisely detect when the beacon was turned off. Mike estimates another 6-10dB should allow him to read the message properly. Signals were weaker later, possibly because of rain here altering the effective loop size within the ground.