LF: My 137.766kHz ERP is approx 6.6uW

[Roger Lapthorn <rogerlapthorn@gmail.com>]

Today I repeated my field measurements to establish the ERP of my 8W QRSS3 137.766kHz beacon feeding my earth-electrode antenna. This time I believe I did the measurement correctly. Here's how.

1. Travel 2km from the home QTH with E-field probe, FT817 and PC running Spectran.
2. Choose a location in the best direction for the "loop in the ground" so the measured signal strength is close to the maximum possible i.e. not off the sides of the loop. I chose a location due west free from wires, trees, pylons etc.
   
3. Set up FT817 so the RF gain is adjustable and turned well back and the AGC is inactive.
4. Tune in my LF beacon and adjust the RF gain to the lowest possible detection level.
5. Measure the S/N of my signal with Spectran and note reading.
6. Retune to the German commercial station DCF39 (138.830kHz) and, without adjusting the RF gain at all, measure the S/N with Spectran.
7. Repeat these measurements 5 times.
8. Calculate the difference in dB between my signal and DCF39, in my case 41.3dB
9. Using the assumption that DCF39 has a field strength of 1mV/m, work out my own field strength: 9uV/m
   
10. Using the formula ERP = (E^2 * d^2)/49 work out the ERP.

Answer?     My measured ERP on 137.766kHz is approximately 6.6uW

Caveats:

1. If DCF39 is not approx 1mV/m then the ERP needs to be adjusted up or down proportionally.
2. Measurement error is approx +/- 2dB.

Stations who have managed to receive this beacon (best DX so far 56.7 and 61km) are doing very well.

The QRPp QRSS3  beacon is still running over the weekend and more reports would be appreciated.

73s

Roger G3XBM

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