Jim, Markus, and the group:
First of all, many thanks Jim for doing those measurements. I don't have the
test equipment to do these things and I am too far away from Rugby. Your
results seem to say that these spurii are even lower in level than 42uW.
Your posting may have crossed with my last one in which I revised the
estimate of the Rugby mean erp down to 2.45kW, calculated from the published
peak value of 250kW and the calculated peak/mean ratio of just under 1%.
The difference between our figures is now just 4dB (10*log(42/16)).
This 1% peak/mean ratio (for the Rugby tx) comes from the published LORAN
waveform which effectively says that the special shape of a LORAN pulse is
equivalent in power to a rectangular pulse of 83.2uS duration. Your estimate
of 2.2% (45:1) is probably stretched because of the narrow bandwidth of your
receiver, or maybe it's stretched by the narrow bandwidth of the Rugby
antenna. If the Rugby antenna is indeed smaller, then the pulse peak/mean
ratio will be less, the peak erp may be less or the mean power may be more,
but I can't figure out if the spurii level would increase or decrease or
stay the same!
Markus: Thanks for doing the calculations. The small difference between our
figures is just the difference between 136 and 137kHz - I forgot to say that
I had used a value half-way between the 135 and 137 kHz estimates from the
spectrum graph. Incidently, your calculation of the spectrum is interesting.
It does show that the Rugby antenna is similar in bandwidth to the
mathematical model, so maybe it's smalller size is not so important after
all.
Thanks again to everyone who replied to my first posting and helped in the
investigation. The best guess is that LORAN spurii are in the 16-42uW range.
Can I close the topic now -it's taken up enough bandwidth already!
73
Peter
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