In a message dated 4/15/00 6:10:06 AM GMT Daylight Time, [email protected]
writes:
<< G3WSC Beacon
Saturday morning ? 34.1 dB microVolt/m
at a distance of 697 km
>>
Hi Geri.
Some information which may help:
As of last night at 00.50 local I had set up the system as follows.
Transmitter. My old MRF linear fitted with class D drive and 4 STW34NB20 FETs
36V supply at 20 Amps. i.e. 720 W DC input.
estimated efficiency 85% after the LPF. or 612 W out. (let's say 600)
efficiency of mast at 137k (Decca figures) 15% so 90W radiated
BUT.......
losses in matching coils are suggested to reduce this to 10% or 60W.
For a 15% efficient antenna to radiate 60W from a 600W transmitter, then the
loss in the loading coils etc. must be 200W.
( since 600 from tx - 200 losses = 400 and 15% of 400 equals 60W radiated)
By 00.30 local we had already bypassed the variometer's antenna current
circuit to save the electronics, but had watched the fwd / ref network expire
in spectacular fashion.
After all those estimates. some more real measurements to ~proove~ them.
The antenna current overnight was measured at 9A.
hence:
9 x 9 = 81 and 81x 5 ohms = 405 Watts (after losses) delivered to the
antenna which at 15% efficiency is just about 60W radiated.
and yes, the variometer ( A litz wire professional unit) was quite warm.
As for radiation pattern / ERP / and the path loss over 697km.. I'll leave
that to the you and the group. - I look forward to seeing the data on the
website.
YXM's TX will take over today.
Hope that helps.
73
David G0MRF
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