Dear LF Group,
Thanks to all who sent reports on the WSPR beacon, which ran from about
1950utc - 0705utc. Was very pleased to be copied by TF3ZH - I think this is
the first report of any description from Iceland that I have received.
The station is running about 90W into my inverted-L antenna at about 10m
high, with antenna current of 1.8A, to give somewhere close to 1W ERP. I am
using the EER tranverter driven by an IC-718 on USB fed from the PC
soundcard.
The 4-FSK mode signal is certainly constant amplitude (I checked...), so can
use a class D TX, although you would still need some means of translating
the 1.5kHz soundcard output to the signal frequency. Or alternatively an
independent way of generating the encoded data and a 4-FSK modulator, as
SM6LKM has mentioned. As far as I could see, it transmits the same 2 minute
bit sequence every time, so for a beacon that should not be too complicated.
As G0NBD says, it is certainly a "rig-boiler" mode when 100% TX is selected,
with continuous key down, 100% output operation, except for a few seconds
every two minutes. The EER transverter rig does OK, since the amplitude
modulator is wide open all the time and dissipates very little power, and
the class D PA is quite efficient. In practice, most of the heat seemed to
be coming from the IC-718, although this was only running at about 5W
output. However, if this beacon mode were more widely used, it would
probably be for combined TX/RX with 20 or 25% TX duty cycle, so as long as
the TX could operate at full power for a few minutes, it would get some time
to cool down.
Cheers, Jim Moritz
73 de M0BMU
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