Hello all,
I have been thinking about the recent debate wether a separate USA and
European channel is a necessity.
Looking at the quoted figures for signal levels the required dynamic range
is a modest 40 to 50 dB.
This should not be a problem for any half decent receiver, but is it
really?
In the case of WSPR we are dealing with signals that are located in a 200
Hz frequency range.
This is something completely different than dealing with strong signals at
HF.
To measure the dynamic range, often a 20 kHz wide spacing is used for the
test tones.
The last years more realistic spacings as narrow as 2 kHz have been used.
Back to WSPR. For adequate WSPR reception the AGC should be switched off
and the dynamic range of the receiver and also the audio channel should be
40 to 50 dB.
Rick Campbell, KK7B wrote in the August 1992 issue of QST a fascinating
article: "High Performance Direct Conversion Receivers".
I have been reading it again today and I think that it shed some light on
the WSPR reception issues.
Rick constructed a direct conversion receiver where the intermodulation
products of two tones (600 Hz and 800 Hz) were 62 dB below the tones. For
a typical receiver this was about 35 dB. A CW pile up sounds like music
and each station can be picked out with ease on the direct conversion
receiver. On a typical commercial receiver this is not the case. The only
exception which I have encountered so far is the AR7030.
To cut a long story short, it might be very well possible that both
parties in the debate are right, but that the main problem is less than
optimum receiver performance.
Lately I have been playing with Tony Parks, KB9YIG, RX LF Ensemble kits.
It is a bit outside the scoop of this email, but with a good sound card
the in-channel dynamic range is awesome. I believe that these simple
receivers outperform most of the analogue current offerings on the amateur
market.
Looking forward to your comments,
Best regards,
Roelof Bakker, pa0rdt
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