Hi Frank,
On 10/19/2018 9:47 AM, Frank Kirschner KF6E wrote:
One thing I haven't seen discussed on this reflector is improving the
S/N by narrowing the receiver bandwidth. It is no surprise that
decreasing the bandwidth received increases the S/N, by 10 to 15 dB,
sometimes more. When I see a station I want calling at -24 or so, I can
narrow the BW and get solid communications. This is very easy with the
graphical presentation and digital filtering of the Flex 6600, but with
a little practice, could be done on any modern receiver.
This means that, if we knew where the stations were calling at -30 or
so, we could focus on them and bring them up to the point of making
contact. Since you can't decode stations at that S/N, it would have to
be done "out of band." Is there any thought being given to setting up an
FT8-only DX cluster with exact frequencies?
What a fascinating hobby!
Desirable settings for received bandwidth are discussed in the WSJT-X
User Guide here:
http://www.physics.princeton.edu/pulsar/K1JT/wsjtx-doc/wsjtx-main-1.9.1.html#TRANSCEIVER
There is NO decoding advantage to setting a narrow received bandwidth,
(for example, 500 or even 200 Hz) centered on a desired weak signal.
Why not? Because the WSJT-X decoders already filter the data in
software, down to a detection bandwidth equal to the keying rate (6.25
Hz for FT8, 2.69 Hz for JT65, 1.74 Hz for JT9, etc. A narrow receiver
bandpass setting will only serve to confuse the decoder and bias its
measurement of S/N, producing unreliable values.
-- 73, Joe, K1JT
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