Re: KPA1500 and FT8

Posted by Jim Brown-10 on Mar 04, 2018; 9:15pm
URL: http://elecraft.85.s1.nabble.com/KPA1500-and-FT8-tp7638861p7638867.html

On 3/4/2018 11:58 AM, Erik Basilier wrote:
> The reason seems to be that they have been taught to use a wide receiver in
> combination with a sound card, so as to get a panoramic view including other
> stations. This lets a strong nearby station control the agc, and affects
> reception of stations on a range of frequencies.

There is a VERY good reason why WSJT developer, K1JT, advises users to
use wide IF bandwidth, and it's NOT the panoramic display. The reason is
that filters introduce phase shift in the passband, and phase shift is
the enemy of good decoding. The same physics, by the way, applies to
other digital modes, including RTTY. Serious RTTY contesters have
learned that 500 Hz is a good setting. Our ears may hear off-frequency
QRM louder than the signal we're trying to detect, but the decoder does
just fine.

This is true of both WSJT and other decoders I use for RTTY. Indeed,
even though a strong signal may APPEAR to cover much of the display, if
the strong signal is  CLEAN and you have your receive audio levels to
the computer set to that the strong signal doesn't overload the
computer, the decoder is likely to copy signals that appear to be
covered by it. If you consider AGC pumping a problem, simply turn it off.

FWIW, with both FT8 and RTTY, I keep AGC on Slow, and set WSJT-X for an
indicated level as high as 50 dB, using the RF Gain. With this setting,
if a strong signal reduces gain in the radio, weak signals will still be
strong enough at the computer to be decoded. I mostly use WSJT-X on 6M
and 160M, but the few times I've gone to FT8 on HF to work a DX trip,
I've more than filled the 36 slots in JTAlert. So I guess it's working. :)

73, Jim K9YC


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