Thanks Jim, K9YC, for the detailed information. I too concur that wide
signals can more likely be the result of the waterfall adjustments, or
the system gain, which has the no signal noise level above 30 dB on the
WSJT-X bargraph indicator. If this is the case, adjust the audio level
in the Windows application to reduce the level.
As to AGC, I run AGC on my K3S on Fast when operating FT-8. Likewise for
CW. Thus I've found no disadvantage in having it on, and little to no
advantage in having it off. Other than I manually have to adjust RF gain.
On that note, for the most part on 160 M, 80 M & 40 M I do run 15 dB to
10 dB of Attenuation and back the RF Gain down accordingly. For higher
frequencies, 60 M and above, I do not use Attenuation and adjust the RF
gain accordingly. This seems to produce optimum receiver performance.
On 6 M I do engage the preamp.
73
Bob, K4TAX
On 7/17/2018 12:59 PM, turnbull wrote:
Jim, Thank you for the solid information.
73 Doug EI2CN
PS I understand AGC should be disabled.
Sent from my Samsung Galaxy smartphone.
-------- Original message --------From: Jim Brown <[email protected]>
Date: 17/07/2018 18:51 (GMT+00:00) To: [email protected] Subject: [Elecraft]
FT8 and Strong Signals
On 7/17/2018 8:52 AM, turnbull wrote:
I agree but many people are suffering from wide FT8 signals from others with
strong signals.
Part of this is perception rather than reality -- a failure to
understand the waterfall display. Because the waterfall displays both
signal strength and spectrum, a very strong signal may APPEAR to be
broader than it really is. I have a half dozen or so neighbors running
FT8 on 6M within about 15 miles, and all are running a power amp (mostly
KPA500, but my closest neighbor, about 5 miles, runs 1.3kW. Most of us
are running K3s. It's not uncommon for one of these signals to SEEM to
occupy 500 Hz or more, the reality is that I often decode weak signals
within that 500 Hz.
Another point. K1JT recommends setting audio level into the computer for
an indicated 30 dB on the bar graph. I think this is part of the problem
caused by strong signals taking over the AGC and greatly reducing the
gain. If, for example, a local who's 30 dB over S9, reduces the RF gain
by 30 dB, an S9 signal would be below the level of the sound card! I set
audio level into the computer for the highest level that doesn't flash
RED (indicating digital clip) on strong signals. My bar graph typically
runs 50-60 dB. With this setting, even when AGC has reduce the gain by
30 dB or more, weak signals are still well above the "bottom" of the A/D
converter, and are decoded just fine.
73, Jim K9YC
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