Posted by
K9MA on
May 23, 2018; 2:29pm
URL: http://elecraft.85.s1.nabble.com/When-to-use-the-preamps-on-the-KX2-KX3-vs-K3-K3S-Wayne-Burdick-tp7641068p7641105.html
The problem with simply reducing the gain is that the AGC may become
ineffective, forcing the operator to increase audio gain on weak
signals. Then the strong signals can be loud enough to be
uncomfortable, or even cause hearing damage. I like to keep the gain
high enough to get some AGC action on the weakest signals, and reduce
"RF Gain" when necessary to distinguish stronger signals from weaker
ones. "RF Gain" in modern receivers really just sets the maximum gain
the AGC will allow, so reducing it only attenuates weaker signals.
That said, turning off the preamp and/or enabling the attenuator should
be necessary only if strong signals are causing overload. Of course, if
the receiver has enough gain for a low enough noise floor and good AGC
operation on weak signals with the preamp off, there's no advantage in
using it.
73,
Scott K9MA
On 5/23/2018 08:07, Bob McGraw K4TAX wrote:
> One of the topics I've discussed with with noted engineers has to do
> with use of a Preamp and use of the Attenuator and use of the RF Gain
> control. In general the optimum legacy receiver performance occurs
> when the receiver noise floor is some 10 db below band noise. Being
> such, how does one attain this? If the no signal band noise is S-5
> or -97 dBm, and receiver noise floor is -133 dBm {i.e K3S}, this says
> one should use a combination to total 26 dB Attenuation and RF Gain
> reduction. Certainly one would NOT want to have a Preamp engaged
> under these conditions. Likewise, if the band noise is -121 dBm or
> about S-1 and the receiver noise is -138 dBm {Preamp engaged} one
> might wish to reduce the RF Gain a bit.
>
> From experience and my observing other hams operations, many seem to
> think more gain is needed to hear or pull out weak signals from the
> noise. I find the proper use of the Preamp and specially the correct
> amount of Attenuation and RF Gain reduction, weak signals seem to pop
> out of the noise.
>
> 73
>
> Bob, K4TAX
>
>
>
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