[Elecraft] K3 receiver noise questionable test results

[K2MK]

Hi Don:

First I tried actually removing the antenna at the SO239 connector in case 
it was an issue of isolation suggested by N4LQ. This provided some minor 
reduction in background noise. So obviously some of the noise is coming in 
on the antenna.

Following your suggestion I tuned in a S5 level CW signal on 40 meters with 
AGC OFF and ATT ON. I reduced the RF gain to eliminate the noise but that 
also eliminated the signal. In order to copy this normal level signal I must 
have some accompanying level of background noise.

With an S9 or greater signal I can reduce either the RF gain or the AF gain 
and be free of background noise. Sometimes an S7 signal will suffice.

The same affect is present in my Sub RX.

After reading the many posts describing RX noise, I don't think I have a RX 
fault. I think my K3 is experiencing what the others have been posting 
about. The background noise is not extreme. It's just always there.

73,
Mike K2MK

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From: "Don Wilhelm" <w3fpr at embarqmail.com>
Sent: Friday, December 18, 2009 9:01 AM
To: "K2MK" <k2mk at comcast.net>
Cc: "Elecraft Reflector" <elecraft at mailman.qth.net>
Subject: Re: [Elecraft] K3 receiver noise questionable test results

> Mike,
>
> That could easily happen if you have the AGC on.  That would be especially 
> true if you have the preamp on when it is not needed and are running the 
> RF Gain at its full setting.  With a signal present, the AGC is acting to 
> keep the receiver gain low, but when the signal is no longer present, the 
> receiver bounces back to full gain.
>
> Try the same test with the AGC off and the preamp off (even with the 
> attenuator on) and the RF Gain backed down so the no-signal noise with 
> your vertical connected is just perceivable.  Then tune in a signal, note 
> its strength and remove the antenna.  The noise level should be absent 
> (unless you have the AF Gain set really high).  If you still get noise 
> with no antenna, you have a receiver fault that needs attention.
>
> 73,
> Don W3FPR
>
> K2MK wrote:
>> One test that I have performed leaves me scratching my head as to its 
>> results. Maybe someone can enlighten me. I tune to a medium strength CW 
>> signal and press my ANT button to switch between ANT 1 and ANT 2. I have 
>> nothing connected to ANT 2. The signal disappears but the background 
>> noise level remains the same.
>>
>> 73,
>> Mike K2MK
>