[Elecraft] KX3 High RCV Noise - need advice

[Don Wilhelm]

Rich,

Your observation that changing the AGC Threshold is the key to your 
question.
The KX3 has adequate RX gain to hear the antenna noise.  The AGC 
Threshold controls just how much of that noise is perceived by the KX3 
as a valid signal and is worthy of being heard as a valid signal.
Some experimentation at your local noise level is in order.

73,
Don W3FPR

On 11/15/2013 9:14 PM, Richard Patrick wrote:
> I began this adventure by upgrading my KX3s Firmware to 1.61 and 1.23.
>   After that I attached my station antenna (which is normally connected to
> an Icom 7700) to make sure the KX3 worked.
>
> >From the KX3 I noticed a high amount of noise whilst receiving.  A flip of
> the coax switch connects the same antenna to the Icom radio and it shows
> pretty low noise.
>
> Quick noise test comparison examples:
>               *  KX3            Icom*
> 40M         S5-6           S2-3
> 30M         S8-9           S0-1
> 20M         S8-9           S0
> 17M         S7-8           S0
> 15M         S6              S0
>
> Both radios were tuned to a no signal portion of the CW bands and the
> radios were in the CW mode.  Both radios bandpass were set to 500 Hz.  On
> each band, the antenna (66 ft doublet w/ auto tuner) was tuned to SWR of
> 1.5 or less.
>
> Before I elaborate further... I Downgraded the KX3s software back to 1.50
> and 1.21 and I still have high noise.
>
> When a signal (higher level than the KX3s receive noise level) is tuned in,
> both radios S meter tracks the same, i.e S9+10 = same.  Also, I got out my
> very old Elecraft XG-1, installed a fresh battery, and S8.5 on the Icom =
> S8-S9 bars on the KX3.  With the antenna removed from the KX3 there is no
> noise.
>
> My KX3 is serial no 1588, the Automatic Ant Tuner is switched to BYP, and I
> do not have the Roofing Filter installed.  AGC Threshold = 005.  Changing
> AGC Threshold to 004 reduces noise, but the S-meter shows the same reading.
>   ATT is off, PREamp is off.
>
> I use my KX3 in the field for SOTA 95 percent of the time.  The times I
> have used it in my home shack it has performed well. Now it's very
> difficult to hear low level signals.
>
> My question to the group is... Why does my KX3 present such high receive
> noise?  Have I set something incorrectly?  Any advise is appreciated.
>
> Thanks and regards,
>
> Rich KR7W
> Tacoma WA
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