[Elecraft] [K3] High internal noise level

[Joe Subich, W4TV]

Pete,

The first thing I would do is get a calibrated signal generator (the
XG-2 is fine if you don't have something more complex) and perform
the RF gain calibration in the K3 Utility.  Follow that with an S-
Meter calibration.  After calibration with S9 = 50 uV (-73 dBm), I
see no S-meter activity with a dummy load or antenna on a "dead band."
The P3 shows the noise floor between -140 and -145 dBm (2 to 3 S units
BELOW S0) with a dummy load and around -130 dBm (still less than S0) 
with my low Windom and no preamp on 20 meters.

Second, your AF Gain may be a bit high ... mine is normally around
9 - 10 o'clock with the Sony bookshelf speakers or the CM-500 and
around 10 - 11 o'clock with the Heil Proset.  That represents a
comfortable listening level for most signals and provides almost
no noise with the antenna on 20 (160/80/40 are a different story)
and quiet with the dummy load/no antenna.  As a reference point, the
"no antenna" noise is noticeable at full RF/AF gain and the 20 meter
antenna noise is at the threshold of becoming uncomfortable at full
AF/RF gain.  Note, I generally do not need the preamp even with a
poor antenna except on 6/10/12 meters and always use ATT on 160/80.

I am not using the default settings for ACG threshold and slope ...
I prefer setting both to "8" which provides for a higher threshold
before the onset of AGC and less flatness after AGC begins.  For an
excellent look at the K3 AGC behavior see Jack Smith's (W8OZA) work:
http://www.cliftonlaboratories.com/elecraft_k3_agc_and_s-meter.htm .

73,

    ... Joe, W4TV


On 8/28/2010 6:18 AM, Pete Smith wrote:
> Ever since I got my K3, I have been a little surprised at what seems to
> be a relatively high noise level with no antenna connected (or on a
> dummy load).  Very unscientifically described, on 20m it registers 1-2
> bars on the S meter, and the background is quite loud on the speaker
> with the audio gain set at 12 o'clock (RF gain full, AGC - fast,
> bandwidth 200Hz with a 500 Hz roofing filter in, no noise blanker or
> noise reduction).
>
> The radio seems to perform fine, and I have not had the feeling that I
> was missing many signals because they were being masked by receiver
> noise.  Nonetheless, I wonder how this compares with others' experience,
> or with the factory expectation?
>
> 73, Pete N4ZR
>
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