There seems to be something floating around that if there's noise, it
must be the K3's fault. While EME frequencies have very little
ambient noise unless the antenna is aimed at the sun or some known
noise source, for MF and HF, there is plenty of ambient noise that
will come in on any antenna.
At my location near Raleigh, NC, on 160m in the daytime, using 500Hz
bandwidth the ambient noise is always 3 uV to 5 uV coming in on my 160
transmit antenna, now and then in the 30-70 uV range (source unknown).
On ten meters the ambient noise is around 0.2 microvolt with my beam
pointed NW. On ten when I disconnect the lead to the antenna, the
noise drops another 11 db, meaning that the K3's internal noise is the
equivalent of 0.06 uV coming off the antenna.
With K3 preamp on, no ATT, AGC off and RF gain to max, the K3's
internal noise is a mild white noise. When I reconnect the antenna,
the noise jumps up to mid-range comfortable audio level, there is
stuff in the noise including some component of 120 cycle hash. It's
not a hiss anymore. Stuff coming off the air.
Switching back to 160m, to get the same pleasant level of noise
audio, I have to turn off the preamp, turn on the attenuator, and back
off the RF gain to 2pm to reduce the overall gain of the K3 to get the
outside ambient noise to match the sound level I want. This is NOT
engaging the AGC. I have reduced the overall gain of the RX to match
the band.
In older radios that seem quiet on 160, the gain is either
intentionally reduced on 160, or the RX just didn't have the gain on
any band, and the performance on the high bands really stunk.
RX gain (RF gain +PRE) that is comfortable for 10 meters will not work for 160.
In the absence of a louder signal, 5 uV noise will be set to regular
signal level by the AGC, the same level it would have put the way in
the clear 5 uV signal on 10m.
In the FT1000MP there was a default menu setting to reduce the radio's
overall gain as the frequency went down. In contests we generally
turned that off, preferring to handle gain controls ourselves because
we had quiet listening antennas for low bands and occasionally quiet
conditions on big antennas.
The K3 has left those decisions to us so I can use the RX preamp on
BOG listening antennas to make up for that antenna's natural loss. I
like that. It gives *ME* the choice on how to set the gain instead of
forcing me to supply a switchable preamp to make up for an
artificially reduced gain
For 160 listening on the transmit antenna it's preamp OFF, ATT ON, and
RF gain backed off to 2 or 3 pm. For the BOGs on the RX ANT port it's
still RF gain at 2pm, but ATT off and preamp ON. No roaring noise, I
can copy all the signals clearly AND use the AGC to keep the 20 over
9's from blowing off my ears. I backed off the RF gain to place the
ambient noise at the audio level I'm willing to put up with.
Using that procedure, I DO NOT have to jockey RF as I tune across
signals. I DO NOT have noise roaring in my ear. I set it for the
band and the setting suffices for the evening.
In the Orion, the RF gain was not a dedicated knob. It was a menu
item set by band. One owner (who had had it for over a year) brought
one to a contest, and everybody was complaining about the AGC bringing
the noise up to a roar on the low bands. The ONE change that was
made? Set the by-band-by-mode digital RF gain in the menu down from
100 (pedal to the metal max) to a number that left the band noise at a
tolerable level. End of problem. End of complaints. It was fine
after that.
Very interestingly, the owner could not understand our complaints and
had never done that himself. Took a room full of hollering peers to
get him to even look at it. Even then it was a guy who had never used
an Orion before that figured it out.
73, Guy.
On Thu, Jan 7, 2010 at 9:11 AM, Wes Stewart n...@yahoo.com wrote:
Doug,
It's been a long time since I was on EME and time has marched on to where the
current ops are using digital modes to pull signals from below the noise and
calling them contacts. But when we actually listened for signals, hours
were spent listening to noise and I can assure you that distortion, artifacts
and whatever else you want to call stuff that shouldn't be there all
contributed to fatigue and the ear-brain's ability to discern signals.
Wes N7WS
--- On Thu, 1/7/10, DOUGLAS ZWIEBEL doug...@gmail.com wrote:
From: DOUGLAS ZWIEBEL doug...@gmail.com
Subject: [Elecraft] three recordings - say what?
To: Elecraft Reflector elecraft@mailman.qth.net
Date: Thursday, January 7, 2010, 6:40 AM
Excuse me, but are all of you guys
listening to NOISE ONLY? I
mean...noise WITHOUT a signal? What good is
that? Sorry, but I never
listen to noise on purpose.
I cannot see any practical value in such a test.
de Doug KR2Q
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