Bill,
AS usual you have made an important observation. You made me curious
about my 6m environment so:
I turned off both my external preamp (RX ANT) and my internal preamp
(PRE) and merely looked at s-meter reading (S=1). I removed the
antenna with no discernable change in audible noise and s-meter is
the same S=1.
So with antenna connected I turned on internal preamp (PRE) and S=2.
With internal preamp off and my external preamp* on (RX ANT) S=2/3
With both preamps on S=4
Both preamps on with antenna disconnected; S=3
So its a pretty quiet area with only one s-unit rise in noise.
For comparison with a 50-ohm termination both preamps see S=4
This indicates the preamps are low-noise below a 290K source.
NOW for that QRO and 8-element long-boom yagi - hmm.
73, Ed - KL7UW
*Note external preamp is ARR P50VDG Gasfet 0.5 dBNF, 22-dBG
------------------------------
Message: 24
Date: Mon, 21 Jun 2010 20:05:00 -0600
From: "Bill VanAlstyne W5WVO" <w5...@cybermesa.net>
Subject: Re: [Elecraft] K3 PR6 preamp [was: Another Happy Customer]
To: <elecraft@mailman.qth.net>
Message-ID: <e78a2106e87a4f55911f00382d8dd...@billhp9250>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
reply-type=original
From: "K5RC" <t...@k5rc.cc>
> I also added the GaAsFet 6M preamp to the station and it makes a HUGE
> difference on Six.
It needs to be pointed out from time to time that whether the PR6 makes "no
discernible difference" or "a HUGE difference" depends on one critically
important variable: YOUR NOISE LEVEL!
Because I live in a large-city metro area complete with big mountain-top RF
outlets broadcasting thousands of kilowatts of RF (along with plenty of
spurious broadband crud), my noise level on 6 meters is relatively high.
Only in my quietest direction (northwest) at the quietest time of day (early
morning) does adding the PR6 preamp allow me to hear anything that I can't
hear just as well without it. Wouldn't it be nice to really NEED that PR6?
Yeah, it sure would... but the realties are what they are.
The WSJT software package (for weak-signal digital modes FSK441, JT6M, et
al.) includes an easy way to roughly assess your noise level, reading out
directly in dB above the receiver's internal noise floor (MDS). If, while
using the K3's internal preamp, your antenna noise reads 8-10 dB or more
above MDS (typical when using a decent gain antenna in a metro area), the
sad fact is that the PR6 probably won't help you. If your antenna noise is
only a few dB above MDS, then the PR6 might help, as it is very quiet (i.e.,
has a low noise figure) and could contribute to a better overall
signal-to-noise ratio.
On the other hand, if you are lucky enough to not really be able to hear any
6m antenna noise with the K3's internal preamp on... First, double-check to
make sure you actually have connected the antenna... And if you have, you
should congratulate yourself and get ready to REALLY have some fun on 6
meters once you connect in that PR6 preamp! You might also want to get a
good RF power amplifier, as you will want to be able to work all the DX
stations you can hear -- some of whom are running REALLY BIG QRO, trust me.
You will be in no danger of being an "alligator" station (all mouth and no
ears).
Bill W5WVO
DM65qh
73, Ed - KL7UW, WD2XSH/45
======================================
BP40IQ 500 KHz - 10-GHz www.kl7uw.com
EME: 144-600w, 432-100w, 1296-60w, 3400-fall 2010
DUBUS Magazine USA Rep dubus...@hotmail.com
======================================
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