Barry,
Not disagreeing. I bought my K3, SN4043, in 2010. It has an
internal preamp (push PRE) which gives about 10-dB gain (I
think). A few years went by and Elecraft announced the PR6 external
"add-on" preamp to improve 10m and 6m receiver performance. They
kind of admitted the bare K3 was lacking gain at those
frequencies. That "system" gain minimum is needed to overcome
following stage NF for best sensitivity (MDS). I've measured -145dBm
MDS on 6m with my PR6. K3 was about -133 dBm without the PR6 on 6m
(-73 dBm is S9; 9 s-units should be 6x9 = 54 dB; -73dBm-54dB = -129 dBm).
Of course ambient noise will rule how weak a signal can be
copied. On lower freq. HF bands thermal sky noise has long been that
limitation; at 25-MHz Tsky starts to drop as one transitions into
VHF. Recent (?) rise in residential/industrial RF noise has affected
pretty much everyone (I live in a widely dispersed community of 4,000
in Alaska and noise at 2m has become terrible (S7 over a S3 noise
floor). Use of a preamp may become unproductive at some level of
noise (maybe).
I do 6m eme and use a GasFet preamp at the antenna for minimizing NF
and it helps enough over just using the PR6 (with internal preamp
off). I use DIGOUT1 to turn on/off the PR6. Since it has a nice
bypass, I use that to connect to my tower-top 6m preamp. BTW I have
copied 6m-eme signals just using the PR6.
I don't have a K3s so assuming preamp-2 is equivalent to the PR6-10
(expanded to 24-MHz).
I actually wonder if there are some arc-welder rock bands? Or
dueling Plasma TV's?
I'm heading up north (frequency-wise) to 1296 for a little quiet-time <snicker>
73, Ed - KL7UW
Hi, Barry,
It's not the signals that determine whether you need a preamp, it's
the noise level. A receiver should have enough gain to put its
internal noise floor below the external, atmospheric noise floor, so
that it doesn't become the limiting factor in hearing weak signals
close to the noise. That's what makes a preamp necessary.
Certainly, if your noise floor is lower than here in urban North
America, there may be cases where a preamp does us no good, but is
necessary for you.
I think I once posted a case study here a while ago... but I would
have to go searching for it. The numbers I used were definitely
US-biased. Life for a ham here has become a really discouraging
exercise in trying to copy signals below your neighbors' app-enabled
pet massagers and internet-controlled wine coolers, all fed by those
infernal switch-mode power supplies. My two neighbors' homes are
really just enormous square wave-producing things. This is also why
everybody you hear is running 1,000 watts or more. It's power
inflation. The military spends millions on radar jamming equipment...
when all they'd have to do is do whatever my neighbor Johnny is
doing. He must have a phased array radar, arc-welding, barrage
jamming plant next door. If you ever bring your rig over here on
vacation, be sure to pack a 60 dB attenuator with it.
R,
Al W6LX
73, Ed - KL7UW
http://www.kl7uw.com
Dubus-NA Business mail:
dubus...@gmail.com
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