[Elecraft] K3 Preamp 2

[Edward R Cole]

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
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