[Elecraft] P3 sensitivity

[Alan Bloom]

On Tue, 2010-02-16 at 07:17 -0800, Bill W4ZV wrote:

> I'd like to see some specs for the P3 to know that it really has the
> sensitivity to do this.  The IF OUT mod regains ~10 dB of the signal lost in
> the original design but I believe that still leaves ~7 dB that may be lost,
> according to Jack Smith's measurements:
> 
> http://cliftonlaboratories.com/elecraft_k3_and_panadapters.htm#What_then_is_the_transfer_gain_of_the_K3_
> 
> 73,  Bill

On my K3 (with IF output mod) I measured a "transfer gain" (gain from
antenna input to IF output) of around -6 to -7 dB with preamp off and +4
to +5 dB with preamp on, depending on the band.

The noise figure of the P3 is a little hard to measure since there is no
access to its "IF" signal and there is no product detector/audio output,
but the design should be capable of around 7 dB NF.  Assuming the NF of
the K3 is 17 dB with preamp off and 10 dB with preamp on, you can crunch
the numbers and calculate that the NF of the K3/P3 combination should be
about 18.6 dB with preamp off and 10.7 dB with preamp on.  (Actually the
18.6 dB figure assumes that all K3 noise is introduced before the IF tap
point, which is probably too pessimistic an assumption.)

So the NF of the P3 display should be within a dB or so of the NF of the
K3 alone.  And of course band noise will totally swamp out receiver
noise in most situations anyway.

You should be able to see signals on the P3 that you can't hear.
(Unless you have VERY good ears!)

Alan N1AL