Conrad,
Assuming this is for 2m-eme, I would guess you have two preamps
before the transverter which are adding gain and setting the system NF.
If the preamp gain is approx 25 dB or higher, it will likely set the
system NF as it has enough gain to overcome the NF of the transverter and K3S.
I have a dual receive transverter that provides 28-MHz to both main
and sub receivers in my K3. I tap the 1st IF of both receivers in
the K3 to provide output to two coherent SDR that provide two IQ
outputs to a four port soundcard and drives MAP65.
My preamps provide 0.26 dB NF which has a MDS of -146.3 dBm with
500-Hz bw. The combination of the 0.8 dBNF transverter with 17-dB
gain, and K3 only add 0.2 to the NF and lower MDS to -146.2 dBm.
adding 6-dB loss after the transverter only raises NF to 0.30
dB. This is using 12 dBNF for the K3; lowering to 9-dB lowers system
NF to 0.28 dB
On 2m this is insignificant due sky noise and man-made noise having
more effect on actual MDS. I used Tsky=250K in above calculations
which is probably not achievable in today's RF environment. If I use
Tsky=1000K, MDS drops to 141.2 dBm.
73, Ed - KL7UW
Date: Mon, 2 Dec 2019 13:19:17 +
From: Conrad PA5Y
To: "elecraft@mailman.qth.net"
Subject: [Elecraft] KRX3A sensitivity
Hello all.
I have a dual diversity Xpol EME system for 2m and a dual coherent
transverter. I am trying to calculate if I have enough gain available
in the transverter to split the output 4 ways with a loss of approximately 6dB.
The K3S has an MDS of -138dBm in a 500Hz bandwidth which is
approximately 9dB noise figure with preamp 1 switched on. Does the
KRX3A have a an independent preamp1? I know that the preamp2 is a
shared resource. What about preamp1?
Many thanks in advance.
Conrad PA5Y
73, Ed - KL7UW
http://www.kl7uw.com
Dubus-NA Business mail:
dubus...@gmail.com
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