[Elecraft] Combo pre-amp

[Ian White]

W4TV wrote:

>I'm talking about a solution that would switch the RX IN/OUT connection
>from the rear panel to board connections on the "KXV3B" much the same
as
>is done for XVTR IN/OUT in the KXV3A.  That means one is not dealing
with
>the narrow space between the KXV3 and KXV3 connector board and all
>returns would come from the KV3B board.
>
I do see what you mean, Joe, but it was beyond the level of modification
that I was prepared to attempt.

>
>BTW, I looked at your web site and don't find any information on
calculating
>NF from MDS ... just curious.
>

You're right, it's all in 'The VHF/UHF DX Book' which is out of print,
but you can find some of the same material in the Agilent Technologies
Application Note AN57-2. 

Here's a brief summary.

Noise floor aka MDS is a power level in units of watts.

Noise Figure is based on the more fundamental concept of noise
temperature (see AN57-2). Noise temperature is measured in units of
kelvin (K) and is calculated from MDS by :

	T = (MDS, W) / (1.38 x 10^-23 x (bandwidth, Hz))

The more common engineering quantity is noise figure (NF) which has
units of dB and is derived from T by a standard definition:

	NF = 10 log10 (T/290 + 1)

For the K3, the specified MDS at 50MHz (internal preamp on) is -136 to
-138dBm in 500Hz bandwidth. If you follow the example calculation, you
will find that -138dBm corresponds to a noise temperature of 2297K and a
noise figure of 9.5dB. 


73 from Ian GM3SEK