[Elecraft] K144XV receive noise figure spec: clarification

[Wes Stewart]

I think you mean the HF transceiver's NF is *higher* (worse) than the transverter. 

Wes  N7WS

--- On Fri, 1/8/10, Wayne Burdick <n6kr at elecraft.com> wrote:

From: Wayne Burdick <n6kr at elecraft.com>
Subject: [Elecraft] K144XV receive noise figure spec: clarification
To: "Elecraft Reflector" <elecraft at mailman.qth.net>
Date: Friday, January 8, 2010, 3:16 PM

The K144XV module's specifications include an input noise figure of  
about 1 dB. This figure should be used when comparing the K144XV to  
external 2-meter transverters such as the Elecraft XV144 (which is  
about the same). This is the traditional way transverters are specified.

When the K144XV (or an external transverter) is connected to an HF  
transceiver used as a 10-meter IF, the composite receive noise figure  
is nearly always a little worse. This is because the HF transceiver's  
noise figure is typically lower than that of the transverter, and the  
transverter's own preamp has finite gain. (There's a "cascade" formula  
for determining the exact composite NF based on NF and gain of each  
stage -- left to the reader as an exercise :)

For a typical combination of a low-noise transverter and its IF radio,  
the composite NF will be about 1 dB worse. That is the case for the  
K144XV+K3. We measure a noise figure of about 2 dB.

If a transverter had a preamp with much higher gain, the effect of the  
IF receiver would be negligible. But the transverter would then be  
much more susceptible to IMD.

73,
Wayne
N6KR

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