[hpsdr] MDS and relatet architectures

[Robert McGwier]

Ulrich:

This sounds like the ideal approach.  I believe that the ISD designs now 
being looked at will have better than needed NF/MDS below 21 MHz but at 
28 and 54 MHz,  will need a preamp.  The push-pull is certainly a way to 
increase the dynamics numbers.

73's
Bob
N4HY





KA2WEU at aol.com wrote:
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> In principle, this is correct. There is no useful low noise ,high IP3 
> and variable gain discrete ciruit know to do this. I would suggest to 
> use a low noise high IP3 GaAs amp, if necessary in pus-pull and  put 
> an GaAs binary coded step attenuator ahead of this stage with 40 dB 
> range and 0.2 dB minimum loss in 1 dB steps , connected to the main 
> AGC, being activated after 50dB AGC of the IF AGC. This does NOT 
> eliminate an high IP3 first mixer , second preamp and second mixere. A 
> similar system was implemented in the R&S ESH3  (10Khz to 30 MHz )and 
> ESVP (20 MHz to 1300MHz )  test and measurement receivers, using a 
> relay based attenuator. The ESH3 did not have a preamp, the ESVP did 
> have one.
>  
> The R&S XK2100L I am using has an optional preamplifier, which so far 
> i have only needed above 21 MHz....
>  
>  
> 73 de Ulrich, N1UL
>  
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