[hpsdr] MDS and relatet architectures

[KA2WEU at aol.com]

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
 
In a message dated 8/13/2006 9:02:12 P.M. Eastern Daylight Time,  
k3bu at optonline.net writes:

*****  High Performance Software Defined Radio Discussion List *****

Amen to  that!

Another important requirement for superior RF preamp is  continuous gain 
control and AGC control with possible programmable levels for  various antenna 
selections.

Continuous gain control is very important  for top notch RX performance, the 
gain of the preamp should be set just at the  treshold of band noise, so you 
know that there is enough gain to hear the weak  one, but not more than needed.


 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openhpsdr.org/pipermail/hpsdr-openhpsdr.org/attachments/20060814/a32382a8/attachment-0003.htm>