[hpsdr] Preselectior switching

[Giancarlo Moda]

Hi all,

for a receiver front end preselector I would suggest
to look at the solution used in the STAR, Software
transmitter and receiver, by G3XJP. The switching
elements are FST3125 and FST3126 as used in the H-Mode
Mixer.
No IMD problems and expensive relays and or PIN diodes
purchase. Fast switching, low insertion losses and
valid filetrs separation.

I am attaching a copy of circuit diagram and article
extract from RadCom.

I have added in copy VK6APH, KK7P and N8VB as they
will receive the attachment and then they may decide
to load it in file directory.

73

Gian
I7SWX

> From: hpsdr-bounces at hpsdr.org 
> [mailto:hpsdr-bounces at hpsdr.org] On Behalf Of Henry
Vredegoor
> Sent: vrijdag 16 maart 2007 5:48
> To: hpsdr at hpsdr.org
> Subject: Re: [hpsdr] Preselector schematic.
> 

> 
> Two observations:
> 
> - There must have been a design issue for using
relays on the 
> LOWER BANDS;
> maybe also the lower (zero) resistance of the relay
contacts

> - The are having the relays switching a (small)
current on 
> purpose, I think
> to keep the contacts clean, keep the resistance low


After studying the schematics a little more, I think
it prevents the 
(other)
PIN diodes from conducting, stopping the HF from all
not selected 
filters.





 
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