[hpsdr] Preselectior switching

[pvharman at arach.net.au]

Hi Gian,

I actually use the PIC-A-STAR filters in the front end of my SDR. They work 
fine but the IP3, even with the bus switches replaced with relays, is a  
little low for Mercury.  The original design for Alex was based on Peter's 
design but since we have a lot of interest in a tunable preselector, to cover 
the SWL bands as well, that is what we are currently working on. 

73's Phil...VK6APH 


Quoting Graham Haddock <grahamh at verizon.net>:

> ***** High Performance Software Defined Radio Discussion List *****
> 
> Gian:
> 
> I didn't see the attachments.
> 
> Please send them direct to me at my email address.
> 
> Thank you,
> --- Graham / KE9H
> 
> Giancarlo Moda wrote:
> > ***** High Performance Software Defined Radio Discussion List *****
> >
> > 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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> 
> 
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