[hpsdr] PING Preselector

[Graham Haddock]

CT1IZU wrote:
> Dependant on the size contraints there would be an advantge in having the
> smaller coil sections as just air wound coils. Better Q on the higher bands
> and less loss. I saw this done on a modified AT11 auto tuner and in that
> application definalty was an improvment on 10 meters.
>
> Some care will be needed in the relay selection. I noted some years ago an
> article in EDN or something similar where somebody was developing a
> pre-selector with fast reed relays. It turned out there were some bad
> impeadance bumps in the SW spectrum ! LDG went over to latching realys for
> later versions of the Z11 auto tuner which is useful if power consumtion
> becomes an issue.
>
> Shel CT1IZU
>   
Hi Shel:

Thanks for the comments.

As soon as Phil H has evaluated the toroids for IP3 performance, I will 
lay out a test PCB
board to look for interactions with the relays and solid state switches, 
looking for things
just as you describe.  We are concerned about the parasitic capacitance 
of both
the solid state switches and relays, in the open state. 

We already know that some of the smallest coupling inductors
will be air core.  The main tuning inductors will need to be toroids, 
due to their higher
inductance, and Phil will have both -2 and -6 mixes to evaluate at 10 
meters.

There are latching versions available of the relays I selected, although 
the samples I bought
for testing are not latching.  Relay power is 180mW for an active relay, 
and there should
not be more than three active at any time, so power should not be a big 
problem.

--- Graham




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