[hpsdr] PING Preselector

[Graham Haddock]

George:

Are you complaining about needing a preselector? 

Or, are you complaining about needing relays to build the preselector?

;-)

The higher the performance of the input ADC, the less likely you are to
need a preselector.

BUT...

The higher the performance of the input ADC, if your application
does require a preselector, the more likely you are to need to use relays
to build the preselector.

If you look at the current block level diagram for ALEX, all of the
switch symbols you see on the diagram are solid state switches, NOT relays.
Most likely Hittite HMC226.  There will be some relays (you can not see) 
inside the
tunable filter, where solid state switches either have too high an
ON resistance, or can't take the voltages that might appear
inside the filter before the ADC goes into overload.

If some future improved MERCURY increased the IP3 by another 10 dB,
then we would have to use relays everywhere in the preselector, today's
Hittite switches are not good enough.

--- Graham


George Medakovich wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> I'm reading as fast as I can, trying to learn enough to contribute something
> besides a pun.
>
> Also wondering where DAC technology where have to be before we don't have to
> use a board with relays as a preselector.
>
> George
> ke5dng
>
> Eric Ellison wrote:
>   
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