[hpsdr] [Hpsdr] Call for Comments - ALEX

[Graham Haddock]

Bob:
Comments below.
--- Graham / KE9H

Robert McGwier wrote:
> The relays should be chosen with some care so that they provide 
> sufficient isolation against leakage paths.  
Rated isolation on the relays is 50 to 55 dB at 30 MHz. 
Improving as you go lower.
> I hope you will allow for full duplex operation when connected to 
> separate antennas for crossband operation and support of satellite 
> operations
Yes.  There is nothing in ALEX that should prevent that. 
I am assuming that you would be using PENELOPE "barefoot"
when you do that (that is, no100watt RFPA at HF.) and the
crossband results from two external VHF transverters.
In this case, the receive transverters will have some responsibility
to not deliver 88 to 108 MHz FM signals to the HPSDR, but
I can't imagine this is a problem

What is the minimum T to R frequency spacing (from the viewpoint
of MERCURY and PENELOPE) when you would
run satellite duplex?  I am sure that we will need to
specify some minimum separation specification such as 500 kHz.

Actual separation may be limited by the card to card isolation between
the MERCURY and PENELOPE cards, when side by side,
rather than ALEX.  I have asked Phil H. for some card to card
measurements, but have not heard back yet.
>
> I would not limit the surface mount parts.  Through hole parts may be 
> thought of best as good parts attached to (may be poor but) antennas.
> The lower profile of surface mount parts contributes significantly to 
> reduce emission and susceptibility to emission.
I will use as many RF Power SMT chip caps as possible, instead of silver 
mica. 
Through hole will be limited to toroids, maybe the relays, and
the BNC connectors.

>
> If the Elecraft experience is any indication,  people like to buy and 
> are more comfortable with prewound toroids.  Some of their after 
> market winders might even be willing to do this work for us as well.
I will contact "The Toroid Guy" and see if he want some more business. 
I personally enjoy winding toroids, but I must be in the minority.
> (in a good shielded box).
Yes.

==


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