[hpsdr] Project proposal - Hermes

[Lyle Johnson]

Hello Phil!

> Looks like a case of dejavue all over again!!

:-)

I just want to be sure Kevin considers the tradeoffs in his design 
before it is frozen.

> One implementation of 
> Hermes is to use Alex for its HPF/LPF/antenna switching and 6m preamp.  
> In which case it will need the LTC6400-20 preamp unless we want to 
> redesign Alex.
> 
> A preamp is essential before the LT2208 if you want to have usable 
> sensitivity on the higher HF bands. As many are finding with Mercury, 
> the inherent selectivity of your antenna system is often sufficient for 
> satisfactory performance on the HF bands without any additional 
> filtering.

I am currently using Mercury with a 3-element SteppIR.  I'm sure odd 
harmonics are getting in but I suspect it does a passable job of 
rejecting severely out-of-band energy.  I am in a reasonably quiet 
location.  I've found that Mercury doesn't need the preamp on 20 meters 
although the increase in band noise when I connect the antenna is very 
slight.

I've been doing side-by-side comparisons with a K3 (surprise!), 
IC-756PRO2 and Mercury.  But that's a tale for another day when I have 
more anecdotal data to help obfuscate things :-)

> By not putting a pre-amp on Hermes you are forcing the user 
> to use an external one.
> 
> Having been through this preamp - no preamp loop a few times I recommend 
> we leave the LTC6400 preamp in circuit at all times and  use a 
> switchable attenuator to take out the excess gain i.e. just like we do 
> with Mercury.
> 
> Happy to debate with you - since I don't have to re-do the PCB if it 
> doesn't work :)

And I suspect I don't either!

73,

Lyle KK7P

PS- Thank you for the help with getting Mercury going.  I've also got my 
built-from-a-bare-board Penelope running now, too.  If I could just get 
an Alex kit...


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