[hpsdr] Proposal for a 'low-end' RX/TX board for HPSDR

[Lyle Johnson]

Hello Shel!

>> This need not be the bleeding edge, but it would be enough to provide a
>> practical radio that can be used without having to add a bunch of other
>> "stuff".
> 
> I wonder about the advisability of rf section on the back plane. Digital and
> rf can be a pain to seperate.  In any case the PA/LPF and BPF are not small
> footprints. Typicaly a 7ele LPF with minature selection realys runs around
> 70x130mm and a 3 stage 8w PA about 60x90.

What if we build the radio for only one band, or only two? The filters 
then require less space.

One of the problems we seem to always run into with "radios with digital 
stuff inside" is that we all do the digital stuff inside and the radio 
doesn't get built!

My SDR-1000 has a 1 watt PA that is really just an op-amp.  It isn't 
very practical, and requires an expensive negative voltage supply.  It 
doesn't tolerate mismatch very well.  I can spend several hundred 
dollars and get a 100 watt HF PA.  Still doesn't help on 6 meters.  I 
can get an HF Packer kit (I did, it is still in the box) but then I have 
a clunky, not-well integrated packaging and bandswitching problem. And a 
one-of-a-kind radio.  I'm hoping we can get a lot of the same radios 
built, so we can better test them, understand and solve the systems 
issues, and discover what we can and can't reasonably do before we try 
to do it with the "bleeding edge" performance modules.

My KX1 has digital stuff inside, runs 2 to 4 watts, and is in a small 
package.  The K1 uses a similar Tx lineup, and a ham in Italy has made 
an SSB version of the K1, so the Tx strip can be sufficiently linear and 
still be quite small.

We have a suggested ATLAS footprint that is much larger than ones we've 
made to date.  The "RF stuff" can fill the space on a larger card.

I'd really like to see a small Tx/Rx module that I just need to attach 
an antenna to, and can then use as a practical radio.  I may still need
an external ATU or whatever to match my antenna to 50 ohms.

And I really don't want to have to collect miscellaneous pieces -- like 
amplifiers, T/R switching, BP and LP filters, etc. -- to turn Phoenix 
into a radio.  I just want to plug it in and start to use it, discover 
its limitations and strengths, and go forward from there.

It'll also give us some system experience with Janus and Ozy (and 
Sasquatch) as a complete device.

> Would make sense to put the DDS and control on the Atlas and then just the
> coaxs and IC2 out to die cast box with the rf section. I'd really like to
> see use of the AD9951

Probably a good candidate for the Phoenix LO.

> as I find the spurs on the 10 bit parts no longer
> acceptable. If the front end is 0-30MHz  and used the divide by 2
> quadrature generator that the QRP2001 used for their Tayoe then at a max of
> 60MHz we should get fairly acceptable phase noise with minimal
> complications.

I'd like to see someone take on the project of the RF deck for low power 
applications to be integrated into HPSDR if it must be separate.  T/R 
switching, robust PA -if it is going to be in a separate module, maybe 
it should be 10W or even 20W - strong front end, easily reproducible and 
cost no more than $100 buying everything new.

I really want a compact, portable HPSDR-based system that I can use 
portable, not just spread out in the ham shack.  I worry about too many 
modules :-)

>> In a similar vein, I've also thought about a "Sasquatch Lite" based on a
>> DSP that is available and cheap, and supported by free or nearly free
>> (as in liquid refreshment) development tools.
> 
> Option A on a DSP-X ? hi.  The STAR transceiver certainly shows how much
> better this option can be. I like the idea of reducing the CPU overhead
> anyway

A DSPx could certainly be pressed into service, but I'm thinking of 
something a bit more powerful...

73,

Lyle KK7P


 1153523918.0