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Re: [linrad] Linrad HW

With regard to the local oscillator, I have a AD9854 DDS board design 
with quadrature outputs to 60 MHz or so.
It could be updated with relatively little effort, though I am not 
volunteering at present. I can make the Autotrax files available to 
anyone who wants. The major faults with the first iteration were the 
regulators (chip no longer available and in any case only just adequate 
from a heat dissipation point of view) and the data interface.
Of course, a DDS is probably not quite clean enough from a spur point of 
view for a high quality LO, but the phase noise is good. The outputs 
would not really be adequate for diode mixers directly, so would have to 
be buffered.
Still it gives an acceptable quality LO for many purposes with accurate 
phase quadrature.
An alternative would be to divide a microwave oscillator down - see 
http://www.qsl.net/ke5fx/ for a design. This should give excellent phase 
noise and spur performance, though it is rather more complex in both 
hardware and software
I have boards for this also.


Josh Logan wrote:

>Hardware for linrad.  That has defintally been a discussion point on this
>list but there still is not any good designs that I have seen.
>I do not have the knowledge to lead this, but would be a very willing
>partisipant in building some simple hardware for linrad.
>Initally is someone will to lead a project that will be usable to receive
>CW, SSB, and AM signals, using a SB Live or similar card.  Possibly even
>only 1 channel and therefor only 1/2 the available BW of the sound card.
>The idea behind this is simple, and possibly as building blocks for
>something more complex.
>As an example.  I have a PTS 160 (signal generator) that is split to two
>TUF-1 mixers by a coax T.  I then have a G5RV jr antenna (with antenna
>tunner) that I use a second coax T to feed the RF side of the mixers.  I
>then take the IF output and feed that to a sound card.  I have a unknown
>length of coax between the to LO ports, ideally this would be 1/4
>wavelength, but I can't terminate coax to get this on the different bands.
>I can decode STRONG CW, but that is about it.  I have two signals on the
>screen for every real signal (one on each side of center line).  SO it is
>not working well.
>I would like to build something that would better feed the soundcard.  I
>would like it to work up to 2M, but am willing to start with something
>that is just HF for the first rev, if the larger frequency range would
>make the hardware too complex.
>Anyone willing to shard thair hardware desigs and help lead some hardware
>						Later, JOSH