[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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