RE: [linrad] Linrad Questions

[Leif Asbrink <leif.asbrink@xxxxxxxxxxxxxxxxxx>]

Hi Terry,

> My main interest in Linrad is for use on 432 MHz EME.
> 
> > > I am thinking of building a KK7B direct conversion 
> > > binaural I-Q receiver but don't know how much 
> > > difference it might make.    Is it worth the effort
> > > to go to a direct conversion radio with IQ output? 
> Noise blanking is not a huge need here.  Since moving up to 432 MHz EME 
> noise is no longer an issue.   A bigger problem is all the birdies.   The 
> lower 20 KHz is almost un useable due to all the garbage.   The 
> ability to "see" the bottow 20 KHz or so of the the band to 
> spot stations on the air would be great.   I don't have any 
> active stations near me on 432. There are one or two in town 
> but they never seem to be active.
OK. I think it is definitely worth going to a wide bandwidth. 
A low cost IQ receiver will give 40 kHz bandwidth or more.
Just feed the mixer outputs into the soundcard without anti-
alias filters. 

I suggest you make a converter from 432 to some HF band and place
the IQ receiver there. You may go from 432 to 28MHz for example.

It may be easier to convert once more with some conventional
VFO to get a variable center frequency and to get a lower frequency
for the IQ mixers. At 28MHz you will probably need Schottky
mixers but below 15 MHz you can use 74HC... switches that cost next
to nothing. 

For 432 MHz the advantage of Linrad will be the monitoring of a wide
bandwidth. I do not know to what extent a dual polarisation system
is advantageous and I do not know if the possibillity to use really
narrow filters on unstable signals will give any significant advantage.
In case the keying speed and path modulation makes it necessary to use
30Hz or more bandwidth, the human brain can do all the filtering anyway
even on an unstable signal so the advantage becomes small.

With time we will know:-)

73

Leif / SM5BSZ


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