[Linrad] Re: Map65IQ and softrock V9

[Edward Cole <acsalaska.net; kl7uw@xxxxxxxxxxxxxxxx>]

At 03:04 AM 3/26/2009, you wrote:

>Hi Dom, Edward and all,
>
> > >in fact , to obtain full adavanrage what we need is a design able to use
> > >fully Linrad , I mean V and H simultaneously and being able to get optimum
> > >signals any time. WSE RX is perfectly OK , but a bit too expensive for the
> > >average ham.We need a " dual channel system for the poor ham"
>It should be trivial to modify the Softrock so two of them
>use the same LO. The second thing needed would be one more
>144 to HF converter that is modified to use the same LO as
>the other 144 to HF converter.
>
>Why not phase-locking two 144 MHz converters as well as two
>Softrocks to a common reference oscillator with very good
>stability. That would solve two problems at the same time:-)
>
> > It is true that MAP65IQ only decodes a single polarity, but if you
> > have a dual-pol antenna system, you can switch pol on the nezt
> > sequence and capture any signals that are coming in on that
> > polarity.  I would guess that one would sample the spectrum with
> > MAP65 every 5-10 minutes else you would have information
> > overload.  Activity would not change that rapidly that one needed to
> > capture everything in one minute.  Obviously, not as sophisticated as
> > WSE Rx into dual channel Linrad, but I think it is workable.
>Yes. The problem is that you will loose 3dB at times when the
>signal level is the same in both polarisations. The loss is
>a cosine function with -3dB at 45 degrees. Someone might compute
>the percentage of time you will loose more than 1 dB. I would guess
>it comes out as more than 50%.
>
>In a contest the time loss will matter. Weak stations that answer
>your CQ may have to be much more persistant when you listen
>in the wrong polarisation 50% of the time and sometimes loose
>3 dB.
>
>There is another thing. In case your noise floor is somewhat
>degraded by high rates of interference pulses, you might find
>that the noise blanker becomes more efficient when it can
>use the information from two antennas.
>
>73
>
>Leif / SM5BSZ

Yes, the ability of Linrad to receive H/V inputs and display to the 
resultant pol is an real advantage.  I may end up with two 144/28 
convertors that may be PLL slaved to my 10-MHz Rubidium Ref.  Too bad 
that the SDR-IQ appears to be too difficult to lock to an external 
ref., else I could obtain a second unit.  But if I only run one 
SDR-IQ behind Linrad with full dual-pol input I would be able to see 
display of all signals, but still have the 3-dB penalty for decoding 
JT65 or MAP65iq when pol=45/135.

My real experience is that doesn't occur 50% of the time.  However, 
when Faraday is very active on 2m considerable percent of the time it is.

I am considering obtaining a K3 with dual Rx.  The problem is 
obtaining wideband output as the final SDR baseband is 
18-KHz.  Taping the 1st IF of 8.2 MHz would work but this still 
leaves one with the need for a dual channel SDR-IQ or such.  Probably 
simpler to go straight from 28-MHz into a dual SDR like you 
suggest.  Or i could be satisfied only sampling 18-KHz of spectrum vs 
95-KHz that MAP65 can do.

More study needed ;-)
  73, Ed - KL7UW



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