[Linrad] Re: Map65IQ and softrock V9

[Leif Asbrink <sm5bsz.com; leif@xxxxxxxxxxxxxxxx>]

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

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