[hpsdr] multiple receivers - is it really nesesary

[Phil Harman]

Alex,

If you  just want to look at what signals are on a particular band without 
the ability to actually demodulate all (say 7 or 8) of them then you are 
correct.  All you need to do is to hop the CORDIC  to each band of interest, 
send a block of samples to the PC, do an FFT and then display the result 
then hop to the next band and repeat the process.

In fact that is where my SDR journey started, I did this in hardware with a 
DDS LO and a 45MHz first IF, the PC code was in VB.  I could see 6 bands in 
'real time' and spot any openings as they occurred.

The problem was I had to sweep the LO to cover each band, and needed a 
narrow IF filter to see weak signals so need to slow the sweep rate right 
down.

So much easier to do this in software and much better performance.

With Mercury we can see 192kHz and demodulate any signal in that bandwidth 
whilst looking at 0-55MHz of spectrum. Soon we will be able to select what 
frequency/bandwidth you want to look at on the wide bandscope and after that 
we will add multiple receivers just as Alex VE3NEA has done.

The limitation of this with one Mercury board is  that your antenna must 
cover all the bands you want to view or you need some form of combiner.

If you are a contester I can imagine being able to run 7 or 8 copies of CW 
skimmer so you can see all signals on all the ham bands at once may give you 
a slight edge....

We also intend to support multiple Mercury boards on the Atlas bus all phase 
locked to the same clock.  That will give you the potential for diversity 
reception or take the output of your Four Square into four Mercury boards 
etc....

As to why you would want to do that....well in my case it gives me plenty to 
think about when I'm wide awake at 2am :)

73's Phil....VK6APH


----- Original Message ----- 
From: "alex" <ajbr at btconnect.com>
To: <hpsdr at openhpsdr.org>
Sent: Saturday, August 01, 2009 10:30 PM
Subject: [hpsdr] multiple receivers - is it really nesesary


> ***** High Performance Software Defined Radio Discussion List *****
>
> on the hpsdr website there was talk of having multiple receivers on a
> single mercury, on the qs1r site it talks about how it is possible to
> fit 7 independent rx into the fpga.
>
> what is the point, if you want to have multiple bandscopes (like w3sz's
> mac setup) then why go to all the trouble of having demod-able signals
> just for the bandscope, by tuning the lo and simply recording the
> amplitude of the if then you get the frequency info without having to
> worry about doing an fft,
>
> infact this could drasticaly reduce the computing power needed for
> normal rx by having the demod and fft seperate.
>
> (i hope that makes some sembelence of sense)
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