[amsat-bb] Re: Planning

Edward Cole kl7uw at acsalaska.net
Mon Apr 30 23:18:49 PDT 2007

At 07:05 AM 4/30/2007, Grant Hodgson wrote:
>MKM wrote :-
>  >We need new IF-DSP  V/H/SHF radios with built in band scopes and
>  >modules up to 5GHZ.
>and Ed wrote :-
>  >The solution is to use a SDR on the IF of your current radio.  Then
>  >software can provide DSP, filtering, spectral and waterfall displays,
>  >decoding...etc.
>  >I am testing the SDR-IQ using the 28-30 MHz output of the DEMI 144/28
>  >converter.  144-MHz is very commonly used IF for microwave converters.
>A more modern approach would be to use an SDR at the RF frequency, with
>direct conversion to baseband, thus eliminating the transverter
>altogether.  This is what the uWSDR (Microwave SDR) project is doing.
>In a nutshell - using the latest components and modern circuit
>topologies to realise a high-performance SDR operating at microwave
>frequencies.  The first products will be for the 2.3GHz (which includes
>2.4GHz) band and a sister product for 144MHz.  The software for the user
>interface is new; the software for the low-level DSP is the same as used
>on SDR-1000 and other SDRs.
>More details can be found on the uWSDR website :-
>and there is a Yahoo group for the developers and lurkers.
>ON/G4KLX will give a remote presentation via the web at Dayton, and I
>might be able to give a talk in person at Microwave Update.
>There are umpteen possibilities for product options for satellite use,
>such as a 2.4GHz only Rx, a crossband 1.3GHz Tx/2.4GHz Rx,  etc. etc.
>Development progress has been painfully slow; if anybody would like to
>help with the design and development please contact one of the team.


I was unaware of your SDR project, but not surprised.  SDR's are at 
the break-out point and one would expect that many new choices will 
appear over the next few years.  The problem holding back direct 
conversion at higher frequencies has been A/D converter that work at 
those frequencies.  This envelope is being pushed quickly forward.  I 
would love a direct 144-MHz SDR as it would fit perfectly into my 
station.  For radio astronomy a direct conversion 1420 MHz receiver 
is desirable.

So no argument that obtaining direct conversion to baseband is very 
desirable from the stand point of elimination of mixing products 
(birdies).  There are some basic issues facing SDR's so time will 
probably solve some of them.

Ed - KL7UW
  BP40IQ   50-MHz - 10-GHz   www.kl7uw.com
144-EME: FT-847, mgf-1801, 4x-xpol-20, 185w
DUBUS Magazine USA Rep dubususa at hotmail.com

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