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Date: Sat, 12 Jan 2008 11:27:15 +0100
From: =?ISO-8859-1?Q?Wolfgang_B=FCscher?= <dl4yhf@freenet.de>
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Subject: Re: LF: LF Receiver
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Hello Andy,


About the SDR-IQ (I'm also a pleased owner of it)...
> The only thing it suffers from is not having a clock locked to a 
> master reference.   Needs 66.667MHz and I've just never got round 
> to making a locked clock yet.  But its probably stable enough for QRSS 
> as it is.
I had the same concern when we used it for a 10 GHz radio-astronomy 
experiment. A simple solution without a PLL:

10 MHz (from reference osc)
divided by 3 , then (using analog frequency doublers etc):
 * 2 * 2 * 5  = 66.66666.. MHz

But, especially for LF / MF, the SDR-IQ's clock oscillator is 
surprisingly stable.


Cheers,
   Wolf DL4YHF .

/3  =: 3.33333
66.6666/20  =: 3.33333


>  
> AGC can be disabled, and is only used for demod anyway, to keep volume 
> constant.   The waterfall display operates independently of the demod 
> and is always at fixed gain.
>  
> Andy  G4JNT
>
>  
> On 11/01/2008, *lawrence mayhead* <laurie.mayhead@googlemail.com 
> <mailto:laurie.mayhead@googlemail.com>> wrote:
>
>     I have for a long time used a Racal 1792 reciever for QRSS modes
>     on LF.
>     This receiver failed recently,and I have been looking for a
>     replacement receiver.
>     This search reveals a problem most modern receivers use DSP
>     techniques
>     for filtering and the AGC is derived from the filtered signal.
>     None of the receivers
>     I have looked at have an AGC OFF  facility.This means that if one
>     of these receivers
>     is used with ARGO or similar FFT programs a strong signal within
>     the pass band
>     will desensitise the Rx. It seems quite possible that a weak
>     signal could quite
>     disapear. It also appears that some AGC is applied before the
>     digital filter so that
>     signals within the roofing filters bandwith will also produce
>     de-sensitisation, and this
>     could be as much as 15kHz away from the tune freq.
>     Any ideas on receivers not using DSP filtering ?
>     Or do I look for another R1792   
>
>     73 Laurie G3AQC
>
>
>
>
> -- 
> Andy  G4JNT
> www.scrbg.org/g4jnt <http://www.scrbg.org/g4jnt>