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* <[email protected]
<mailto:[email protected]>> 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>
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