[AMPS] Receiver performance

[Michael Tope]

Has anyone had a chance to play with the ICOM 756-PRO??
They are claiming a 24 bit A/D ahead of the DSP, but I
don't know what its effective number of bits is. If its
truly 24 bits, then it would have a 48 dB DR advantage
over its nearest competitor, although AGC pumping will 
still be a problem if they used the same implementation 
as the TS-870. 

Mike, W4EF.............

----------
From: 	Peter Chadwick[SMTP:Peter_Chadwick@mitel.com]
Sent: 	Monday, March 13, 2000 8:35 AM
To: 	jono@enteract.com; cgroen@image.dk; amps@contesting.com; 'RichyRusso@aol.com'; 'W8JI@contesting.com'
Subject: 	RE: [AMPS] Receiver performance


Tom says:

>At present price levels, it is impossible to get a quality low-noise 
>high dynamic range A/D converter that is fast enough to do any 
>good processing for anywhere near the price of a good crystal filter.

I'm not sure price comes into it......I don't think they exist with enough
bits at enough accuracy. The only real advantage I can see is the controlled
group delay for data modes. But I don't see why you can't use a crystal
filter, then DSP and equalise out the group delay - except for cost. Having
said all that, the Timewave is well worth having after all the crystal
filters. But DSP is the modern buzz word....

	>what I want is a clean transmitter and a receiver that can crawl
right up 
	>against a 50 over nine signal and dig out an S3 signal.

Frequency synthesisers are not always the best approach for that...even a
DDS needs a 17 bit DAC accurate to 17 bits to ensure DAC spurs are more than
100dB down. (17 bit DAC accurate to 17 bits sounds silly - but many fast
DACs are not accurate to the number of bits)

73

Peter G3RZP


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