Re: [IRCA] [NRC-AM] THREE NAIVE QUESTIONS

[Aaron Kreider <aaron@xxxxxxxxxxxxxxxxxx>]

I'm not an expert, but I think that the number of bits on the ADC of a 
Software Defined Radio is pretty important (for dynamic range) - and 
maybe also the ADC noise figure.

QS1R uses the LTC 2208 with 16 bits (and I cannot comment on the noise 
figure).  By contrast, the Perseus is 14 bit (and old technology).

There appears to be a tradeoff between bits and bandwidth. So the 
wideband radios have fewer bits (ex. the cheapest dongles are 8 bits).  
You might be ok with a fewer bits if you have a preselector, or don't 
have strong locals.

QS1R is a great radio (and one of the cheapest 16 bits with coverage up 
to 60 mhz).  The GUI might be the best of the lot.    Support is very 
limited and development, at least of the software, has stopped.  The 
spectrum recorder is weak (Ex. you cannot jump to any point in your 
recording - you can only start at the beginning). I've been using it for 
almost 3 years.

The ELAD FDM-S2 is 16 bit and with the Euro so cheap, it is a great 
price ($550 USD - as you don't pay VAT).  I think the noise figure for 
its ADC chip is 2 db worse than the QS1R chip  (Does this mean the noise 
floor in 2 db higher?).  On the pro side, it has FM coverage and 
probably a larger market than QS1R.  Haven't used it.

My limited research into ADCs is that they aren't improving that quickly 
and Linear Technology doesn't sell a 18 bit high speed ADC. So if you 
buy a SDR, it probably won't quickly go obsolete.

The FPGA is a key component as well, though I'm not sure if it is a 
limiting one.

I'm guessing that SDRs, based on good chips, will all have superb 
selectivity (blows away any non-SDR - like my Drake R8) and synchronous 
detection depends on good software (QS1R again crushes the Drake R8).  
As I've got limited space, I never use my Drake R8.

Aaron


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