[Premium-Rx] The new R&S EM510 Direct-Sampling HF Receiver

[Pieter Ibelings]

Francis,

That's another misconception. I am going to give you the example of an 
SDR-14. There are times when there are only 4 bits wiggling and I can see 
the whole band and demodulate SSB, CW and all signals with no problem. You 
need to remember that the few bits are being sampled at 67 MHz in this case. 
They have an EXTREMELLY large amount of information. This is not 4 bits 
wiggling after a 2.4 KHz bandpass filter being sampled at 8 KHz like in a 
soundcard.

Let's do the numbers. Let's say you have a 2 bit radio and that you are 
sampling at 100 MHz. The S/N in the nyquist band is 2*6.02+1.76 or roughly 
14 dB. The nyquist band is 50 MHz wide so you get a per Hz improvement in 
C/N of 10*log (50MHz)= 77dB. that means that if I used a digital filter that 
is 100Hz wide (a 20 dB hit from 1Hz) you could still get 70dN of C/N. This I 
would say is more than sufficient to demodulate CW, FSK, PSK etc.

This technology is right around the corner with better performance and lower 
cost. I hate to say it since I am a die hard RF guy, but the more I play 
with this technology the more potential I see.

Regards,

Pieter, N4IP


>
>Yes but how many bits above the noise floor are required to demodulate real 
>information.
>   Even cw is going to take a few bits to decode. This will cut into the 
>noise floor of the A/D.
>   The DSP needs more than 1 bit to determine if there is a carrier or 
>noise. I got tricked into looking at displays rather than listening to the 
>audio coming out of the DSP.
>   Yes this stuff is here to stay but it will be a while until we can 
>afford real performance.  gfz

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