[hpsdr] New RF Digitizer

[Nyall Davies]

COMPARISON OF SDR-IQ with HPSDR
The signal noise ratio of the fast AD converters does not allow the full use 
of all the bits. The extra bits in the AD should mean that the quantization 
loss in the AD can be ignored - it should provide its own dither noise.

The picture of the SDR-IQ shows that it uses the AD6620 which comprises the 
digital mixer and set of CIC filters. The processing gain the AD6620 is such 
that 23 bits are required at its output
I cannot see what AD it uses but we have to assume that it is the AD6645. 
This part has a S/N ratio around 74dB
It states that the sampling is done at 67MHz (the max spec of the AD6620)
If we are using the LTC2207 sampling at 100MHz - it has a quoted S/N of 78.2 
dB so we are better due to the AD SN by 4.2dB
If we sample at 100 MHz we gain 10 log(100/67) dB of processing gain =1.739 
dB

So we can expect a performance 4.2 +1.7 = 5.9dB better than the SDR-IQ

It has been suggested to me that we Linear tech can supply a device to 
sample at higher rates say 150MHz so we may, depending on the S/N of this 
device, be able to gain another 1.7dB

Nyall G8IBR

----- Original Message ----- 
From: "Ahti Aintila" <oh2rz.sdr at gmail.com>
To: "Lyle Johnson" <kk7p at wavecable.com>
Cc: "High Performance Software Defined Radio Discussion List" 
<hpsdr at hpsdr.org>
Sent: Tuesday, November 14, 2006 5:23 AM
Subject: Re: [hpsdr] New RF Digitizer


> ***** High Performance Software Defined Radio Discussion List *****
>
> On 14/11/06, Lyle Johnson <kk7p at wavecable.com> wrote:
>> ***** High Performance Software Defined Radio Discussion List *****
>>
>> This from RF Space, the guys that make the SDR-14:
>>
>> <http://www.rfspace.com/sdriq.html>
>>
>> A sort-of Ozy+Mercury, albeit with fewer bits and a lower sampling rate.
>>
>> 73,
>>
>> Lyle KK7P
>
> Not bad and very compact! I hope that our heavy-weight champion
> Atlas+Ozy+Mercury combination can put the dynamic range at least 20 dB
> better. Am I asking too much?
>
> 73, Ahti OH2RZ
>
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