[hpsdr] ADC Question

[Andrew]

Hello Larry,
I'm intrigued by what you mean by 'bit closer to analog performance' sounds like a backward step to me!?? As it is, you are very unlikely to suffer intermodulation issues or phase noise issues as Mercury / Hermes is way ahead of practically any analog receivers unless you run a really larger antenna system or like in an exceptionally high signal area. 

The IMD performance at full scale for Mercury / Hermes should be around 25-30dBm, which is excellent, but typical HF band noise should push any IMD into the noise due to the dither effect in the ADC.
You will find it difficult to find an ADC better than the LTC2207, ADI and TI etc devices can't touch them.

Andrew
G4XZL



________________________________
 From: Phil Harman <phil at pharman.org>
To: Larry Gadallah <lgadallah at gmail.com>; Andrew <irbsurfing at yahoo.co.uk> 
Cc: hpsdr at lists.openhpsdr.org 
Sent: Friday, 27 July 2012, 6:51
Subject: Re: [hpsdr] ADC Question
 

Hi Larry,
 
I confirm that the LTC2209 is a drop-in replacement for the 2208 and runs 
fine at a higher clock frequency since I have one installed on a Mercury 
board.
 
The NF of the LTC2208 is about 30 dB  (as long as you don’t follow the 
data sheet and resistively terminate the input) so is usable up to about 17 m 
without a preamp when connected to an efficient antenna. 
 
73 Phil....VK6APH 
 
  
From: Larry Gadallah 
Sent: Friday, July 27, 2012 11:36 AM
To: Andrew 
Cc: hpsdr at lists.openhpsdr.org 
Subject: Re: [hpsdr] ADC Question
  ***** 
High Performance Software Defined Radio Discussion List *****


________________________________
 Hi Andrew:


On 26 July 2012 13:46, Andrew <irbsurfing at yahoo.co.uk> wrote:

***** High Performance Software Defined Radio Discussion List  *****
>
>
> 
>Hi Larry,
>Unfortunately the LTC2207 and LTC2208 are not pin compatible, the former  is 48 pin QFN and the latter a 64 pin due to the use of LVDS for the output  data lines.
 
Hmmm, I must have confused it with the LTC2209. Regardless, the point is 
that it would be interesting to experiment with an HF-only arrangement where an 
ADC with the absolute best ENOB and SFDR was used in an attempt to get a bit 
closer to analog Rx performance without needing a preamp. From my casual 
research it doesn't look like anyone (TI, LTC, ADC) has anything much more than 
2-3 dB better than the LTC2208, so it seems that this might be a 
process/technology limitation.
 
I had already thought about doing this! Trying to make it fit would be  very interesting and not recommended without a specially designed pcb carrier  - that just might work.....mmm.
>
 
I keep thinking that if we limit ourselves to a maximum Rx frequency of 30 
MHz or so, it should be possible to build a nice little Rx with 100-Base-T 
Ethernet (maybe even PCI). It probably wouldn't be much cheaper than Mercury 
given the costs of the ADC and FPGA, but it would be getting close to having a 
"blade" receiver architecture :-).
 
73's,
>Andrew
Cheers,
-- 
Larry 
Gadallah, 
VE6VQ/W7                          
lgadallah AT gmail DOT com
PGP Sig: B5F9 C4A8 8517 82AC 16B6  02B6 0645 
69F0 1F29 A512

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