[hpsdr] Dither and Random

[Jeremy McDermond]

On Jan 3, 2013, at 4:12 AM, "Mike Seguin N1JEZ" <n1jez at burlingtontelecom.net> wrote:

> ***** High Performance Software Defined Radio Discussion List *****
> 
> Can someone explain the settings in PSDR:
>  
> 'Dither Enable' or 'Random Enable' in Setup | General | HPSDR?
>  
> I experimented with a really weak carrier and Dither helped while Random obscured the signal....

Dither and Random turn on the corresponding functions on the LTC2208 ADC on Mercury/Hermes.  I'm not an ADC expert, so I can't explain it in detail, but this Analog Devices document talks about dither (it increases SFDR):

http://www.analog.com/library/analogDialogue/archives/40-02/adc_noise.html

I'm not really sure about random, but you can check out the brief explanation on the LTC2208 datasheet at:

http://cds.linear.com/docs/Datasheet/2208fc.pdf

RAND (Pin 63): Digital Output Randomization Selection Pin. RAND low results in normal operation. RAND high selects D1-D15 to be EXCLUSIVE-ORed with D0 (the LSB). The output can be decoded by again applying an XOR operation between the LSB and all other bits. This mode of operation reduces the effects of digital output interference.

I'm sure that someone 10x as smart as me will come along and explain more.

> 73,
> Mike, N1JEZ
> "A closed mouth gathers no feet"

--
Jeremy McDermond (NH6Z)
Xenotropic Systems
mcdermj at xenotropic.com




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