[hpsdr] WG: Dither and Random should be enabled for best performance of Mercury

[Walter Schellenberg]

Hi all,
My analysis of the IMD performance of Mercury is now available at

http://openhpsdr.org/wiki/index.php?title=Mercury_-_intermodulation_(IMD)_te
sts 

I would like to thank Phil, VK6APH, for his excellent introductory comments,
and Richard, VK2NRA, for wiki formatting my original document and uploading
it. 
73, Walter, HB9AJG

Phil wrote:
> Hi Ron,
> Thanks for your work on measuring the performance of Mercury. Ron is 
> quite correct that if you measure the IMD performance in the lab 
> without Dither and Random enabled then you get lower figures than
> expected.
> However, the performance when connected to an antenna and in the 
> presence of in-band and out-of-band signals also need to be 
> considered. Unlike conventional analogue receivers, large signals 
> (within certain limits) actually improve the IMD performance of DDC based
> receivers.
>
> We are about to publish some ground breaking work by Walter, HB9AJG, 
> on the effects of dither, random and band signals on the IMD performance
> of Mercury.
>
> This is quite possibly the first time such and analysis has been 
> undertaken for an Amateur DDC receiver and makes interesting reading.
> Walter is presently formatting his document for inclusion on the Wiki 
> and will announce when it is available.
>
> 73's Phil...VK6APH

Ron wrote:
>> All,
>> Phil Harman reminded me about Dither and Random last week, but I must 
>> confess I forgot about it this week until I started getting IMD 
>> Dynamic Range numbers that were about half of what I expected. As a 
>> result, I have added this to the section on Receiver Performance, IMD 
>> Dynamic Range on the Wiki:
>>
>> Important note: To get good performance with respect to the IMD 
>> Dynamic Range tests, be sure to check "Dither Enabled" and "Random 
>> Enabled" in the PowerSDR >Setup > HPSDR > Mercury Options panel. If 
>> this is not done your IMD Dynamic Range will be reduced by about 50%.
>>
>> Ron, W9KFB
>> Indianapolis