[hpsdr] VHF-millimeter up/down converters?

[Helmut]

Sorry, I forgot to mention B = 2.5 kHz( SSB bandwidth)

Helmut, DC6NY 

-----Ursprüngliche Nachricht-----
Von: Glenn Elmore [mailto:n6gn at sonic.net] 
Gesendet: Sonntag, 19. April 2015 17:52
An: Helmut; 'Joe Martin'
Cc: hpsdr at openhpsdr.org
Betreff: Re: AW: [hpsdr] VHF-millimeter up/down converters?

Helmut,
I think this need not be the case. By using same-architecture LO1/LO2 along
with wide PLL bandwidth, phase noise can correlate out far enough to cancel
and not be an issue. You'll notice that with the mix-up mid-down approach,
correlated noise cancels. This is the done in high performance spectrum
analyzers and gives performance as good as the references can provide, even
out to millimeter wavelengths some times.  
I only suggested 6 GHz as a target because filtering can be done within
common PCB materials (stripline filters etc) and SMD parts and connectors
can work just fine to there without heroic efforts. Parts are pretty cheap
too.

There will certainly need to be pre/post amplification provided, just as
there is presently in Angelia. That can be done as it conventionally is. 
For EME and weak signal this may mean both are antenna mounted even.  
The goal is to get clean Angelina performance, say 25 MHz of bandwidth,
translated to/from VHF-6GHz and let the banded details be done separately -
akin to putting LPFs and HPFs on Angelia's in/out for the QRO arrangements.

I believe it is possible and practical to do all this at reasonable cost
- though I'm unsure of exactly what price/performance target OpenHPSDR
targets.  Has a charter or statement for OpenHPSDR been written that talks
about this?

Glenn n6gn




On 04/19/2015 08:39 AM, Helmut wrote:
> Hi Glenn,
>
> Just my 2 cents: I think this three-mixer-design will not provide 
> adequate performance for severe weak signal and/or contest application 
> on the VHF, UHF and SHF bands. The phase noise of LOs at that these 
> frequencies is on principal too bad and dominates the dynamic of the 
> whole system. A lot of pre-amplification is necessary to meet the 
> noise figure requirements. This degrades the dynamic performance further.
> At the present time conventional transverters are the better choice. 
> As some guys know I run on VHF  a  modified Mercury  and Penelope in 
> undersampling mode with similar performance to the HF bands (details 
> http://www.hamsdr.com/data/GlobalFileUploads/9636__VHF%20DDC+DUC.pdf ).
> That's a nice option for the 2m band.
>
> 73, Helmut, DC6NY
>
>
>


 1429461861.0