[hpsdr] VHF-millimeter up/down converters?

[Glenn Elmore]

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
>
>
>


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