[hpsdr] VHF-millimeter up/down converters?

[Helmut]

Glenn,

Phase noise was a 'part of my life', hi and I know very well what is
possible, determined by physics and currently offered on the market at
reasonable prices. I wish you a successful design. Maybe you will give us
more information after selecting and evaluating the components.
Good luck.

73, Helmut, DC6NY
 
-----Ursprüngliche Nachricht-----
Von: Glenn Elmore [mailto:n6gn at sonic.net] 
Gesendet: Sonntag, 19. April 2015 22:17
An: Helmut; 'Joe Martin'
Cc: hpsdr at openhpsdr.org
Betreff: Re: AW: AW: [hpsdr] VHF-millimeter up/down converters?

Whether one does a traditional banded transverter (up/down converter) or one
of the architecture I'm suggesting, everything still depends upon
LO(s) spectral purity. The best one can do is to transfer the best aspects
of the best references at various offsets to the output signal. 
Long term stability from Rubidium, GPS, quartz,  mid-offset from quartz or
SAW and wide offset from the fundamentals of the resonator, probably
varactor or perhaps YIG. All of these are candidates but at different cost
points.  The goal would be to come as close as possible to maintaining
Angelia's spectral purity to as high as possible at microwave/millimeter at
a reasonable cost.  I think that this is a reachable target. The
specifications of a modern spectrum analyzer, which are considerably better
than your(Helmut) example, are probably a good starting place. Even economy
ones can do -125 dBc in 1 Hz bandwidth at 100 Hz offset at 100 MHz, how they
roll off beyond that, at other offsets, depends upon the design. Long term
generally is not a problem. 
At SSB sorts of offsets, 1 to 10 kHz, it depends on the references chosen,
implementation and architectures.

I have operated meteor scatter, weak signal and EME on bands  in the range
of 2m through 10 GHz. I know about at least some of the issues. 
My goal is to produce (first for myself!) an "all-band" companion for my
Angelia to allow the benefits of SDR through at least our 5.7 GHz band. 
Having already done this in the more traditional banded way I would probably
chose to do it in a wider-band continuous way which could also easily extend
SA and VNA SDR applications to mid-microwave.  In a previous career, I
designed references and converters for HP spectrum analyzers, some of which
are still in production.

This is fundamentally an analog rather than a purely digital architecture.
Until we all have inexpensive 16 bit converters to 50 GHz I think we're
stuck with this!  Even so, I think much of Angelia's performance can be
translated to/from these higher bands. Some aspects will not likely be quite
as good but probably in use, these shortcomings will not be obvious. In any
case, I'd expect it to work as well as the best available conventional
banded transverters.

If I do continue on this, I will likely not be interested in spending a lot
of effort on the HPSDR interface. It will likely be satisfactory to stop at
I2C or similar control/monitor of the system. I can do this myself with
Arduino/PIC sort of control. But it would probably be more useful to
OpenHPSDR if someone else wanted to contribute to this by working on
integrating and interfacing to the rest of the system. This would make, for
example, extension of the VNA application to 6 GHz a lot cleaner and
possibly faster.

If anyone else is interested in helping, contact me off list.

Best,
Glenn n6gn


On 04/19/2015 09:40 AM, Helmut wrote:
> Glenn,
>
> unfortunately things are not so easy to handle at these frequencies:  
> Assume a typical phase noise of the LO1 say -90 dBc/Hz @ 10 kHz offset.
Relative to
> our bandwidth B we will get:    -90dBc + 10logB = -56 dBc . That means
that
> a strong neigbouring signal – say -53 dBm- at a distance of 10kHz 
> produces a noise of -109 dBm. This will flood all weak signals within this
distance.
>   
> 73, 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
>>
>>
>>
>


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