[hpsdr] VHF-millimeter up/down converters?

[Glenn Elmore]

While I understand the interest in multiple, independent channels (more 
than receivers; akin to additional ADCs on Angelia) I don't think I'm 
interested in trying to solve all problems at once. I'm definitely not 
interested in doing an amateur-banded approach again.

What I'm pondering is essentially a stepping 25 MHz wide block up/down 
converter that can quickly go anywhere from 50 MHz to [6 GHz].  With 
this approach, if someone wants simultaneous different amateur microwave 
bands, they would have to purchase additional block converters.

It would be possible, I suppose, to put hooks into the last fixed IF 
(somewhere a bit above [6 GHz]) and sum independent bands up there but 
that has the problem of broadband noise floors degrading things, since 
narrow filtering probably isn't always practical at the higher bands. 
Better to just do the whole thing again and go into a different Angelia ADC.

This architecture could solve the scope shortcoming but still requires 
the purchase of additional hardware in order to get simultaneous multple 
bands.  But each band already requires post(power) amplifier, LNA and 
filtering on a per-amateur-band basis, no matter how it is done. Even 
the traditional approach has this characteristic. The extra cost of two 
additional fixed frequency conversions would likely only increment the 
per-band cost a modest percentage of the amateur-band total, depending 
upon what one chose for performance.

My thought would be that this stepping block converter would leave the 
user with, say +20 dBm and 10 dB NF, improvements to this would be 
expected to take place however and wherever the user wanted it, e.g. 
mast or near-mast mounted LNA and kW for EME.

On receive,  external gain will eat into dynamic range, but as has been 
noted, microwave is a different context and super-high dynamic range and 
IMD, and even superlative phase noise performance, are probably not as 
crucial in practice.

In my view, the trick is to come up with an architecture/scope that is

  * easily reproducible
  * attractive to the majority of SDR users as a means of extending range
  * at a tolerable per-band price point
  * also able to act as broadband spectrum analyzer and vector network
    analyzer

The per-band enhancements would be out of scope.

I'm still considering if/when I would want to take on this limited task. 
It looks like a several man-year project to me.

Glenn n6gn


On 04/22/2015 12:04 PM, Duane - N9DG wrote:
> If pursuing the traditional heterodyne mixer down converter approach, I would strongly suggest that they each be designed with different IF output frequency ranges. That way multiple bands can be fed into a single SDR IF radio that can then be watching and listening on multiple bands simultaneously. And therefore have multiple panadapter / waterfalls always running at all times. And at least 1 (preferably 2) RX per band for as many bands as the user can successfully listen to at one time.
>
> The common DC - daylight radios that are out there all have MAJOR shortcomings when it comes to usability. These usability shortcomings are primarily in two key areas: 1) poor or non-existent scopes, 2) they can only be used on one band at a time.
>
> Duane
> N9DG
>
>

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