Re: [Discuss-gnuradio] Computer controllable antenna tuner

[Marcus D. Leech]

I believe he is looking for something more like an antenna coupler/tuner used in HF applications to tune and impedance match for maximum power transfer:

  http://en.wikipedia.org/wiki/Antenna_tuner

As for not talking about hardware on the GNU Radio mailing list - I find that a little silly.  While GNU Radio is more about a framework for processing baseband signals, there's also the real need to interface to the outside world.  Dynamic range, gain, and all the little hardware bits in the radio front end are all valid discussion points and completely on topic, in my opinion.

Brian

I agree with Brian.  If it's radio related and kinda-sorta touches on SDR, it's a valid thing to discuss here.

A quick google yielded this:

http://www.universal-radio.com/catalog/hamtune/0323.html


There are probably others.

Also, some of the HF-only SDRs out there have a built-in switchable filter bank.

Once you move beyond HF, it becomes increasingly difficult to *decide* where to put your filter responses, which is why SDRs that are intended for
  "DC to light" use tend not to have much in the way of front-end selectable filters -- any choice the manufacturer makes would likely be "wrong" in
  as many cases as "right".  Any any filters in the front-end, before the first gain stage, will contribute to an increase in noise figure.  So you have to
  filter after the LNA stage to maintain noise figure, but you're still, then, in the tenuous situation of likely continuing to run into analog non-linearity
  problems with strong signals within the DC-light passband of the first-stage LNA.

What we need is either:

    (A) Microwave filters that have impossibly-low insertion loss (made from super-cooled unobtanium, likely)
     
or

   (B) HEMT/GaAs/SiGe transistor technology that can offer insanely-low noise figure at the same time as offering insanely-high linearity, like
         OIP3 of +50dBm with small-signal gains of 25dB or better, and 1dB or better noise figures :-)

-- 
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org