[Amps] Checking for IMD

[Bill Fuqua]

         Now we are back to my first suggestion.  Use a good mixer and 
local oscillator to feed a sound card. If you don't need more than 20kHz 
bandwidth you don't need the quadrature oscillator and mixers which could 
extend it to 40kHz if the sideband rejection is sufficient to see the lower 
level IM products that you may be looking for.
          Also, since you will most likely be making measurements using a 
variable frequency TX you could use a crystal controlled oscillator at 4x 
the operating frequency and some D-type flipflops to generate the I and Q 
oscillator signals.

73
Bill wa4lav


At 08:17 PM 8/14/2006 -0700, Michael Tope wrote:

>----- Original Message -----
>From: "Gary Schafer" <garyschafer at comcast.net>
>
> >> Sounds like the Flex Radio SDR-1000 would be ideally suited
> >> for this task. It has very a simple conversion scheme, high
> >> dynamic-range, and no analog AGC (either derived or applied).
> >> With a 44 KHz sampling rate sound card it should easily provide
> >> 15 to 20 KHz of useable spectrum viewing with good dynamic
> >> range.
> >>
> >> 73, Mike W4EF...........................................................
> >
> > Isn't that an FM radio? If so no good for a spectrum analyzer front end.
> >
>
>No, Gary, it's an HF receiver/transceiver that uses a PC soundcard
>to handle IF filtering and demodulation:
>
>http://www.flex-radio.com/
>
>http://www.flex-radio.com/articles_files/SDR-1000%20April%202005%20QST%20Review.pdf
>
>With a quality sound card, the close-in dynamic range of this rig
>rivals some of the better high-end HF transceivers, and it is doing
>that with absolutely no analog AGC, which says to me that the
>analog stages ahead of the DSP must be very linear. Since filtering
>is DSP based, this scheme should be capable of very narrow
>resolution bandwidth.
>
>I mean if somebody could write the code to turn one of these
>things into a poor man's HF spectrum analyzer capable of doing
>quality transmitter IMD measurements, I'd probably buy one.
>
>73, Mike W4EF...................................................
>
>
>_______________________________________________
>Amps mailing list
>Amps at contesting.com
>http://lists.contesting.com/mailman/listinfo/amps