Posted by
N8LP on
May 24, 2007; 1:13pm
URL: http://elecraft.85.s1.nabble.com/K3-course-wanted-Panadaptor-101-tp447983p447986.html
I don't have a SDR, but have been pursuing this idea on my LP-100
reflector with some sharp guys who do. What I have been able to gleen is
that with the best sound card currently available (which requires a
Firewire interface), you can get 192 kHz bandwidth to sample. After
filtering to avoid aliasing, I assume this would be maybe 180 kHz of
clean display. With the best board tested by QST, the bandwidth would be
about half that.
The dynamic range would be in the 100-110 dB range... adequate for a
panadapter in a normal RF environment. The ADC will overload in the
presence of strong signals, however, unless you pad the signal from the
IF. I assume this would result in a flat line on the display at the top.
There is the chance that signals outside the display width could cause
interference as well, since the only filtering would be the bandpass
filters in the K3, and a 3-pole filter on the input of the softrock, but
they would have to be very strong.
Adding some attenuation between the K3 and softrock (beyond what would
be needed for proper interfacing to the K3 IF output), would help
protect the ADC in the soundcard, but you would lose some sensitivity.
The amount would depend on the strength of the ADC. Depending on
soundcard, 10 dB would give you a range of about -10dBm to -110 /
-120dBm between MDS and 1dB compression point... a bit less if the upper
limit is more stringent. This should be fine for most
locations/situations, although I can think of a couple very specific
exceptions.
To sum up, I would expect that you would spend about $250-400 for this
setup, assuming you already have the PC, and depending on the level of
sound card you use, with the high end required for a BW > ~90 kHz. You
would not have the ability to point and click to jump to a signal like
the Z90/91 offers... although it's possible that some enterprising soul
could add this feature to one of the open source SDR apps I suppose. And
you don't have much portability.
73,
Larry N8LP
Jack Smith wrote:
> I'll give my views as the designer of the Z90/91 panadapters. Others
> may well have different views.
>
> First, I have a definite bias to stand-alone equipment that works
> without a computer. And, I have more computers around here than I can
> keep track of, going back to a 386 monochrome laptop residing at the
> back of a closet someplace. Hence things like the Softrock don't meet
> my stand-alone requirement. I have enough trouble finding space on my
> operating desk for radios. And, the more computers running, the
> greater the likelihood of noise being generated.
>
> How one uses a panadapter depends on the mode of operation used. If
> you are a VHF/UHF operator, for example, a panadapter, particularly
> operated in waterfall mode, can quickly let you know whether there is
> any operation on the band. On HF, a panadapter can show you a pile up
> quickly, or in general give you a good idea where the activity is at
> any given instant.
>
> For these uses, in my view, a panadapter requires a span of at least
> 100 KHz, and preferably more. The Z90 has a maximum default span of
> 200 KHz, and maximum user-defined span of 250 KHz. In retrospect, I
> wish that I had made it 500 KHz, with perhaps 3 KHz resolution
> bandwidth, as it would provide a greater overview of most of an HF
> band (excluding 10 meters, of course).
>
> Another use of a panadapter with frequency flexibility is as a piece
> of test gear, suitable for measuring and adjusting carrier and
> unwanted sideband suppression and transmitted intermodulation via a
> two-tone test. For this, the panadapter must have a minimum resolution
> bandwidth of 200 Hz or less.
>
> In my personal opinion, a panadapter with a maximum span of 48 KHz is
> less useful than one with a wider span. Others may disagree, as it
> depends on how one operates.
>
> My web site has many examples of modulation analysis, transmitter
> measurements and the like made with the Z90 panadapter, but these are
> generic and are applicable to any panadapter with similar performance.
> They can be found linked at the main site www.cliftonlaboratories.com.
>
>
> Jack K8ZOA
>
>
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