[TenTec] How to Choose an SDR RX for the Pan-Adapter?

Jim Brown k9yc at audiosystemsgroup.com
Thu Dec 25 12:34:20 EST 2014

On Thu,12/25/2014 3:16 AM, Rick - DJ0IP / NJ0IP wrote:
> Probably the most interesting use would be to see the transmitted spectrum
> of stations on the band.
> If I hear broad splatter, it would be nice to easily see where its coming
> from and see just how broad it is, compared to other signals.  Same for key
> clicks.
> It would be nice to look at my own signal and see how broad it is, if it is
> flat topping on peaks, etc.

Flat-topping on peaks will show up as splatter.

Another important use of a spectrum display is evaluating and chasing 
noise. For example, impulse noise will show up as horizontal lines, 
whereas electronic noise will usually show up as broad humps of noise. 
If they are clocks associated with microprocessors, they will be stable 
in frequency. Noise from other electronic sources will generally drift 
around, either due to warmup, or as a result of dithering.

You've noted that you would like to avoid the need for a computer to run 
the display. Depending on what computer is in your shack, it may do 
double duty to run the display (although not at the same time as a 
contest logger with cluster spots in a major contest). But if a computer 
is not required, the cost of the spectrum unit, whatever you choose, 
will be greater. The Elecraft P3 is a great example of that, and it's 
part of the $700 cost of the kit version.

Another point -- you really do want a display that gives frequency 
readout, not just +/- from the dial frequency. That requires either a 
standalone RX connected to an antenna, or communication between the 
display software and the radio. The integration of the P3 with the K3 is 
really quite good, and does that. I don't know if it will do that with 
other radios.

If you want to know how broad a signal is, you'll need a way to measure 
it. That probably means a cursor with frequency readout. But the 
precision of this measurement will depend both on that readout and on 
the resolution bandwidth of the FFT.

Another set of issues are the linearity and dynamic range of the RX 
system, including radio it's being used with if the signal goes through 
that radio.

FWIW, virtually all SDRs that feed Skimmer spots use some antenna other 
than the TX antenna, often a vertical.

And another thought -- I'm an OT like you, and surface mount soldering 
is not on my list of skills. Although I did learn it well enough to 
solder the larger SMT components in two sets of 5B4AGN's excellent 
contesting bandpass filter kits, I wasn't to proud to ask for help on 
learning the skill, and on having hams with younger eyes to do SMT 
repairs and build stuff with smaller SMT parts. I suggest you keep that 
as an option for taking an IF out of your Eagle.

Here are some measurements I've done recently with the P3 of gear in my 


I'm trying to borrow an FTDX5000 to measure. :)

73, Jim K9YC

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