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

Rick - DJ0IP / NJ0IP Rick at DJ0IP.de
Thu Dec 25 12:44:14 EST 2014

This is excellent information, Jim.  THANKS.
I'll need some time to digest all of it.

The only bad part about your plan is, in my local vicinity, I am the
youngest ham!  :-(
They all look to me for help.
I refuse to do SMD work on anyone else's rig.
I hope to avoid it on my Eagle.

The chasing noise aspect of it was totally new to me.
I'll have to think about that... and write it down so I don't forget which
was which (hi).

Gotta run now.  The XYL is sick, in bed and I have KP.

Merry Christmas!

73 - Rick, DJ0IP
(Nr. Frankfurt am Main)

-----Original Message-----
From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Jim Brown
Sent: Thursday, December 25, 2014 6:34 PM
To: tentec at contesting.com
Subject: Re: [TenTec] How to Choose an SDR RX for the Pan-Adapter?

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

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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