[RFI] My Ultrasonic Parabolic Reflector Receiver System Build and Website

[Richard Karlquist]

I investigated building a homebrew detector like this some 20 years ago 
or so, and found that the ultrasonic transducers that I could find had a 
fairly narrow angle of reception.  The only parabolic reflectors I could 
find were very "deep" and it turned out that those transducers would 
poorly utilize the dish.  We would say they wouldn't "illuminate" much 
of the dish.  It was obvious from a catalog page showing the Radar 
Engineers product, that it used a much "shallower" dish, which would 
give much better "illumination".   It is not sufficient to say that the 
dish is accurately parabolic and then you just locate the focal point 
and put the transducer at the FP.

I just wanted to give everyone a reality check.  My suboptimal device 
did "work", but probably not as well as the Radar Engineer's one, and 
was much larger to boot.  If I had to do it now, I would make a 3D 
printed shallow dish and as much as possible clone the Radar Engineer's 
dish.  I would say that the dish in the photo looks much shallower than 
the one I tried to use, but it is hard to say just from the photo.  The 
key figure of merit for a dish is the ratio of diameter to focal length. 
  My dish was such that the focal point was in the plane of the rim of 
the dish.

Another thing is that the transducers are very narrow band in terms of 
frequency, probably because  they are optimized for TV remote controls, 
I guess.  Since we are looking at wideband noise, I suppose it doesn't 
matter a lot, except we lose a lot of sensitivity that way.

---
Rick Karlquist
N6RK

On 2026-03-25 13:42, Don Kirk via RFI wrote:

> I finally decided it was time to add the one missing tool I had from my 
> RFI
> detection/direction finding toolbox so I undertook the building of my 
> own
> ultrasonic parabolic dish receiver system for detecting arcing on power
> line hardware based on the W1TRC design that was in the April 2006 
> issue of
> QST.  Unfortunately Jim (W1TRC is an SK).
> 
> I know this tool has been discussed many times over the years on the 
> RFI
> reflector but thought I would share my recent build information with 
> the
> group as it might be helpful to those currently wanting to build one, 
> and I
> also think I kept my build very simple.
> 
> I had a lot of assistance from Charles (N0TT) and I also picked up a 
> lot of
> great information from Jeff (W4DD) and Frank (K7SFN).
> 
> Here is the link to my simple website that I created today for those
> interested in my build:
> https://sites.google.com/view/ultrasoundarcdetector/home
> 
> 73,
> Don (wd8dsb)
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