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)
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
|