I came across this article a couple days ago;
http://www.kk4ice.com/wp-content/uploads/2015/01/KK4ICE_Ultrasonic_RFI_Detection.pdf
Use's a 18" satellite dish and surplus ultrasonic. Few details in the
article though. But the pinpoint accuracy he claims is encouraging.
I happen to have a unused 18" offset satellite dish and a unused
refrigerant leak detector. Thinking about trying that combo to see if it
works any better than the QST article dish I built. Will be heavy but I
have tripods. Need to make a test range and install sights on both of
them too.
Would the end of a air compressor hose slightly leaking make a good test
source?
Chuck
W4NBO
On 5/8/21 3:08 AM, Charlie Delta via RFI wrote:
Hi
Can someone who owns a Radar Engineers model 250 or model 251 Ultrasonic RFI
receiver kindly tell me the dimensions of the dish?
I am particularly interesting in the dish depth and the focal distance point. I
understand that dish is 18 inches in diameter.
The plan is to get a suitable parabolic dish molded by a local Dome skylight maker
who thinks that he can mold a suitably accurate true parabolic dish.
I am curious to know if the Radar engineers dish falls within the 0.5 to 0.6
F/D ratio? Since it works so well I thought I might as well start off with a set of
dish dimensions that is proven to work around the 40khz Ultrasonic frequency.
Since the beam-width is so sharp , I presume that the dish dimensions and the
illumination from the dish of the ultrasonic mic will be critical. I have already
played around with the W1TRC detector and various odd ball dishes and the results
have not been that great since these dishes have a far from optimum F/D ratio.
From playing around it seems that a deep dish with the focal point deep within the dish
produces a very poor result and may even produce minor sidelobes that causes confusion.
Depending on the strength of the signal, an ultrasonic signal can disappear
because of the poor illumination of the microphone sensor. So it does appear that an
optimum f/d ratio dish would produce a better result.
Any input or comments would be welcome from anyone who has tried to build a
similar project.
(pick your mould VS mold spelling)
73CraigVK3OD
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