RE dish choices:
Really nice looking and cheap and light, available at Walmart, Amazon,..
$22 > $25
AUDUBON NACLBAF16 Clear Squirrel Baffle, 16-Inch
Has anybody measured the profile, focal length, etc?
Might be available direct from Audubon at a lower price.
Grant KZ1W
On 5/8/2021 08:14, Charles Plunk wrote:
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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