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