I found a parabolic metal dish at Lowes being sold as a squirrel deflectors for
bird feeders. See link
https://www.lowes.com/pd/Black-Squirrel-Baffle/1000931908I have since seen
plastic ones that are similar at other stores.Chuck K9LC
-------- Original message --------From: Dave Cole <dave@nk7z.net> Date: 5/8/21
8:20 AM (GMT-06:00) To: rfi@contesting.com Subject: Re: [RFI] Radar Engineers
Model 251 Parabolic dimensions? You might check out this
dish...https://www.midnightscience.com/ultra-kits.html73, and thanks,Dave
(NK7Z)https://www.nk7z.netARRL Volunteer ExaminerARRL Technical Specialist,
RFIARRL Asst. Director, NW Division, Technical ResourcesOn 5/8/21 1:08 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> _______________________________________________> RFI mailing
list> RFI@contesting.com> http://lists.contesting.com/mailman/listinfo/rfi>
_______________________________________________RFI mailing
listRFI@contesting.comhttp://lists.contesting.com/mailman/listinfo/rfi
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
|