[RFI] Radar Engineers Model 251 Parabolic dimensions?

[chuck.gooden]

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 at nk7z.net> Date: 5/8/21  8:20 AM  (GMT-06:00) To: rfi at 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 at contesting.com> http://lists.contesting.com/mailman/listinfo/rfi> _______________________________________________RFI mailing listRFI at contesting.comhttp://lists.contesting.com/mailman/listinfo/rfi