[RFI] Radar Engineers Model 251 Parabolic dimensions?

[Mike Martin]

It's kind of early for me and my mind's a little cloudy as I had a late night last night. However, there is a really nice dish available made of lexan. It was made to be a squirrel guard for bird feeders. I have one of those in storage I'll see if I can find it and get any information off of it I can. I do have a 250 and 251 that are used frequently. The 251 definitely outperforms the 250 in accuracy and range, more so in the range. 
I have a busy weekend and a busy week ahead but I'll see what I can find. If you design something as convenient as the 251 and performs as well or better, I'll be here first customer.

⁣Be safe,
Mike

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On May 8, 2021, 4:08 AM, at 4:08 AM, Charlie Delta via RFI <rfi at contesting.com> 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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