[RFI] Radar Engineers Model 251 Parabolic dimensions?

[Grant Saviers]

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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