[RFI] Radar Engineers Model 251 Parabolic dimensions?

[Charlie Delta]

Thanks to all that replied.
1. Midnight sciences have closed down W0xi has retired and no longer sells kits or dishes.
2. I appreciate all the suggestions for a parabolic dish source. However I more interested in spending money on a true parabolic shape with the right F/D ratio. Its a fruitless exercise building good electronics on an imperfect dish  geometry platform

3. I have gone down the road of trying, wok lids, Skylight domes, Cake display stands, salad bowls, Sony parabolic dish, and all sorts of  odd objects that have a half decent parabolic shape. Sure it  works however range and sensitivity wont get near a Radar Engineers or even a MFJ5008. Even the ARRL review of the MFJ5008 mentioned that the Radar engineers had a detection range of in excess of 200 ft whereas the MFJ  units range was in the 100 to 150 ft range. Other professional  dishes by companies like SDT and Sonaphone in Germany have  stated specifications of 50 to 100ft for electrical airborne dischare detection.  Even the Super Fluke ii910  that costs 30,000 dollars has a range of 70 meters.

4. I used a weak signal Sparak source which was an iridium spark plug and my Associated Reseach 15KV Hypot to generate a test signal. If the signal is strong enough any scrap dish will hear it, even with a funnel as a dish! However when you want to hear a weak signal then the whole setup becomes important and the dish design becomes critical to the success of detection. Sounds a lot like ham radio and having the right antenna!

5. What is clear is that  anything parabolic in shape works however the sensitivity and directivity  varies a lot to the point of causing  frustration.
6. Symptoms  include weak  signal detection,   washed out signal detection ability  and off axis  sidelobes which make the device usesless for pin pointing.
So with all of the above in mind I wanted a fresh start  by 1st building a proper dish. There are a number of parabolic dish sources availableI am more interested in experimenting by trying to building something that works. After shippings costs and paying the high prices in US dollars its really cheaper for me to get something molded locally by a plastic molding specialists who do this kind of thing everyday.
7. For those wanting  a really good dish thats optimum you can buy one from Wildtronics. There webpage has some excellent information on parabolic dish design which I used as a reference. http://www.wildtronics.com There is another company on Italy called Dodotronic that makes nice ultrasonic mic's and also sells optimum parabolic dishes.

8. I have 2 X Sony Parabolic mics 330 and 400 models which are 33 cm and 40cm's in diameter. These have a far from optimum FD  ratio and work no better than random junk dishes. Most parabolic mic's on the market   have poor dish designs and only the specialist wildlife people have taken care with the design paramters(Telinga and Wildtronics)

9. If someone does have access to the Model 251 and if they could measure the dish depth and focal point since this would give us the optimum dimensions for the correct size dish for 40khz frequency and with the correct F/D ratio.
10. Every time that you drop the dish size by 10 cm in diamter the gain drops 6db according to the research. This suggests that the radar engineer size of 18 inches  or about 50cm is close to optimum.  A 60cm dish would be even better.11. The critical part is the illumination of the Mic or transducer and this is where building a proper parabolic dish with the right  FD ratio and focal point will reap rewards.

If all else fails I will sell the house and buy a Fluke ii910.
73CraigVK3OD