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
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