Making a Bigfoot?

[Altra]

See post #6

http://www.geotech1.com/forums/showt...ign-schematics

[kt315]

... ...

[bklein]

That looks like an XTerra board, they have a micro embedded. Sov/Excal do not.



Excal is a simple square-wave drive but with a fundamental of 3kHz, so I would expect the critical thing is to keep the TX coil resistance low. There is no resonance cap for TX, and surely not for RX either. Somewhere there is a schematic for the coil PCB.

I put the Excal over a 8" multiturn loop of wire connected to my spectrum analyzer and 3 Khz doesn't show up but 24.56Khz seems a peak. Why doesn't the fundamental show up, I must be doing something wrong?

[bklein]

Here we go, this shows 3Khz.

[bklein]

I communicated with Bill Lahr and he suggests a Bigfoot won’t work right with an Excal as it needs a 4 filter detector. Only one half of the coil would detect right. A DD would work though, like the Cleansweep. I have no experience with one. Never seen one taken apart or heard of someone trying to make one.

[Skippy]

The "3kHz" frequency you're looking for is actually 3.125kHz, 25kHz divide by 8. Spectrum analysers tend to make a mess of the BBS waveform, the 25k stands out because there is 8 continuous cycles of it, then a gap ( for 1 cycle of 3.125k ) then repeat.

I would say the extra-long DD configuration of "bigfoot" is be easier to design and build, compared to the more exotic figure-8 etc types.

[Carl-NC]

I communicated with Bill Lahr and he suggests a Bigfoot won’t work right with an Excal as it needs a 4 filter detector. Only one half of the coil would detect right. A DD would work though, like the Cleansweep. I have no experience with one. Never seen one taken apart or heard of someone trying to make one.

He's partly right, the Bigfoot needs a detector designed to respond in all 4 quadrants. 2-filter vs 4-filter doesn't matter. Most detectors can't do this.

The Cleansweep is just an ordinary DD, except long & rectangular.

[kt315]

https://www.reviewdetector.ru/index....ost&id=4230979
https://www.reviewdetector.ru/index....ost&id=4242998
a pcb of mars coil. has two frequencies. 2 micros = 2 freq-s.