Fisher F4 8" Coil inductance

[mustafayilmaz]

Hi,

I'm thinking of making a VLF metal detector with this coil.

Can you measure coil inductances?

I'm looking for a simple coil. Can you suggest another coil?

[kt315]

hi
bounty hunter has 2.4mH TX coil with 220+22nF cap. that gives 6.6Hz (another source gives 6.7Hz). i try collect a data on BH one.
RX winding is unknown. so you can begin making with me.

[homefire]

Some info I had stashed from where ??? Don't remember.

FISHER COILS ???? (- General)

by Dave J., Friday, November 18, 2011, 04:40 (1 day, 6 hours, 58 min. ago) @ BIG SILVER CLARK

Over the last several years we've introduced a lot of new models in several different product lines. At times it has resulted in some confusion as to what's what. Knowing firsthand what dying pains feel like, I prefer the pains that come with growing.

So much for editorializing.

* * * * * * * *

The F2/F4 coil is electrically the same as the legacy BH series. But with a CB mike style connector. Nowadays. Originally it had a BH compatible DIN connector and is still available in that configuration for BH and original F2/F4 machines.

It is not electrically compatible with other Fisher or Teknetics products. It probably won't damage them but will NOT work correctly.

If someone has coils they can't figure out what's what, here's the straight skinny: get an LCR meter that tests at 1 kHz. And probe around the contacts until you find what is obviously the transmitter.

F2 Series: Receive coil (pins 1 and 2) is 2.4 mH , R = 5 Ohms.
Transmit coil (pins 3 and 4) is 2.4 mH in parallel with (220 nF + 22nF), resonant at 6.6 KHz. DC resistance of coil is 8 Ohms.
An alternative TX would be 220nF and 2.65 mH, though I haven't tried it.
Capacitors: the 220 nF would be best if polypropylene, though polyester/mylar would be OK. The 22 nF will be fine in polyester (and could be 20 nF)

Legacy BH series: approx. 2.4 mH.

T2 only: approx. 680 uH, center tapped with some positions reading about 170 uH.

F75/F70: approx. 660 uH.

GB, GB Pro, G2, F5, Platinum, Gold, Gamma, Alpha, Omega, Delta: approx. 880 uH. Concentrics in this series are NOT specified for use on the GB, GB Pro, or G2 although in some instances they may seem to work.

If this information was useful to anyone please let me know by posting here.

--Dave J.

[kt315]

HF
i recently read that F2/F4 use same BH coil, but their board has a cap on TX part.
it is decreased the frequency to 6.0kHz.

[Skippy]

Sounds like some of my posts being quoted there...
And yes, the F2/4 have an additional 47nF across the TX coil, dropping the resonant freq down to 5.9 / 6.0kHz.