Blue Max 600

[Geo]

Hi.
I am interesting about the inductance and resistance of Whites BM600.
Also has it both coils tuned at the same frequency (Rx and Tx)?

Regards

[mikebg]

Hi.
I am interesting about the inductance and resistance of Whites BM600.
Also has it both coils tuned at the same frequency (Rx and Tx)?

Regards

Geo, you should be interesting and about capacitances
Here are design parameters for BlueMax family:
TX tank circuit
Resonance frequency 6590 Hz max
Capacitance 1uF min, 1.2 uF max (3 caps in parallel)
Inductance 540 uH nominal
Resistance 1.6 ohm max
RX tank circuit
Resonance freq. 4900 Hz max
Capacitance 30 nF min, 36 uF max (3 caps in parallel)
Inductance 36 mH nominal
Resistance 70 ohm min, 120 ohm max

Note: Six capacitors are inside coil housing

[Geo]

Thank you Mike
I want to construct one without shield for experiments.

Regards

[Geo]

Ohhh.... i just saw it.
At Rx tank the max capacitance is 36uF or 36nf(i think it is nF)???

Regards

[mikebg]

Ohhh.... i just saw it.
At Rx tank the max capacitance is 36uF or 36nf(i think it is nF)???

Regards

Yes, my errata. The true value is maximum 36 nF with three capacitors in parallel.

[Geo]

Mike, do you know about the diameter of Tx and Rx coils?? Is the ratio 2:1 ??

Regards

[kt315]

Resistance 70 ohm min, 120 ohm max

there may be an resistor ~51 Ohm in serial of coil. so real resistance of coil is more less. for example, according what Carl shared a data on coils
White's Spectrum XLT 9.5" has:
Rx 1,2 36mH 123 ohms
Tx 4,5 540uH 1.4 ohms
measured:
Rx - 34,6 mH 60 Ohms + resistor 51 Ohms
Tx - 537uH 1,1 Ohms

[Altra]

Kt315
I think you posted this along time ago?

Mark

[Altra]

For some reason file did not attach?

[Geo]

there may be an resistor ~51 Ohm in serial of coil. so real resistance of coil is more less. for example, according what Carl shared a data on coils
White's Spectrum XLT 9.5" has:
Rx 1,2 36mH 123 ohms
Tx 4,5 540uH 1.4 ohms
measured:
Rx - 34,6 mH 60 Ohms + resistor 51 Ohms
Tx - 537uH 1,1 Ohms

I see at a photo (maybe your) that there is a resistor 6M8 between Tx ans Rx coil. Do you know the reason???
Also why the Rx coil is tuned at 4900Hz and not near to 6590Hz. I know that coils are not tuned exactly at the same frequency but not so big difference. Any idea????
Does it help for better nulling???

Regards

[kt315]

Kt315
I think you posted this along time ago?

Mark

not so hard to repeat something. yes, I did open XLT, good coil if tuned. but Fisher coil seems more advanced inside. Fisher for example uses conductive spool for RX coil for the Faradey shield. graphite in plastic? - I dont know...

[mikebg]

I see at a photo (maybe your) that there is a resistor 6M8 between Tx ans Rx coil. Do you know the reason???
Also why the Rx coil is tuned at 4900Hz and not near to 6590Hz. I know that coils are not tuned exactly at the same frequency but not so big difference. Any idea????
Does it help for better nulling???

Regards

Geo, the RX tank circuit acts horrible for GND balance and TGT discrimination when it is tuned near to TX frequency. In the resonance frequency region, the RX tank can change phase shift from +90 deg to -90 deg because the earth operates as a variable core for RX coil.

However an incompetent designed project can be tuned to operate at resonance because this is great at AIR TEST. As you know, NEXUS metal detectors outperform at air test all other metal detectors. Now you know why.

If you use a SPICE program, simulate the phase shift of a LCR tank circuit to see how steep is the phase diagram when the coil has low resistance and if there is no additional damping resistor.

Both resistors inside search head (together with resistance of RX coil) play role for balancing. They operate as voltage divider delivering voltage for balance. The producer of search heads should tune both resistors for each head individually at closed shielding shells. To adjust nulling, you can connect for example a potentiometer 10Meg in series to resistor 6M8 and a potentiometer 100R in series to resistor 51R.

[kt315]

I see at a photo (maybe your) that there is a resistor 6M8 between Tx ans Rx coil. Do you know the reason???

balance compensation on plastic and polyfoam inside the coil stuffed. remember - I do not work on Whites and my name is not E.Foster. I may not know something you need in full ascertainment on.

[mikebg]

The attached below simulation shows voltage transfer functions (frequency response) of RX tank circuit without load. Operating without load is realised in most preamp circuits - RX tank is connected to noninverting input of operational amplifier.

The marker shows TX frequency about 6500 Hz used in most White's machines.
The RX tank operates as second order low pass filter. Resonance frequency divides frequency spectrum in two regions - passed region in left and stopped region in right. Low pass filter means that we can receive larger signal if TX frequency appears below resonance frequency. In this region TX tank will add too small phase shift.

However the designer of White's search head decided to operate in the beginning of stopped region where RX tank attenuates signal and adds phase shift near to 180 deg.

Now let we see how operates NEXUS. The TX frequency appears at resonance of RX tank. At this coil we will receive a near 9 times more large amplitude, more sensitivity at AIR TEST. But look how steep is phase response in this region. We will have strong angle and amplitude modulations when search head changes height or when the soil has different electromagnetic properties. That means variation of GND setting and change of discrimination level.

CONCLUSION: If I was designer of search heads, I would use minimal capacitance for RX tank. This allows to increase turn number, ie the RX coil will receive more strong signal. In addition, when TX frequency appears in passed band of the LP filter, the RX coil will receive more strong TGT signal than at White's machines. Unfortunately the improvement is insignificant because in practice the sensitivity of RX is not limited by thermal noise.

[kt315]

CONCLUSION: If I was designer of search heads, I would use minimal capacitance for RX tank. This allows to increase turn number, ie the RX coil will receive more strong signal.

not. ideal nulling you will get of if you have IDEAL transformer, ie RX coil turns number=TX coil turns number, using one wire for both. also you have to use geometrically ideal DD coil form.