Fisher Gold Bug

[Nandor]

I also use the CD4060 to drive the crystal. Last year I tried it so hard and without succes but now I know that the amplitude from CD4060 needs to be trimmed. It works just fine with the TGSL coil 10.5Vpp from +5 volts, pretty clean. My o-scope is a Hantek DSO5202P it's a decent one, had succes with it bringing to life many failed projects before I had it.

What about the Q of the coil, Less Q is better for forced driven coils right? Seen some Fisher coils on eBay.
I wish I could give you tips have a great time doing the Fisher Gold Bug!

regadrs

[ivconic]

I hope you made advances in your project, Im very interested in your progress. I have made a quartz oscillator as it's on the Gold Bug schematic you posted, installed it to one of my non working pcb and it's alive! Kicks 30 cm on a 1euro coin easily .
The oscillator works on +5 volt and I has 10Vpp on Tx, so basically double of the supply voltage. With my transistor oscillators I could not make double voltage of the powersupply without distortion, this quartz oscillator is usefull I like it. Also would like to try the phase shifter with CD4013.

Best regadrs to you!

Always put 1M resistor parallel to crystal. So as i noticed; sometimes 4060 will not work without it.
Also since you used that part and it works for you; you shall use also TX output as original, with one transistor and trimmer to adjust amplitude.
It is better solution than the "alternative" i put also on schematic.
At my board supply is from two Lipo 18650 wired in series, middle point is GND.
Rails are +/-3.8v. TX supplied with bit less than 8v. And TX amplitude is 16Vpp.
Cleanest possible sinus that you can see.
TX out works only when coil is attached. Without coil the transistor is closed.

[ivconic]

Ususally I try to use low hFE transistors for low distortion on the Tx, if I find, had good results with less than 170 hFE. But what about crystal driven oscillators, what transistor have you got on you Gold Bug pcb for the TX?

I am stuck at last opamp before the audio stage.
The threshold part.
It is having very weak signal at the output. Not capable to drive audio.
Also have found several mistakes, not mine, from original schematic.
Everything up to that last opamp i trimmed to work just nice.
It is dual. One half is alright, another half is having problems.
Configured badly. Not by me.
So ... lot of labor is waiting me yet.

[Nandor]

Ususally I try to use low hFE transistors for low distortion on the Tx, if I find, had good results with less than 170 hFE. But what about crystal driven oscillators, what transistor have you got on you Gold Bug pcb for the TX?

[Nandor]

I hope you made advances in your project, Im very interested in your progress. I have made a quartz oscillator as it's on the Gold Bug schematic you posted, installed it to one of my non working pcb and it's alive! Kicks 30 cm on a 1euro coin easily .
The oscillator works on +5 volt and I has 10Vpp on Tx, so basically double of the supply voltage. With my transistor oscillators I could not make double voltage of the powersupply without distortion, this quartz oscillator is usefull I like it. Also would like to try the phase shifter with CD4013.

Best regadrs to you!

[ivconic]

I made pcb, populated it and now testing it.
Auch!
I find lot of mistakes that i made drawing pcb, one after another!
That's what you get when you rush into several parallel diys.
But this not worries me.
There is another thing that i would like to distinguish; the coil.
I am having original coil, but taken out of enclosure, without Faraday cage, only two short coaxial coming from it.
One is Hot-Red with litz shield and another is Hot-White with litz shield.
- Hot-Red = 2.2 ohms, can't measure inductance because obviously there are some components, hidden in epoxy, preventing that.
- Hot-White = 19.6 ohms / 1.02mH.
Instinctively one will reach and connect Hot-White to RX and Hot-Red to TX. Common sense. WRONG!
Output transistor stay "closed" when Hot-Red coil is connected to it.
But when Hot-White connected instead; output works just SPLENDID!
Giving PERFECT sinus and can be adjusted with trimmer up to 16Vpp and remains perfect sinus.
So... by now; complete TX stage with +/-90 degree phase shifter and TX out; works PERFECT.
Also RX appears to work perfect with LME opamp. Giving also perfect sinus at output, reacting very fine on scope when detection occurs.
Synchro-demodulator works also PERFECT!
I shall take photos of what i see on scope and keep them as referent examples of how things should work.
But later in channels i made total mess drawing pcb! I probably was very tired.
Also audio output was not working from a start. It was chocked totally.
So i had to remove BD136 and short E and C at it, to make audio to appears and work fine.
Obviously this is due different power supply that i used. I will solve this later because right now it is insignificant.
Must tell here that direct supply from two LiPo batteries in series, without any regulator, was excellent move!
Rails are +/- 3.8V. Because i put 10 ohms at both rails for supplying opamps.
Audio supply is ~ +8V so as 4060 part.
I see NONE hum on the scope, anywhere on the pcb.
...
I would like someone to confirm me (or not) only situation with coil.
Is there anybody having old Gold Bug to check where and how TX and RX coils are connected?
Just to be sure.

[Skippy]

That CZ-6 pre-amp WILL have a noticeable phase/gain behaviour, it's mostly defined by the R's and C's in the feedback network.
The 1K0 & 4n7 pair give a low-pass roll-off at f_c = 34 kHz , and the high-pass roll-off, determined by the 47R & 1u0 pair, give an f_c = 3.4 kHz.
There may be some additional contributions from the input filter ( the 47R + 47R etc low-pass filter circuit ), and the 200pF stability cap will affect things at high freqs, I don't know what, though.

[6666]

I completed pcb this morning at 5-6 o'clock, haven't slept at all.
Whole day feels like zombie. Not even tried the pcb.
Even now i feel very tired and not able to continue
So probably i will test it tomorrow or day after tomorrow (other responsibilities too).
I am not in such shape any more... like i was 10 years before.
Parallel i am working on resmeter and two more pcb's to complete.
And above all , the other night; happens George with his book, which distracted me totally!
So... i will probably have first reports within next several days.
I put LME 49720 at RX front end.
Other opamps... not sure what to use, soldered sockets there.
So tired...
Very good job with simulations! Thanks!

Its 5:00 am here right now, back to bed.

[ivconic]

I completed pcb this morning at 5-6 o'clock, haven't slept at all.
Whole day feels like zombie. Not even tried the pcb.
Even now i feel very tired and not able to continue
So probably i will test it tomorrow or day after tomorrow (other responsibilities too).
I am not in such shape any more... like i was 10 years before.
Parallel i am working on resmeter and two more pcb's to complete.
And above all , the other night; happens George with his book, which distracted me totally!
So... i will probably have first reports within next several days.
I put LME 49720 at RX front end.
Other opamps... not sure what to use, soldered sockets there.
So tired...
Very good job with simulations! Thanks!

[dbanner]

Here I put CZ6 rx preamp ltspice file. There is definitely a marked frequency dependent phase response. Say at 4 khz vs 20khz.

[dbanner]

I apologise for uploading wrong files, the correct files have now been uploaded.

[dbanner]

Something I thought about was the phase response of the original rx preamp( with bunch of solid state devices). I ran a simulation of the circuit and found the output ( before 10k trimmer), there was zero phase shift of the signal at 20khz)
I thought that by replacement of this stage with an opamp topology would be careful to observe any phase response inherent in pass filtering. I assume that most likely the original coil parameters would be used in an updated version. Also consider whether a series resonant rx coil vs a parallel resonant coil would be implemented.

I put here the corrected original gold bug preamp ltspice file.

[dbanner]

I put an option of a power supply circuit. It delivers output of +6V , +3V , and ground.

[ivconic]

It is forced oscillator.
Frequency will not change.
Amplitude may change insignificantly within 0.5vx2=1v p.s. drop.
But voltage drop at batteries is not sudden. It is slow in time.

[Nandor]

Cheers for you Ivconic!

That regulator less power mode is iteresting for me. I can only imagine power consuption around 30-40mA for Gold Bug, and its not much for 2 Lipos but what about the oscillator?

Maybe its worth trying with other detectors also, I always thought that noise in the power supply has effect on op amps performance, like charge pump or DC/DC boosters.

Tomorrow I will experiment with my pcbs, I have some lipos in the drawer .

regards