PD Discussions

[WM6]

This is strange for me why designer ALONSO or ……. Use this type detector .
What theory and philosophy behind.??????

It is about very known QGT (Quantum Greedy Theory). Not much philosophy behind.

[Geo]

Hi Geo
Yes, thank you for your guide , I know very well heatkit GD 348 problems
I never see and never work with original heatkit GD 348 . all of my knowledge
From my clone circuit . I did more practical work in laboratory with it .
This is strange for me why designer ALONSO or ……. Use this type detector .
What theory and philosophy behind.?????? Instability at GD348 not produced
by frequency drift, not very Important oscillator frequency drift ,
This type detector base on amplitude changing .
Best regards.

Hi aft.
I don't know why Alonso prefered this schema. It is sure that the GD348 is more sensitive than every bfo and has a very very strong oscillator. Now about instability..... i had the same problems for long time. Now i solved them and it is very stable. Try to make it stable and after it you will see that it is a good detector.

Regards

[aft_72005]

Hi aft.
I don't know why Alonso prefered this schema. It is sure that the GD348 is more sensitive than every bfo and has a very very strong oscillator. Now about instability..... i had the same problems for long time. Now i solved them and it is very stable. Try to make it stable and after it you will see that it is a good detector.

Regards

Hi Geo
Thanking , I will try build it more stable .
Best regards.

[Geo]

I found diference by changing the LM-317 with a 7809. LM-317 had 25mv shift on 15 minutes.

Regards

[aft_72005]

I found diference by changing the LM-317 with a 7809. LM-317 had 25mv shift on 15 minutes.

Regards

I will try
Thank you

[J_Player]

Hi Geo
Yes, thank you for your guide , I know very well heatkit GD 348 problems
I never see and never work with original heatkit GD 348 . all of my knowledge
From my clone circuit . I did more practical work in laboratory with it .
This is strange for me why designer ALONSO or ……. Use this type detector .
What theory and philosophy behind.?????? Instability at GD348 not produced
by frequency drift, not very Important oscillator frequency drift ,
This type detector base on amplitude changing .
Best regards.

Hi Aft,
The philosopy of using a heathkit detector is common with Alonso and other builders of LRLs which are modified metal detectors. The reason to use this design is because it uses all transistors, with no IC in the circuit. The early transistor designs were simple and they did not have internal filters built into them like ICs do. They wanted pure transistors so none of the signal they receive will be lost in a filter or compensating circuit like they are in a design with op amps.

They like the early circuits also because these detectors detect all of the signal. They hear very weak signals that modern detectors do not because modern detectors filtered out weak noise signals. But this same noise is the problem with old detectors, They are unstable partly because of the excessive noises they pick up from stray RF, EMI and ground capacitance or other sources. But this is the sensitivity that LRL experimenters are looking for to find thir treasure signal. This Heathkit detection design is more sensitive than modern VLF circuits, or even BFO designs.

When you use 1970 electronic designs you do not have modern methods to keep the circuit stable. Take a look below, and you will see the most unstable part of the GD348 is the audio amplifier which must bring the weak detector signal to a usable signal. We see they put in a pair of diodes to act as temperature compensation, and a zener diode to keep the voltage constant. You may be aware there are better modern methods to keep the supply voltage for this transistor from drifting. This is one place where you can solve some instability at this critical part of the circuit.

But keep in mind the Alonso PD made modifications to the GD348 detector, The speaker was replaced with a beeps generator, where some of the output signal is mixed with the ferrite signal. But more important, there were big changes made in the front end by the omega coil and the resistor network that sends part if the TX signal into the RX coil. You cannot expect the Alonso circuit to work the same as the GD348 because the beginning signals at the omega RX coil are different in level and in the amount of feedback.

In any case, assuming you can get reasonably similar circuit performance as a GD348, the biggest problem I see in most PD designs is when builders mount their circuit boards too close to the coils. If you look closely at the Alonso design, he took measures to keep the coils separated from the control box, which prevented the circuit from being detected as treasure metal. But it is also important to keep the boards separated from the coils so the coils will not induce eddy currents in the early stages of the RX that can make the circuit impossible to work. (Remember the GD348 had the coil at the end of a shaft separated from the controls, and only a small board for coil-related parts at the omega coils).

See diagram below. And also see in zip file for original GD348 schematic. You can compare this schematic to your PD and see how much it is different at the end by the coils.

Best wishes,
J_P

[aft_72005]

Hi J_Player
Thanking for your attention and thanking for your help , your are fine engineer , you pointed to points which also I thinking about it !!!!!!
I must be use reference zener diode( instead ordinary zener diode) , other instability was Darlington transistors at output ( see PD circuit-not original heatkit circuit) .
My built and modified MD vas very stable on workbench !!!!!!!!!!!! . it can detect 17 inch computer monitor from 1.5 meter easy in workstation . !!!! but problem will begin
When begin moving PD in search aria!!!!!! ., may be must be
Not tuned for very fine null ( null tuned very fine) but when a little out of fine null . sensitivity is fall down and didn’t act as LRL
maybe this is sky ground effect but Coil far from ground !!!!! . crux is here, be stable
in high sensitivity .
I remember Qiaozhi ideas , super fine , super sensitive detector but point here with stability .
Best regards.

[aft_72005]

Hi Qiaozhi
You are after Carl leader of this forum . excuse me , our dissection was long because as this is zahori thread, May be better will begin other thread about Alonso or ….X designer ofPD problems .
But I cannot copy and paste all messages about heatkit GD 348 detectors
Best regards.

[Geo]

You can use a voltage regulator in place of zener but the reference zener must be better.

[aft_72005]

You can use a voltage regulator in place of zener but the reference zener must be better.

Zener 5.1 volt or TL431 with 20ppm

[Geo]

Zener 5.1 volt or TL431 with 20ppm

Try and tell us

[FrancoItaly]

Hi All
The better system to eliminate slow drift in DC signals it's to use a motion circuit, I use a comparator, the signal goes to one input by a capacitor and the same input is polarized at half DC power and the other input goes to a potenziometer for sensibility regulation: If you use a CA3130 or CA3140 the capacitor may be about 1 microfarad.

Best regards

[Qiaozhi]

Hi Qiaozhi
You are after Carl leader of this forum . excuse me , our dissection was long because as this is zahori thread, May be better will begin other thread about Alonso or ….X designer ofPD problems .
But I cannot copy and paste all messages about heatkit GD 348 detectors
Best regards.

Hi Aft,

Do you want to start a new thread and copy certain posts to that thread? If so, which ones do you want to copy?

[aft_72005]

Hi Aft,

Do you want to start a new thread and copy certain posts to that thread? If so, which ones do you want to copy?

Yes, better move because this is zahori dissection
But don’t important move to which one !!! what is your opinion ?
Thanks for my trouble .
Best regards .

Best regards .

[aft_72005]

Try and tell us

I must be go to electronic market and buy them. Test this,
But I think don’t solve problem !!!! because instability began when
Coil over ground