Nexus Coil Design

[Unregistered]

Nexus

@Gosho

plastmasova construction ?
serach on angli4an4eta not not zna4i 4e ?
schematic for zarqd ?

write english here or go away !!!

You are right. This is a forum for people who speaks english, not blabish.
The Gosho guy just wanted to bite me about the origin of the Nexus and he got the arrogance to call that thing on the pics Nexus, but he is a little bit away from the truth, not to mention the western market.
He strongly believe that everithing was invented by Grozdev, but that`s his object for worship, not mine.
Unfortunately many individuals in Bulgaria, suffer lack of information and can not comprehend the possibility that somewhere else in the world there is other smart guys, capable of inventing the same even better stuff.
My apologies for this Bulgarian inconvinience.
All best.
Georgi Chaushev

[Qiaozhi]

Registration

Hi Georgi,

I see that you are still an unregistered user. Please register and post the schematics as I described earlier.

Thanks.

[Nexus]

Original Grozdev`s schematic

Hi there. This is one of the original detector schematics done by Grozdan Grozdev from BG plust some other BG detector diagrams.

[Unregistered]

Bulgarian Detector Schematic

Hi there. This is one of the original detector schematics done by Grozdan Grozdev from BG plust some other BG detector diagrams.

Thanks Georgi,

Very interesting TX circuit in the Bulgarian schematic.
If you don't mind, I have a few questions. Are you able to answer these?

Do you know the output power of this High-Power TX Osc? If not, I can simulate it and post the results to this forum.

There are 3 coils in the TX, but only a description for one coil.
D = 0.18m (7")
N = 78 turns
d = 0.6mm wire diameter
I presume all 3 TX coils are in the search head?
It appears to me that there are two main TX coils of 1.3mH (confirmed by the capacitor values and the operating frequency) and the coil above these (marked 52) is a pickup coil for feedback and nulling purposes. Am I correct?

Significance of numbers next to coils - 52, 13 and 13?
Should this be 5.2mH, 1.3mH and 1.3mH?
5.2mH seems a bit high for a feedback coil. Perhaps this is 520uH?

Inductance of RX coils? I can calculate this if not known.

I'm guessing that this configuration is acting like two detectors in one. i.e. there are two TR coils side-by-side with the feedback coil in between.
Very interesting...

[Qiaozhi]

Bulgarian Detector Schematic

Quote:
Originally Posted by Nexus
Hi there. This is one of the original detector schematics done by Grozdan Grozdev from BG plust some other BG detector diagrams.

Oops!
Forgot to login before posting.:o

Thanks Georgi,

Very interesting TX circuit in the Bulgarian schematic.
If you don't mind, I have a few questions. Are you able to answer these?

Do you know the output power of this High-Power TX Osc? If not, I can simulate it and post the results to this forum.

There are 3 coils in the TX, but only a description for one coil.
D = 0.18m (7")
N = 78 turns
d = 0.6mm wire diameter
I presume all 3 TX coils are in the search head?
It appears to me that there are two main TX coils of 1.3mH (confirmed by the capacitor values and the operating frequency) and the coil above these (marked 52) is a pickup coil for feedback and nulling purposes. Am I correct?

Significance of numbers next to coils - 52, 13 and 13?
Should this be 5.2mH, 1.3mH and 1.3mH?
5.2mH seems a bit high for a feedback coil. Perhaps this is 520uH?

Inductance of RX coils? I can calculate this if not known.

I'm guessing that this configuration is acting like two detectors in one. i.e. there are two TR coils side-by-side with the feedback coil in between.
Very interesting...

[quink]

Hi Georgi,
big thankx for the schematics. Very interesting elektronic solutions in this schematics.
Have you more details abouts this detectors ? about search-deep and metall-differenz at search ?
And can you poste the schematic for the nexus please ?
greets

[Unregistered]

Thanks Georgi,

Very interesting TX circuit in the Bulgarian schematic.
If you don't mind, I have a few questions. Are you able to answer these?

Do you know the output power of this High-Power TX Osc? If not, I can simulate it and post the results to this forum.

There are 3 coils in the TX, but only a description for one coil.
D = 0.18m (7")
N = 78 turns
d = 0.6mm wire diameter
I presume all 3 TX coils are in the search head?
It appears to me that there are two main TX coils of 1.3mH (confirmed by the capacitor values and the operating frequency) and the coil above these (marked 52) is a pickup coil for feedback and nulling purposes. Am I correct?

Significance of numbers next to coils - 52, 13 and 13?
Should this be 5.2mH, 1.3mH and 1.3mH?
5.2mH seems a bit high for a feedback coil. Perhaps this is 520uH?

Inductance of RX coils? I can calculate this if not known.

I'm guessing that this configuration is acting like two detectors in one. i.e. there are two TR coils side-by-side with the feedback coil in between.
Very interesting...

The three coils you see on the oscilator are infact the sections of one transmit coil.
The output power of these oscilators depend on the diameter of the wire, the power supply of the transmit circuit, the number of turns between the colectors of the transistors and out to the tunning capacitors.
This type of oscilators do not transmit a lot of power, but because they are oscilating with the transmit coil in the circuit it makes them very efficient since the transmit coil if always in resonance.
To meagure the actual transmit power of this oscilator you have to meagure the current in the resonance circuit. Disconnect the tunning cap. from where is connected to one side of the coil and between those two ends connect ampermeter. The measured current x the transmit voltage will give you the power output of the oscilator.

The two 13 coils are the balanced section of the transmit circuit. The 52 coil is the amplifying section of the transmit coil which gives you higher output swing than the power supply rails. You can manipulate the 52 turns section in any other number to make what ever output voltage you want. The greater the number of the 52 section the higher the output voltage will be, but the stability will go lower. You have to find the balance in accordance to your design needs.
All best.

[Qiaozhi]

TX Circuit

The three coils you see on the oscilator are infact the sections of one transmit coil.
The output power of these oscilators depend on the diameter of the wire, the power supply of the transmit circuit, the number of turns between the colectors of the transistors and out to the tunning capacitors.
This type of oscilators do not transmit a lot of power, but because they are oscilating with the transmit coil in the circuit it makes them very efficient since the transmit coil if always in resonance.
To meagure the actual transmit power of this oscilator you have to meagure the current in the resonance circuit. Disconnect the tunning cap. from where is connected to one side of the coil and between those two ends connect ampermeter. The measured current x the transmit voltage will give you the power output of the oscilator.

The two 13 coils are the balanced section of the transmit circuit. The 52 coil is the amplifying section of the transmit coil which gives you higher output swing than the power supply rails. You can manipulate the 52 turns section in any other number to make what ever output voltage you want. The greater the number of the 52 section the higher the output voltage will be, but the stability will go lower. You have to find the balance in accordance to your design needs.
All best.

Hi Georgi,

Ah - now I understand!
The coils marked 13 and 52 refer to the number of turns. If you add 13+13+52 you get 78, which is the value of N shown in the schematic.

Hopefully you can answer one more question:
What is the configuration of these coils? Are they wound together as one coil?

[Unregistered]

Hi Georgi,

Ah - now I understand!
The coils marked 13 and 52 refer to the number of turns. If you add 13+13+52 you get 78, which is the value of N shown in the schematic.

Hopefully you can answer one more question:
What is the configuration of these coils? Are they wound together as one coil?

The configuration is #8 as the Nexus coils. The three sections of the transmit coil are wounded in one round loop.

[Unregistered]

Hi Georgi,
big thankx for the schematics. Very interesting elektronic solutions in this schematics.
Have you more details abouts this detectors ? about search-deep and metall-differenz at search ?
And can you poste the schematic for the nexus please ?
greets

The schematics for the Nexus was not drawn in any pc so far. I do not have time to do it. But as I said the schematics which I posted are very much the same with only component or value differences.
There is no principal advantage for the Nexus schematics to the ones I posted or the oposite.
The performance results depend completely on the proper adjustments of the whole system.
Now that is a trade which is well known by only few people.

[Qiaozhi]

Bulgarian Detector - SPICE simulation

Here are the results I've obtained from simulating the TX circuit of the Bulgarian detector.

First some calculations:

Georgi says that all 3 TX coils are located in the search head. It is clear now that the coils marked 13 are in fact the feedback coils for the oscillator, and the coil marked 52 is the main TX coil.

For the 52 turn coil:
Inner radius = 90mm
Wire thickness = 0.6mm
Number of turns = 52
Mean radius = 92.79mm
Coil thickness = 5.59mm
Inductance = 1.16mH

For the 13 turn coils:
Inner radius = 90mm
Wire thickness = 0.6mm
Number of turns = 13
Mean radius = 91.4mm
Coil thickness = 2.79mm
Inductance = 80uH

With the arrangement shown, the 52 turn coil is placed in series with one of the 13 turn coils on alternate half-cycles. This means that the effective number of turns on the coil is actually 65. For a 65 turn coil the inductance calculates to be 1.77mH, which gives a TX frequency of 8KHz, ignoring other circuit effects. This matches the information provided on the schematic.

Here are the measurements obtained from a SPICE simulation:
Voltage across 52 turn coil = 99.8V peak-to-peak (28.4V RMS)
Current through coil = 1.4A peak-to-peak (395mA RMS)
Power in the coil = 34.6W peak-to-peak (9.4W RMS)
Note - this was a correct power calculation, taking into account the phase shift between the coil's voltage and current. You cannot simply multiply the voltage by the current. Otherwise (in this case) the power would be incorrectly calculated as 139.72W (peak-to-peak)!

By the way - there is a power dissipation in the TX transistors of 470mW, so you will need to use a high power NPN silicon type.

The frequency of oscillation, as measured in the SPICE simulation using an FFT algorithm, was 6.73KHz. The sine wave was very clean with most of the power delivered at the fundamental frequency. The third harmonic was the next largest peak in the frequency spectrum, and was 52dB down from the fundamental.

I'll simulate the rest of the circuit later when I get time.

[Mike]

Thank You

Hi there. This is one of the original detector schematics done by Grozdan Grozdev from BG plust some other BG detector diagrams.

Hi Georgi,

Just like to add my thanks for sharing these schematics.

Mike

[Unregistered]

Nexus

Here are the results I've obtained from simulating the TX circuit of the Bulgarian detector.

First some calculations:

Georgi says that all 3 TX coils are located in the search head. It is clear now that the coils marked 13 are in fact the feedback coils for the oscillator, and the coil marked 52 is the main TX coil.

For the 52 turn coil:
Inner radius = 90mm
Wire thickness = 0.6mm
Number of turns = 52
Mean radius = 92.79mm
Coil thickness = 5.59mm
Inductance = 1.16mH

For the 13 turn coils:
Inner radius = 90mm
Wire thickness = 0.6mm
Number of turns = 13
Mean radius = 91.4mm
Coil thickness = 2.79mm
Inductance = 80uH

With the arrangement shown, the 52 turn coil is placed in series with one of the 13 turn coils on alternate half-cycles. This means that the effective number of turns on the coil is actually 65. For a 65 turn coil the inductance calculates to be 1.77mH, which gives a TX frequency of 8KHz, ignoring other circuit effects. This matches the information provided on the schematic.

Here are the measurements obtained from a SPICE simulation:
Voltage across 52 turn coil = 99.8V peak-to-peak (28.4V RMS)
Current through coil = 1.4A peak-to-peak (395mA RMS)
Power in the coil = 34.6W peak-to-peak (9.4W RMS)
Note - this was a correct power calculation, taking into account the phase shift between the coil's voltage and current. You cannot simply multiply the voltage by the current. Otherwise (in this case) the power would be incorrectly calculated as 139.72W (peak-to-peak)!

By the way - there is a power dissipation in the TX transistors of 470mW, so you will need to use a high power NPN silicon type.

The frequency of oscillation, as measured in the SPICE simulation using an FFT algorithm, was 6.73KHz. The sine wave was very clean with most of the power delivered at the fundamental frequency. The third harmonic was the next largest peak in the frequency spectrum, and was 52dB down from the fundamental.

I'll simulate the rest of the circuit later when I get time.

Very scientific analisys. Good work.
Now about the power of the transistors needed. I use 250mW BC type transistors and they are more than enough. This type oscilators do not require high power transistors since the the power disipation of the oscilator system falls on the coil it self due to the resonance.
This type of transmitters are called paralel resonance circuits.The voltage and the current gets amplified in electromagnetic process by the coil, not by the transistors.
It is truth that this specific oscilator may be better build with a little bit more powerfull transistors, because of the small number of turns between the colectors.
What I use is 4 x 25 turns = 100 on the transmit coil in the following connection; external end-25-colector point-25-negative power rail-25-colector point-25-external end. Between the two external ends is the tunning capacitor.
Now that gives me tramsformation 1 to 2 which means that the voltage between the colectors is dobled by the external 50 turns equaly distributed on the both sides of the colectors.
This type of conection is more efficient regarding the transmitted power relative to the current drain, but it is more dificult to acheive good null balance with the receive coil.

[Siliquae_Sid]

I have, courtsey of a photocopier, a scan of the original Mk1 Nexus and another modified version. I am NOT however prepared to divulge it's secrets to anyone, not will I say how I came by these diagrams.

The claims made by Gerorgi for the nexus are genuine, I have seen one in action. yes, you may think it is overpriced, but the built quality alone put it into the "military grade" category, and the amount of R & D Georgi has done means his reward in asking (and getting) this price is deserved.

I know Gary of Gary's UK Detecting very well and the claims he makes are true also.

[Unregistered]

beginer

Hi Georgi,

would you tell us a little bit more about shielding of coils?
& what about transformer in "X" demodulator`s loop?