RELIC HAWK

[mikebg]

Hi Olivier,
Can you open with CircuitMaker the compressed file attached in post # 941 ?

[o.mag]

hi mike
Yes i can you open with CircuitMaker the compressed file attached in post # 941
but I did not have time to fully understand

olivier

?

Hi Olivier,
Can you open with CircuitMaker the compressed file attached in post # 941 ?

[mikebg]

Hi Olivier,
I analysed your idea in post #943 to use Vee rail for supply rest part of RX.
For this purpose I increased 4 times current from Vee source (placing 500 ohm resistor instead 2k).
To see collector curent of Q2, hold pressed Shift + click on collector lead.
The attached image shows two drawbacks:
1. Low efficiency of pumping pulse. We should decrease resistance of R1 until B=2A or conducting angle of Q2 decreases to 120 deg.
2. Distortion of negative half-wave (shown with green arrows). To avoid this, we should use center tapped TX coil and full wave rectifiers.
I will show the analysis of this when I have time for our hobby.

[mikebg]

Distortion of negative half-wave (shown with green arrows). To avoid this, we should use center tapped TX coil and full wave rectifiers.
I will show the analysis of this when I have time for our hobby.

Here it is:

[Davor]

IMHO every oscillator that is running near saturation, supplied with well stabilised and low noise voltage supply will perform very well. The only difference comes from the oscillator design, and if it is symmetrical like push-pull - it will do very well.

When you look at it, every amplitude stabilisation circuitry works the same way voltage stabilisation would do, and that's the whole point.

You can always make a PI regulator that will push the oscillator transistor deeper into C class as amplitude rises. Its stability and noise will depend solely upon the power supply.

[bernte_one]

hello all here

where can i find last pcb files of relic hawk?

many thanks

[o.mag]

hi mike
I understand why you changed only the load side negative (positive being powered by the battery) but for tested the oscillator I changed both and the distortion appear on both sides. a higher current for IC does not really help anything
The schemat of post 949 please me well. but I have problems for the simulation. I look for the mistakes I make

olivier

[HECTOR]

Are you sure the test points you are indicating are correct?
It would seem to me that the readings would/should be identical if taken from those points.
Are the test points located far apart on the PCB?
What am I missing here?

[o.mag]

the green curve is the current IC (missing scale)
the yellow curve is the voltage

olivier

Are you sure the test points you are indicating are correct?
It would seem to me that the readings would/should be identical if taken from those points.
Are the test points located far apart on the PCB?
What am I missing here?

[mikebg]

IMHO every oscillator that is running near saturation, supplied with well stabilised and low noise voltage supply will perform very well. The only difference comes from the oscillator design, and if it is symmetrical like push-pull - it will do very well.

When you look at it, every amplitude stabilisation circuitry works the same way voltage stabilisation would do, and that's the whole point.

You can always make a PI regulator that will push the oscillator transistor deeper into C class as amplitude rises. Its stability and noise will depend solely upon the power supply.

Davor, I'm sure that your hobby is not design of QRP amateur radio :-). An amateur designer of QRP thinks for maximal TX efficiency and minimal TX modulation. Your expression "Well stabilised and low noise voltage supply" means waste of battery energy to heat the regulator because its output voltage differs from voltage of battery rails. For max efficiency, we need battery rail to rail amplitude across pumping transistor despite battery voltage changes.
The TX of Relic Hawk is powered direct from battery rails, but it can't deliver rail to rail amplitude. More than 3 volts are wasted in an incompetent used cascode amplifier.
Here is attached the SPICE analysis for a powerful and efficient push-pull TX designed according QRP principle. The idea for this I posted in Jan. 2010
http://www.geotech1.com/forums/showp...3&postcount=59
"The idea is TX to be powered without voltage stabilizer for maximal efficiency. The oscillation amplitude is
stabilized by P-I controller. For its reference voltage is used a LED. Thus, the amplitude of TX
oscillation decreases with depletion of the battery, but this change is slow, so no impact."
We can take any conventional metal detector and make two tests for unwanted TX modulation:
1. What happens when its loudspeaker beeps.
This makes extremely small change of battery rails voltage, but the synchronous demodulator senses it.
There are Garrett detectors where for better sensitivity are used separate batteries to supply audio section despite all other supply rails are stabilised with very low efficiency (36V battery rails are stabilised to 15V rails).
The threshold audio hum of a maximal sensitive machine should sound as random noises in frequency band 0.2Hz-16Hz. This band modulates as AM or FM an audio carrier frequency (for example 400Hz).
2. When TX coil changes height (distance to ground) and/or passes over different soil. The modulation spectrum of AIR signal in this case also coincidents with mentioned frequency band attributable for TGT and GND signal.
If we design a machine to detect 1uV target signal, a modulation index of AIR signal in order of 0.0001 will cause false alerts.
Therefore we should redesign not only TX section of Relic Hawk. We should redesign supply circuit for its audio section. The battery should see the audio as slowly (below 0.2Hz) changing load.
Here is an explanation for the attached circuit:
The TX circuit contains an additional schematic (not shown) to avoid deep battery discharge.
U1 is shown as powered with low voltage V2 to set initial operating point of M1 and M2. In reality U1 is powered direct from battery rails via a slow charged circuit to avoid oscillation start with large drain currents of M1 and M2.
Voltage V3 is obtained by a red LED.

[ivconic]

Davor, I'm sure that your hobby is not design of QRP amateur radio :-).........

I agree!
There is one of his posts indicating exactly that, somewhere on IGSL thread.
I suspected that long time ago!
Very conversant and fine radio expert - that's seems to tend to be our fellow Davor!
That's why he already founded so many "lacks" in a typical VLF/IB design!
I knew it from a start!


"...Thus, the amplitude of TX
oscillation decreases with depletion of the battery, but this change is slow, so no impact."..."

That's excatly the case here.

"...1. What happens when its loudspeaker beeps.
This makes extremely small change of battery rails voltage, but the synchronous demodulator senses it..."

Now you also gave proper answer for that audio transformer question from the past.
One of it's role is exactly to smooth up the unwanted "pulls" from the speaker (at Musketeer, RH is not having such issue).

"...Therefore we should redesign not only TX section of Relic Hawk. We should redesign supply circuit for its audio section. The battery should see the audio as slowly (below 0.2Hz) changing load...."

Good points. Fist task would be easier than second one.

P.S.
"Uncle" Bozo Metzger is laughing now from heaven, i suppose...!

[mikebg]

Ivica, for Davor I can't agree with you, but incompetence of Minelab designers is because they have not knowledge of radio amateurs.
The powerful TX showed in post #955 is suitable for operation in a two box system. At conductive trace of a metal
pipe, it can operate with 200 ohm load between electrodes delivering 16W heat into ground :-).
The conductive method is described in Gemini-3 operating manual.
For a conventional metal detector, no need of such TX power and so expensive batteries. Below is showed SPICE
analysis with CircuitMaker of push-pull TX which uses a simple centre tapped TX coil and 12V lead acid battery. Note
that unlike original TX in Relic Hawk, here the pumping transistors operate at almost battery rail to rail amplitude.
To make SPICE analysis of this variant using LTspice, you can open the compressed file attached in post #955, delete
two sections (windings) of TX coil and change other parameters and battery voltage.
With this TX circuit we can end the redesign of TX section in Relic Hawk and start redesign of its RX section. The RX is
also incompetent designed.

[ivconic]

Usually i am collecting ideas during the Summer and start to work on those when Winter comes.
So i will write down all your suggestions for sure.
I am interested in such oscillator and most probably i will make it.
Thank's for sharing!

[o.mag]

hi
hi
in the same style but the oldest of the oscillator vlf 770
olivier

[Davor]

...Your expression "Well stabilised and low noise voltage supply" means waste of battery energy to heat the regulator because its output voltage differs from voltage of battery rails.

(a late reply) Yes, but not too much. You may lose a few milliamps here, also a few there, but at the very end - Tx oscillator is not the most power hungry device in your design. QRP is a bit different, and you don't have much going on besides Tx while transmitting - it is not a full duplex.
I try to follow the KISS principle in my designs, and my thoughts about the IGSL oscillator were that there is nothing wrong with it. Amplitude is stabilised by virtue of 7808 voltage stabilisation, and it is very much in line with the KISS principle. It is true that you lose over 50% power when stabilising 12V to 8V and using such reduced voltage to power the oscillator, but it produces well stabilised oscillations, hence power well spent.
We can turn this topsy-turvy:
1) Oscillators DO perform well when supplied with well stabilised power supplies.
2) Amplitude stabilisers DO reduce amplitude obtained by the oscillator, so in effect there is no difference between amplitude stabilised oscillator and an oscillator with stabilised power supply, yet the latter is simpler.
3) There are ways other than 78xx stabilisers that can provide isolation and noise reduction with smaller voltage drop, and not involving super-sexy amplitude stabilisers that are also power-hungry (and using them does not spare much juice in a process... if any)
4) We need power sparing stabilisation that does not involve additional "spend to save" features that make no sense, but look very intimidating and complex - suggesting a well design that it most probably is not.