RELIC HAWK

[Max]

Hi,
this is rev. 1.7 of schematic: U7 must be an op. amp. so I changed it to 27M2 as well as for others, not anymore LM393 (wrong there).

PCB doesn't require to be modified cause of this change.

Kind regards,
Max

[nakky]

Hi Max,is hand draw schematic that Ivconic has posted.Grt Nakky.

[Max]

Max,
With 2 changes you can make it oscillate with coil resistance up to 5.5 ohm. Change the zener that is between +6V and the base of the PNP driving the coil to 8,2V; and change the resitor at the emiter of the NPN feed back driver to 10K.

That is about as high as I can tweak it without making it unstable at 2.2 ohm coils resistance or a significant decrease in oscillator voltage.


See attached (run with coil resistance at 5.5 ohm)!

Regards,
J. L. King

Hi,
yes I know, you told me already... but at now I think I will use the 20AWG coil that's not bad coil...

The signal is strong so I can use it without modify the oscillator circuit.

Kind regards,
Max

[Max]

?????

Hi,
reversed ? Do you have a different schematic ?

I tested on simulator and this doesn't work at 2.5ohm resistance.

Kind regards,
Max

[nakky]

?????

[KingJL]

Max,
With 2 changes you can make it oscillate with coil resistance up to 5.5 ohm. Change the zener that is between +6V and the base of the PNP driving the coil to 8,2V; and change the resitor at the emiter of the NPN feed back driver to 10K.

That is about as high as I can tweak it without making it unstable at 2.2 ohm coils resistance or a significant decrease in oscillator voltage.


See attached (run with coil resistance at 5.5 ohm)!

Regards,
J. L. King

[Max]

Hi
If problem is hfe maybe a small darlintong work better in these position.
Or changing the gain of TL071.
Not sure of course!

Bye Max

Hi,
tested with hfe = 550 on the pnp and 600 on the npn... change nothing.

Tested 6 different op amps... and nothing.

I don't know what they used... but for now I will do some more tests with my heavy coil... I gained exactly 5Khz and 15Vpp on it, so I think it's enough to start making something different... i could return on this topic when other stuff will be more clear.

Kind regards,
Max

[maxbiri]

Hi
If problem is hfe maybe a small darlintong work better in these position.
Or changing the gain of TL071.
Not sure of course!

Bye Max

[amtech2005]

RELIC HAWK

Hi,
I think I found the source of all troubles... at least in my previous simulation... the dang 22K resistor I have in the circuit I had like 27k in previous simulation.

Now, I changed it to 22K and got 13.6Vpp for a 2.5ohm resistance coil, 1mH and about 18Vpp if the coil resistance drops to 2.2ohm.

So, for the simulator... the 2.5ohm coil MUST work though not optimal one... and with ideally maximum voltage of 13.6Vpp on it.

Now the problem is that I have the dang 22K in the real pcb but it doesn't work... cause probably the NPN I've used is low gain BUT I used an BC547B so still don't understand that, must check again.

Simulations are cool... but often reality is truly different stuff..

Kind regards,
Max

I do not have my simulation software installed yet , a few more days But was wondering if BC537 would be a better "npn" than BC547 for the tx circuit ?? Thanks.............Eugene

[ivconic]

No. It is ordinary transistor.

[Fred]

Hi Max,

Could it be a Jfet or similar?
could try with mpf102 or something.
Fred.

[nakky]

Hi Max,minelab use in sovereign c368 c369 bc556 and lm385 z-2.5,maybe say this someting to you.Grt Nakky.

[Max]

Hi,
I've made a simulation using BFT92 pnp UHF transistor...but nothing: no oscillations at 3.1 ohm resistance.

Maybe there was something truly special in the original RH pcb... the SMT thing, whatever it is, must be something a bit exotic... cause all I tested so far failed in simulation to reproduce oscillations at desired resistance range.

Real puzzle...

Kind regards,
Max

[Max]

Reffering coil doubts,
yesterday i asked friend to bring professional resistance meter to me and we measured again original RH coil resistances.
TX= 3.1 ohms (including cable)
RX= 41.3 ohms (including cable)
So...
I do have few unimeters and we checked resistances with all. My meters showed approx. same values with minor drifts.
I think catch is in the last TX transistor. On original pcb that (only that) transistor is smt and without any label?
I dont have pcb anymore so i cant measure its hFe.
Possible that transistor is specific in a way?

Hi Ivconic,
nice to see your posts here. Well, yes, probably the transistor at osc is really critical... simulations showed that all components are critical, the more effects due to coil series resistance.

Now that we know sure the coil is around 3 ohm resistance we know also that can't be a BC557 there on coil. But what if not a BC ? Probably is something like BFR99 uhf transistor thing (up to 2GHz)... not cause of frequency cutoff but cause they can oscillate with minimal residual signals along the path: I have one of these in one resonant oscillator stuff... and oscillates from 10Hz to 300Mhz pretty easy changing the LC stuff connected.

I don't know if the BFR99 could be employed in this circuit but I think will probably change our actual situation where just lower resistance coils work.

I have to find the SPICE model of it and use in the simulation to see if I can fix the problem this way.


Kind regards,
Max

[ivconic]

Reffering coil doubts,
yesterday i asked friend to bring professional resistance meter to me and we measured again original RH coil resistances.
TX= 3.1 ohms (including cable)
RX= 41.3 ohms (including cable)
So...
I do have few unimeters and we checked resistances with all. My meters showed approx. same values with minor drifts.
I think catch is in the last TX transistor. On original pcb that (only that) transistor is smt and without any label?
I dont have pcb anymore so i cant measure its hFe.
Possible that transistor is specific in a way?