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Author Topic: Towards a 45.525MHz 16 Watt Amp  (Read 6036 times)

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I've been trying out the L-LC tuned circuit from that article, driving from my 1.5 Watt pre amp through the pi network, feeding a capacitor and then feeding the parallel LC, I used the circuit from figure 11 and 1 ohm resistors to monitor current, when i tune the LC current for max level and then disconnect and use a GDO to drive it loosely coupled, max current appears at about 33Mhz which is indeed 0.7071 of C-LC driven circuit at 45.250Mhz, this appears to prove the math of the article.

https://www.accelinstruments.com/Applications/WaveformAmp/Magnetic-Field-Generator.html

I am have trouble with current measurements across my 1 Ohm resistor see waveform at 4.95V RMS, which would mean i am dissipating 4.95 Watts, which is pretty clever seen as i am driving it with 1.6Watts, and as the resistor is not getting really hot (31 Deg C in 15 Deg C ambiant) i must assume these resistors do indeed have inductance.

So i will try next a film resistor to see if that cures my problem, until i get an accurate voltage i cannot work out the current or the magnetic field strength, i will say that there is a strong magnetic field around the coil because it's the first time i can easily sniff 45.250Mhz sine around the area with my scope probe with a couple of turns (35V pk-pk) or even with the earth clip on the probe end.

The impedance of the C-LC circuit is 4R or 4Ohm in the above case
« Last Edit: 2019-02-15, 20:46:37 by Peterae »
   
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I am have trouble with current measurements across my 1 Ohm resistor see waveform at 4.95V RMS, which would mean i am dissipating 4.95 Watts, which is pretty clever seen as i am driving it with 1.6Watts, and as the resistor is not getting really hot (31 Deg C in 15 Deg C ambiant) i must assume these resistors do indeed have inductance.
...

It is only recently that I realized how difficult it is to measure high frequency signals with a scope.
The end of the probes is not coaxial, it acts as an antenna or is capacitively coupled. Then the ground wire creates a loop, in which we have induced currents.
The probes must be eliminated and the scope connected directly to the resistance by a coaxial cable designed for high frequencies (very well shielded).
In addition, the cable length must be small in comparison to the shortest wavelength of the signal, otherwise there are phase shifts or resonant line effects, because the input impedance of the scope is unrelated to the output impedance of the setup.



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Certainly would explain the problems i am having, i am now thinking that the easiest way to do power measurements is to measure the heat produced by the resistance load. :(
   
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With a series circuit composed of a germanium or schottky diode and a capacitor, in parallel on the resistance, the peak HF voltage can be measured as a DC across the capacitor, provided that the signal exceeds the diode threshold (about 0.3v, to be added to the measured voltage). It's a basic method but I find it much more accurate than the scope.



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I found a pro's build of my amplifier for sale, it's interesting seeing what he has done.

https://www.ebay.co.uk/itm/151274234687

From today, I tried a parallel LC, for some reason I can only sniff 2nd harmonic with a coil.
I tried C-LC and sniffing this is comparable in amplitude to the sniffing I did with series LC.


I think for ease, Series LC is the way to go, but how to deal with a very low impedance that the amp will see, maybe a series resistor could be used, we know the current the inductor see's is common for the resistor, capacitor and inductor.


So as follows

Inductor is 12 Turns of 1.5mm wire wound to a length of 50mm inductance calculates to 559nH


for series resonance with a 559nH inductor I need a capacitance value of 22.13pF


if we use a 5 Ohm Series resistor and we manage a 30pk-pk drive voltage then we get


Xl = 2pifl = 158.93Ohms Inductive Reactance.


Xc= 1/2pifc = 158.93Ohms Capacitive Reactance.


Circuit Impedance Z = sqr(R2+(Xl-Xc)2) = 5 Ohm R is effectively the load resistance.


I = Vs / Z = 30/5 = 6 amps

Vr = I * R = 30 Volts

Vl = I * Xl = 953.58 Volts


Vc = I * Xc = 953.58 Volts


Magnetic field flux = 18.0956 Gauss


« Last Edit: 2019-02-17, 17:52:24 by Peterae »
   
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I think for ease, Series LC is the way to go, but how to deal with a very low impedance that the amp will see, maybe a series resistor could be used, we know the current the inductor see's is common for the resistor, capacitor and inductor.
...

Hi Peter,

No need for using a series resistor if you meant it for easing the matching of the very low impedance, it can be transformed up by a  matching network.

I attached the schema again with the addition of a possible matching network to transform a small (2-3 Ohm at resonance, indicated in the blue block) real impedance to the drain output circuit of the MOSFET. It is called an L matching network and needs a coil (L) and a capacitor (C) only. The C capacitor should include the drain-source output capacitance of the MOSFET plus a trimmer to make up for the needed value. For the coil a toroidal winding would be the best with ample core cross section but an air core one could also be used. See this link on calculating the L and C values:  https://home.sandiego.edu/~ekim/e194rfs01/jwmatcher/matcher2.html

Source resistance 50 Ohm (this would be the up-transformed impedance the drain circuit will see as a load)
Load resistance    2 Ohm (this is either your "current amplified resonant" or a simple series LC resonant circuit)
For the Source and Load Reactances use zero
For the Desired Q use say 5
For Frequency use 45.25e6

The L and C values you need will appear under the LOWPASS Hi-Low MATCHING NETWORK circuit schematic (first row on the right), I received L=34.46 nH and C=344.6 pF. 

You can use a normal series LC resonant circuit within the blue block too, for simplicity, if you wish, instead of the current amplified resonant circuit.

The tuning procedure (to use first a normal series resonant LC as the load for the power amplifier output) would be advisable like this (fully separate the coil mentioned below from the circuit) :

1) fill in the iron powder for the coil assigned for exciting it. (you have already that plastic coil holder for this right?)
2) try to measure the inductance of this coil with the L meter. perhaps first without the iron powder, then with it.
3) then try to find a capacitor which when connected in parallel with this coil (that filled with the iron powder) gives a parallel resonance around 45 MHz, checked with your grid dip meter. IF the capacitor needed for this comes to be a very small value like under 10 pF, then reduce the number of turns of the coil. Beware: if the iron powder can move inside the coil, as you handle the coil holder with your hand, its inductance will surely change!
4) aim for a capacitor of at least 15-20 pF to give resonance around 45 MHz with the coil.
5) when done, you now have a simple series resonant LC circuit if you connect the capacitor in series with the coil, giving a very low value real impedance (any value like 1-3 Ohm) which will be stepped up towards 50 Ohm by the LC matching network.

Before you build and switch on this total circuit, I advise to go through the procedure first with the 50 Ohm dummy load connected into the drain circuit as I wrote in the previous post.

When that is done and seems ok, there may come placing the choke coil into the drain with the matching LC circuit as calculated from the link and the L coil is wound and the C cap value is considered with the output cap of the MOSFET (CDSS=55 pF at 25 V supply), and also the pretuned output series resonant circuit could be connected. Start with 12 V again first, only then raise the supply voltage higher and higher to 50 V. The main tuning may involve the trimmer cap adjustment across the drain-source for voltage maximum indicated by the scope probe with a sniffer coil. The L coil may also be tuned by pulling away the turns or pushing the turns closer slowly and carefully, it can greatly influence the up-transformed impedance towards the drain, hence the output power too. Notice if you increase this coil value, then the C cap would need to be decreased to keep the network at resonance (but the loaded Q is around 5 only, so bandwidth will surely be wide).

Gyula

ADDITION:  here is  shorter link to the ebay offer,  https://www.ebay.co.uk/itm/151274234687  you may wish to use it in your above post, so the horizontal width of the page will be restored to normal  (for those who do not use wide screen).

By the way, the same FM Linear Amplifier is available as a DIY Kit here:
https://dutchrfshop.nl/en/diy-kits-pcb-s/589-diy-kit-15-watt-amplifier-87-108mhz-rd01mus-rd15hvf1.html     

The schematics, the Bill of Materials are also included to see.  All the L and C values used for matching and in the filters are valid for the FM band which is roughly twice as high as the 45 MHz needed here.  Also, the output impedance is surely matched to a 50 Ohm load, as usual.
The kit does not include the coils but the wire for winding them...    :D   By mentioning this kit, I do not hint to buy it... you decide.   :)
« Last Edit: 2019-02-16, 23:08:57 by gyula »
   

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Hi Gyula

Thats a nice amp kit, very tempting, i will give the home build a go first ;)

I'm going to need some high voltage caps, looking at 10Kv 22pf and adjust the inductor length for fine tune.


I have enough to start the build now.

thankyou very much for your help, very much appreciated, you are an incredible engineer.  ;)


Just ordered a radiation detector https://www.ebay.co.uk/itm/143006383989

and 2 of these caps
https://www.ebay.co.uk/itm/273236302508
« Last Edit: 2019-02-17, 19:19:30 by Peterae »
   

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I am still working on this in the background, still plenty to do.

I made the framework for the fuel rod out of 3d printed hollow sections and poured resin into it, this is to make it more durable from the harsh conditions it will operate under and elevated temperatures which plastic alone is not good at handling.

The fuel rod was made of 2 round printed formers filled with 1200 Deg C compound to glue the quartz tube in place, each end has a copper wire coiled inside the tube to make electrical contact with the iron powder filling.

At first the iron did not conduct very well over 10 MOhm, but after heating with a blow torch it now measure about 1 Ohm and heats nicely with a dc supply connected, I will need chokes at each end to isolate the circuit from the 45MHz oscillations.

2 pictures below have the magnet assembly fitted as well.

I forgot to add the 45mhz coil onto the quartz tube before gluing the end caps on, OOPS the coil is small diameter than the end caps, so i will need to devise a way to wind the coil over the quartz tube without breaking anything, i have some kilm paper which i will wrapp around the quartz tube to insulate it and stop the heat affecting the Inductor coil.
   
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Hi Peter,

Nice progress and build of the magnet assembly. Is the quartz tube fully packed with iron powder filling? (so that the powder should not move freely within the tube?)

Well, on the 45 MHz coil winding: probably only a few turns is needed to have the max some hundred nH inductance, so making that around the quartz tube may not cause much problem versus say making 20 turns.
The iron powder will certainly increase inductance and this is why I think of a few turns (4-5 maximum) only. This seems to be a limitation because the process or effect may perhaps happen more readily when the number of turns is higher excitation_wise, while a higher number of turns gives higher inductance at 45 MHz which then involves a higher inductive impedance hence less current for excitation,  unless the excitation power is increased and increased. But the supply voltage to the 45 MHz power amplifier can be increased if needed, maybe at a price of using a better MOSFET.

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Hi Gyula

Thanks

Yes the iron powder is packed in the tube, I first glued one end and let that dry, I then heated the quartz tube slightly with a blow torch to get any possible moisture out and once cooled slightly I place the wire in the end and then added a little more iron powder to burry the electrode and then packed glue into the quartz tube end, once that was dry I added the printed end shell and packed that with high temp glue.


I believe it maybe possible to use 2 fets in parallel to double the power, I will see how many turns the inductor requires with the iron in place, although the objective will be to heat the iron above it's curie point after initial tests

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Well, on the 45 MHz coil winding: probably only a few turns is needed to have the max some hundred nH inductance,
...yes and you really should use fine Litz wire for all HF windings.
   

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Hi Peter,

Indeed the 50V supply voltage must have been too high as a start for the amplifier if there was no any previous matching / tuning attempt at a lower supply voltage.   

Regarding a setup process, here is a possibility.  This text is going to be long, sorry,  I think it is needed. 

See a modified input circuit for the amplifier attached,  I added a resistive divider ("a resistor Pi") ahead of the input Pi filter. The 470 Ohm potmeter can be any normal one, not a wire wound type, to be able to reduce the > 1 W RF power from the output of your preamp to 0.2-0.3 W level, not to overdrive the linear amplifier.

Next, remove the MOSFET, put a 360 pF across the 22 Ohm resistor and drive the input of the resistive diivider from the preamp. Adjust C1 of the Pi filter for max sine wave amplitude around 45 MHz, measure across the 22 Ohm resistor with the scope probe. Check by turning the 470 Ohm potmeter between what minimum and maximum range it can vary the RF voltage amplitude across the 22 Ohm.  Leave the wiper at say 2-3 V peak to peak across the 22 Ohm, if this low amplitude is not possible (i.e. at the full 470 Ohm wiper position the voltage is still higher than that), then place  say a 100 or 150 Ohm resistor in series with the potmeter and repeat this adjustment.

Now remove the preamplifier, i.e. no RF drive, and also remove the 360 pF cap which so far substituted the gate-source capacitance and put the MOSFET back to the circuit.  Also, remove the choke from the drain and put a 50 Ohm dummy load instead,  capable of the expected 15-20 W dissipation.  It is ok you wish to see and check the signal at the drain but you have to have a load there too for feeding the MOSFET with the supply voltage. 

You may wish to start with much lower than 50 V like say 10-12 V DC input only.  First the DC operating point is to be adjusted with the Set Bias potmeter: you need to measure the DC drain current and set it first say to 200 mA only at the 10-12V supply voltage and no any RF drive yet. The wiper of the bias potmeter should be set in advance to start from about 2V because the minimum threshold voltage for this MOSFET is 2V.  But your MOSFET may have say 3.2V threshold voltage from where drain current can start flowing at all, so slowly turn the bias pot up from the 2 V and watch the drain current rising to about 200 mA.

Now if you increase the supply voltage towards 40 or 50 V,  still monitor the DC drain current, it will increase above the previous 200 mA of course (without touching the already set bias potmeter) and the heat dissipation at 50 V will increase beyond 10 - 12 W, a big heat sink is needed for the MOSFET of course. Naturally the same drain current will dissipate heat in the dummy load too, it should be able to dissipate it.

I suggest to run the MOSFET at this operating point for at least several minutes to check temperature and drain current stability (with still no RF drive input yet). 

If all seem ok, then increase drain current up to 400-450 mA, supply voltage is at 50 V and see how heat sink temperature increases, hopefully a small ventilator would not be needed to cool it.  Run the setup for several minutes at least.

Then, if you think, apply the smallest RF drive the 470 Ohm pot let through (as previously set above) and check the RF amplitude across the dummy load or across the drain and the negative rail, ideally they have the same voltage across them.  Then you could increase RF drive by turning the 470 Ohm pot and monitor the drain current and the RF amplitude at the drain or the dummy load. 

It is possible you need to retune a little the C1 cap in the input Pi filter when the supply voltage for the MOSFET is in the 40-50 V range because the gate-source capacitance changes to a lower value and this may affect input Pi filter matching.

It is possible the RF input drive to the MOSFET (depending on where the 470 Ohm pot is set) will increase drain current beyond the DC current previously set by the bias pot.  Well, a small overdrive is not yet a problem but you can see this as a starting clipping (limiting) at the peaks of the drain-source voltage wave form.  It is also possible you adjust DC drain current to say 600 mA to increase output power, this would allow an increased input drive too to achieve higher output, only the MOSFET dissipation is the limit.

If all seems ok, then so far the 0.5 A drain current at 50V supply voltage will provide roughly 12.5 W RF power in the 50 Ohm dummy load (the other 12.5 W is dissipated in the MOSFET). Such is the case for an ideal Class A power amplifier. 

Next step is to agree on how you try to match the coil with the iron powder core to the drain of the MOSFET.  The Pi filter at the output first sounds good but your coil will represent either a much higher than 50 Ohm impedance load when tuned to be a paralell resonant LC tank at 45 MHz  or will represent a much lower than 50 Ohm load when tuned to be a series resonant LC circuit,  so the output Pi filter should be thought over.

Gyula

So starting the amp again and going through Gyula's post, I am up to adding the 360pf cap in place of the fet, see shots below, waveform at the fet gate position is varying up to 3.8v pk-pk, currently set at 2v pk-pk.

I'm using blue/yellow toroids size 55, for the output inductor i am wondering if this will be big enough, is there any problem stacking 2 cores and winding the stacked cores as one core?

Placing my hand on the ground plane of the circuit board makes the sine look clean, instead to get the below scope shot I had to alter the first cap of the PI network to a lower value, it's in parallel with a 0-75pf variable cap and moved to a 100pf instead of a 220pf, infact because in the picture the variable cap was open, I have now moved even lower to 47pf.


if I hold the ground plane then the calculated value 220pf+var cap works and gives a clean sine.


Anyway time to move on and add the bias circuit and fet with load.
   
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Hi Peter,

Normally there is no problem with the stacking of toroid cores and it is okay as you described their 'how to' winding, but then the inductance may increase too high for even 2 turns only at 45 MHz and you would need to retune the filter of course and even change a trimmer cap if it goes out of range. But you know this, you nicely described how you went about it.
 
You wrote toroid size 55, did you mean 44 instead? Sizes are 30, 37, 44, 50, 68 etc.

Placing your hand on the ground plane of the PCB: well, hard to tell what the body's capacity picks up at such a high frequency which then goes to the ground. Perhaps the ground clip of the scope probe influences this too, try to clip it to other ground area, I am not sure.

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OK finally got the 50 Ohm load resistor as the last one went missing.

Quote
Now remove the preamplifier, i.e. no RF drive, and also remove the 360 pF cap which so far substituted the gate-source capacitance and put the MOSFET back to the circuit.  Also, remove the choke from the drain and put a 50 Ohm dummy load instead,  capable of the expected 15-20 W dissipation.  It is ok you wish to see and check the signal at the drain but you have to have a load there too for feeding the MOSFET with the supply voltage. 

You may wish to start with much lower than 50 V like say 10-12 V DC input only.  First the DC operating point is to be adjusted with the Set Bias potmeter: you need to measure the DC drain current and set it first say to 200 mA only at the 10-12V supply voltage and no any RF drive yet. The wiper of the bias potmeter should be set in advance to start from about 2V because the minimum threshold voltage for this MOSFET is 2V.  But your MOSFET may have say 3.2V threshold voltage from where drain current can start flowing at all, so slowly turn the bias pot up from the 2 V and watch the drain current rising to about 200 mA.

Now if you increase the supply voltage towards 40 or 50 V,  still monitor the DC drain current, it will increase above the previous 200 mA of course (without touching the already set bias potmeter) and the heat dissipation at 50 V will increase beyond 10 - 12 W, a big heat sink is needed for the MOSFET of course. Naturally the same drain current will dissipate heat in the dummy load too, it should be able to dissipate it.

I suggest to run the MOSFET at this operating point for at least several minutes to check temperature and drain current stability (with still no RF drive input yet). 

If all seem ok, then increase drain current up to 400-450 mA, supply voltage is at 50 V and see how heat sink temperature increases, hopefully a small ventilator would not be needed to cool it.  Run the setup for several minutes at least.
I scorred a super large heatsink with holes drilled and heat washers with screws from a discarded power supply.

So i am running at about 520mA @ 50V without any input for over half hour,520mA as this seems to give me an equal voltage across load resistance and fet, the heatsink sits at 44Deg C, 23Deg C above ambiant, the front of the fet is at 65Deg C and the resistor is only about a degree above the heatsink temperature.


I need a longer sma lead to reach the board from the DDS now :(


Good progress so far.



   
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Good progress Peter, and following with interest.


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Hi Peter,

You have a nice Class-A amplifier now with the resistor in the drain, so dissipation in the MOSFET should not go higher than 25-26W when driven by.  And when you have an AC impedance transformed by the matching circuit back to the drain to a similar value to that of the present resistor, a similar dissipation could be expected,   except that choke coil DC resistance will be much less than the present load resistance of 48 Ohm, the drain current will go up by some ten mA (drain voltage versus drain current characteristc curves are not horizontal but slightly rising),  so you will have to readjust the bias potmeter to have the 510-520 mA drain current then too.   
Good progress.

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OK got everything bolted down and wired 3 psu's, 1 for 5v bias supply, 1 for DDS & CPU control, and 1 for 50V supply, these are all buck converters fed from 24V.
I am wondering if the operating frequency of these is affecting operation, unfortunately I ran out of time to run many tests.

but here's a scope shot with 50Ohm load and inductor in the 50V supply feed.

The yellow trace is ground to drain, the cyan is ground to inductor side of 50Ohm load.

Edit I need to look at the inductor i placed in the supply, it is heavy guage inductor, i did measure it before but cannot remember the value but it was over 100uH, maybe i'm operating above it's SRF.
I did try adjusting the PI filter but this did not seem to clean up the sine, i suppose it could be my scope probes giving false signals.

Ah Maybe I should not have the supply inductor in place while testing with a 50 ohm resistor in the drain?
« Last Edit: 2019-05-04, 21:56:05 by Peterae »
   
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Ah Maybe I should not have the supply inductor in place while testing with a 50 ohm resistor in the drain?

Okay, just noticed your above addition and yes, that is what I asked when was preparing an answer:

Hi Peter,

What would you like to test with putting the 50 Ohm load in series with the choke (inductor) in the supply feed?

If you wanted to do the next step after the undriven DC 'soak' test you showed in Reply #88, then place either the choke alone in the drain or the 50 Ohm alone in the drain but not both. AND if you decide say to use the choke in the drain to feed in the 50 VDC, then you would need a 50 Ohm load too for the drain because the choke has many kOHm inductive impedance at 45 MHz. The 50 Ohm load could be connected between the drain and ground via a DC blocking capacitor to imitate the output load, to be transformed later by the output Pi filter when the fuel road etc assembly is connected.

The 'unclear' waveforms may come from the huge near field the choke coil radiates around itself hence sprays on quasi any nearby things. 

Gyula
 
   

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Thanks Gyula

I have now removed the inductor from the drain, i just wanted to see the sinewave on the drain so i am scoping across my drain to ground and 50v supply to ground, yellow trace is now on 50v and cyan on drain side of 50 ohm load, this is so i can do a math subtraction to see whats across my 50 ohm resistor, see below, purple is the math trace A-B.

first thing i dont get enough drive and could do with more, in the scope shot i fully turn the amplitude pot up to max.

There does seem to be a low frequency component the 45.5mhz sine rides on, i am not sure if thats a problem, seen as we are driving a resonant lc i imagine it should not be an issue.

I also have some ripple from the DC-DC converter on the 50V supply, not sure if thats an issue, maybe i could add more capacitance on the supply, maybe this ripple is causing the low frequency component.

I scope shot i zoomed out on the timebase to capture the low frequency noise.

When i comes to the drain inductor i will use 2 of my cores stacked to constrain the mag field. ;)

Next I need to see if it's possible to heat my iron tube to above the currie temperature and control that point by monitoring it's resistance, ie a resistance controlled temperature control of some description.
   
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Hi Peter,

Try to check the ripple riding on the 50 V DC voltage by using AC coupling temporarily for CH1 yellow channel, this way you can set the 10 V/DIV to a more sensitive range and see the AC amplitude better (though this not really needed because its amplitude 3.6 V is small wrt 50 V).
By the look of it, it also seems a 45.5 MHz waveform riding on the 50 VDC rail. Very likely you can reduce its amplitude by using the choke coil (you used yesterday) inserting it into the 50 V wire coming from the DC-DC converter and is connected to the top end of the 50 Ohm load.
And use a filter capacitor to the negative ground from the common point of this choke and the top end of the 50 Ohm. The choke and this capacitor will form a low pass filter inserted into the positive 50 V  rail. You can use another filter cap to the ground from the other leg of the choke coil which receives the direct 50 V from the DC-DC converter. These filter caps could be some hundred nF poli or ceramic type (goal is low loss at 45 MHz), if you do not happen to have such, then use some uF electrolytic type, 63 VDC.

I assume when you turned the amplitude pot to max drive, you checked the settings of the Pi filter trimmer caps too whether they need some retuning?

Another possibility to have more drive is to omit the 62 Ohm from the left side of the 470 Ohm amplitude pot because now that the pot practically has near zero resistance, the two 62 Ohms are directly in parallel and may cause too much load i.e. loss in the input signal. I refer to the schematic attached to reply #80 above, I assume you use that.

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Thanks
Yes tried retuning the pi input filter, the sinewave get a little noisier like yesterday with the choke in place but not as bad.
I will try removing the 1st resistor left of the input pot, and try a filter on the 50v line as suggested. ;)

   

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Tried the CLC 50V filter, the only thing that makes a little difference is moving the scope probe away from the 50R load resistor and placing directly on the filter, but it's still there,the inductor measure 57uH so I was wrong with my previous guess, strangely the DC-DC converters current meter reads zero at 45.5Mhz and the sinewave seems to have a little noise on it, I tried 40Mhz and 50Mhz and these are nice and clean, maybe there's iron nearby that's interfering :)


I did remove the left resistor of the pot and that has increased my drive amplitude, it could still do with a little more, but I am not going to get hung up on this as it is only 5V each side of the sinewave, it maybe because I lowered the PI cap value during tuning, I might try increasing that cap back up again.


I am very happy with it and it sits there quite cool running.
I am running at 55V.

I have some scope shots 40Mhz, 45.5Mhz & 50Mhz.

and a couple of pictures.

Thanks for all your help Gyula ;) It's been fun, theres still a lot to do yet.
   
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Hi Peter,

Okay, good progress again. Yes, the scope probe placement surely has its 'sweet spot' to place, even small distances may influence the waveforms (also the length of the probe ground wire to the croco clip) and there may be other inherent yet unknown issues, these are always hard to rectify when high level, high frequency is present.  I do not think either that you would need to bother with further clean up of the 50 (or 55) VDC supply.

When you have the L matching network (L, C in the schema above) connected to the drain of the MOSFET, driving the 'current amplified resonant circuit'  (Cs, Cp and the coil with the iron powder in it), then the power amplifier output will have more selectivity and things may change again... so even more fun is guaranteed.   :)  O0     

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Hey Peter,

Out of curiousity, what are you going to be investagating with your frequencies in this range?  Does it have anything to do with the magnetic precessional rates of 42.4923 MHz that Ken Wheeler suggested?  I noticed you put a little smiley emoji when it was suggested that Iron was distorting your signal..

Thanks,

Dave
   

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Buy me some coffee
Thanks Gyula ;)

Next I need to heat up the iron until an insulated magnet drops of to indicate we reached our Currie temperature, make note of the voltage and current at this point, work out it's resistance and then build a circuit that on/off controls that temperature every second by locking onto the known resistance.

Hi Dave
It's a sort of version of a Michel Meyer device, we also know Coleman guilespie did similar using cobalt metal.
Some time ago we discovered a paper which said the NMR frequency for iron is different where the NMR frequency is stable at 45.5Mhz in varying magnetic field strengths, which gives us the chance to align the iron atoms spin and resonate it at it's NMR frequency, with the hope of destabilizing the atom and releasing some energy in the form of beta radiation and dropping to a lighter isotope.

With iron we have a penetration problem due to skin depth, I hope to alleviate this by passing a current through the pure iron powder to heat it above it's Currie point.
« Last Edit: 2019-05-07, 20:26:29 by Peterae »
   
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