A collection of modules for building medium to high power Amplitude Modulation (AM) transmitters. Each module includes a schematic PDF, essential construction details, and many include links to Gerbers for the PCB.
Module AM#1: Triple DC buck regulator
A PCB design for three variable voltage 0..35 volt, 3 amp buck regulators, using the LM2576 switching regulator, and designed for use in a homebrew AM transmitter, but generally useful. Unwanted sections of the board may be hacksawed away if only one or two regulators are needed in a project.
Gerbers, BoM and other supporting files are available in this Github repository.
Module AM#2: 100VDC (500 watt) buck regulator
A schematic and PCB design for a DC power buck regulator capable of delivering 0..100 volts DC from an input of up to 120 volts DC at 3 to 5 amps continuous, and at peaks of 2 to 3 times. Designed as the main power supply regulator for a 250 watt AM transmitter.
Gerbers, BoM and other supporting files are available in this Github repository.
Module AM#3: Digital SWR and power meter
A schematic and PCB design for a simple digital RF power and SWR meter. The following video demonstrates the meter:
Gerbers, BoM and other supporting files: email me.
Module AM#4: Balanced microphone amplifier with phantom power and equalisation
A schematic and PCB design for a balanced microphone amplifier with phantom power and equalisation, and using all discrete transistors. The module runs on a single 12 to 18 volt DC supply.
Gerbers, BoM and other supporting files: email me.
Module AM#5: H-Bridge Class D RF Power Amplifier
This module is an H-Bridge class D switch, not a power amplifier in the pure sense as it is non-linear, rather a switching module capable of delivering over 100 watts of power into a 50 ohm load, or other loads with a different output transformer turns/impedance ratios.
The FETs are Infineon devices (IRFP4019) aimed at classs D audio amplifiers, and cost a few dollars each (if a supply can be found, as of Apr 2022 due to the global semiconductor shortage). Better performance is delivered by another Infineon FET, the IPP530N15 (out of stock globally at time of writing ).
The module includes a gate driver (IXDD614, still available), which can be driven with a 5V TTL square wave from a crystal oscilator, synthesiser or PLL, followed by a 74HC-series TTL buffer. This selection of driver and FETs has worked with an efficiency of around 90% from LF to 7MHz.
A subsequent set of photos will illustrate the angle aluminium heatsink piece using 50x25x3mm stock angle. Two of these PCBs fit side by side under a 150x60x25mm finned aluminium heatsink, commonly available on aliExpress, eBay and other sources. These H-Bridge modules may be combined for higher power levels, either by using an RF power combiner (W8JI has an excellent one), or by arranging the secondaries in series whilst adjusting their impedance so as to sum to 50 ohms.
Gerbers, BoM and other supporting files: email me.
Module AM#6: Universal VFO Drive
This module takes as input a 3 to 5 volt square wave clock (such as a VFO generated by a crystal oscillator and buffer, si5351 multisynth PLL or similar source), and delivers one, two or four equivalent drive signals (I/Q or I/Q/I-bar/Q-bar). Outputs may be configured to be all in phase, or in some combination of 90 degree shifted phases. The input frequency may be at the desired frequency or at twice the desired frequency. An TTL-level enable line is provided for (on/off) drive control.
A schmitt trigger may be added to square up an imperfect drive clock. This board is intended to be used in a multiphase AM transmitter, to drive one, two or four H-Bridge modules, but is universally useful for any projects that require VFO/clock conditioning, with or without frequency division, or up to four phase-differentiated outputs.
Gerbers, BoM and other supporting files: email me.
Module AM#7: PDM Driver and LPF
This module takes an HT supply in the range 0..100 volts DC, and a modulated pulse stream at the chosen Pulse Duration Modulation frequency, and performs power switching into a low pass filter. The result is a modulated DC voltage, suitable for powering an H-Bridge module to generate high quality Amplitude Modulation. This module is sized to power and fully modulate up to two of the H-Bridge modules (module #5).
Switching is done with a pair of Infineon IRFP260 power FETs, driven by a high and low side IR2110 gate driver. A modulated PDM (PWM) signal at 5V is required at the input. A TTL-level enable control turns the switching stage on or off, for transmit/receive switching, or to drop the (modulated) DC output to subsequent H-Bridge(s). An Over-sample line provides a degree of over-sample error correction back to the multi-phase modulator (to be described).
The Low Pass Filter is designed for a PWM clock (sampling) frequency of 100 to 125kHz). It has a -3dB cutoff at around 28kHz with the components as specified. Inductors are wound with 1mm ECW on RM10 cores. Capacitors must be metallised polyester (MKT) and rated at 200V for a DC supply of 100VDC. Electrolytic capacitors are Low ESR.
The PCB is identical in side, mounting holes and heatsinking arrangement to the H-Bridge module. One of these modules will power one or two H-Bridge modules, for a conservative 150 to 200 watts of fully modulated AM carrier power. With two H-Bridges running 200 watts carrier power, passive cooling using a 150x60x25 heatsink on each of the H-Bridges and the PDM Driver module without a fan will suffice. Two of these modules will power four H-Bridge modules, for up to 400 watts of fully modulated AM carrier power.
If using two modulators, the PDM drive may be supplied to each modulator in phase, or at 180 degrees for a multiphase configuration (using module #8). It is possible to use four of these modulators and four H-Bridges, and drive each with 90 degree phase shifted PDM drive, for a true quad-phase modulation configuration. This is probably unnecessary but would make an interesting test!
Gerbers, BoM and other supporting files: email me.
Module AM#8: Multiphase modulator
This experimental module contains a crystal oscillator and divider, followed by four Miller Integrators and Linear Comparators to deliver one, two or four audio modulated Pulse Duration Modulated clocks at the selected PDM base frequency (typically 250 or 125kHz). To be described.
Module AM#9: RF Power Combiner
To be described.
Module AM#10: Triple Low Pass Filters
This module is a set of identical low pass filters with relay switching for an AM transmitter or high power linear amplifier. The board is designed for components in the 300 watt continuous carrier range, and is physically arranged so that it may be cut down for a single or pair of LPFs.
To be described.
A complete single phase 150W AM transmitter
Pictured is a complete AM transmitter for 160 and 80m using the modules described above. It was used as a test rig for the modules, and after the RF Power and LPF boards were added, was used on-air as shown with good results on both bands.
HT for the rig was supplied by two 30V 5A bench power supplies in series ( not shown). A separate 12V supply powered all of the 12V circuitry. These supplies provided HT current limiting. No SWR protection was used. A digital scope was used for signal and modulation monitoring and RF output power measurements.
To complete this transmitter would require an HT DC supply capable of 120V DC at 5A continuous, followed by the 100V DC Regulator module above. This module incorporates preset DC current limiting. The SWR meter shown above would monitor SWR and antenna match, as well as a high SWR lock-out line back to the Regulator.
The next experiment to be tried on this test rig is to use two PDM phases to drive two modulators and two RF Power modules, either in series, or, into an RF power combiner. This should deliver 250 watts of AM at close to 90% efficiency without any significant heatsinking and without fans.
VK3HN 
Hi,
congratulations for your very interesting web site!
Of course I need ( as always…) some more info, especially about AM#5 H bridge class E rf power ampli:
As connected, both high side and both low side of H bridges will go on at the same time , IMHO two trasformer must be inverted ( primary or secondary) on one side of H bridge: I’m I wrong?
Can I use only 2 transformers on gates with 3 winding each?
Some more infos on out transformer: in your full schematic you write: 8T bifilar 1T primary 2T secondary: can you explain?
Sorry for my terrible english!
Thank you
Paolo from Italy
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Hi Paolo,
thanks for commenting. You are very observant, and you are correct, when I built up this board, the drive was wrong across the four gates, and it wasn’t until I reversed two of the gate transformer primaries that it worked. If you look carefully at the coloured insulated primaries on the left-most two transformers in the photos or video, you will see that they cross over each other.
I always fix the schematic but I must have omitted to re-publish the fixed PDF on my blog.
The H-Bridge circuit is simple and you can easily experiment with the key parts. I’ve tried different FETs, changing the output transformer turns ratio, and I’ve omitted the modulated HT decoupling capacitor. I’ve not experimented much with the gate drive or gate transformers, other than trying FT50-43 which worked, but got too hot. I cannot think of a reason why you couldn’t use two gate transformers with two secondaries, there tend to get hot, so obviously pay careful attention to getting the phasing correct, and monitor toroid temperature.
The IXDD614’s output can overdrive the gate transformers at lower frequencies. You can address this by dropping the IXDD614 Vcc from 12v to 10v or even 8v, while monitoring the H-bridge output waveform. Keep reducing Vcc until the output wave just starts to deteriorate (lose its square edges) . The IXDD614 will run a lot cooler if you do this, another bonus.
If you do experiment with this module, let me know what you find. It is an excellent design, >90% efficient, can work 630 to 40m, up to 250 watts carrier power, reliable as long as the gate drive is set up correctly.
73 Paul VK3HN.
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Paolo, I forgot to clarify your question on the output transformer. Another schematic error 😧 It should be 8Turns Trifilar. Use one turn as the primary, put the other 2 turns in series for the secondary. I have used both a single T140-61, and a pair of stacked T114-61 toroids. They seem to be about equivalent.
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Hi VK3NH,
thank you for support and good ideas!!!!!
If primary is 8 turns and secondary is 16 turns ( 1:2) so impedance is
1:4, and primary is 12.5 ohm.
If I want to have more power and I use two circuits in series, so
secondary must ( I suppose….)
be only 25 ohm each, right? so 1:2 impedance, that is 1: 1.4 turns say
about 8: 11 turns. I never did this before,
but I want to try. I’m not a broadcaster, but I will only heat up my 50
ohm dummy load and listen
modulation on an old Marantz radio.
Lot of good ideas on your web site, I’m an old 66 y.o. technician, and I
hope to have time to test them all.
Thank you for your web site and support.
Sorry for my very primitive english…..
Paolo from Italy
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Hi Paolo,
Don’t apologise for your English, I think you are far smarter than me, I speak no Italian 😉
Regarding, putting two modules together to get twice the power — I believe your suggestion should work. Build two boards, use 8T primary and 11 turn secondary, and put the secondaries in series. Drive both modules with the same clock or 5Vpp signal. Use your Modulator to modulate the HT to both modules. I have thought about doing this but have never tried it.
One of the K7DYY AM transmitters does exactly this. I went looking for his schematic but I cannot find it, he has probably taken it down.
When combining the power from two of these modules, I have used the W8JI RF power combiner with success. See schematics on my 200w AM Transmitter post. W8JI has an excellent page on this, read it carefully for the theory of operation.
It presents a 50 ohm load on both input ports, and delivers the combined power into a 25 ohm load, which you can step up to 50 ohms with a simple transformer. The cool thing is that if one module fails the transmitter keeps working at half power. It is also simple to build and requires no adjustments. You could try substitute toroids, but you will need two high power 50r stud resistors, available on eBay fairly cheaply. Most of the work in this module is mechanical mounting.
73 Paolo and let me know if you get this working. Paul VK3HN.
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Sorry, again on H bridge.
What kind of wave can be expected on gates of mosfets?
Trying with different mosfets ( from IRF530 with Ciss 900pF to
IRFP360 Ciss 5.6nF) but, also driving only one, wave is
absolutely not square on gate. Also experimenting
with high “al” toroids I have. Can you please put a pic
of waves you can see on gates? What Vpp too?
Thank you
Paolo
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Hi Paolo, I will look for a video that shows gate waveforms. There do not have to be square, and may be a bit rough, but at a minimum must turn the FET s on and off. Two of the H-bridge gates are driven with respect to ground, the other two are floating. On the former, you should measure a 12 to 18Vpp waveform.
It also depends on frequency, my H-bridge modules have worked on MF, 160, 80 and 40. Start on MF or 160, the lower the frequency the easier the testing.
IRF530 should work on 160 and 80. IRFP360, not sure, I would guess not. IRF640 also worked on 160 and 80 for me. Also IRFB4019. The standout FETs are IPP530n15, buy 20 of these if you can.
I was told not to substitute the gate drive toroids, the ones specified work to 40m.
My H-bridge modules produce RF power at 85 to 90% efficiency on supply voltages from 10V to 60V. They will go harder but you need overload protection, otherwise they can go short S to D.
Assume you are using IXDD614 driver. Correct drive is critical.
I will look for a test video and post a link.
73 Paul VK3HN.
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Watch the last 5 mins of this video for a trace from 5V clock signal to antenna socket.
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good morning I’m Davide and I write from Italy. I saw your modulator for am and I was trying to build one for an old eddyston marconi transmitter am 1kw. I have to modulate power supply to 100v modulated and when I saw your modules (really well done). Could you send me only the gerbers of Module AM#7: PDM Driver and LPF . I saw that the pwm modulator is missing but I can design it, or if you keep a diagram with input bf output pwm for your module. I’m looking for your email but I can’t find it and I could only write to you here. thank you very much for your answer. sorry for the inconvenience Davide
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Hi David, thanks for your comment. The quick answer is my multiphase PWM /modulator module can be used, it takes line audio and delivers single, double or quad phase PDM to one, two or four of the PDM switching modules. A simple 100W AM Tx requires only one phase.
Further, all my AM transmitters as described on blog posts use complete single phase PDM modulators. Look on my blog posts or click on the AM tag to pull up everything I’ve posted about AM. The post on 200W AM Tx includes schematics.
I think you’ll need a considered approach to designing your modulator for a 1kW RF Deck. Perhaps you can clarify what power you wish to run, and what load you wish to modulate.
You need to match the modulator’s LPF output impedance and the switching stage to a known load, that is, the impedance presented by your RF deck. I don’t know what impedance your load offers, but my H-bridge RF modules look like 10 to 12 ohms.
Feel free to email me, my email is available on QRZ.com.
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Hi VK3HN,
right now i’ve finished the rf H bridge and it works as expected: perfectly.
With 59.7Vcc it gives 100Vpp on 50 ohm (25Wrf, no LPF yet) ,using 33W power supply ( not so good efficiency…), so with 120Vcc it must ( I suppose) give 100Wrf ; I’m using 4x IPP530n15: is everything right? Must I add some turns on secondary to have 25Wrf at 50Vcc, and 100Wrf at 100Vcc?
It stays perfectly cold having fun at 1.5MHz ; drivers works perfectly at 10Vcc, no gain working at higher voltage. I’m using two FT114-61 toroids, with 8-16 turns of 1.1mm wire. I’ve still built the pwm modulator, in some days I will connect it, it seems to work OK with a resistor as load.
Congratulations, simple and good rf module.!
Thank you for support
Paolo from Italy
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Thanks Paolo, I answered your followup comment first, before seeing this. Yes, the efficiency you report here seems well down, although you do not indicate current, only the HT volts. At 100V this module should deliver 250 watts or more, and will be close to it’s limits, you only need 50 to 60V. Remember that with no modulation, the modulator will deliver half it’s maximum voltage into its load. That allows for modulation to swing it between 0V and 90V on a 100V modulator HT.
73 Paul VK3HN.
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Hi,
I’m using a IXDD614CI bolted on cooling fin near IPP530N15. Everything is from RS components, but this ic is the only part from TME.EU . All the parts are absolutely new and never used before.. Datasheet says it will work with signal from 3Vpp.
I’ve mesured it again, at 10Vcc it needs 8.8Vpp on input to work, at 15Vcc it needs more than 14Vpp signal : not normal. Using a perfect square wave ( 50%) it gives on output a rectangular wave, changing duty cicle as I change Vcc: not normal. I will place an order from a well known reseller, as Mouser, Farnell, ( RS components does not have it). Also with a non 50% square wave H bridge gives a lot of power, and , more important for me, it gives a quite perfect square wave on output, no dangerous peacks: this is very appreciable,
’cause lot of mosfets died for this reason!
Have a nice week-end
Paolo
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There’s something wrong with your IXDD614C driver IC, or the connected components, or the physical layout. Are you using good quality MKT polyester capacitors? Cheap to average quality ceramics should not be used in RF switching applications like this.
You could try lifting its 1uF output capacitor from the gate transformers and connecting in a suitable resistor load, say 120 ohms (just a guess from the inductive reactance of the four 4-turn gate transformer primaries). See if it behaves under those conditions.
Another thing to try is to physically move the driver away from the switching FETs. Move it to a corner of the board, on its own heatsink. There may be grounding or supply decoupling issues with the driver close to the switching FETs.
Let me know if you try any of these suggestions. Using premium Mouser drivers will eliminate the unknown quality of your devices.
— VK3HN.
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Hi,
sorry, please delete my last mail.
Your rf H bridge works perfectly first time. No problem to have 150Wrf ( after LPF) with 60Vcc ( no modulator yet). Some suggestions: output trasformer is 2x FT114-61 ( as in your older schematic) , FT50-75 ( Amidon) are equivalent Fair-rite 5975000301. Output trasformer MUST be tri-filar: I built it as normal 8+16 turns and I loose lot of power. Some problems with IXDD614: It was buyed from TME-Poland ( first buy from them), but I have some problems: It needs much more than 5Vpp input, it gives a rectangular ( not square) output variable with
Vcc, with perfect square input, no good for me. This can be the reason I can not have efficiency more than 70%. This is first time I do not have voltage peaks on drains working in digital class: H bridge is really the way to go, so simple, no problems. Thank you again for support,
Paolo
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That is great news Paolo. Thanks for letting me know. I won’t delete earlier comments as they record your progress with the module.
I had a lot of success with this H-bridge RF module. I had a few FET failures in the early days at higher power but I did not take time to carefully measure and balance the drive across high and low sides. I assume you are using IPP530N15 FETs. If not, tell me which ones are working for you.
As you know, I run these modules singly or in pairs. A single one delivers 100 watts at up to 7MHz as I’ve said. They are capable of twice this power but I prefer to run them cooler for reliability. I use a pair driven in parallel and an RF power combiner module for 200 watts on 160 and 80m.
They are sensitive to the correct load, if your LPF input impedance is not matched to the H- bridge’s output secondary impedance you see a degradation of efficiency.
Thanks for noting the need for the trifilar output transformer windings. I have never attempted it any other way.
Re the IXDD614, I never had problems with them. On 160 and 80 on 12v supply they can produce too much drive, although this is not a problem, just wastes power in heat. Mine were from Mouser I think. Never had to drive them with anything other than 5v. If you didn’t use one of these, what driver did you use instead?
I am pleased you got it working. Now, just modulate your 60V HT and you have a fine AM Transmitter.
73 Paul VK3HN.
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I confirm results of VK3HN incredibly good , simple,and inexpensive H-Bridge Class D RF Power Amplifier: 10Vcc at driver IXDD614CI drived with a TTL square wave 50%, 41.3Vcc at H-bridge, 2.65A = 109.445Win for 200Vpp RF out after LPF, and that is 100Wrf, so I have the incredible efficiency of 91.37% !!! Right now I’m testing PWM modulator with a very simple TL494 and only a BS170 at 200kHz: it works without problems on a 12ohm 50W test resistor, giving , at clipping, 16Vpp sinusoidal with 20Vcc on circuit. Minor problem is a sort of “notch” only near 5kHz, where it gives only 14Vpp: why? It still gives a good 16vpp sinusoide at 20kHz. Next test I will use 50Vcc. Someone other had similar problem?
Paolo
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Thanks for the update Paolo. To be fair, the design is from VK3SJ, and I was guided by VK3ALK t get the circuit working. But I experimented over 12 months and was able to reproduce them easily and will excellent results. 91% efficiency is good, I dont think you will get much better than that, and in practice your heatsink is dissipating only 9 watts of heat. No need for a big heat sink or a fan with these modern digital designs.
I have not tried a TL494, my PWM modulators all use discrete ICs and components, the design (also VK3SJ) is elsewhere on my blog. Not sure how you audio-modulate the TL494. Also, you obviously need some big switching FETs to swing an 80V Vcc around its midpoint (40V) at well over a hundred watts, to run your H-bridge at 100 watts of fully modulated carrier for AM. The VK3SJ design uses a pair of IRFP260s to do this power switching — this stage is followed by a high power LPF to effectively transform the 100V PWM digital signature to an analogue modulated DC supply line. For the LPF I used RM10 cores and some large poly caps in a 28KHz LPF, design on my blog. I don’t see what you can do with a BS170, but may be worth a try an an experiment, at low power.
I don’t know what’s going on with the 5kHz notch, if you share your schematic I may have a clue, there must be a resonance somewhere. Pleased that you have had success with the H-bridge.
I assue you are familiar with Steve WA1QIX Class E designs? http://www.classeradio.com/ I think H-bridge is far easier to build and scale than Steve’s class E designs, but each to their own.
— VK3HN.
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OOOPS!!! I use only one BS170, not 3 as your Module AM#7: PDM Driver and LPF, because it is enough for me an for TL494. Now using 2x IRFP250 as PWM
power mosfet, I’m ordering componets for second H bridge, and some IRFP4229 too for PWM, lowest Ciss, 200V, 50A, 310W.
For audio LPF you use RM10, but this seems to be the model ( dimension) there are a lot of RM10, we appreciate if you specify the right model too ( and turns number).
I’m using. 2x T106-26B toroids for PWM and I must remember last LPF capacitor is the sum of PWM filter output capacitors and H bridge bypass capacitors too: 360nF total.
I’ve lost lot of time ( and money…) having fun :-))) with class E, that is tuned, no large band, and critical, due to tolerance of parts ( toroids are +-20% ). Class E and Class D push pull ( both voltage and current mode ) have the problem of voltage peaks, they simply destroy mosfets in milliseconds !!!! A well designed and tested H-bridge gives a nearly perfect square wave on secondary, no voltage peaks, till now no mosfet destroyed, and it is perfect for continuos use, saving expensive big heat sink and noisy fans. Electronic is funny, but is much more funny when electrons go immediatly the right way :-))))
Thank you again for support.
Paolo
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Very FB Paolo. My first AM Transmitter was the FAT5 PA and PWM modulator. It was push pull with four IRF640 FETs. It used TransOrb avalanche diodes or peak suppressors, despite this I still had many failures and smoke, I gave up on it after I discovered the H-bridge which has proved to be much more reliable. I’ve also used IRFB4019 in the H-bridge, they worked up to about 5MHz but we’re only about 82 to 85% efficient. The IPP530n15 FETs have the best all round suitability. The PWM driver FETs are not critical, a lot of devices will switch at 125kHz no problem.
The RM10 cores must have the right ferrite, I will try to find the exact specs. Toroids should work fine. RM10 were used by the original designer because they are compact.
Do you want to try a pair of H-bridge boards for higher power? The W8JI Magic T combiner is easy to make and works first time. Two H-bridge s will easily deliver 200 watts carrier, or, do as I did, run them at 120 to 140 watts RF output and they both run luke warm!
Are you building a broadcast AM Transmitter or for use on 160 or 80m?
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An MW transmitter allows the use of a common radio to evaluate modulation. I only want to study digital ways to produce RF , interested in “small” differences between theory and a working circuit. I’ve built a PCB with one H-bridge and now I have a single PCB with 2 H-bridges too. A magic T combiner sounds good. For bigger power I will try a more powerfull driver ( custom built driver) and common IRFPs, very same schematic, only bigger toroids. H-bridge is not only simple and low cost, but also very reliable and really large band ( tested on LW and up to 2MHz, limited by my generator ). All this is possible thanks to the sharing of your experiences: thank you!
Paolo
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Thanks Paolo. Your H-bridge should work and maintain > 85% efficiency up to at least 5MHz. I have one working on 40m. It will be very happy at 1.5MHz.
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Hi Paul VK3HN,
sorry, I forgot.
Here it is: schematic of my PWM modulator with TL494 ( similar
schematics can be found on web )
….If you want to laugh you can see also my circuit….
PS What the advantages of multiphase modulation?
Paolo
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Did your URL get stripped off by WordPress?
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It seems impossible to send attachement as “reply”, so I answered you by
simple mail with attachements.
Whath’s the right way to send you pics?
Paolo
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Use my email, it’s on qrz.com then let’s continue the discussion here as I like these module discussions to be public.
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…but on QRZ.com your e-mail is for ham members only…..
This is how simple things go complicated.
but my attachements were not so important, no problem.
Paolo
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You just need to log on to see it.
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No, I must be registered as a ham to see your mail
*
You are not registered as a Ham Member*
In order to be a Ham Member, your user name must match a listed callsign
in our database.
VK3HNAustralia flagAustralia
Paul Taylor
Eltham, Victoria, VI 3095
Australia
Email: (Ham members only)
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Bugger that!
P r t 4 5 9 at g m a I l . c o m
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Curiosity killed the cat, but……I’m working on PWM modulator, with a TL494 and your circuit, now with 2 x IRFP250 : enough for only one H-bridge. Is it normal if minimum voltage of modulating signal is 7—8V and not more near 0V? A good
AM modulation must go up to 80–85%, and with peaks about 45Vpp max and only 8Vpp min, it is impossible: I need a way to go to minimum 3–4V. What do you suggest?
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Hello Pablo, a very cordial greeting from Argentina. Excuse me, my English is very bad. I have been working on the multiphase modulator for some time, the idea is to use the IR2110 in half bridge and apply its circuit. I have breaks in the IRFP260 fets, the 3 resistors R28-R30 and R31 take a lot of temperature. Many times I check the BS170 and the Low and High inputs to see if they are 180 degrees out of phase and that is fine. In another circuit of his he places a 3.3 ohm / 3 watt resistor, but the temperature is very high. Can you give me a help? I will be forever grateful to you. I have also seen that you do not place resistors in the gates of the irfp260, I have tried putting different values and the problem continues. Thank you very much for your time, I am waiting for some help, I have been working on this project for over a year and I cannot get it to work. Thank you pablo.-
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Hola Pablo
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Hello Pablo, a very cordial greeting from Argentina. Excuse me, my English is very bad. I have been working on the multiphase modulator for some time, the idea is to use the IR2110 in half bridge and apply its circuit. I have breaks in the IRFP260 fets, the 3 resistors R28-R30 and R31 take a lot of temperature. Many times I check the BS170 and the Low and High inputs to see if they are 180 degrees out of phase and that is fine. In another circuit of his he places a 3.3 ohm / 3 watt resistor, but the temperature is very high. Can you give me a help? I will be forever grateful to you. I have also seen that you do not place resistors in the gates of the irfp260, I have tried putting different values and the problem continues. Thank you very much for your time, I am waiting for some help, I have been working on this project for over a year and I cannot get it to work. Thank you pablo.-
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Pablo,
I have not used gate resistors on the IRFP260s in the modulator, and this design has worked well and has been reliable for me.
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Dear Paul,
I wrote to his email but no luck. Today I reconnected the modulator and after a short time, the fets and the IR2110 broke. I have taken Mr. Laurie’s configuration that does not use a dumper diode and it also breaks. In that circuit there is no resistance between source and drain, I don’t understand. How can I tell you that resistance takes a lot of temperature, you have put three 10 ohms in parallel, what power (watts) should they be? Or if you can give me some help I will be very grateful. May God bless you dear friend.-
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Hi,
Thanks for your comments, and it’s interesting that you have built a modulator. I will help you with it as much as I can.
First, you mention the IRFP260s. Have you built the 28khz low pass filter? And what kind of a load is your modulator driving?
For testing, I used a resistive load of around 12 to 15 ohms and rated for your modulator ‘s output power level. (You can see that the LPF is designed with input and output impedances of 12 ohms).
The 3x10r resistors between the FETs take the full switched HT and mine do get hot. I spaced them above the PCB for some airflow. How hot they get depends on the HT and the match with the LPF, and the load on the far side of the LPF.
If you can tell me exactly what you have built I may be able to help.
Regards Paul VK3HN.
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Oh no! Sorry to hear you lost some FETs. I always used a current limited power supply, and I set the Max current to relatively low values when testing, such as 0.5 to 1 amp.
Remember also that you can run this modulator on surprisingly low DC voltages, it works perfectly right down to 6v on the HT supply. So for a typical test, I would start at 10v HT limited to 0.5 amps, and make sure things are working as expected, before gradually turning up the HT (which can go to 120V DC with these FETs).
I think I used three 2 watt carbon resistors. Do not use wire wound resistors there, they will be reactive at 125khz.
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For what it worth: I’ve built it without 3 x10ohm resistors , and without
D1 MUr1560, but I’ve used 2 resistors and 2 diodes 1n4148 on gates of
IRFP250: no problem at all working at 110Vcc. Please note: UN4007
and not 1n4007! and yes, it can be tested at very low voltage. The use of an oscilloscope is highly recommended, checking each stage before assembling the next one. It works perfectly with 2x H-bridges and with more powerful ones too!
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Hi Someone,
Thanks for commenting and reporting your results. Interesting you dropped the series 3.3r resistance and added gate resistors/diodes.
I’ve also used this modulator to drive 2xH-Bridges with success, up to around 110V HT to the modulator, half this with no modulation on the H-bridges.
My plan was to use two phase PDM to two separate switching stages/LPFs, each driving an H-bridge. Then use a W8JI Magic T RF power combiner. This combination should deliver 400W carrier power and barely get warm.
Would be interested to hear what you’ve built!
Paul VK3HN.
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My audio PWM driver ( the one you suggest) with CD4013, LM311 and NE5534
plus a BS170 can drive more than one PWM audio power circuit, that’s the way I’m going on.
Interested in driving RF stages with different phase modulators…….
that’s the way used by professionals, but what the advantages?
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Paolo ,
You are correct in asking about multiphase advantages, I’ve never been able to explain it.
Take a look at this pack from Canadian AM Transmitter manufacturer Nautel. They use 9-phase PDM, described therein. They suggest each additional phase adds another SampleRate precision, hence dual phase should effectively double the sample rate , reducing sampling distortion, and reducing harmonic load on the LPFs.
I think you’ll like this document 😁
Design Considerations for AM Transmitters – Nautel http://www3.nautel.com/pub/Post%20NAB%202023/Design%20Considerations%20%20for%20AM%20Transmitters.pdf
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Thank you, Paul
poli-phase modulation is well explained in that file by Nautel.
Now it starts to be more clear.
I suppose it is a better idea for broadcasting than radio amateur use.
If we need two phases it is very simple, an inverter or a x2 frequency and a flip-flop; to have 4 perfect phases 90° I suppose the use of 4 flip-flop, but to have 9 phases….40 degrees each… that’s art! I love complications, now studiyng C-QuAM stereo MW encoders…..I’m retired, now I can finally design and build what I want… at least still money allows to! ;-)))
Paolo from Italy
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The other advantage I can see is that you split the power switching across multiple paths, and combine them before the Tx LPF. Thus each modulator H-bridge handles less power, runs cooler, etc. This parallel architecture is how all of the big solid state MW AM transmitter s are designed. I like the idea of running two or four boards, all operating well under their limits.
You’re right about Nortel’s choice of 9 phases.. why 9? They must have a good reason.
Two would be worth trying, four absolute max! Laurie VK3SJ uses four.
… Paul.
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Forgot to say the Nautel pack describes the design of a 50kW 9-phase modulated AM Tx, solid state impressive!
They identify the HBridge FETs too 😆
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No advice, just some considerations by another hobbist. The circuit
by VK3HN has no problems: the problem can be on the driver circuit,
and, again, can be easely solved with an oscilloscope , better if 2 channel.
Pin 11 of IR2110 is only an “enable” and can be grounded, avoiding the use of
Q10, R20-21-22. Driving signal on gate of Q8 must be really rectangular.
Rectangular waves on pins 12 and 10 must be perfectly mirrored, the same on gates of mosfets: if not, do not proceed!
If resistors 3×10 Ohm go very hot, can be because both mosfets are “on” at the same time, because driving signal is not perfect.
The problem can be highlighted in a very .short time using an oscilloscope.
I know, IT IS WRONG, but I tested output at very low voltage using 50 ohm RF dummy load , because I do not have a powerfull 12 ohm resistor, before connecting to RF circuit. Do not forget on output you have Vcc/2.
Have you drived the circuit with a perfect square wave from a signal generator?
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Hello Paul. I send you a very big greeting. I thank you very much for responding, you are very kind. I tell you that I built a transmitter with two IRP460 mosfets in class E. The transmitter works very well with good efficiency. The problem I have is with the modulator that I can’t get it to work. I tested the modulator with 10 ohm 100 watt resistors, it is a resistance similar to that offered by the output stage. I tried the ir2110 only using the high side (HI) and it works there, but I want to use the half bridge mode and I have those problems. If I lower the supply voltage the resistors do not heat up, but when I go up to 115 volts they cannot be touched after a minute. I see that it is not normal. Adding the different resistors to the gates did not work. I found a VE3elq circuit that had the resistors and did not have the damper diode. That’s how it broke too. I use irfp250 transistors in the modulator, I don’t think that is the fault. I am very disappointed because I have not been able to make it work, it is already a year of work. I found your page and dared to write to you. Dear Paul, do you have any final version of the complete modulator circuit that you can send me? I think it is not possible here, I have sent you an email, if you could send it there I would be very grateful. I reiterate my greatest gratitude, my blessings and a very warm greeting from Argentina. Sergio.-
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Hi Paul,
if he wants, I can send you-him my working PCB ( see attachement)Â
,for free.
Missing parts: 2x BS170, 2x IRFP250, IR2110, power diode if needed.
PWM generator is completed and tested. I can add LPF pcb too.
This can be a little “thank you” to you Paul and all your support.
Paolo from Italy
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Hello Paolo. I send you a very big greeting. I want to thank you very much for contributing and helping me get the modulator working. It has been a blessing to find you here, and I apologize if I answer in the wrong places, I am already 66 years old and I am having a hard time… Please, Paolo, if you can send me the circuits you are using, I would copy everything you You have already tried it and so I will finally have the modulator working. If you can give me the pulse generator, the driver, everything that would be the modulator, I will be forever grateful. Unfortunately I am breaking many fets, and here in Argentina everything is very bad and many things are missing. Whatever you can send me I will be forever grateful. If you can send it to my email address, it is locoavion@gmail.com. My blessings to you and family, have a nice weekend. Thank you.-
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Paolo, your offer is very generous. I will leave it to you to make email contact with scbanfi in Argentina. He has obviously worked on his transmitter project for some time so he will welcome a working modulator.
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Hello Paul. Thank you thank you very much. I have written to your email. A very big greeting from Argentina.
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Paolo,
I don’t mind supporting your work on these modules. I had a lot of support from VK3SJ and VK3ALK when I started. And with your electronics and design skills you have moved your project along considerably. It has been fun to see what you have built. And you will get to a working multiphase modulated transmitter well before I will!
When I published these pages and designs I hoped a few people would try them. They are not for beginners, particularly when you turn the power up.
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Hi Paul,
I’m sorry, I did something wrong so mail was sent as Anonymous,
it was Paolo from Italy
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Hello Pablo again, good to hear from you. Any further developments from your AM transmitter workshop?
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I wrote to you on private mail
Paolo
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I’ll reply there 👍
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Hello. Someone who can help me. I have assembled the modulator, I have not broken the 2110 or the mosfets but the problem I find is a lot of temperature in the IRF250. In 3 minutes they reach 60 degrees, that’s a lot.
It has a very good trigger. I don’t know what the problem is, can you help me? There are things that I don’t understand, for example in your circuit you use an 8 Mhz xtal and you go out through pin 5, there then there is 250 Khz, Paolo’s circuit is the same, but then I read that it must be 125 khz, it could be the high frequency? I didn’t install the MUR1560 damper diode, could that be it? And I didn’t put the 3 10 ohm resistors between source and drain either, I put resistors in the gates, and I don’t know. The waveforms are perfect in the gates, the low pass filter calculated and echoed exactly. I don’t know where to go. When you can, if you can help me, I will be very grateful.
Paolo sent me a modulator but in Argentina everything is very bad, change of government and a lot of corruption, I don’t think the shipment will arrive.
My greetings and thank you very much for your time.-
Sergio.-
//
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Hi Sergio,
I don’t think it matters whether you use 250 or 125kHz clock rate for the PWM, at 250kHz you will sample twice as fast, but I dont think it makes any difference, as at 125kHz you are so far above the highest audio that you would wish to capture in a sample period (let’s say 12kHz). The higher sampling rate may be more effectively filtered out by the LPF which from memory cuts off around 28kHz, but again, I dont think it will make any difference.
I believe you need the MUR1560 diode. I had this discussion with Paolo, who pointed out that the IRFP260 body diodes would make the external MUR1560 diode redundant, however, the MUR1560 is a high speed part and I believe it is necessary.
The 3.3r resistors are in place to limit any momentary series current thru the two MOSFETs in the event of shoot-thru, which is a short period during which both devices are partly conducting (operating in the linear region) as they switch on and off. If the drive is perfectly 180 degrees out of phase and the IR2110 is working properly as a high current gate driver, this should not happen, so the 3r3 ohm resistor will run cool. If the drive is not exactly antiphase, or there are other gate drive factors influencing the switching, the 3r3 dissipates some current as heat. Their effect on the switching waveform under correct operating conditions and drive is marginal. I know that small series gate resistors (say 10r) have the effect of delaying gate charge up and discharge and that this assists with minimising shoot-through, however, I cannot say which method is preferrable.
How are your IRFP260s heatsinked? They must be bolted to a reasonably sized heatsink with mica (not silicon) washers and good heat conducting compound before power is applied. The attached photo shows a modulator switching board with the IRFP260s bolted to a 3mm angle aum piece. This is an absolute minimum heatsink. Before asking this modulator to handle even 100W it needs a 6 inch finned heatsink bolted to the top (flat surface) of the angle piece.
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Dear Sir.
My name is Sergio, I write from Argentina. For a while I tried to make the modulator with the IR2110 in half bridge configuration. I’m still having problems, I can’t get it to work properly.
I have doubts with the published circuit, can you help me? please.
My doubts are in the VK3HN circuit, is the C18 capacitor 100 uf electrolytic type? The 100 NF capacitor C13, what type of capacitor should it be? ceramic, polyester, or what? Don’t the mosfets have resistors in the gates?
I have these doubts, I ask if someone can help me, or if there is another circuit, because I see differences between them, I found one from VK3sj and when I tried it everything broke. Years ago I consulted Mr. Laurie and he told me that a resistor was missing between Source and Drain, that was not there in the circuit. Afterwards he didn’t answer my emails anymore. If anyone can help me I will be very grateful.
Greetings from Sergio.-
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Dear Sir.
My name is Sergio, I write from Argentina. For a while I tried to make the modulator with the IR2110 in half bridge configuration. I’m still having problems, I can’t get it to work properly.
I have doubts with the published circuit, can you help me? please.
My doubts are in the VK3HN circuit, is the C18 capacitor 100 uf electrolytic type? The 100 NF capacitor C13, what type of capacitor should it be? ceramic, polyester, or what? Don’t the mosfets have resistors in the gates?
I have these doubts, I ask if someone can help me, or if there is another circuit, because I see differences between them, I found one from VK3sj and when I tried it everything broke. Years ago I consulted Mr. Laurie and he told me that a resistor was missing between Source and Drain, that was not there in the circuit. Afterwards he didn’t answer my emails anymore. If anyone can help me I will be very grateful.
Greetings from Sergio.-
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Hello. Can anybody help me? please. Thank you.-
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Please type your question.
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Dear Paul vk3hn
You are a very dedicated ham, and an engineer. I am very impressed.
I have an application for a VHF AM low data transmitter. 200KHz ~ 1250KHz, I basically want to transmit low speed morse code data.
Would you/ I be able to modify your AM Transmitter to work on the VLF frequency too.
Please give me you expert comments and a price for 4-5 kits, if I / you can adapt it to the lower frequency range.
73’s de AP2HJ HAROON
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Hi Haroon,
Most Class D or E transmitters, including my H-Bridge boards, should work very well at LF and MF, and as the output transformer is broadbanded I do not think you would need to change anything, on the transmitter board at least. I once plotted RF power output from an H-Bridge from about 500kHz to 7MHz and the RF output power and efficiency was fairly flat across MW up to about 2.5MHz, dropping off slowly, still good at 3.6MHz, but then dropped off signifciantly at around 5MHz. The H-Bridge with IPP530N15s can work well ast 7MHz but require more drive and the output transformer ratio gets more fussy. Anyway that is an aside, yes these and most other solid state transmitters will go like rockets at your required frequencies.
If you want to cover the range from 200kHz to 1.25MHz you will need a number of LPFs.
I am a hobbyist, not a business, I share my projects online with other enthusiasts, I don’t offer kits.
Good luck!
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