The AM Forum

This is the cliplead 400 - a 400 watt *output* transmitter.

The transmitter is ultimately to be packaged in a large briefcase (Zero case), and features an off-line (no power transformer) modulator-power supply.  The modulator provides an isolated and modulated 45 volts @ 10 amperes (carrier) output, and will deliver 130V at the crest of the positive peak.  The push-pull RF amplifier is self-contained, including the IXDD414 drivers, and takes a TTL level input at the operating frequency.

The modulator is a push-pull forward converter operating at 140kHz.

Cute little project !

Below is the overall transmitter:
(http://www.classeradio.com/cl400_overall.jpg)

Below is the modulator:
(http://www.classeradio.com/cl400_modulator.jpg)

Below is the RF amplifier:
(http://www.classeradio.com/cl400_rf.jpg)

Here is the PWM filter (4 poles):
(http://www.classeradio.com/cl400_filter.jpg)

And finally, the modulator switching transformer (push-pull modulator):
(http://www.classeradio.com/cl400_transformer.jpg)

""Below is the overall transmitter:.....""

Don't you mean "all OVER"  ?!

 ;D


Sounds good on tha ayah!

let me know ahead of time when you plan to travel with this briefcase. I want to avoid that airport.  ;D

Looks interesting Steve. Will you have it on the air this weekend? What band/bands?

Mike

By the way, I have a small, empty Zero suitcase. Not a briefcase but it might do. Interested?

Yo Steve - You know that I think that thing sounds
great and as always, breaks some more new ground.

I think you got the name backwards, however.  It
should be the "400 Cliplead" transmitter.

If I were an electron, I would be afraid to go through that maze. I might get lost!!

fred

Steve,

Another fine Cloutier prototype!!   :D

Cool new design.  Full strap power, no PS transformer, isolated modulator...  As always, thanks for the great work Steve.  Looking forward to learning more details.  Just wish I could make clip leads work like you do.  ;)
Look forward to hearing the new rig.

73, Karl    KD3CN

It looks like it's going to be pretty cool Steve.  I especially like the fact that it can fit in a  briefcase.

73,
Ellen - AF9J

Oh the Humanity!!!!

Mike,

I heard you on the air last night (Friday) talking with Don, K4KYV.  Good sound from your end (and Don's).  I was working on the Cliplead 400 - had it up to full power (450 watts) in to the dummy load, modulated to 200% positive.  So, the little modulator-power supply has to develop over 4000 watts peak output to do that !!  I still have only 2 MOSFETs in the modulator, but I need to expand that to at least 4, and probably 6 to leave plenty of head room.

So far, the circuit is fairly simple (for all that it does) and I am trying to keep it that way !

Oh, Mike, I would be interested in the zero case if you're interested  :)

If this circuit proves effective and bulltproof, I will probably make this the "standard" modulator for class E rigs of 500 watts and under.

Good stuff!!

Regards,

Steve

The leading edge of Serbo-Croiation Technology! Brought to the satisfied masses by Muppet Labs!
I'm not on much this time of year but this stuff may even convert me to try the waters!!!
Cool!
Keith
HZK

That is pretty darn cool!

Hi Steve,

I wish you had dropped in last night, I'll bet that thing sounds good. What will the power supply for the transmitter and modulator consist of? I'm wondering about the size, weight and voltages needed for the supply. Another question, is it a single band, tunable rig?

You can have the case for postage Steve. It's covered with worn security and other stickers from my international travel days. You'll have some cleaning and polishing to do but it's serviceable.

75 meters was in rough shape last night (early this morning). Don was strong for a change but I couldn't hear Skip (K7YOO). Usually it's the other way around. I think I'll try 40 meters later today and this evening. 40 is fun but activity isn't as common. Thanks for the signal report.

Drop me an email with your mailing address and I'll send the case soon.

Mike

Pay no attention the man behind the curtain!   

I think Guy has it correct.  To sound that good (I heard you on 75), the clip leads must certainly be oxygen free. 

N1 Prime Suspect

I just have one question,how do you calculate the stray capacitance and inductance of all the clip leads in order to know what values to insert in the circuit when it all comes together to make it work in a case?  ;D

BTW, good job.

Steve:

Looks...er...good (?).

I'll hafta listen fer it.

Congratulations on another Frankenstein noise silencer!

Dan
W1DAN

How does he keep the clipleads clean?? mine are all rusty and covered with rosin smegma. 

klc

Well, I've been doing some more work on the ClipLead 400  8)

Doubled the number of MOSFETs in the modulator from 2 to 4 - which SIGNIFICANTLY improved the modulator efficiency.  Now, the heat sink is cold under operation...

Also, changed the output RF transformers in the class E output stage, and now these just get warm after an extended period of long buzzard transmissions.  The previous transformers became very hot after extended operation.  I used 8 cores in each instead of 4.  The cores cost under $2.00 each, so not a big change in expense.

The positive modulation capability is over 200% positive, not that you'd ever use that, but I was pleased with the results, nevertheless.

It's almost time to document it and perhaps lay out a PC board for the modulator ;)

Regards,

Steve

You could make it even more compact by replacing those bread-slicers with vacuuuum variables shunted with fixed micas.

Last weekend when I went to Dayton, I stayed up at Gary's, K4XK, at his QTH in the thriving metropolis of Shinbone, OH.  He demonstrated his class-E rig, which uses a power supply of several times the size and many times the weight of the transmitter.  But he told me that the cheap MOSFETS he uses, designed for applications as pulse-width power supply regulators, are getting harder to come by.

I don't understand why they would be discontinuing to manufacture them since it would seem to me that demand for that technology would be increasing, but what is going to happen if those MOSFETS become unobtainium like everything else we need for building rigs?

Those are just the particular mosfets HE uses...

There are at least hundreds of mosfet types that will work, with new types coming out regularly....


CHEAP, well, that may be another story!

Oh, I'm familiar with Gary's rig - quite a piece of work.  Gary uses an analog modulator, which is why the modulator is rather large as compared to the RF amplifier.  Nothing wrong with it - kind of a "boatanchor" class E rig, so to speak  :D

As far as the MOSFETs - the FQA11N90s that Gary uses are still readily available, although they are being replaced with newer designs.

The manuracturers are coming out with newer MOSFETs all the time, and this is great!

Think about this: My first class E rig used the Motorola NTP10N100E MOSFETs.  These were discontined by Motorola about 7 years ago... so I went with another device (better device) which was discontinued, so I went with a BETTER device.  Each time, the devices got better and less expensive.  The MTM4N85s that I used to use back in the 80s were SO BAD - and very expensive.  The same device today would cost under $3.00 each.  At the time, (and in 1980s dollars), the MTM4N85s were some $8.00 each !  These were used in a solid state audio driver I designed.

Another good thing about MOSFETs is that they are generally the same physical size (there are standard case sizes, thank goodness), making interchange very easy when using an existing physical design.

Regards,

Steve

I caught a few transmissions this evening Steve. It sounds sweet and looks clean. Good job.

Mike

Thanks !

I've really got it cooking along, and the positive modulation capability is over 200% positive.

I'm looking into using physically small parts for the tuning network.  I think I'm going to try one of the ATC 100E series capacitors for the series cap (with a small variable), and some variable mica caps I have for the loading.  Should be an interesting experiment.  If the series cap gets warm, I'll probably to to a vacuum fixed cap, with a small variable across it.  The tuning range of the variable capacitor does not need to be very large to cover the whole band.

This has been an interesting design project, for sure.  Now I start falling apart because the design part is done (my favorite part!), and now its a matter of details and implementation  8)  Oh well, the necessary evils of building - you have to actually build something and not just design it and test with a clip-lead laden prototype  :D ;)

Regards,

Steve

Steve,
 You might take another look at ATC's website...
They've "extended" the voltage range of the 100B, and 700B caps.
They are lower capacitance values , I think they have  an "extended" voltage of 1kv at 200pf.

The 100B is $275. for 100pcs...the 700B is $225. for 100pcs.

You can buy those right on line, without even picking up the phone...

Might be worth a shot!

My first solid state rig used TO3 FETs 2N6766 that sold for $80 in 1882.
My first 4 fets came from used breadboards.
It took 4 of them to make 100 watts on 75 and ran quite hot. Dean KNX built one befor me with similar pigs. New die designs happen all the time but we all need to deal with the surface mount monster.
The bad thing avout vacuum caps is they don't like mechanical shock. Good old bread slicer can take a beating in a portable rig.

1882 !
wow, imagine what they'll come up with next year.  ;D

sorry for lurking.
Rick

Gee no wonder my hair is turning gray

I have created a preliminary schematic of the ClipLead 400 transmitter's modulator output section (all of this is new).  The remainder of the modulator (PWM generator, etc.) is from existing schematics (and boards) and is already documented at the class E web site as part of the Pulse Width Modulator and Power Supply.

The ClipLead 400 modulator takes a standard PWM signal from the existing PWM generator board.  This signal is then fed to a phase splitter, drivers, and ultimately to the output MOSFETs operating in push-pull.  All of this circuitry is included in the new schematic.

This schematic is subject to change, etc.  Don't build any of this without contacting me first !

Comments welcome  8)

Click on the link below to view the schematic.
http://www.classeradio.com/off_line_pwm_output.pdf (http://www.classeradio.com/off_line_pwm_output.pdf)

Regards,

Steve

Steve:

SAWEET!!

And sounds good too!

Dan
W1DAN

Steve...

PUSH PULL TRANSFORMERLESS PWM "OUPTUT" SECTION

Really?

Something doesn't look right in your clamp circuit at the transformer primary

Hi Frank,

I included the circuit snippet and explanation of the clamping function in general, so everyone can see what we're talking about..  The purpose of the clamp circuit is to hold the line on spikes which result from leakage inductance and other stray elements in the circuit.  It is possible for there to be very short and very high spikes during the turn-off cycle of the MOSFETs.  In order to control these spikes, clamping and other circuits are employed.

(http://www.classeradio.com/temp.jpg)

In this case, D800 and D801 conduct energy into C807, charging the capacitor.  The "normal" voltage will be twice the power supply voltage.  High, but otherwise low energy spikes will have very little effect on the voltage across C807, however the diodes, working into C807 will effectively clamp the maximum drain voltage at twice the power supply voltage.

The voltage is sent back to the power supply through R805.  A small amount of power is lost in R805, however we are looking at only a few watts.  If one wanted to conserve the energy, it could be utilized in some way, using a buck switcher or other switching regulator.  In the interest of simplicity, I chose to drain off the few watts.

Anyway, what did you see as odd in the circuit?  It definitely works, although there may be other ways to accomplish the clamping function.  Let me know !!  ;)

Thanks !

Steve

you are limiting the flyback energy in the transformer by ac coupling it to ground through the 3 uF cap. Yes it will peak charge but I think you are wasting power. Any spikes are going directly to ground. You may have excessive leakage inductance in the transformer and lead length and this bypass is the fix but usually this energy is dumped back into the supply not ground.

Interesting idea !  I'll try an experiment by moving the 3uF capacitor's "ground" connection to the power supply and not ground.  I'll let you know if I see any change in efficiency.  Everything is metered, so I'll be able to tell right away.   Let you know  8)

Regards,

Steve

Steve

Look forward to hearing it on the air! Which material are you using for the 48613 core?

P material.  That's right, I have to specify that on the print.  The number isn't enough!   ;D

Also, I did the experiment - moving the snubbing capacitor's return from ground to the power supply.  I was unable to measure any difference in power input, output, voltage or current.  It there were a change, I couldn't read it.

I didn't necessarily expect much because the modulator is VERY efficient, and nothing gets warm that one would not expect to get warm.  It appears as if the greatest loss (and it's not much loss) occurs within the switching MOSFETs due to the R D-S on (I'm only using 2 MOSFETs per side - 4 would really do it), and the diode drop loss in the switching diodes that are part of the bridge and damper.  Again, small losses, but I'm trying for 95%  :D   That's where conducting the snubbing energy efficiently to the power supply using a switcher would make a difference of a 1 or 2 percent - but now that's starting to get rediculous  :o  (but isn't that the whole point?).

Anyway - I'm so pleased with how this is working, that I am contemplating laying out a PC board and making a kit of parts, like I have for the other modulators. Thing thing about this one is, it can be built very lightweight, and that's attractive as we AMers start pushing old-buzzard-ness.  And, of course, these units can be combined for greater output if one were to need it for whatever reason, and the weight would be very reasonable.

Regards,

Steve

Steve,
I have a real good app note on snubber design somewhere on my work computer. I will send you a copy when I find it. One other thing is R805. A wire wound resistor has a lot of inductance and ineffective in eliminating high frequency transients. 5K and 3 uf is a 15 ms time constant on a 130 KHz switcher is very high.
P material is cool stuff for power supplies.

I'd like to check out the app note if you can find it !  I figure the 3uF is pretty much a short circuit at 150kHz (.35 ohms) as compared to the 5K load.  The voltage is pure DC at that point (checked it with the 'scope)  - no 150k stuff showing up.  I've talked with a few power supply engineers and they tell me they usually have to use snubbers with this sort of application.  But, in this case the transformer is pretty good, so I don't have a lot of energy to "snub out", so to speak.

If I weren't so concerned about modulation linearity at the extremes of the pulse widths (1% - full off, to 49% which is full on), I wouldn't worry so much about the snubbers (the voltage doesn't go that far out of line), but I find that if I do not snub these tiny pulses out, they affect the modulation at the extremes - not a lot, but it's there!!  Anyway, not a big deal but definitely worth getting as perfect as possible (are there degrees of "perfection")  ;)

That P material is GREAT, and amazingy enough, not expensive.

Oh, on another note - I've tried some experiments with toroidal inductors in the filter and air wound inductors.  The air wound inductors dissipate slightly more heat in the windings due to DC resistance (about 2 watt for both inductors wound with air), but the core in the toroidal filter dissipates about the same amount of power due to magnetic stress - so it seems to be a wash.

Now, I do believe the air wound inductors work better, and are more stable over the wide current variations one gets with modulators for AM transmitters, and the air wound inductors are MUCH MUCH less expensive.  Each core in the filter costs about $22.00 - I'm using the very best cores - HI FLUX cores (check out the CH777060).

The downside of the air wound inductors is the size.  They are a lot larger, and cannot be mounted against metal as can toroidal inductors.

Regards,

Steve

Yes you want to use a snubber but you just want to quench the high frequency overshoot and ripple on the drain pulse. I just worked on a switcher running at 300 KHz and due to wrong snubber design it was making a pile of crud up to about 80 MHz. We had to burn about 1/2 watt to get rid of it.
The problem was layout and transformer design. Snubber design is all about the little things you can't control like leakage inductance and interconnects.
I'm sure 15 ms TC hanging off 130 khz is well integrated. WW resistor is also acting like a RF choke. 

1/2 watt ain't bad :-)   If you find that snubber document, I'd like to have a look at it - definitely!

I may add 2 more MOSFETs to the output, to slightly increase the efficiency, and to bring up the power.  I think a good design value for this project is around 550 watts (or thereabouts) carrier power (output from the modulator), to yield 500 watts output from the RF amplifier.  So, I would like to design the modulator/PS to do up to 600 watts at full output.

Then, one just needs to choose a filter to choose the actual operational carrier power.  My particular filter gives me 450 watts output, but I have other filters which will let me run 500 watts and 400 watts (DC input) at carrier.

500 watts makes a good "building block" power level, either for standalone or for combinations of 500 watt building blocks.

Fun!

Regards,

Steve

Steve,
The 1/2 watt was in a 100 watt supply so you may dissipate more unless your transformer design is perfect and very short connections. Secondary side needs to be just as good. Well read the app about 10 times and notice the time constant you need. I think we had 4700 or 10,000 pf and 2kohms in our case.

Hi - thanks for the comments, etc. so far.

I am about to release Rev D of all of the Pulse Width modulator output section boards, and the PWM generator board.  I am currently out of PWM generator boards, so this is a good time to make minor changes.

On the PWM generator, the main functional change I'm looking at so far is a 50 ohm, low impedance 12V output for the pulse width signal, in addition to the medium impedance TTL output that's part of the current rev.  This low impedance output will allow the PWM signal to be cleanly transmitted over many feet of coaxial cable, in the event the PWM generator is not located right next to the PWM output (which is often the case).  The low impedance output will be the output used with all of the rev D pwm output boards.  The signal is converted to standard TTL at the output board.

I will probably make changes to the current output board - heavier etch runs, and possibly add another MOSFET to the board for higher current capability.

The new PWM modulator output section will get a new board, as none currently exists.

I am also going to create a "sequencer" board, which will implement complete transmit/receive control for antenna relays, receivers, VFOs, etc.  The board will implement a "first on, last off" type of system - the first thing switched (like the antenna and VFO and driver) will be the last thing turned off.  This will give an orderly transition from transmit to receive, without any glitches or "overlaps".

Any other suggestions, etc. would be appreciated.

Thanks and Regards,

Steve

How about the pwm board you replace the 1n34 with an opto to flash a led if you are hitting the negative peak limiter. You might be able to use the led in the otpo in place of the 1n34. I use a led in the 160 meter rig and 75 meter rig modulators. That is a modification I plan to make.
Output board I'm not sure you need so many "damper" diodes.
The pwm output chip Z is low but the voltage swing is high. I wonder if you could just reduce the resistor divider values?? I was thinking of a load resistor at the output boards with a lower series resistor off the pwm. This would save adding another ic or transistor. fc   

1) Balanced / unbalanced line level audio input. Maybe eliminate phase select switch...most folks probably already handle this before the transmitter.

2) Can the pdm chip drive more than one output board? If so, maybe some extra pads. Thinking of the possibility of multiple output boards with multiple filters powering multiple TX modules.

50 ohm between pdm chip and output board(s) would be a good idea.

 

I agree with Jay on the switch. Heck a field of jumpers would be fine.
Jay look up the chip it has a fairly low output Z but the voltage swing is up around 12 volts. I'm going to drive two boards and just put a load resistor at each output board and a lower series in the voltage divider. I have about 1 foot of shielded wire to each output board. I'll load it and increase current until the waveform is clean. I would think the opto input z high so the load would just match the shielded wire z for a clean pulse. another option would be to use an 74AC00 and invert twice to get a strapping 5 volt low Z pulse.
This would allow 3 outputs. AC gates are 25 ma source / sink and faster than s logic using less power.