The AM Forum

I'm still waiting on a few major parts to come in, but this will be the overall look of the rig.  It's very similar to my last rig.  

One heat sink will mount all of the IXDD's and the other will mount the FETs.  I'm going to lop off the top of the IXDD heatsink so that all the cores will fit nicely and have a short run to the FET bus'.  

I found 470pf Russian doorknob capacitors with solderable leads.  They're smaller and have a 2kv rating.  I'm thinking they should be perfect for the shunt capacitors.  I'll use the two 540 Transzorb zener diodes on each drain bus, and that should give me a little extra capacitance on the drain to equal around 500 pf.

I'll use one IXDD to drive each individual FET.  In the center of each IXDD bus, I'll mount an input IXDD (10 IXDD's total... 8 for drive and 2 for input wave shaping).  That way all leads will be short and neat.  The input IXDD will be connected to the output of the DDS VFO.  I'll use a sine wave with variable DC offset to drive each input IXDD.  That will give me an output square wave with variable duty cycle.  

It's a start!

Jon

Hi Jon,


Good to see you're keeping the homebrew art alive!

Suggestion:  It looks like you taped the cores together using black electrical tape?   I did the same thing on my 24 FET KW E-rig.  Unfortunately, they produced loud acoustical talk-back and sang when modulated. During a dead carrier, they would sometimes feed back into a 1 KHz note.  

The cores get warm and this is sometimes enough to make the tape slip.  This produced the tiny core gaps that made the acoustical talk-back, I suppose.

I was told by an experienced E-rig  builder that GLUE (epoxy?) is a better way to hold them together. More permanent without slip.  Hold them tight together in a clamp until the glue dries.

Later -

T

I used Gorilla Glue to hold them together.  I don't always build class E transmitters.  But when I do, I use Gorilla Glue to hold my cores together.   :)

I also lopped off the top of one of the heat sinks to allow the core assembly to pass over it.

I didn't think about it until now, but the heat sink is just long enough to hold 8 FETs with a little gap in between. 

Jon

Good- you should be OK now.

I ran my cores with electrical tape for a few years and could never understand why I had the acoustical feedback.  To solve it I wrapped a towel around the cores and it did the trick. However, the towel held in the heat and eventually caused some other problems.  The cores and surrounding components need good ventilation, especially when we build 1 KW rigs.

T

I will add that super glue works as well.

I had the same 'talk back'  problem in my legal limit hf mobile amp.   I noticed the cores where stacked beads that had enough slop on the brass tubes they could move around.   

Google said super glue would work,  and it does!

--Shane
KD6VXI

I got a few more parts in.  I still need to place the order for all the semiconductors, but I won't be in a position to mount all that for a little while anyway.  Mounting all this big stuff is a piece of cake compared to all the fine, intricate work of the FETs and drivers.  There's a lot going on in such a small area.  I have a plan to make it all come out nicely, but I'll do that when the mood hits me. 

You can see my shunt capacitors on the photo on the heatsinks.  Russkie 470pf's. 

The terminal connector block is a little overkill.  It's a Chinese 100 amp thing.  It looked really good on Amazon, but I didn't realize it was so big. 

Jon

I did a little more work this evening, and I'm really starting to like the way it's turning out.  It almost looks like some secret military weapon, or something.  If I get it working, I won't use this as my mobile rig.  Some well meaning law enforcement officer might mistake this for something other than a radio. 

I realized that I have to watch drain current on both sides, so I ordered another meter/shunt combo.  It's on the slow boat from China so it'll hold me back two weeks. 

Jon

Ok, I finished the heat sink assembly.  I wanted to test it before I put it into the RF deck, so I hooked a 13.8 vdc power supply up to the IXDD bus and checked the gate of each FET.  I adjusted the DC offset pot to get roughly a 40% duty cycle. 

It seems to work fine, but it seems to draw a lot of current.  I have a radio shack 19 amp power supply (with no amp meter), and the fan on the power supply kicks on when I add the second bus of IXDD's.  Could they draw over 19 amps of current? 

It's past midnight and I don't feel like doing any more testing... going to bed.

Jon

I went with my Astron power supply instead because it has an amp meter included.  I also lowered the voltage to 12.75 vdc.  The Astron has a pot for a slight adjustment.  And, it's drawing 6 amps total.  3 on one bus, and 3 on the other (measured both).  

I did add the grounded bus bar in between the gate and the drain busses.  Sort of like a grounded grid design... no neutralization required!  

I'm going to add three good sized electrolytics from the IXDD supply bus to ground.  After that I'm going to install it into the RF deck and start hard wiring it.  

I'm still waiting on a 30 amp, 12 volt regulated supply to come in for the IXDD bus.  For testing, I'll use 12.75 volts on the drain from my Astron power supply.  

Jon

Jon,

What's your target carrier and mod voltage?

I,  too,  found lower vtage testing to be great lol.

--Shane
KD6VXI

Once I have 12 volts drain tested, then I'll move to 40 volts. I have a large transformer for that. 

If all goes well, then I'll worry about the modulator. 

Jon

Jon,

   Your tenacity is amazing!

Looking at the waveforms, I wonder if that is the drains or the gates?

Always try to use the probes at 10X since that will have less capacitive loading..

That 19 amps on the drivers sure seems like a lot to me, but working 40m with all that capacitive loading makes getting the gate swing that fast take a lot of power.

I am pulling for you Jon!

Jim
Wd5JKO

Done.  Ready for testing!

https://www.youtube.com/watch?v=ESidBrr2cxk (https://www.youtube.com/watch?v=ESidBrr2cxk)

It was fit to be tied on 40 meters.  I couldn't get it to work.

It seems to work fairly well though on 75 meters.  Once I started to get a class E waveform, I reconfigured everything for 75 meters.  I made a larger coil and put a larger doorknob capacitor in parallel with the loading cap.  In the picture is the waveform I'm getting for the gate and drain of side "b".  

For numbers, I'm using 12.63vdc drain and getting 24 watts output.  I can get more, but this was the cleanest waveform I got.  I haven't adjusted too much the duty cycle going into the gates, so I could probably squeeze some more from there.  Efficiency is at 80% right now going into a dummy load.

I didn't plan on this transmitter for 75 meters, but that's where it's taking me.

Jon

Jon experimenting is great fun and the best way to learn. Like you a while back I tried many circuit configurations and lots of different FETs.  I found for 40 meters the best FETs I tried are the C2M0280120D.  They switch about 10 times faster than the 11N90 and are much easier to drive. Your driver current will drop to about 1/3 and they will sing at 7.4 mhz.

Good building, 73s  Nigel

Yeah, this wasn't happy at all at 40 meters.  You and others have been advising me against the 11N90's at 40 meters, but live and learn.  They do seem to behave on 75 though.  I've put a lot of money into the heat sink assembly, so I think I'm just going to try to get this working well on 75. 

Now that I have the rig "tuned in" at a low drain voltage, I'm going to step it up a little bit.  I've ordered a 24 volt regulated supply that will serve as an intermediary voltage for testing.  I'll also wait until my 12 volt regulated supply comes in for the drains rather than using the 12.63 volt that I'm using now. 

In the meantime, I'll focus on the drive and getting that right.

Jon

We could also consider an alternative driver:

http://www.ixyscolorado.com/index.php/ixys-rf/mosfets-drivers-diodes-power-modules/drivers-sic-diodes/item/ixrfd630

The rise and fall times into a 1000pf load is under 4 ns......
The rise and fall times into a 4000pf load is under 7 ns......

That is screaming guys!

Here is a pasted email from an IXYS application engineer:

"I would like to suggest that you look at our IXRFD630 driver on our driver page that is well suited to high frequency operation and 13.56MHz. The 630 replaced the 420. The IXD_614 from the IXYS IC division and all of the other drivers there are primarily limited by power dissipation Pgate=Vcc*Qgate*Freq. Their driver die are small in comparison to ours. The ones in the small SOIC packages are the ones really limited to 2MHz as they use epoxy attachment for the die to substrate, the ones in the TO-220 package I believe use solder die attachment with larger surface area and so you may be able to operate them at higher frequencies. But our driver is in a bigger package (more surface area) with a bigger die using solder attachment for the die so we can dissipate a lot more power than all of the others."

Jim
Wd5JKO

My 24 volt regulated power supply just arrived and I'm getting 140 watts output.  Total drain current draw is 7.25 amps, so that puts efficiency at 80% into a dummy load.  The picture attached shows the gate and drain waveforms for side "a".

Now that I've tested it at a medium voltage and it works, I'll finish building my 40 volt unregulated power supply. 

Jon

If you are still contemplating pwm,  remember you need a higher than carrier voltage power supply,  by like 60 pct plus (I use double on mine).

If your going heising,  no worries.

OR,  you could go class H modulator,  and have TWO 40 volt supplies!   Complications.....   Err,  I mean.   Contemplations!

--Shane
KD6VXI

I know it completely makes sense to go PWM, just like it makes sense to go class E over tubes.  I just like the simplicity of Heising.  I'm going to build the whole modulator (power supply, modulator and audio amp) on a 19" rack in my closet.  That alone will take me a while to do.  I also need to put up a 75 meter dipole and build the sequencer box. 

One thing I've found with class E is that meters tend to grow on your operating position.  Check out my collection...

Jon

I built my power supply and I'm getting 400 watts carrier at 47.9 vdc on the drains.  Attached is scope picture of the 'a' side gate and drain waveforms.  Side 'b' draws a little more current, but it's within reason.

Total drain current is 10.08 amps.  That puts efficiency at 83%. 

When I build the Heising modulator, the choke will have a little voltage drop and bring the resting drain voltage down a little bit. 

Jon

The modulator.  

The shelf has the 48 volt power supply and the regulated 11 vdc power supply for the IXDD bus.  The large transformer sitting there is 5 volts at 15 amps.  I used it in my last linear, but now it'll be part of the power supply for the negative peak limiter.  

The Heising components will sit on bottom since they're so heavy.  The audio amp will be a rack mount unit.  

Jon

That is a good driver, but the cost is around $22 _EACH_, which is kind of expensive.  The IXDD chips are only about $5.00 each...

Which driver IC did you end up using?  The IXDD614 or the IXDD414?  The gate waveform looks quite good.

I used the IXDD614's because DigiKey sells those and not the 414's. 

I'm getting things wired more permanently now than when I did the testing before, so I'll tweak the drain waveform to look a little better.  As it turns out, the easy part was building the RF deck.  There's MUCH more work getting everything else done that's needed for the transmitter, but I'm getting there.

Jon

YUUUP!


--Shane
KD6VXI

(really tired of autospell screwing up my intended words.......)

Like Tom Petty says, the waiting is the hardest part.

Here's a 10 hour loop of Mission Impossible to kill some time...  :)

https://www.youtube.com/watch?v=FCO95esUzBw (https://www.youtube.com/watch?v=FCO95esUzBw)

...or more fun, 10 hours of Benny Hill

https://www.youtube.com/watch?v=8yoSM9G00b0 (https://www.youtube.com/watch?v=8yoSM9G00b0)

...and if you've watched that video, you REALLY need to watch this one!

https://www.youtube.com/watch?v=SKb_zHHNvY4 (https://www.youtube.com/watch?v=SKb_zHHNvY4)

Jon

The power supplies are all built.  The top is the 3 volt negative peak limiter supply, then 11 volts for the IXDD bus, and then 48 volts for the drains.  The drain voltage will get dropped a little bit by the Heising choke.  

Jon

The audio amp arrived.  It'll be on its own 120 volt circuit and the power supplies for the RF deck are on their own as well. 

I'm waiting on the Heising choke and I'm still building the sequencer.  Haven't gotten to the antenna yet.

Jon

The choke just arrived.  Now I just need to finish wiring the Heising circuit along with the negative peak limiter.  The series diode for the negative peak limiter will be mounted on the PVC cap in the picture. 

The two gold resistors are 50 ohms / 100 watts each.  In parallel they'll be 25 ohms and be connected between the "open" end of the Heising capacitor and ground.  The audio amp output will be switched into the circuit in a properly timed manner. 

I was actually disappointed when the choke showed up... I was hoping for something bigger.  Now this rig won't qualify for the Heavy Metal category.

Jon

Done.  I just finished the modulator and it appears to work very well.  I've set the carrier for 400 watts and I'm getting 1500 watts PEP when I do a "Helllloooo radio" in the microphone.  Everything sounds good in the headphones when listening to the direct RF pickup on the back of the transmitter.  I still need to tweak things a little bit, but the first test was good.  No smoke and it didn't blow up.  It doesn't take too long though before my MFJ cantenna gets hot.  More testing needs to be done with a real antenna.

And that's my next thing to do... I need to put up a 75 meter dipole.  I have all the stuff, I just now need to build it. 

So, barring any surprises, after I get the dipole up I'll be on 75 meters class E with a half decent carrier.

Jon

Jon,

  I have been watching your progress. I presume to make room for this rig that the dual 3-500z linear went bye bye?

I am sure I will copy you from Central Texas once the noise level drops.

Keep up the good work Jon. You inspire a lot of folks to get off their butts to build something.

I thank you for that.

Jim
Wd5JKO

Thanks Jim.

Yeah, both the dual 3-500 and the triple 3-500 amplifiers are gone. I'm just a solid state guy now. Not that there's anything wrong with tubes, it's just that I didn't want the danger of high voltage around with little kids.

I also pride myself now on not having typical amateur commercial gear around. Other than a few MFJ trinkets and an SDRplay, I'm all homebrew. I need the SDRplay though... I probably couldn't build a receiver if my life depended on it.

Anyway, the antenna will be up in about two weeks when I can get my hands on a tall extension ladder. It's going to be a fan dipole for 75, 40 and 20 meters.

Jon

You are right Jim....  Jon, keep up the good work, you have inspired me too.  I will be watching how you make out on your 40 meter rig.  I will probably follow your lead after I get the rig finished for the other two bands.  I understand 40 is a bit more of a challenge than 75 or 160.

I got off my butt and finally put together the WA1QIX three-board set: the PDM generator, PDM output, and the Overload/Efficiency boards over the past couple weeks. (I have had the parts in the zip-lock bags for over a year.) Am now waiting for shipment of the VFO and two-phase driver board.  

Currently doing the metal work for the power supply and modulator in one cabinet, and the RF section for 160 and 75 in another.  I am using a couple HP instrument cases, suitable for either desktop or rack installation.  

All the other parts are here, even the power transformer and filter capacitors.  I have a transformer that provides 88 volts RMS at 15 amps from an HP tape drive, and four computer grade electrolytics, 77,000 uF at 175 volts each.  I think two should be sufficient for one rig.  I will go with the tried and true 400 watt RF unit, using two modules of 4 FQA1190 FETs in each module.  I am building out the modulator to go a full gallon down the road.

I am recycling as much as I can from the old computers, for instance some massive heat sinks.  But for all the other caps, resistors, and solid state components, all new purchases.  I will post some photos once I finish the metalwork and start assembly.

...and of course, the associated YouTube video.  If you have 4 minutes to kill, here you go:

https://youtu.be/74LZiuD1qqQ (https://youtu.be/74LZiuD1qqQ)

Jon

One of those 77000uF capacitors will be sufficient !  I use 64000uF in a kw modulator/power supply.  Definitely use a step start in the power supply to protect the rectifiers and other components from excessive inrush current.

Thanks for the tip, Steve.  Yes, I definitely planned to include step-start circuitry.  The transformer does not have a secondary center tap, but it does have two primary windings with taps to allow the use of 120/208/240 mains.  I will switch the windings in series for tune, and parallel for operate, as you did in the class-H modulator schematic.

I am leaning toward a single RF unit for both 75 and 160, rather than two separate units.  From your documentation, I understand the need to switch in more shunt capacity with low-inductance connections on the relays for 160, but I have a question regarding the tuning capacitor.  Your 450 watt 80 meter RF amplifier circuit specifies 20-500 pf for c-tuning, with 5uh L1.  I wonder if you find that you use most of the 500 pf at the low end of 75 meter phone, or if this value capacitor is also sufficient for 160?  Being that the tuning capacitor is one of the largest components in the rig,  I would like to get it sized appropriately when I do the initial metalwork.  I would rather not have to switch in additional C for tuning 160.  Depending upon what components I have, it might be more practical for me to make two separate amplifiers, one for each band.  If I knew the output impedance of the amplifier with two modules of four FETs each, I could calculate the values, but I have no starting point or experience here, and your guidance is appreciated.  I did not find anything on your website that specified the c tuning value needed for 160, and if I understand correctly, your transmitter that switches between these two bands has four FET modules rather than two.  Thanks for your input.

I've used 1000pF (or more) for every RF deck I've ever built that covers 160.  You end up using pretty much all of it, particularly at the low end of the band.

In my 1kW rig at Rattlesnake Island, I have a 300pF fixed vacuum cap in parallel with 40-700pF variable.  Keeps the size a little smaller, and works great!

The more capacitance you have, the lower the voltage rating has to be (within limits).  I would not go over 1400pF on 160 and would not go over 750pF on 75 meters.

Steve, that information is very helpful, just what I was looking for.  Of course the impedances are much lower with solid state than with vacuum tubes (where most of my experience lies).  And we are working with a series resonant circuit here instead of the parallel resonant circuit common in the tube finals.

The capacitor I planned is definitely too small, but now I know I can build it with the right values to make a dual-band final.  I looked at your photos, and it is very ingenious the way you used braided cable with the shunt relays on 160 meters.  I am still studying all your documentation and photos, and learn and remember more each day.  Thanks again!

Oh yeah!  The dipole is up and I'm on the air on 75 meters.  I made the maiden voyage of this transmitter just now and talked with Billy in Tucson, N6YW.  He just piled on the compliments about the audio of this rig, and I don't think he was making it up. 

I took my liberty with old buzzarding, and the heat sink just barely got warm at 350 watts carrier.  I - like - it! 

My thanks to everybody here, especially Steve, for all the help and info to get this rig built.  I've probably clicked on the class E website an accumulated 1000 times, but I got there.

Jon

Hey, that's fantastic Jon!!  Nice work !  Looking forward to hearing it.

I don't know if you have one of the R.E.A. modulation monitors, but if you do, make a short transcript file with the rig transmitting (File -> Capture Audio and Modulation Data..)  and send it!  I'd love to hear and SEE the modulation.  If you do, I can post it for anyone who is interested to be able to download and check out.

As the year wears on, it should be possible to communicate between New England and your location at night.  Do this quite regularly to the West coast, and to people in AZ.

Thanks!  I'm hoping that I'll be able to hit the east coast with this.  I was 20 over in Idaho a couple nights ago, so things look promising.  My 75 meter dipole is an inverted V sloping dipole.  The apex is about 25 or 30 feet off the ground and the ends are only about 5 feet off the ground.  It's not great, but it's the best I can do at my house. 

I don't have a modulation monitor, but Christmas is coming!  I can throw it into my wish list along with Bose computer speakers... I'm high maintenance. 

I made one final touch to the modulator rack.  I added a Broadcast emblem from a 1950's or 60's RCA broadcast transmitter.  It's kinda cool.

Jon

...but, I can't wait for Christmas. I just ordered one!

Jon

John,

   I was on the Boat Anchor last night on 3870 from Texas. Definitely some "bad blood" between the Texicans on vintage SSB and the west coast AM'ers coexisting on the same frequency. I was looking for you last night from the Sedona, Az. SDR receiver. There was a huge group of AM'ers in there. Some of the Texan stations were pretty strong your way. The best I could do was make a faint 1 Khz tone if I keyed up on 3871 with 10 watts with my Flex.

Sedona SDR:
  http://w7rna.dyndns-remote.com:18901/

Jim
Wd5JKO

Hey Jim

I actually don't get on a whole lot.  But, when I got on a few nights ago, I was in QSO with Joe from Utah.  A sidebander switched to AM so he could talk to us and said that we were on the frequency that they used every night for an SSB group.  Joe said that we were there and wouldn't move.  The sidebander then said that they would talk over us, and the argument ensued from there. 

I made a comment that they were more than welcome to join our conversation by switching to AM, but they decided to move up in frequency.  My guess is that they wouldn't have been able to talk over us anyway. 

This could get fun though!  Maybe a 24 FET rig is the next project?   :)  Nah, I've got to go home tonight and put together my kid's backyard playset that just got delivered.

Jon

24 Fets would be good, but getting the antenna way up in the air will give you more of a boost !!  It really does make SUCH a difference !

Well Steve, I just got your modulation monitor and it works pretty slick!  I did a quick on-the-air check and I'm getting around 135% positive peaks and the negative never seem to get near 100%.  At quick look, the seemed to be limited to 90% or so. 

I'll send you a file sometime this week.  Right now there's an AM net on 3870, but I don't feel like jumping in.  Long story, but I'm tired... Just got home from work and recovering from my kid's birthday party over the weekend. 

Anyway, again, great product!  You sure can't beat the price either!

Jon

I made a short YouTube video showing a recorded CQ call using the transmitter.  Carrier power is 400 watts.  The audio is being played by my computer speakers.  Negative peaks never exceed 100% and the highest positive peak is somewhere around 150%.

https://www.youtube.com/watch?v=bp6JwcHdCHs (https://www.youtube.com/watch?v=bp6JwcHdCHs)

Jon