A Clean Canvas - 24 Pill Class E Rig Construction

[K1JJ]

Fabio's final tube exit temperature was about 84 degrees the other day. I figured it's time to build a rig for the summertime.

Here's my new flame named "Rico Suave." (Ree-co - Swa' vay)   Rico will be a 24 pill PDM class E rig.  I work on it a little each day. It all adds up. The RF tank circuit is now installed using vacuum variables and turns counters. He will have a sequencer, all full digital drive - even a digital VFO with frequency readout.

Rico will be self contained with everything in a 24" tall, 19" wide cabinet.   Of course, the guts will be viewable thru Plexiglas.

The heatsink in the front will house the PDM modulator MOSFETS. The rear heatsink is for the (24) 11N90 MOSFET RF finals.

I plan to have Rico Suave band switchable for quick 160M and 75M capability.

Pictures will be posted as he gets built and tested.  Most of the parts are on order.   See the PDM generator pictured below and the beginning of the PDM filter.  The vacuum variable caps are mounted on fiberglass sheet cuz the main tuning cap (C1) must float above ground. The coupling shaft for C1 is well insulated.  

The 4" hole in the front Plexiglas is so I can stick my hand in there to feel how hot the pills are running - and make occasional measurements, etc.

Notice the burn marks on the front heatsink. Those are the remains of my last 20 pill class E rig I built about 6 years ago... I jacked the HV up too high and paid the price. It did run FB for 9 months however....  

Wish me luck!

T

[KX5JT]

Excellent Tom!  You may consider 40 meters for spring and summer as I hope to stir up some activity on 40 and 20 meters. 

John

[KF1Z]

Neat stuff Tom.

But I wonder what all those big electrolytics are for?

[K1JJ]

Neat stuff Tom.

But I wonder what all those big electrolytics are for? 

To pad the rig for occasional 18 khz operation?      (The 5KVA power transformer is also located in the back, below the electrolytic caps)



BTW, Bruce, I understand you built one of the digital VFO's and the big blue readout ?   Is there standard documentation enuff to built one somewhere?   I could dig thru the E site, but thought you might have it posted handy somewhere...

[Todd, KA1KAQ]

Wow. It just looks so....so.....vacant compared to a Fabio or Dr Love. You know, you could've just gotten a Flex radio and joined in the SMUG.... 

Some comments you could hear:

"Nice cabinet, when's he gonna put a radio in it?"

"Did he paint it with invisible paint?"

"He needs to feed that thing some red meat"

"Plexi-King, my ass"

"Oh yeah - this is that kid who ran a Gotham vertical hyper-tuned with 3 feet of coax, it all makes sense now..."


All kidding aside, I'm sure you'll have fun with it, Tommy.  You always do.

[The Slab Bacon]

"I got a 24 pill! a 24 pill! And a muddy watta slappa! !"    


or, will it be Tom and Rico's most excellent adventure..................

[WA1GFZ]

Tom,
That inductor is way to big unless you plan to work 600M.

[steve_qix]

Hi Tom,

Looks like a good start!  You probably won't need too much of that inductor....  and it is more efficient to use 2 inductors than one.  Don't short out any turns under any circumstances.  With my rig, I use 2 inductors at 90 degree angles to one another, and short out the 160 meter coil when on 80 meters.  Anytime there are shorted turns, you get unnecessary heat and power loss.  You could leave the end "hanging out" for 75, but individual coils is much better.  You could also put the inductors one above the other and that would work as well.

Suggestions:  Don't provide any ground paths from the power supply to anything other than the modulator heat sink.  Create a single, contiguous ground plane with the modulator heat sink and the filter ground (extend the heat sink if necessary with a piece of stiff aluminum), and build the filter over this with all PWM filter capacitors tied into this ground plane.  Doing this will minimize "coupling around" the filter through the ground.

Are you interested in an experiment?  You could use magnetics rather than air would inductors for the last 2 inductors in the PWM filter.  Now, if you did that, you would need to break the filter into 2 paths following the first input inductor.  Yes, it would most likely be possible to construct a single filter using magnetics, but the current is quite high under heavy positive peak modulation, and the filter must be designed around this, and not the carrier (unmodulated) DC current.. Stacking cores does not double the current, and I fear you be stacking many of them to create a single-path filter.

So, you would have an air wound input inductor of some (relatively small - maybe 12uH) inductance as the input inductor, and then break out into 2 paths.  Each filter would serve 2 modules.  You would significantly reduce the size of the filter.  Magnetics has a new material called X flux, which is just about as good as Hi Flux, but is quite a bit less expensive.  I have 24 of them here for my next transmitter, which will use an air core inductor as the input and magnetics for everything else.  The filter will be very small as compared to using air for everything.  Just an option I though I'd mention...

[w3jn]

Tom, with that big rig I'd tend towards an analog L/C VFO instead of a DDS...  I built one of the N3ZI DDS kits and I'm not too thrilled with the phase noise performance.  I don't have anything here to accurately measure phase noise, but I hooked it to my Agilent service monitor and it's sayin there's a 500 Hz or so FM deviation on the signal.  Compare that with a 6BQ7 Franklin VFO I whipped together for a HB RX project, the Agilent sez 50 hz FM deviation.   Course the voltage out on the 6BQ7 VFO is a lot more, but I can certainly hear the noise difference when listening to both in a RX.

Otherwise the N3ZI kit is quite nice and simple.

[steve_qix]

Here is a picture of my pulse width modulator that modulates the same transmitter you're building.  This one uses air core inductors.  The PWM output section is visible mounted on the heat sink, and the overload shutdown board can be seen to the right, above the large knife switch.  The overload board is not mounted to anything other than the heavy wires going in and out, which are more than sufficient to hold the board in place.

The heat sink surface was extended with a piece of aluminum, and the filter constructed over the resulting ground plane.

[flintstone mop]

Will this turn into a TV series with the love life of Fabio and Dr Love and who is the new kid on the block?

Phred

[K1JJ]

OK, Johnny, on the digital phase noise. I wonder if Bruce or Steve have measured the noise on these VFOs?  I haven't studied it all yet, but intend to soon.  If need be, I could easily go with an analog watt or so from my ricebox as RF drive for the new digital drive board, if need be.

Steve, I will probably stick with the air PDM coils simply cuz that's what I am most familiar with from the last PDM E rig. I do like your idea of mounting the complete filter on the heatsink/ groundplane of the PDM modulator.

Yes, the tank coil is too big. I figured I wud tap it (not short it) for both 160M and 75M and see where it worked out. I can easily cut the coil and shorten it later.  I have bigger 3/8" coil stock too, but thought it wasn't enuff for 160M.  I still need to know what the approximate inductance will be on 160M and 75M??

Frank, the new PDM driver board requires a 12V pulse out of the PDM gen. My old Rev C board puts out 5V. Maybe you have a simple chip/circuit I can add to amplify it to 12V?  I don't want to have to build a new PDM gen just for that minor issue.


It's good we post our thoughts and solutions here to make this an ongoing construction project. Putting it all together is not easy the first time through and this will help others who are on the fence.  This project is somewhat overwhelming when looked at overall, but when taken in small chunks it can be digested.  


Just axe Rico Suave.  (Ree-co    Swa'- vay)

T

[WA1GFZ]

Tom, An IXDD414 would make a great level shifter and easily drive a long cable. Plenty of drive so you could terminate the far end at 50 ohms so there is no ring.
Short run you could use a smaller clock driver 4427 I think is noninverting.
You will be a lot cleaner with a solid ground system under the whole modulator.
This way you don't have high frequency currents floating around the cabinet.

[KF1Z]

Neat stuff Tom.

But I wonder what all those big electrolytics are for? 

To pad the rig for occasional 18 khz operation?      (The 5KVA power transformer is also located in the back, below the electrolytic caps)



BTW, Bruce, I understand you built one of the digital VFO's and the big blue readout ?   Is there standard documentation enuff to built one somewhere?   I could dig thru the E site, but thought you might have it posted handy somewhere...

Nope, not me...
I use Steve's hartley, and NO readout..
I don't need one, as I use an SDR reciever...
Just hit the spot button, and tune by sight.

 

[KF1Z]

Tom, with that big rig I'd tend towards an analog L/C VFO instead of a DDS...  I built one of the N3ZI DDS kits and I'm not too thrilled with the phase noise performance.  I don't have anything here to accurately measure phase noise, but I hooked it to my Agilent service monitor and it's sayin there's a 500 Hz or so FM deviation on the signal.  Compare that with a 6BQ7 Franklin VFO I whipped together for a HB RX project, the Agilent sez 50 hz FM deviation.   Course the voltage out on the 6BQ7 VFO is a lot more, but I can certainly hear the noise difference when listening to both in a RX.

Otherwise the N3ZI kit is quite nice and simple.

The N3ZI DDS is nearly useless....

Noisy as h*ll, and you still need a follower amp to get usefull levels..

My O-pinion.

The NORCAL kit was much better...
But until they get off their year long vacation... those kits are unobtainium.

[K1JJ]

OK on using the IXDD414 Frank for the PDM gen leveler.  I'll order one and install it.

Guess I'll stay with an analog VFO then, Bruce. I guess it was Wayne/SSJ who just built one as well as Steve.



I was just looking to pimp my new digital ride a little:

[KF1Z]

OK on using the IXDD414 Frank for the PDM gen leveler.  I'll order one and install it.

Guess I'll stay with an analog VFO then, Bruce. I guess it was Wayne/SSJ who just built one as well as Steve.



I was just looking to jazz Rico up a little:

No they didn't Tom....

They bought "sold for CB" type frequency counters, with the big blue displays.
To go with the Hartley oscillators they built.

[w3jn]

Hey Tommy, I've been messing recently with Franklin VFOs.  By far superior to any Hartley or Colpiss I've ever built.

It has two advantages - you can bandswitch easily since the tank only has two terminals - one goes right to ground with no funky taps  (L or C) for feedback.  Also it's very stable due to the very light coupling from the tank to the active elements.

The 6BQ7 VFO I previously mentioned achieved <50 hz/hour drift with no temp compensation tricks.  You can build one just as easily using JFETs.  Use one of those cast aluminum boxes for rigidity...

BTW did you ever get that package I sent ya a while back?

[K1JJ]

Bruce, OK, I see.  So they went analog for the VFO itself. When Steve mentioned, "all digital drive" I assumed he meant the VFO too.  I'll stay with the ricebox "VFO" drive then since I use it for everything else.

Johnny -  Yes, I got the package, but sorry, can't remember what it was. Was it a CD? I've had trouble wid my CD player and couldn't play it if it was...  Tom Vu get thousand of package a day from well-wisher, so you understand...

T

[steve_qix]

Hi Tom,

The oscillator itself is a hartley and everything else is digital.  I find it far preferable to using a rice box for a variety of reasons, not the least of which is simply ease of switching and much lower heat generation.  Rice boxes (at least all the ones I've seen) get quite warm, even in receive.  And, you tie up a whole multi-function piece of equipment just for VFO service..... and there's the human error factor (power up too high, not selected, etc. etc. etc.).

On the PWM generator, you could use an IXDD414 and it would work quite well.  Here is the output circuit from REV D of the PWM generator.  The output of the PWM generator chip is fed (in 12V mode) directly to a complementary pair of transistors (a 2n3904/3906 pair).  I have about 8 feet of 50 ohm coax between my PWM generator and the PWM output.

[steve_qix]

Hey, Tom - I would like to come to your shack the day you are ready to fire everything up    Can also go over a whole lot of things.  Always fun to see a new rig being "born" 

Then sushi afterwards !

[w3jn]

Was 4-pack of DVD roms Tom

[N3DRB The Derb]

here's the official music video to Tom's rig:

http://www.youtube.com/watch?v=xeX9zoWSut8

I should do a mixdown of this , bet I get plenty of LOL's.  

Then sushi afterwards !

then a ambulance ride! get down! 

[Steve - WB3HUZ]

I eat it raw, like sushi.   

[flintstone mop]

Tom, with that big rig I'd tend towards an analog L/C VFO instead of a DDS...  I built one of the N3ZI DDS kits and I'm not too thrilled with the phase noise performance.  I don't have anything here to accurately measure phase noise, but I hooked it to my Agilent service monitor and it's sayin there's a 500 Hz or so FM deviation on the signal.  Compare that with a 6BQ7 Franklin VFO I whipped together for a HB RX project, the Agilent sez 50 hz FM deviation.   Course the voltage out on the 6BQ7 VFO is a lot more, but I can certainly hear the noise difference when listening to both in a RX.

Otherwise the N3ZI kit is quite nice and simple.

NOT good to read this, John. I built the N3ZI DDS to be a VFO for a Class D TX. Would this shift be heard over the air? Or wuld this be unacceptable as a L.O. in a RX?
Also reading feedback from others here who have built the N3ZI. Noisey and not enough ooomph???  Norcal still hard to get?

Good vid Tim
FRED