A Clean Canvas - 24 Pill Class E Rig Construction

[w3jn]

You can use FETs for the Franklin oscillator, Tom.  The big advantages are (a) very light coupling to the tank so the drift is focused there, not in the active devices and (b) one terminal tank (one end grounded) making bandswitching really easy.

I think your "A/D converter" isn't really an "A/D converter" but rather a Schmitt trigger that just squares off the sine wave.  A real A/D converter will convert a voltage into a binary number representation.  No reason I can see for that in a class E xmitter.

Anyway, if you use a good Schmitt trigger (74AHS series is one) you won't notice the phase noise, particularly since you're dividing by two.

Skizmatic:  http://homepage.eircom.net/%257Eei9gq/lo.GIF

[K1JJ]

Thanks for the schematic, Johnny.

I printed it out and it's on my list of thangs to do for now.

The "A/D" converter is a phase splitter to drive the two p-p RF modules.  I don't know how the sine to square wave conversion gets done until I get a schematic from Steve/ QIX.

As alternatives, I have an old tube Collins PTO I may convert over to an FET.  Or, if anyone knows of a analog VFO kit out there, let me know.

T

[K1JJ]

Here's what the RF deck looks like all wired up.  Pictured are (24) 11N90 RF Mosfets driven by (eight) smaller  IXDD414 drivers.    Full digital drive.  I need to build up a VFO yet.

The rig is maybe 65% finished.

T

  

[KF1Z]

Tom,

Here's Steve's  VFO circuit...

It is Hartley vfo, into 74ac112 Flip-Flop that squares off the sine wave, into 2 phases 180 deg .

Then there is adjustment for duty cycle of those square waves...

Just what you need....

Or, you can get Steve to send you the newer schematic....

But I still use this one in my own rig, and works fine...

http://classeradio.com/vfo_2_band.pdf

[w3jn]

I can see some room for improvement with the oscillator.... I wouldn't tap directly off the tank to the buffer amp with that 8K resistor, nor would I use a twisty gimmick for the coupling - that's begging for some mechanical instability.  The strategy of using min coupling to the tank is sound, but a 10 pF or so trimmer solidly mounted would be a definite improvement, as would coupling from the emitter of the oscillator transistor to the buffer.

THe most important thing is using good components in the tank, though.  Air-dux or B&W stock (as heavy a wire as you have) is great.  A high C/L ratio works best for stability.  Minimize the trimmer capacity as much as you can, they're another source of drift.  Use good quality fixed polystyrenes instead and connect the tuning cap to various coil taps until you get the tuning range you need.  A 10 pF N750 disc cap in parallel with the tuning cap will help knock out any residual drift.   I didn't need any temp compensation in the Franklin I built using a 6BQ7 - and I got a good 20 volts of RF outta the thing at 100V B+.

[K1JJ]

Johhny and Bruce -

Ya know, I actually have an old Collins tube PTO that I replaced with an FET.   I modified it to tune 3.5 - 5.5, but cud change it to 7mhz easily.  I shud use that little battle ship as the core and add a buffer stage to that.

I checked it out the other day and worked FB.

T

[WD5JKO]

Tom,

   That VFO since it runs 7-8 Mhz continuously is a natural for a "Huff & Puff" VFO stabilizer. There are many H&P discreet circuits, but to me one stands out, and that is the X-Lock 2.0 from Cumbria designs.
This is a PIC based H&P which will lock your VFO to a +/- 10 Hz window. The cost is about 20 Euros.
It samples the frequency and then creates an error voltage to correct the frequency with an AFC like control circuit. The kit uses an LED as a varicap to use with solid state oscillators.

      I use one on a tube VFO which works very well for me. With a tube VFO it will be necessary to have good regulation of the B+ and filament voltage. I use dual 1N4005 diodes as 'varicaps' which work very well without VFO rectification.

      The links below take you to the Cumbria Design web site, and to what I did to make this X-Lock work with a Lakeshore "Band Hopper" 5-5.6 Mhz VFO.


       Once you try X-Lock, you won't go back. This H&P is that good.


http://www.cumbriadesigns.co.uk/x-lock.htm

http://pages.prodigy.net/jcandela/Band%20Hopper/

Jim
WD5JKO

[w3jn]

Be careful with these huff-n-puff circuits though.  You can't use 'em to polish a turd.

If the VFO drifts to the point where it's outside the ability of the loop to maintain lock, it's gonna go spinning into orbit and probably suddenly jump a couple KHz or more.  With a RX you can tell when this happens.  Not so with a transmitter till you turn it back after your old buzzard and everyone's laughing at you.

I find it easier just to do it right in the first place... but if you get the VFO drift within reason one of these circuits will make it rock stable.

I have a receiver with this feature (a Sylvania R-1414, as well as a HP 8640B with the same arrangement) that use the 100 hz digit off the freq counter to maintain lock.  I wasn't at all impressed - you hafta unlock it before you tune and if it's locked on the edge of its tuning range, it'll lose lock with the attendant frequency jump.

[steve_qix]

I can see some room for improvement with the oscillator....

That's a fact    But, by the same token, the oscillator works very well and is amazingly stable as long as you're not bouncing it over a bumpy road     The thing that might be helpful would be temperature compensation.

I went for K.I.S.S. ; reliable and simple.  But, there are better basic oscillator circuits out there....If you want to do the extra work! 

Regards,

Steve

[w3jn]

I haven't tried that Franklin with the FETs I posted, but the one I made with a 6BQ7 was by far the most stable VFO I've ever made.  No temp compensation either.  About 100 hz drift from turn on, and about 5 min later 10 hz/hour drift.  You can knock the thing on the table and it'll shift about 100-200 hz - mostly because of the bigassed airwound coil.

Mebbe I'll mess with it this weekend and build one up.  I'm not a big fan of the Colpiss anymore...

[Opcom]

That RF stage is slick. Gonna make all the keyclowns cry.

[W1IA]

Here's what the RF deck looks like all wired up.  Pictured are (24) 11N90 RF Mosfets driven by (eight) smaller  IXDD414 drivers.    Full digital drive.  I need to build up a VFO yet.

The rig is maybe 65% finished.

T

  

Fine work Mr. VU!!!!

[K1JJ]

I've decided to add a VFO to the rig.  Instead of driving Rico Suave with a ricebox, the VFO will be used with a divide by 2 digital circuit and a phase splitter to drive the class E RF finals.  A ricebox is prone to key up spikes and full power mistakes that can blow out the RF fets in a microsecond.  The low level VFO circuitry as shown below is more controlled and stable as a driver.

It was not an easy task to get the unit mechanically stable. The first variable capacitor I used had a mechanical resonance and had to be replaced.  There is also a fine tuning capacitor.  I plan to add a frequency counter to the output.

Tests show the unit to be very stable and drift is less than 10hz over a 10 minute period. I can also push and pull on the cabinet and the frequency barely moves around.   With the divide by 2 for 75M and divide by 4 for 160M, it will be even more stable in all aspects.

I still need to add the digital divide / phase splitter board into the next compartment. The VFO is fully shielded from the digital board and outside whirl.

This should be a nice addition to the new rig and make it completely homebrew from VFO to antenna.


I've posted the schematic for those interested.

T


Picture #3:  

Top - VFO  
Middle - PDM Modulator    
Bottom RF Deck

[K1JJ]

VFO and splitter/ digital driver schematic-

http://www.classeradio.com/vfo_2_band.pdf

[WA1GFZ]

I find the huff n puff in the HP8640B a problem that adds to phase noise. Much better to let the generator warm up for a 1/2 hour so it is stable.

[KF1Z]

VFO and splitter/ digital driver schematic-

http://www.classeradio.com/vfo_2_band.pdf

Tom,

That is NOT the schematic of the board you're using.

bruce

[N3DRB The Derb]

only huffin an puffin going on will be when that things keyed down on the channel.

how about a built in SBE warbler - push a button and the vfo strobes about within about a KC range - would drive slopbuckets kray zee     but nobody on am would notice unless they have a sync detector, then you'd drive them kray zee too.  

[K1JJ]

http://www.classeradio.com/vfo_2_band.pdf

Tom,
That is NOT the schematic of the board you're using.

bruce

Hmmm.....  let me check into that, Bruce. Thanks.

T

[w1vtp]

only huffin an puffin going on will be when that things keyed down on the channel.

how about a built in SBE warbler - push a button and the vfo strobes about within about a KC range - would drive slopbuckets kray zee     but nobody on am would notice unless they have a sync detector, then you'd drive them kray zee too.  

Yup - my sync AM does NOT work on Timtron's SBE -- gotta go regular AM and go wide.  Then it ain't half bad

Al

[K1JJ]

VFO and splitter/ digital driver schematic-

http://www.classeradio.com/vfo_2_band.pdf


Tom,

That is NOT the schematic of the board you're using.

bruce

Bruce,

Yes, the present splitter board I have is set up for a ricebox.

But it can be configured for a VFO as shown in the schematic.

The board doesn't include a VFO which I already hand wired and is working FB.

T

[KF1Z]

Tom,

Yup, just wanted you to be aware that the board I sent you does not go with that schematic...

Though the VFO section (only) of that schematic CAN be used with the board....

We all built that circuit up completely dead-bug, or perfboard style.

Works ok-fine, hi-hi, fb, om...   

[K1JJ]

We're progressing slowly but surely.

Here's the red PDM filter for your viewing pleasure.

The inductors are 28.8 uh, 28.8 uh and 14.1 uh.   I measured them using a signal generator and scope - put a cap across the coil and found the parallel resonance point. Very accurate.  Thanks to Jay, W1VD, for modeling the values for this "infinite impedance" PDM filter for me. In simulation it appears to have excellent ripple characteristics.

Notice the positioning of the coils so that they are all at rights angles to one another. This will keep coupling small and the filter will have good isolation.  I could always add shielding if needed later.  The coils each use #6 wire for good Q. The aluminum ground plane below is important as well as the distance each coil is from any objects. (At least one coil diameter.)

The coils are wound on 4.5" PVC pipe and have a good length to diameter ratio giving optimum Q.

I will need to build a second PDM filter, a duplicate of this one, if I plan to add on and make this a 48 piller later...

T  

[N3DRB The Derb]

I wish I was not as indoctrinated and set in my ways as Mr. Vu. When he builds he just rolls it and straps.

I kept my racks and my big plate iron, let em cool off for a year or two and maybe I'll hire a machine shop to cut my stuff and start up again. On ice for now. I need to operate and have fun on the air for a while. 

[K1JJ]

I wish I was not as indoctrinated and set in my ways as Mr. Vu. When he builds he just rolls it and straps.

I kept my racks and my big plate iron, let em cool off for a year or two and maybe I'll hire a machine shop to cut my stuff and start up again. On ice for now. I need to operate and have fun on the air for a while. 

Yep, "operate and have fun on the air for a while."  I'm not sure I've been keeping to that 2010 resolution lately, Derb...

Lots of this building is right on my edge of abilities and understanding. So, I learn a lot and get stretched all the time. I'm always sending out emails looking for advice from the gurus here...

So, likewise, you're doing what you can there and the big iron you have coming soon will be a great filler for operating while you decide what to do with your homebrew stash of parts. A mix of both is good. Once you get a big mawl on that sounds really good (Raytheon) the pressure will be off and you can slowly put together what you want at a leisurely pace.

I know the Derb BJB will be back in FB form to strap the summer static - soon.

T

[WA1GFZ]

Nice filter layout Tom. (Nice to see layouts that don't look like they fell off the back of a cow.)
Keep an eye on temperature rise with the caps you might need more lower values in parallel.