Need Help Designing PDM Switching Filter for 4X1 Rig

[WA1GFZ]

Tom,
Why not get a number of different tubes 8,6,4 ,2 inches and build multi layer with a good space between layers. I bet that would work. Steve wound his with layers of wax paper between layers to keep them smaller.

[WA1GFZ]

BTW #26 700 ma and #23 1.4 amps. Current doubles every 3 wire sizes.

I wound your pdm coils out of high temp insulation enamel #26.......that is why they fused. (spec change after CDR to QRO)

[K1JJ]

Tom,
Why not get a number of different tubes 8,6,4 ,2 inches and build multi layer with a good space between layers. I bet that would work. Steve wound his with layers of wax paper between layers to keep them smaller.

Hmmmm... now that's a very interesting idea, Frank!  Steve saw problems with the thin wax paper spacing, but maybe with a BIG 1" space between runs it would work. [or maybe even 2" spacing....   4", 8" and 12" tubes.   The form factor will go to hell though. It will be a diameter to length ratio of like, 10:1 ++,   instead of a nice 2:1 or less for higher Q. But maybe the pulses won't mind like an RF tank circuit would.

Do you wind the turns in the same direction each time, ie, run a lead back to the beginning and start again, or does it matter?

I also wonder how the coils affect each other to reduce or increase the total inductance. Though, I'll probably simply resonate the completed coil with a cap to determine it's final inductance anyway.

OK on the current ratings of the wire sizes. Well, looks like I better stay wid #22 insulated wire to have a decent safety factor.

BTW, I was reading about construction of big Tesla coil and these guys coat the enamel wire of the completed coil with many coats of Polyurethene. They coat until the surface is smooth and flat.  I wonder if this may be a good idea to keep the turns in place from the tug and pulls of chaotic operation ?

T

[WA1GFZ]

You wind everything in th esame direction or they will buck. Yes Steve had to limit the number of turns per layer. Your form factor would improve if you sleeve the inductor as the values of each layer would add. I remember Steve later made a wood form fron 1X2s about 14 inches od and did it on 1 layer.
You could get some of those Home Depot fiberglass rods and mount them in a circle and wind over them ?? Coating just adds more insulation so can't hurt as long as the coating isn't conductive or absorbs moisture. Humiseal absorbs moisture big time.

[K1JJ]

You wind everything in th esame direction or they will buck. Yes Steve had to limit the number of turns per layer. Your form factor would improve if you sleeve the inductor as the values of each layer would add.

Yes that makes sense, wind them in the same direction or they will tend to cancel and buck... tnx.

Please explain form factor with sleeving...  Let's say you have two 12" long coils that are 12"  and 10" in diameter. One alone would have a form factor of 1:1.  Lets say you slide one into the other and put them in series, electrically. Are you saying the form factor is STILL 1:1 or now 2:1?

The Q of the coil is best when the form is 1:1, right? And Q deteriorates as form moves above 1:1 or more I understand.

I was thinking if the "EFFECTIVE Q " form factor increased, then it would be better to  build the sleeves as large in diameter as possible. Like 16", 14" and 12" diameters,  all 15" long, sleeved together to give 62 MH -  might do the trick, and the whole thing would be reasonably compact.  I'll play around with the coil calculator to see what I come up with.

T

[w3jn]

I sold almost all of that wire, Tom, all I have left is a few rolls 100' ea of hookup wire as well as a shitload of ribbon wire.  How about an inductor wound out of ribbon wire?

Are you wed to 100KHz, Tom?  Higher the freq the smaller the inductors and the spurs will be further attenuated by the final tank.

73 John

[K1JJ]

I'm not sure why the godfather chose 112 kc for the class E FETs or made the older PDM generators for tube rigs down around 90 kc.  I'd agree it sounds like an easier solution for smaller coils or better specs to run it up over 200Kc or so.  I did axe him once but forgot the answer.

It's easy to ramp up the speed with the new chip... just a cap change I think.

Anyway, what do you think, Franz?  Would other things start showing up like unwanted coupling, ratty pulse shaping or something undesirable at higher speeds? Would I have to talk faster to keep up?


T

[WA1GFZ]

at 100 KHz you need a 100  ns pulse for 1 % modulation. The faster you go the harder it is to produce clean modulation at low modulation levels. Then there is the N9NEO phasing method but I don't suggest you try it at 7500 volts unless you grow a third BA.