Re: Tesla Receiver Coil ..........success?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Ed Phillips <evp@xxxxxxxxxxx>

I have a few questions about your beacons.  First is your call sign 
still IZJ out of California?  Also, have you been awarded a license 
to run a 2200 meter (135.7-137.8 kHz band) station under Part 5 rules 
or are you considering filing an application for same?  Can you tell 
the list a little bit about your present LF transmitter?  Is it 
crystal controlled or PPL?  I assume it's a solid-state 
transmitter.  What solid-state device does it use? Is the output 
waveform to the antenna a squarewave?  If so, do you think your 
transmitter could be used as a solid-state Tesla coil driver?  As for 
transmitter power, how do you measure the input to the final stage in 
order to comply with the one-watt restriction in this regard?  And 
finally in regards to your antenna, I notice your article "Lowfer 
Antenna Introduction" at 
http://www.fix.net/~jparker/curry/1750mtb.htm has been removed from 
the web.  Is it available elsewhere?  Do you prefer the buried ground 
plane, the fully insulated counterpoise elevated on supports, or 
something in between? What size wire do you use for your loading 
coil? and what are the coil form dimensions and material.  What do 
you use to tune your LowFer antenna?


> Gary

Gary:

   That's awhole bunch of questions!  When it's On IZJ is the sign 
of my 181.167 kHz beacon.  It's been off for quite a while because it 
fouls up all the WWVB clocks in the house and besides I hadn't gotten 
a report (except from Dave) for years.  I have no plans to do 
anything under Part 5 as I have a lousy location here.  The antenna 
is the same modified HyGain "High Tower" I use for 160, 80, and 40 
meters; it stands on 12 Mycalex insulators (3 groups of 4 2" 
square).  It's 50 feet high in total and, because of the taper from 
bottom to top, has an effective height of less than 25 feet so my 
signal was never a world beater.  I heard it as far as San Diego and 
Mike Mideke always heard it at his place, but of course he could hear 
anything!  There are at least three problems with the radiating 
system.  First, the tower is over a 10 foot strip of very dry soil 
between the house and the driveway.  Second, it is between two close 
oak trees which seem to soak up quite a bit of energy although I 
can't prove it.  Third, I have a very high ground resistance, of the 
order of 20 ohms are more.  Taking all that together there's not much 
point in trying to do anything more and I really have no antenna options.

   The transmitter is solid state and was built in 1976 and modified 
a bit later.  Uses a crystal oscillator at 32 x the output frequency, 
a CD4024 divide by 32 circuit, a CD4007 buffer amplifier driving four 
Siliconix VN66AF "power" fets.  The output stage is driven with as 
1/4 cycle rectangular pulse and is closer to Class C than anything 
else; it is pretty efficient as none of the output transistors has 
ever been warm to the touch no matter how much power I've 
run.  Originally it use a single Siliconix VMP-1 but I accidently 
blooied that and went to the VN66's instead, which work almost as 
well.  Power output can be between a watt and over 10 watts, but I've 
usually run it at a couple, rationalizing with my conscience based on 
the lousy antenna system.
Cliff Walker and I made several transmitter kits and gave them to 
guys but I don't think any of them ever got on the air.  Jack 
Althouse of Palomar also kitted a transmitter using the same 
schematic but packaged in such a way that it generated RFI from DC to 
light.  The output is inductively coupled with the primary coil the 
tank circuit of the transmitter.  It is tuned with 0.08 ufd of 
polystyrene capacitors and stuck down below the loading coil and 
arranged so I can move it up and down to change the coupling.  I 
think the antenna current is pretty well a very clean sine wave as I 
don't see much harmonic radation when I get beyond its immediate 
vicinity.  The power supply to the final is adjustable from about 3 
volts to 15 volts and normally runs about 8 volts at two watts input.

   The antenna capacitance measures to about 450 uufd and the 
loading coil is a surplus bank wound-litz coil about 5" in diameter 
and 6" high.  It originally was apparently intended as a dummy load 
because it came with several pounds of very lossy powdered iron slugs 
in it.  When I took those out I got an inductance of about 2 mH 
end-to-end; Q measured about 450 at 200 kHz.  I picked a tap point 
which was a bit lower than needed for resonance and have a small 
variable capacitor across a tap down the coil to tune it; tuning is 
surprisingly sharp.
Not an efficient way to go but the ground circuit loss dominates so 
who cares?  I have a 500 ma TC ammeter to measure antenna current for 
tuning.  The total measured antenna circuit resistance is about 40 
ohms and the antenna current runs between 200 and 250 ma depending on 
how wet the insulators and the foliage on the oak trees happen to be.

   That article was written long, long ago when I used a TRS-80 
Model 1 and any copy is left on a 5.25" floppy which I can no longer read.
There is probably a paper copy around somewhere because at one time 
Mike M published it along with some of his material.  Nothing really 
exciting in there but if I can find a copy I'll scan it and mail it to you.
Basically says that the ideal antenna would be a small diameter 
vertical with a big flat top, working against a low-resistance ground 
and with a very high Q loading coil.  No surprises there but a lot of 
guys were trying to put a transmitter on the air with no loading coil 
or such nonsense!  I figure if they didn't know better no magazine 
article would help them but I still put it together when Mac McIntosh 
was trying to get editorial material to fill the Lowdown.  I did 
include some copies of diagrams from 1910-1920 "Wireless Manuals" 
showing different antenna installations which were good then and 
would be equally good now.  Some of those guys in "the good old spark 
days" really appreciated good antenna design, even going to the point 
of flat tops strung between 200 foot towers and a giant elevated 
counterpoise system at roof-top level.
No one (or I should say no one except some of those Part 5 guys) 
would go to that much trouble.  For tuning the works I'd make a 
variometer as part of the loading coil.  That works very well and 
it's easy to keep the Q high.

   As for what I'd favor, that's another matter.  I'd like to have a 
50 foot array of top-loading wires fed by a vertical wire and using a 
good high Q loading coil.  For ground I'd like a set of radials 
buried just deep enough that they would get caught in people's feet, 
or else an elevated counterpoise which would be impossible for most 
of us to install.  To do all that would take a dedicated space of the 
order of at least 75 feet on the side and I just don't have it.  Some 
of the "big boys back east" do.  As I think I mentioned Sunday Dave 
has an 87 foot tubular crankup tower and dangles a wire from the top 
for his lowfer antenna.  I can't remember but I think he's using a 
variometer for tuning, in series with a big loading coil.  I got him 
off on variometers when he first got started and he's liked them ever 
since.  They only have to be adjusted occasionally so no fancy shaft 
arrangement or bearings are needed.  Main thing is, if it's mounted 
outdoors, to keep it completely dry!

   If you work out the useful Q for a system with the poor grounds 
most of us are stuck with you'll find out that it doesn't take an 
exotic loading coil to give better than 90% efficiency.  Building a 
great big coil is fun but probably a waste of time for most of 
us.  I've wound some 6 mH loading coils for TV pushup masts (about 
120 uufd capacitance) on 5.25" cardboard mailing tubes, sealed with 
shellac, and get Q's of the order of 350 or so, plenty good 
enough.  Somewhere I have some calculations I made for different 
antenna capacitance and ground circuit resistance which convinced me 
that a Q much of 300 was a waste of effort, except for those with 
pride in craftsmanship.  The use of ferrite cores is always a 
possibility but it takes a lot of area to avoid saturation and I've 
never tried it.

   Not sure if I answered all of your questions, and probably none 
to your satisfaction.  I would point out that, at least at this QTH, 
there has been a very serious compromise between theory and practice, 
in favor of the latter!

Ed

   I'm attaching a picture of the transmitter.  Notice that it's 
sitting inside the house and the antenna lead is the  center 
conductor of some RG-8, run about 4 feet to the base of the 
antenna.  I have a lot of pictures of the antenna somewhere but don't 
think they'd interest you.

http://hot-streamer.com/temp/WHOLE_STATION.JPG