This is some additional information
about my outside SS-Tran installation
that was built in 2007. It was my
different kind of approach to the
3 meter antenna loading coil issue.
This is some additional information
about my outside SS-Tran installation
that was built in 2007. It was my
different kind of approach to the
3 meter antenna loading coil issue.
I opened a section in the circuit
board of my SS-Tran AMT-3000 and
took out one of the internal loading coils.
(The one that tunes the transmitter
to the lowest part of the AM BCB.)
I hooked up some wires to that empty
space and ran it out to an external
coil. This coil is a much larger coil
with much higher Q than the coils that
were in the transmitter. (If you try to
do this somewhere down the line, you do
so at your own risk. It was not easy
for me to make the mod.)
Anyway, this external coil worked
very very well with the AMT-3000.
This coil had been lost for 3 years. I
found it in my backyard a couple of weeks
ago. I had never written down the coil's specs
so I thought I would present them here.
Using this coil, with the transmitter on the
ground, and with a 16 radial ground system,
the transmitter was heard weakly, but clearly -
two miles away. This was on the car radio on
1690 kHz, in a doctor's office parking lot.
Again, we have seen that a Part 15.219 (TX on the
ground) installation has peaks and nulls within
the coverage area. But at this particular point,
2 miles away, the signal was there and you could
listen to it without straining your ears. (It is
a good car radio, though.) It is worth noting,
however, that on another day - I was out at that
doctor's office again, and could not hear my
station. The ground conductivity (or something
else) must have changed.
Anyway, I wanted to tell you about this coil,
because I couldn't even remember everything
about it. I'm sure it's not perfect, but
its specs are worth noting here.
The coil was wound on a piece of PVC pipe from
the local hardware store downtown. It's green
PVC (whatever that means) and it is 4.25 inches
in diameter.
The wire appears to be #22 or #24. The conductor
is stranded wire. I wound 38
turns on the coil form. I attempted to put a
slight amount of space between the windings.
I can't believe it's only 38 turns. I keep
counting it over and over. Well, maybe it's
37. It's hard to tell. (The coil is a little
messed up from being out in the backyard for
3 years.) The windings cover about 3 inches
from the top of the coil form down toward the
bottom.
Because this was an experiment, I put a tap on
EVERY TURN. Yup, you can laugh because I'm laughing
also. I know that taps hurt Q, but that's what I did
back in 2007.
I took the transmitter outside, and put it on the
ground. It was set up very much like Neil's recent
outside test installation with the
Class E (or almost Class E?) transmitter that he
designed and built. Except to start, there were
no ground radials. (As many of you know, 16 radials
came later on. As these radials were added, the
transmitter range went from a questionable amount
to a large area.)
I got everything running and tried all of the taps
on the coil. Using a $20 CB/ham field strength meter,
I looked for some kind of peak. Many of you have
heard this before. There was only a small peak on
one particular tap. This tap was about 19 or 20 turns
down from the top. A wire on this tap went to the
transmitter circuit board. The last turn on the
TOP of the coil went to the transmitter circuit board
as well. The bottom turns on the coil were not connected
to anything, but I left them there. Even though they
were not connected, they were still part of the coil
from an RF standpoint. I made no attempt to remove
them.
As mentioned, I only was able to get a very small RF peak
on one coil tap. I didn't know what to do. So I tore
apart an old radio and retrieved a large "ferrite bar"
and decided to try to tune the coil with that.
Luckily, this actually worked. I inserted the "ferrite
bar" into the coil and suddenly I had a large RF peak.
What a surprise! Then things went on from there.
In discussions along this line, RFB and I agreed that
one could use an external coil in a slightly different
way. This would be just to feed the coil from the
final section of the transmitter and not even connect
the other end back into the unit. I'm sure this could
be made to work too. Right now I'm not going to get
into that subject, because I don't remember what
I said then. I just remember discussing it with RFB
a couple of years ago.
At least in this particular experiment, the
coil would be no good without the "ferrite bar." I
had found it and lost it and found it and lost it
again. Then I found it. Now everything is together in one place.
Having found this special coil after 3 years, I thought
info about it would be worth noting here. It was out
in my backyard from 2007 until a couple of weeks ago.
Bruce, DRS2
Bruce, thanks for the report on your experiment. I was a bit surprised that the coil only has 38 turns and that the tap at 20 worked. It seems that there is not enough inductance with this few turns and I think that is why you obtained better results with the ferrite bar inserted. This would raise the inductance considerably.
Your range report is encouraging. I never did find the limit of my range during the test but I do know that I was hearing the signal at distances previously not attainable.
Keep us posted on your progress.
Neil
Well, we are all very interested in
what you are doing with your home built
transmitter. I have thought about it
quite a bit. You just plunked it
down in the backyard, put out 10 radials,
and then it worked so well. It's a
big accomplishment.
I, too, am surprised that my coil required
only 38 turns. I've seen a lot of different
kinds of transmitters, and it just doesn't seem
right. But the coil is sitting right here.
Along with my other experiments, I had built
another coil on the same kind and
size PVC pipe. I put 52 turns on that coil,
but never got around to testing it.
When I found the old one in the backyard, I was
surprised, and I kept counting the turns over
and over. I am fairly certain that none of the
remaining internal inductors in the SS-Tran
were in line. If one had been, the overall Q
would have been lowered, and I don't think the
set-up would have worked as well. Then again,
there is that "ferrite bar"... I just don't
know enough about this. I do remember reading
that some of the longwave experimenters have
needed "ferrite" rods to tune some of the huge
coils they have needed to build.
Well, anyway, maybe soon I can just plunk the
whole thing down in the backyard like you did,
and we'll see what happens. You know - put
the whole thing in one of those big strong
plastic toolboxes, take it outside, set up the
vertical - guy it, and lay out the radials.
In other words, deploy it when needed and put
it on the air.
I hope you keep us informed of your experiments,
too. This Class E stuff is beyond me right now,
but I am learning as I read.
Best Wishes,
Bruce, DRS2