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I just wanted to send up a flag saying
that this project (as named above) is
starting to happen.
It’s a big fat coil which will load up a
Part 15 AM “3 meter” stick.
I have built several in the past. I built one
many years ago for a Ramsey AM-1 transmitter
which had been modified for crystal control.
With this coil and some radials and a 3 meter
stick, I was able to get the AM-1 to transmit
to around 1/2 mile or so.
I made another one for my SS-Tran AMT-3000
years later. The furthest that transmitter “went”
was 2 miles. The SS-Tran was modified, somewhat,
though.
This coil is made out of junk, really. It is just
another experiment that is going on here.
It is not a polished project like some of the
great work I have seen here on the board
fairly recently.
It’s just a test coil, using a variometer and
a movable ferrite rod, with lots of coil taps.
Anyway, I’ll be reporting on this.
A parallel project is a magnetic receiving loop
for HF. These kinds of things are fun and don’t
cost much.
Oh yeah, if you are not familiar with variometers –
Google is where you want to go. There is not much
to a variometer and it is fun.
Best Wishes,
Brooce, Part 15, Hartford, CT
Total posts : 45366I had mentioned the term “variometer.”
Then I suggested that if one wasn’t familiar
with the term – it could be “Googled” and that
would give good information.
It turns out I was wrong. Variometer means
different things to different people and it is
a very old term.
So anyhow – a variometer for a Part 15 AM
antenna loading coil is just another coil with
a rotatable coil inside it. It can be part of
“the main coil” or it can be separate and
put in line before or after the big coil.
In a variometer with it’s 2 coils, I have connected
these coils in series in my past experiments.
Rotate the inner coil and the inductance of
“the whole thing” can be varied.
Here’s somewhat of a connection.
So there is a “new” amateur radio band
that is in operation in some parts of
the world (but not in the U.S.)
This small band runs from 472 to 479 kHz.
Canada has that ham band and I have
monitored some stations there. Usually
you don’t hear much between 472 and 479,
but there are scheduled operating events
every once in a while and a bunch of stations
get on there. There are also some hams in
the U.S. that have STAs to operate in the
allocation, and I have heard a few of them
with just a Sony ICF-2010 receiver out in
the front yard.
Hams refer to this band as “600 meters.”
There is a lot of homebrew experimentation
going on there. Hams use homemade variometers
to tune transmit antennas. It sounds like a ton of
fun to operate there. However, for a variety of
reasons, the U.S. does not have the allocation
approved and I wonder if it ever will happen.
Some of the LF and MF experimenter websites
show pictures of variometers.
Oh yeah – this band, as it is around the world,
does not have a voice allocation. The operating
modes are morse code and all kinds of cool
digitial modes.
I would really like to get on there (I have a
ham license) but I have barely had time to
get my portable 40 meter QRP rig running.
That is just starting to happen.
Anyway, it’s all cool.
I hope this is helpful to anyone who
is interested in this sort of thing. Please
excuse any spelling or grammatical errors.
Brooce, Part 15, Hartford CT
Total posts : 45366I think a variometer is probably the most efficient and most adjustable tuner at the same time. I knew about them being used in early radios around the 1920s, before the advent of the Superheterodyne and the change over to variable condensers. Instead, the variometer varied the inductance, with a fixed condenser.
In the usual Part-15 transmitter, you have a large fixed coil, maybe with taps and a small variable capacitor between the antenna side of the coil to ground. The little trimmer cap can tune your antenna on frequency and make it most efficient, but also acts as a load on the output and it steals some power. If you can eliminate the trimmer and use a pure coil, then loss is reduced and you should get more power into your antenna.
Total posts : 45366I’ve got a few comments about
Part 15 AM transmitter coils.
I’ll be back in a little while.
Brooce
Total posts : 45366chimes in on efficiency of tapped coils with tunable cap vs. verometers.
Total posts : 45366So my coils from the past were “designed”
(haha) for the highest Q I could get.
(And From the info I knew at the time. There
was no way to measure the Q – it was all
trail, error, and “look-and-see-what-happens.”)
The coil for the Ramsey (this was about 13 years
ago) was made on a HUGE bucket from the hardware
store. The bucket was so big and the turns were so
far around that I had so put several coil taps on each
turn that was tapped. Sometimes if I was taking turns
off or putting them on in order to try to tune the thing –
it was hard to tell where the turn ended and the antenna
started. The bucket was so BIG that it was easy to put
a small bucket on the inside for the variometer coil form.
That thing put out a pretty good field. Some radios ceased
to function when placed next to that coil. It was tons of
fun and very inexpensive. The Ramsey AM-1 (all I had at
the time) did pretty well. One thing about that AM-1 –
I had to use an audio equalizer to get maximum modulation.
And the modulation I got may not have been 100%.
The coil I made for the SS-Tran a few years later had a much
smaller diameter. I think the PVC pipe was 3 inches wide.
It had lots of coil taps. I now know taps aren’t great for Q but this
was an experiment anyway. The coil was fine tuned with a
ferrite rod from an AM radio in the junkpile. I did not take the
RF output from from the SS-Tran in the usual place (the rear
antenna jack.) Instead, I took it from the final transistor line
after the DC blocking cap. After tons and tons of trial and
error – this seemed to be the best way to do it.
It was so much fun. I can’t wait to start building this
next coil. It will be different from the other two.
Brooce
Total posts : 45366hey bruce, i got an antenna analyzer. i’d be interested to see what the curve and readings from that are. we both live in whalers nation
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