--
Political correctness is a doctrine, fostered by a delusional, illogical
minority, and rapidly promoted by an unscrupulous mainstream media, which
holds forth the proposition that it is entirely possible to pick up a piece
of **** by the clean end.
"Jeff Liebermann" wrote in message
news
On Thu, 23 Jan 2014 21:06:12 -0700, "Irv Finkleman"
wrote:
I already have a small 12v motor and have tested it with a number of
different capacitors. With a simple 10k wirewound pot I can slow it
down to almost nothing, or bring it back up to some value, and
that beautiful pot just gets lukewarm. Using a DPDT toggle switch
I can control the direction as well. Remote tuning on a shoestring!
Loose the potentiometer and replace is with a gearbox reducer. You
want to retain all the torque and power from the drive motor. Also,
don't forget to hi voltage insulate the motor, so that you don't arc
over to the motor in transmit.
I don't want to get any more complex or expensive than is absolutely
required. I am building it myself with limited shop facilities (my
operating table) The motor had more than enough torque in all situations.
I have an old plastic ball point pen cut to match the motor to the cap
which should suffice -- if not, I'll find a better pen! :-)
I plan to cut a big cloth circular case to drop over the loop. It will be
some nice flowery design, and a plan to put it over the back of a
lawnchair so that anyone who walks by and looks up to my
3rd floor balcony will see what appears to be a nice comfortable
highback chair! That's mainly for subterfuge!
If the lawn chair has an aluminum frame, it will detune the magnetic
loop antenna. All plastic lawn chair is required. Also, don't fire
up the transmitter when someone is sitting in the lawn chair.
The chair is plastic. Hmmmm, wonder if my ex-mother-in-law
would like to sit in the sun!
At the same time, having been experimenting with assorted antennas
over the years (before I began to deteriorate) I had a big yard full
of wire, ground rods, and a tower with all kinds of things hanging
off of it. I always kept an eye on the SWR bridge for any
variations, so any of that sun heating drift will be watched
carefully. Thanks for the tip though! For all my reading that is
one thing I hadn't encountered before.
It's only a problem with high Q antennas. Figure on a Q of 100 to 200
for the lower bands. On 80 meters, that's a 2:1 VSWR bandwidth of
about 25 to 35 KHz. It doesn't take much to drift the antenna off
frequency. Most magnetic loop users don't notice because they're
constantly tweaking the tuning capacitor.
I plan to mount it vertically using a piece of 2X4 sitting in a big pot or
tub filled with gravel.
So much for the disguise antenna. Don't forget to pound a ground rod
into the gravel. It won't do anything useful, but will make an
interesting conversation starter as to whether a ground is necessary.
I will have a drain hole in the bottom of the pot/pan
Anticipating lots of experimentation once I get
on the air, I can drill it, nail it, or whatever for various forms of
support, and even clamp a whip on it. I also anticipate that I will
eventually turn it into something akin to swiss cheese, and when that
comes about, I can replace my 'cheapo balcony tower' with ease.
Let me know when you're ready to build my inflatable antenna tower.
Now that sounds interesting. Is it anything like my inflatable dart board?
I will also constuct a small platform to hold the tub/pot and
by using some of the small plastic swivel casters I'll make the
whole works rotatable.
Lazy Susan works well. I use that for my direction finder hacks. Use
lots of grease if left outside as the bearings tend to rust.
Good idea, thanks!
I'm counting on the MFJ Analyzer for lots of help. I'm very away
of the losses, and where they occur and will be careful. As far as losses
are concerned, when running QRP why worry?
If you only have a little power to work with, then losses become even
more important than if you had hundreds of watts to waste.
Under good band
conditions like we had in the good old days (with propagation ever again
improve?) you can work the world with only a few watts. some guys do it
with milliwatts! I only want 75M for very local work within about
200Km, but I know I'll be quite efficient on 20 which is where I have
always had the most fun.
They still do it with milliwatts.
http://hflink.com/jt65/
I'm not sure what's wrong with propagation these days. Probably
global warming, or a government conspiracy.
It's bad enough that maybe there is a conspiracy!
A few of the magloops I've looked at on the net were not all
soldered -- many just used nuts, bolts and starwashers.
They don't work well. One of those I rescued was initially thrown
together but not soldered on the assumption that future modifications
would be easier without soldering. It didn't work until after it was
soldered.
I have a small handheld torch and do intend to solder the
critical points, i.e. the capacitor to the loop gap.
Whenever
I ran across them, I'd get back to the builder/operator and ask
how they worked, and had they taken the resistance losses into
consideration. In all cases they were happy with the way things
were and making lots of contacts.
You can also make a fair number of contacts with a dummy load. I
know, I've done it by accident. I also made a fair number of contacts
on one Field Day using a coax cable that was not connected to any
antenna. In some cases, a dummy load or no antenna would be an
improvement over some of the home brew antennas I've seen.
I've got to agree with you on some of the home brew antennas. I did
have a friend who is one of the top of the lists of DXCC and others who,
when he got his first rig, didn't know how to tune it properly and was
only putting out 15W -- but like the bumblebee who cannot possibly
fly due to mechanical principles, he worked WAC and DXCC
quite happily unaware of the problem! And don't forget that antenna
they used to advertise in QST et al which was no more than a dummy
load with some wire attached. At least you could get a great match!
One of the Manufactured loops is made of aluminim strips bolted
together, and it seems to get good ratings on EHam.
You can test that yourself with your MFJ antenna analyzer. Build a
loop that way. Measure the VSWR curve and impedance at resonance.
Then, rattle the loop a bit to move the bolts a little. Measure
again. My guess is you'll see substantial changes every time you bang
on the antenna. It might also be interesting to use an ESR
(equivalent series resistance) meter to measure the DC resistance.
That's also going to vary.
I rely on the MFJ Analyzer for a lot of things and don't know how
I got along without it. And other than a cheap $20 Canadian
Tire Digital Multimeter that is about as far as my test equipment
goes. When I sold my house I gave all my 50 years accumulation
of test equipment, rigs, and such to the local ham club. Most of
all miss my Fluke Multimeter (Model 75 or 77 -- I forget now)
which Sony allowed me to keep when I retired. I keep watching
for one on E-bay although some of the newer multimeters are
reasonably economical and have lots of nice features.
On hand, I also have a yoyo antenna, a Miracle Whip antenna, and the
MP1 which will be on the air as soon as I can measure the radials and
see how it works indoors.
Anything with amazing, magic, miracle, ultimate, or other superlatives
is usually over-rated.
The Miracle Whip was picked up used and repaired (a simple matter
of a loose solder connection on the coax male). It was dirt cheap
and surprisingly there are quite a few hams using it and having fun.
It's no beam, and no Miracle, but on the higher bands it seems to be
a not bad performer. I just had to try one out. When the weather
warms up I'll see what I can do with it.
Did I mention two Slinky's that I want to
try -- first as a short vertical, and then as a helical magnetic loop!
A what? Never mind. I don't have time to model a pretzel made from a
Slinky.
The Pretzel Slinky might just be a new twist!
I can hardly wait to get going -- and I'm getting closer every day!
Oh-oh. Slow down. It might be more fun doing cut-n-try, but it's
much easier if you plan your antenna carefully, and build it once, not
20 times.
That's exactly my plan Jeff -- and aside from the weather, it keeps me
busy checking things out that others have done in pursuit of the
'measure twice cut once' principle.
Thanks again
Irv VE6BP
Thanks for the tips Jeff -- your contributions to the group are
always great.
Y'er welcome. Good luck.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558