RadioBanter - View Single Post - Current in antenna loading coils controversy

November 2nd 03, 04:06 PM

oSaddam (Yuri Blanarovich) wrote in message ...
I once had an occasion where the bottom of a coil did get warm, while
the top did not. Yet my RF ammeters showed the same current on both
ends. What was going on?

What was he measuring, where was the coil?
W9UCW used 100 mA at the bottom, I doubt that this would "cook" the coil. You
see the pictures, they are good quality coils and he use two meters and
flippped the coil to eliminate possible error as described here.

NO , I didn't see the pictures. Like I said, they didn't load on that
site. All the pix load except his.

I ultimately determined that the soldered connection from the coil to
the lower antenna mast (for experimentation, it was copper) was adding
some undesireable resistance. Solder is not a particularly good
conductor of electricity. I copper-plated over the solder joint. Not
only did the bottom section of the coil no longer get warm, but the
two RF ammeters both showed about 20% more current flowing in the
antenna. And my far-field instruments showed a 1.5dB increase in field
strength.

Again, put on the fricken Hustler 80m resonator, feed it 100W and feel it! No
meters, no hokus pokus, just "naked" antenna.

What would that mean? The hustler coil is known to be flawed, and
makes a poor coil to be tested in this manner. The effects of it's
metal end caps, and overall design problems are fairly well known. I
refuse to use such a lousy coil. You can feed my homebrew coil 100w
all day long, and you won't feel anything except the finger on the
mike button hand start to go numb from holding the key down.

This is one example of being fooled....If you took coil temp at face
value, you would think the current taper was quite steep, judging from
the temp's of the windings. But nope...A resistive connection seemed
to be the culprit. Note that his meters showed the same current on
both ends. :/ You can see why I'm afraid of that "hook" that usually
is lurking ready to bite at a moments notice.
Don't worry, if you are right, it will come out in the end. But that
hook...Ouch.. MK

One insufficiently described measurement is enough to throw rest out of the
window?

No, it's just a good example of why you have to watch out for that
"hook" when doing measurments like this.

W9UCW has shown data from various measurements and positions of the
coil (pictures how it was done) and W5DXP backed it up with explanation of
reflected wave and simulation and comparison with loading stub. It came out,
this is the ned. If you choose not to believe, its a free country :-)

Yep, it sure is. I sure as hell won't have anything shoved down my
throat. I'm sorry, but you all haven't convinced me yet that your
measurements are any more accurate than the one I quoted on that same
web page. And the one I quoted did give a fairly good description of
how he went about it. The guy I quoted said he saw constant current
across the coil. How do you explain that? Should I automatically
dismiss his findings just because you all have a web page and a bunch
of pictures? How do I know who did the more accurate test? I DON'T!!!
So I will trust neither of you until I have further info. Thats life
in the big city, and like I said before, nothing personal. I'd subject
anyone else to the same rigid standards. Go ask the poor suckers
building EH antennas if I cut them any slack...:/ I imagine they hate
my guts the way I talk about their antenna.
I can take all the time I want to decide who is right. I'm in no big
hurry. You can't rush something like this when only a few even have
the gear set up to properly measure this. Like I said before, you all
may be perfectly correct. I have no problem with that. But I'm not
totally convinced yet that you may not be seeing the effects of some
measurement error. I just don't have enough info on the "hooks"
involved in doing a test like that. I've never done them. Obviously,
judging from the other guys results,and many other comments, there are
a few hooks lurking. He said he saw constant current across the coil,
and explained why he saw hot lower windings. And his explaination made
perfect sense to me. I give his test just as much weight as I do
yours at this point. Either one of you could be correct, and I have no
way of telling who is at this point. MK