Owen Duffy wrote:
What has feeding an antenna at the current node got to do with feed
line length?

Feedline length for an average system may be about 75 ft.,
the distance from the antenna to the transceiver. If a
current maximum point occurs at 87 ft., make the feedline
87 ft. long with (usually) no tuner required.

I assume what Fred thinks sucks is your implication that the
average ham feeds his antenna with 100 meters of feedline.
What percentage of hams do you think actually use 100 meters
of transmission line?
--
73, Cecil http://www.qsl.net/w5dxp

On Wed, 09 Nov 2005 15:02:35 GMT, Cecil Moore wrote:

Owen Duffy wrote:
What has feeding an antenna at the current node got to do with feed
line length?

Feedline length for an average system may be about 75 ft.,
the distance from the antenna to the transceiver. If a
current maximum point occurs at 87 ft., make the feedline
87 ft. long with (usually) no tuner required.

Well, I guess you are guessing at what Fred meant. But such a current
maximum on the feed point repeats every electrical half wave, and such
an approach doesn't preclude using feed lines much longer than 75
feet.


I assume what Fred thinks sucks is your implication that the
average ham feeds his antenna with 100 meters of feedline.

That is his misinterpretation if that is the case. I did not say an
"average ham", but I assert that it is not all that uncommon to have a
ham antenna located at 100m or more, and the ROT falls down.

Thing is, about averages, is that the detail you throw away to
calculate the average may have been relevant. Further, there is little
consolation to the guy who has 10dB worse than average performance
because he has used longer feed line under your ROT, to know that a
whole lot of guys using shorter feed line are enjoying better than
average performance and on average, it all balances out.

It is quite feasible to place an antenna at longer distances if you
want, but ladder line should be operated at lower VSWR for acceptable
losses, or better feed line used... and the ROT doesn't say that.

It is the unstated length assumption (of apparently 75') of your ROT
that makes limits its validity to the people who are most likely to
lap it up.

What is an "average ham" now days? Is it one that doesn't have a real
interest in the technical side of the hobby, the "I just wanna talk on
the radio" set... they like ROTs, gives them something to parrot on
air.

Owen
--

Owen Duffy wrote:
Well, I guess you are guessing at what Fred meant.

Nope, not a guess. Fred and I are on the same wavelength. :-)
We use the same "notuner" method for resonating our antenna
systems.

That is his misinterpretation if that is the case. I did not say an
"average ham", but I assert that it is not all that uncommon to have a
ham antenna located at 100m or more, and the ROT falls down.

But it is indeed extremely uncommon for an *American* amateur
radio operator to have a feedline that is 100m long. I personally
know of only a handfull of cases in my 55 years of hamming and
most of those involved getting vhf/uhf antennas to the top of a hill.

Thing is, about averages, is that the detail you throw away to
calculate the average may have been relevant.

It may be relevant to a "rocket scientist", such as yourself, and
completely irrelevant and indeed beyond the understanding of the
average ham who must necessarily rely upon rules of thumb.

It is quite feasible to place an antenna at longer distances if you
want, ...

~99.99% of hams don't want to. Why make things more difficult?

It is the unstated length assumption (of apparently 75') of your ROT
that makes limits its validity to the people who are most likely to
lap it up.

Sorry to disagree, the great majority of "people who are most likely
to lap it up" are people with 60-100 foot feedlines. Most assertions
on this newsgroup are in the context of the average ham.

Owen, it's obvious that you deliberately picked 100 meters to try to
prove a point that you couldn't make otherwise. You chose an inferior
ladder-line that I wouldn't even allow on my property. Your attempts to
save face by dragging the discussion down some primrose path involving
minute details is interesting but not interesting enough to follow
you down said path.
--
73, Cecil http://www.qsl.net/w5dxp

On Thu, 10 Nov 2005 00:08:51 GMT, Cecil Moore wrote:


Owen, it's obvious that you deliberately picked 100 meters to try to
prove a point that you couldn't make otherwise. You chose an inferior
ladder-line that I wouldn't even allow on my property. Your attempts to
save face by dragging the discussion down some primrose path involving
minute details is interesting but not interesting enough to follow
you down said path.

I chose 100m as a round number that is practical and long enough to
demonstrate that at very high VSWR, the approximations that might hold
for shorter lengths and lower VSWR are no longer valid. Open wire
feeders well in excess of 100m are practical, but ladder line with
very high VSWR isn't.

(On the other hand, your 75' "standard" is about enough to reach the
feed point of a medium height antenna directly above the shack, and
might be argued as a minimum practical length for a good antenna.)

The ladder line I chose was one of the four that have reasonably good
characterisation (by N7WS) and it wouldn't matter much which of the
four you chose, they are fairly similar... I chose the first one on
the list. (The last one on the list, 554 with 25:1 load SWR give 5.6dB
against 6dB or 551... I wont bother checking the others.) No, I did
not deliberately choose an inferior ladder line.

Owen
--

Owen Duffy wrote:
I chose 100m as a round number that is practical ...

328.1 feet is NOT a round number. :-)
--
73, Cecil http://www.qsl.net/w5dxp

Owen Duffy wrote:


(On the other hand, your 75' "standard" is about enough to reach the
feed point of a medium height antenna directly above the shack, and
might be argued as a minimum practical length for a good antenna.)

As opposed to the standard full height backyard antenna with 100 meter
feedline which would then be something more like this:

http://www.kkn.net/gallery/hcjb/hc15

;-)
ac6xg