On Wed, 28 Sep 2011 15:46:35 -0500, Jeffrey Angus
wrote:

On 9/28/2011 11:37 AM, Jeff Liebermann wrote:
Hmmm... why do you need an antenna tuner? Can't you build an antenna
that's close to 50 ohms? Or, are you like me and just hang any random
length of wire in the trees and hope for the best?

For close to 40 years I bought into the myth of 50 ohm antennas.
Absolute crap results. (Well, I've always had very good luck with
a dipole for one band.)

Mythology went out with the Greeks and the Romans. Modern antenna
design requires newer beliefs and religions. Apparently, your
practices within the Cult of 50 ohms has failed to bring about the
desired miraculous DX. You might want to petition the radio gods for
a review of your design before you discard the cult completely.
However, there are alternative religions.

In my case, I switched and am now a practicing member of the Cult of
75 ohms. The difference is subtle. While worship of the 50 ohm idol
results in the maximum power transfer, the change to 75 ohms results
in minimum coax loss and somewhat easier antenna design. However, the
major benefit is it allows one to minimize the tithe paid to vendors
as CATV coax is cheap and readily available. I suggest you consider a
religious conversion.

Earlier this year I put up a 102' doublet fed with open wire line
and have been working the entire planet with less than 100 watts.

Hmmm... perhaps that's because the bands were miserable all last year
and have only recently begun to show signs of life. Timing is
everything.

I thought you were trying to load a barbed wire fence. I'm
dissapointed.

But you're right,

Far right, please.

I'm a lazy ******* and would like the frequency
agility rather than having to tweak the knobs on the MFJ tuner
every time I change frequency.

Yeah, I know the problem. Every time the kite at the end of your
102ft doublet looses altitude, and the middle scrapes ground, you have
to retune. However, the IC-761 has plenty of knobs and switches to
play with. I don't see how a few more on the tuner could make any
difference.

Jeff-1.0
wa6fwi

Why is my mouse glued to the mouse pad? Sigh.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com
# http://www.LearnByDestroying.com AE6KS

On 9/28/2011 6:03 PM, Jeff Liebermann wrote:
Mythology went out with the Greeks and the Romans. Modern antenna
design requires newer beliefs and religions. Apparently, your
practices within the Cult of 50 ohms has failed to bring about the
desired miraculous DX. You might want to petition the radio gods for
a review of your design before you discard the cult completely.
However, there are alternative religions.

Well, I've come to a few conclusions.
1. Dipoles with a 1:1 balun work very well.
2. See #1. However, the trees and other things they are attached to
are hard to rotate.
3. Vertical antennas load nicely. So do Bird Termalines. And they
radiate about the same.
4. See #3. If I had room for a bunch of radials to make the vertical
work properly, I'd have room for a real antenna.
5. Yagis do nicely. _IF_ you have the tower and rotor to put them on.
6. A 102' doublet with open wire feed line and a tuner works amazing
well and considering the cost difference is flat out outstanding.

#4. Having moved to a small rural town in central Texas, I have
a lot of room now living on 1/2 an acre.

I already had a used 40' tower and was given the tuner as a bribe to
try the 102' doublet. And I had a 500' spool of #14 THHN house wire
to play with.

Isn't half the fun of all this seeing what works well for you?

Jeff-1.0
wa6fwi

--
"Everything from Crackers to Coffins"

On Wed, 28 Sep 2011 19:26:49 -0500, Jeffrey Angus wrote:


3. Vertical antennas load nicely. So do Bird Termalines. And they
radiate about the same.
4. See #3. If I had room for a bunch of radials to make the vertical
work properly, I'd have room for a real antenna.


I have an MFJ-928 ATU at the feed point of an elevated 43' vertical, with
a half dozen radials of various random lengths. It works great for
30/20/17/15. It starts making significant multiple lobes above 21 MHz.
I'm going to try a coil for 80.

"Jeff Liebermann" wrote in message
...

... am now a practicing member of the Cult of
75 ohms. The difference is subtle. While worship of the 50 ohm idol
results in the maximum power transfer, the change to 75 ohms results
in minimum coax loss and somewhat easier antenna design. However, the
major benefit is it allows one to minimize the tithe paid to vendors
as CATV coax is cheap and readily available. I suggest you consider a
religious conversion.

Yes. Somebody in this group (you, maybe) previously promoted 75 ohm cable.
This past spring, I was modeling my 20m Field Day dipole, varying size and
height for best pattern shape and minimum VSWR. At optimum, it had almost
exactly 75 ohm feedpoint impedance. Having plenty of TV coax, I didn't
hesitate to go with it. The antenna worked wonderfully well at FD.
Transmitter seemed to like it just fine.

"Sal"

"Sal" wrote in :

Yes. Somebody in this group (you, maybe) previously promoted 75 ohm
cable. This past spring, I was modeling my 20m Field Day dipole,
varying size and height for best pattern shape and minimum VSWR. At
optimum, it had almost exactly 75 ohm feedpoint impedance. Having
plenty of TV coax, I didn't hesitate to go with it. The antenna
worked wonderfully well at FD. Transmitter seemed to like it just
fine.

Sal, you will have discovered that the feed point impedance of a half
wave dipole at resonance is dependent on height above ground, type of
soil etc.

This need not be a choice between 50 ohms and 75 ohms.

My 40m inverted V dipole uses 75 ohm feedline (RG6), and the impedance
looking into the feedline is close to 50+j0. Dipole height was
determined prior to design of the matching system (ie height was not
constrained by the matching solution, rather the height set a
requirement for the matching solution). The transmitter has its rated
load impedance, the feedline is efficient and inexpensive. There is a
W2DU style choke balun near the feedpoint, and measured common mode
current is quite low.

Of course, the feedline has standing waves, and the dipole is not
resonant, to be frowned upon by some (many?). The antenna system can be
readily modelled, and it has higher efficiency than a resonant half wave
with comparable coax (say RG8X), indistinguisable pattern, marginally
higher gain.

Owen




"Sal"

On Wed, 28 Sep 2011 23:26:24 -0700, "Sal" wrote:

"Jeff Liebermann" wrote in message
.. .

... am now a practicing member of the Cult of
75 ohms. The difference is subtle. While worship of the 50 ohm idol
results in the maximum power transfer, the change to 75 ohms results
in minimum coax loss and somewhat easier antenna design. However, the
major benefit is it allows one to minimize the tithe paid to vendors
as CATV coax is cheap and readily available. I suggest you consider a
religious conversion.

Yes. Somebody in this group (you, maybe) previously promoted 75 ohm cable.
This past spring, I was modeling my 20m Field Day dipole, varying size and
height for best pattern shape and minimum VSWR. At optimum, it had almost
exactly 75 ohm feedpoint impedance. Having plenty of TV coax, I didn't
hesitate to go with it. The antenna worked wonderfully well at FD.
Transmitter seemed to like it just fine.

Probably me. I tend to promote the use of 75 ohm coax and systems.
Most of the coax cables to my rooftop antenna farm are 75 ohms. The
justification was convenience and price. I obtained five 1000ft rolls
of RG6a/u mutations (some with messenger wire), and some used hard
line, and couldn't resist using it. The only problems seem to be
getting accurate readings on my test equipment and having enough
F-to-N or F-to-BNC adapters.
http://www.qsl.net/n9zia/wireless/75_ohm_hardline.html

Note that using 75 ohm coax on a VHF/UHF repeater is a really bad
idea. Duplexers, isolators, circulators, cavities, and such are very
sensitive to mismatch. For repeaters, use only 50 ohms.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558