You haven't mentioned a balun at the 259B, or any other device to float
the measurement terminals to make a true differential mode impedance
measurment without significantly disturbing the thing you are measuring.

There are issues regarding balance of the feedline with an OCF dipole,
but reversing the meter for different readings suggests that the meter
terminals are not sufficiently isolated from the environment (ground, the
adjacent transmission line, possibly a power cord).

What have you done to make the 259B appear as an isolated impedance
meter?

Owen

Owen,

My recent experience and your post has convinced me that a direct
termination of my balanced transmission line (300 ohm twin lead) to
the 259b is going to be problematic. I am now measuring through the
4:1 current balun in my MFJ tuner. Wish I had a 1:1. At 7.185 Mhz
through the 4:1 balun (tuner bypassed) I get 19 -j48. Assuming an
ideal balun I believe your previous post stated this would be 76 -j192
on the high side. At most even harmonic frequencies I've measured, it
appears the 4:1 balun in the tuner is actually resulting in too low a
resistive term impedance. As I write this I recall some text in the
antenna book about calculating the proper 1/4 wave Zo transmission
line impedance needed to transform to a desired impedance. Will this
work for any odd multiple of a 1/4 wave transmission line? On second
thought this wouldn't work on the harmonics would it? If I set it up
for 20 meters it wouldn't work on 40. The whole deal with the off
center feed is to be able to use it on even harmonics (80, 40, 20
meters). Guess I'll just work on figuring out the best compromise
transmission line, but I'm fairly convinced I can do better than the
300 ohm twin lead.

This is all just for the challenge of understanding the theory and
making it work in application. The tuner is doing fine for all 3 bands
in my current configuration.

Thanks for helping out a Stuggling Crippled Newbie Street Urchin.

On 12 May 2007 21:25:33 -0700, dykesc wrote:

My recent experience and your post has convinced me that a direct
termination of my balanced transmission line (300 ohm twin lead) to
the 259b is going to be problematic.

The way you described it (presuming an efficient choking BalUn) with
battery operation and you remote from it, suggests any issue of
"unbalance" is strictly academic. You can force it to become a real
problem if the case of the 259 is close to ground where the chassis
adds a capacitance to ground, but that is a rapidly diminishing value
as you raise it (couldn't be more than 1 or 2 pF at 6 feet up).

I am now measuring through the
4:1 current balun in my MFJ tuner.

This is extremely unlikely (being a current BalUn) unless it is
specifically specified as one (and even then, many professed 4:1
current BalUns are in fact no such thing).

You have the means to test the assertion, use your 259 to measure the
isolation of the BalUn. This was the subject of a recent thread.

Wish I had a 1:1. At 7.185 Mhz
through the 4:1 balun (tuner bypassed) I get 19 -j48. Assuming an
ideal balun I believe your previous post stated this would be 76 -j192
on the high side. At most even harmonic frequencies I've measured, it
appears the 4:1 balun in the tuner is actually resulting in too low a
resistive term impedance.

Fixation on BalUns has clouded a simpler solution: wind a choke in
the line and dump the ferrites of suspect quality.

As I write this I recall some text in the
antenna book about calculating the proper 1/4 wave Zo transmission
line impedance needed to transform to a desired impedance. Will this
work for any odd multiple of a 1/4 wave transmission line?

Yes, but discrepancies mount up dramatically as you multiply them
(tolerances at 1/4 demand greater precision at 3/4, and even greater
at 5/4). Besides, this doesn't address the odd readings you
experience.

On second
thought this wouldn't work on the harmonics would it? If I set it up
for 20 meters it wouldn't work on 40.

Sub Harmonics wouldn't suffer terribly. You do have a tuner after
all.

The whole deal with the off
center feed is to be able to use it on even harmonics (80, 40, 20
meters).

Off center feeds merely give you different Zs for the same resonances
- something of a shell game where you get to move your problems to
another band (guess what? This is what may be happening.).

Guess I'll just work on figuring out the best compromise
transmission line, but I'm fairly convinced I can do better than the
300 ohm twin lead.

It would be simpler to hang a second, half-length dipole beneath a
full size dipole and forget the off center feed.

This is all just for the challenge of understanding the theory and
making it work in application. The tuner is doing fine for all 3 bands
in my current configuration.

Many antennas work just fine until the operator discovers a new tool
that proves it doesn't (in spite of a wall full of QSL cards).

Thanks for helping out a Stuggling Crippled Newbie Street Urchin.

Wait until you face the sewer rats of Rio.

73's
Richard Clark, KB7QHC

dykesc wrote in
oups.com:

....
Owen,

My recent experience and your post has convinced me that a direct
termination of my balanced transmission line (300 ohm twin lead) to
the 259b is going to be problematic. I am now measuring through the
4:1 current balun in my MFJ tuner. Wish I had a 1:1. At 7.185 Mhz
through the 4:1 balun (tuner bypassed) I get 19 -j48. Assuming an
ideal balun I believe your previous post stated this would be 76 -j192
on the high side. At most even harmonic frequencies I've measured, it

In my experience, the balun integrated into MFJ tuners is far from ideal,
and it is usually a voltage balun.

appears the 4:1 balun in the tuner is actually resulting in too low a
resistive term impedance. As I write this I recall some text in the

I don't really understand what you are hoping for.

antenna book about calculating the proper 1/4 wave Zo transmission
line impedance needed to transform to a desired impedance. Will this
work for any odd multiple of a 1/4 wave transmission line? On second
thought this wouldn't work on the harmonics would it? If I set it up
for 20 meters it wouldn't work on 40. The whole deal with the off
center feed is to be able to use it on even harmonics (80, 40, 20
meters). Guess I'll just work on figuring out the best compromise
transmission line, but I'm fairly convinced I can do better than the
300 ohm twin lead.

You seem to be trying to operate a dipole over multiple bands.

The issues that this brings include:
1. is the pattern acceptable;
2. can you get power from the equipment room to the antenna reasonably
efficiently;
3. can you deliver the rated load impedance to the transmitter.

Impedance transformation for 3. can conveniently be done and is often
done in the equipment room, eg an ATU.

In that case, the feedline will operate at high VSWR at some frequencies
if you use an unloaded dipole.

Such a dipole with say 20m of feedline is difficult to feed efficiently
if it is shorter than about 35% of a wavelength.

A dipole of more than 120% of a wavelength has a pattern with multiple
lobes and intervening nulls, which may or may not be an issue.

Low loss open wire feedline can operate with very high VSWR (as would be
encountered with a multi-band dipole) without great loss. It is most
unlikely that coax is acceptable for this application, and possibly even
lossy forms of open wire line like TV ribbon or ladder line... depending
on your acceptability criteria.

Balun loss may be an issue if the balun is operated at very high
impedance (ie high flux for moderate power). If the balun gets very hot,
you have your warning.

Have a look at my article on feeding a G5RV, in particular Fig 10, the
classic tuned feeder configuration. a 30m long dipole with low loss open
wire line and an efficient balanced tuner is a frequency agile antenna
with good efficiency and good pattern up to 12MHz. Above 12MHz, the
pattern breaks into many lobes and nulls.


This is all just for the challenge of understanding the theory and
making it work in application. The tuner is doing fine for all 3 bands
in my current configuration.

That is what real ham radio is about!

Owen

dykesc wrote:
I am now measuring through the
4:1 current balun in my MFJ tuner. Wish I had a 1:1.

Most tuner baluns are voltage baluns. What you need
is a 1:1 current balun with a choking impedance of
a few thousand ohms. That is generally the balun of
choice when the impedances are unknown.
--
73, Cecil http://www.w5dxp.com

Owen Duffy wrote:
Have a look at my article on feeding a G5RV, in particular Fig 10, the
classic tuned feeder configuration. a 30m long dipole with low loss open
wire line and an efficient balanced tuner is a frequency agile antenna
with good efficiency and good pattern up to 12MHz. Above 12MHz, the
pattern breaks into many lobes and nulls.

As a matter of interest, Mr. Varney, G5RV himself, designed
his antenna for 20m operation because he liked that multi-
lobed pattern. In AZ, I had each of the four major lobes
pointing toward one of the world's large land masses.
--
73, Cecil http://www.w5dxp.com

On May 13, 2:07 am, Richard Clark wrote:

The way you described it (presuming an efficient choking BalUn) with
battery operation and you remote from it, suggests any issue of
"unbalance" is strictly academic. You can force it to become a real
problem if the case of the 259 is close to ground where the chassis
adds a capacitance to ground, but that is a rapidly diminishing value
as you raise it (couldn't be more than 1 or 2 pF at 6 feet up).

Richard, I tired measurements again with my twin lead directly
terminated to the 259b. I got better, more consistent results after
taking great care to insure the analyzer and line were well isolated
from ground, other conductors, and myself. I then took the same
measurements with the 4:1 balun between the twin lead and the
analyzer. Unfortunately the results create new concerns. For example
at 7.185 Mhz with the balun in the circuit (tuner in bypass mode) I
got 19 -j48. Again at 7.185 Mhz with the balun out (twin lead directly
terminated to 259b) I got 159 -j443. Doesn't look like 4:1 to me.
Similar spreads in the 80m and 20m bands.

This is extremely unlikely (being a current BalUn) unless it is
specifically specified as one (and even then, many professed 4:1
current BalUns are in fact no such thing).

The MFJ manual for the 993b tuner says the balun is a 4:1 "current"
balun. Haven't looked inside to confirm this.


You have the means to test the assertion, use your 259 to measure the
isolation of the BalUn. This was the subject of a recent thread.


Thanks. I'll search for the thread. Sounds like fun.

Wish I had a 1:1. At 7.185 Mhz
through the 4:1 balun (tuner bypassed) I get 19 -j48. Assuming an
ideal balun I believe your previous post stated this would be 76 -j192
on the high side. At most even harmonic frequencies I've measured, it
appears the 4:1 balun in the tuner is actually resulting in too low a
resistive term impedance.

Fixation on BalUns has clouded a simpler solution: wind a choke in
the line and dump the ferrites of suspect quality.

Would you please elaborate on this? Wind a choke where? In the twin
lead? In the short transmitter to tuner coax line?
Thought I read somewhere that only coax can be used for simple 8 to 10
turn chokes. Balanced lines (i believe because of mutual conductor
inductances) can't be coiled as chokes.


Many antennas work just fine until the operator discovers a new tool
that proves it doesn't (in spite of a wall full of QSL cards).

Partly the reason I'm trying to learn all I can about the
configuration I've currently got. That and I like the technology
aspects of the hobby as much or more than I do operating.

Thanks for helping out a Stuggling Crippled Newbie Street Urchin.

Wait until you face the sewer rats of Rio.

OK I'll bite. Who are the Rio rats?

Thanks for your help. Any thoughts on those measurement results
earlier in the post will sure be appreciated.

73's
Dykes Cupstid AD5VS

On May 13, 2:15 am, Owen Duffy wrote:

Have a look at my article on feeding a G5RV, in particular Fig 10, the
classic tuned feeder configuration. a 30m long dipole with low loss open
wire line and an efficient balanced tuner is a frequency agile antenna
with good efficiency and good pattern up to 12MHz. Above 12MHz, the
pattern breaks into many lobes and nulls.


Where can I find this article Owen? Would probably help me out quite a
bit.


Thanks and 73's

Dykes Cupstid AD5VS

On May 13, 5:31 am, Cecil Moore wrote:

Most tuner baluns are voltage baluns. What you need
is a 1:1 current balun with a choking impedance of
a few thousand ohms. That is generally the balun of
choice when the impedances are unknown.
--


The manual speciffically calls it a "current" balun Cecil. Doesn't
make it so. I need to look inside and determine how its wound. Most
4:1 current balun configurations I've seen use two toroids.

Thanks and 73s.

Dykes Cupstid AD5VS

dykesc wrote in news:1179100892.793896.55150
@e65g2000hsc.googlegroups.com:

On May 13, 2:15 am, Owen Duffy wrote:

Have a look at my article on feeding a G5RV, in particular Fig 10, the
classic tuned feeder configuration. a 30m long dipole with low loss open
wire line and an efficient balanced tuner is a frequency agile antenna
with good efficiency and good pattern up to 12MHz. Above 12MHz, the
pattern breaks into many lobes and nulls.


Where can I find this article Owen? Would probably help me out quite a
bit.

Sorry,

http://www.vk1od.net/G5RV/index.htm

Owen

dykesc wrote:
Where can I find this article Owen? Would probably help me out quite a
bit.

http://www.vk1od.net/G5RV

http://www.w8ji.com/g5rv_facts.htm

http://www.cebik.com/wire/g5rv.html
--
73, Cecil http://www.w5dxp.com