OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

I just aquired an MFJ 259b analyzer. I'm using it to measure the
impedance at the input of the 300 ohm twin lead I have feeding a
sloping off center fed dipole. I measured 75 -j236 at 3.94 Mhz. When i
reverse the txmsn line leads where they connect to the 259b I get 175 -
j237. Does anyone have an explanation as to why the resistance value
changes simply by reversing the way the txsmsn line is attached to the
analyzer? I have repeated this numerous times, attaching and
reattaching always with very near the same results. Does the fact that
the antenna has unequal leg lengths somehow explain this? If it
matters, there is a 1:1 current balun between the txmsn line and the
antenna feedpoints.

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

On 10 May 2007 09:28:52 -0700, dykesc wrote:

Does the fact that
the antenna has unequal leg lengths somehow explain this?

That, and it is sloping (compounding asymmetry).

If it
matters, there is a 1:1 current balun between the txmsn line and the
antenna feedpoints.

It may not be very useful.

73's
Richard Clark, KB7QHC

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

dykesc wrote in news:1178814532.207062.89230
@h2g2000hsg.googlegroups.com:

I just aquired an MFJ 259b analyzer. I'm using it to measure the
impedance at the input of the 300 ohm twin lead I have feeding a
sloping off center fed dipole. I measured 75 -j236 at 3.94 Mhz. When i
reverse the txmsn line leads where they connect to the 259b I get 175 -
j237. Does anyone have an explanation as to why the resistance value
changes simply by reversing the way the txsmsn line is attached to the
analyzer? I have repeated this numerous times, attaching and
reattaching always with very near the same results. Does the fact that
the antenna has unequal leg lengths somehow explain this? If it
matters, there is a 1:1 current balun between the txmsn line and the
antenna feedpoints.

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

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

Owen Duffy wrote in
:

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

I did mean to add that in this case, the impedance at the end of the
isolated feed line is not necessarily (and not likely to be) the same as
when it is connected to your transmitter. Again the same issue arises about
the path to ground for common mode current, and the influence that has on
the antenna feed point impedance transformed by the transmission line.

You need to think about the purpose of the measurement.

Owen

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

On May 10, 4:14 pm, Owen Duffy wrote:
Owen Duffy wrote :

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

I did mean to add that in this case, the impedance at the end of the
isolated feed line is not necessarily (and not likely to be) the same as
when it is connected to your transmitter. Again the same issue arises about
the path to ground for common mode current, and the influence that has on
the antenna feed point impedance transformed by the transmission line.

You need to think about the purpose of the measurement.

Owen

Owen I am operating the 259b on battery power and keeping the meter
away from all conductors including myself (hands). I have searched
posts on the internet about using unbalanced analyzers to measure
balanced line input impedances with little success other than one post
which spoke to the need to measure impedance in 3 connection
configurations and then mathematically solving for the final impedance
value. The 3 configurations were balanced line lead A to ground with B
gounded. B to ground with A grounded. And A &B connected together to
ground. (Ground was defined as the common on the analyzer.) The author
then mentioned some mathematical determination of impedance which he
didn't elaborate on. Are you familiar with this method? What is the
mathematical solution once you have the data?

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

On May 10, 4:14 pm, Owen Duffy wrote:
Owen Duffy wrote :

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

I did mean to add that in this case, the impedance at the end of the
isolated feed line is not necessarily (and not likely to be) the same as
when it is connected to your transmitter. Again the same issue arises about
the path to ground for common mode current, and the influence that has on
the antenna feed point impedance transformed by the transmission line.

You need to think about the purpose of the measurement.

Owen

One more question Owen. If I measure the complex impedance on the low
side of a 4:1 current balun. Is the impedance on the high side simply
4 times the low side? Can I just multiply the resistive term by 4 and
the complex term by 4?

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

dykesc wrote in
ups.com:

On May 10, 4:14 pm, Owen Duffy wrote:
Owen Duffy wrote
:

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

I did mean to add that in this case, the impedance at the end of the
isolated feed line is not necessarily (and not likely to be) the same
as when it is connected to your transmitter. Again the same issue
arises about the path to ground for common mode current, and the
influence that has on the antenna feed point impedance transformed by
the transmission line.

You need to think about the purpose of the measurement.

Owen

One more question Owen. If I measure the complex impedance on the low
side of a 4:1 current balun. Is the impedance on the high side simply
4 times the low side? Can I just multiply the resistive term by 4 and
the complex term by 4?


If the balun was ideal, you could do that. To the extent that it isn't,
error will be introduced.

I think some of this comes back to the question "what do you want to
know".

If you want to know the load as connected to your transmitter, simulate
that connection including baluns, earth connections etc.

If you want to make an isolated measurement for some reason, I would have
expected that the 259B on batteries at low HF frequencies and supported
clear of other objects would be sufficiently isolated to not get the
differences you observed.

My suspicion is that if you follow the calculation path you described,
the inherent range / accuracy of the 259B will be a problem, and the
precision introduced by the measurement approach will be lost due to
instrument error, indeed you might be worse off.

Owen

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

Richard Clark wrote:

On 10 May 2007 09:28:52 -0700, dykesc wrote:


Does the fact that
the antenna has unequal leg lengths somehow explain this?


That, and it is sloping (compounding asymmetry).


If it
matters, there is a 1:1 current balun between the txmsn line and the
antenna feedpoints.


It may not be very useful.

73's
Richard Clark, KB7QHC

Richard

I hate to revisit my main problem with you, since you are normally so
amusing, but if you aren't going to help the poor newbie, could you
please keep quiet and not make his confusion worse?

tom
K0TAR

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

On Fri, 11 May 2007 19:53:30 -0500, Tom Ring
wrote:

I hate to revisit my main problem with you

but....

As you see it, I just kicked out the crutches from beneath a cripple
newsboy who is struggling in the street and you as the social reformer
prefers to convert this evil sinner instead.

"Won't somebody think of the children!!?"

Does that put us back on the amusement track?

73's
Richard Clark, KB7QHC

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

Richard Clark wrote:



but....

As you see it, I just kicked out the crutches from beneath a cripple
newsboy who is struggling in the street and you as the social reformer
prefers to convert this evil sinner instead.

"Won't somebody think of the children!!?"

Does that put us back on the amusement track?

73's
Richard Clark, KB7QHC

I hate conversion attempts specifically and football in general, so
you'll never find me trying it.

I am also of the opinion that children are way overrated. They are easy
to make, and not worth nearly as much as an experienced middle aged worker.

tom
K0TAR

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

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.

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

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

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

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

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

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

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

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

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

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

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

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

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

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

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

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

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

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

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

On 13 May 2007 16:55:44 -0700, dykesc wrote:

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.

Hi Dykes,

It should be comforting that observing standard precautions produces
repeatable results.

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 sounds like you've inserted the entire tuner to obtain the 4:1
BalUn (once you threw the right switches).

If, as you say, education is a principle goal, then build a proper 4:1
current BalUn. It is actually quite simple and requires only two
transmission lines and a several dozen beads. Basically it is two 1:1
current BalUns fed in parallel and loaded in series.

You will be simultaneously checking your system, and testing the
authenticity of the MFJ claim:
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.

If after a fruitless search (it's easy enough to get slogged down in
the snow drift of useless posts here) you don't find it, ask for help
here. Mentioning you tried the archives will save others from whining
about how much effort they went to answer a stupid question. (I won't
whine, and I never call any question stupid - although I frequently
dope slap some of the denser questioners.)

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?

Sure, twist it candy cane (or barber shop pole) style and wind it
around a liter bottle with at least its width as separation between
windings.

In the short transmitter to tuner coax line?

Actually for severely unbalanced dipoles (and yours qualifies for
Queen of the May), you may need a choke at the feed point to the
antenna, and then again a quarter wave away from there.

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.

Even if I'm wrong, it is both cheap and instructive. So few here
actually step up to the bench that I don't take their flabby word that
I'm wrong. You may be the first with authentic achievement to break a
record! You've already lapped the field of these arm-chair analysts.

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.

Where this hobby whose technological demand largely consists of
pushing a credit card across a sales counter, antennas still have the
capacity to stretch the imagination.

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?

This is an allusion to an SK who compared those who couldn't exercise
their minds as being fodder for the orphans of Rio, who had more will
to succeed than they did. He characterized them as sewer rats gnawing
on our lazy carcasses.

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

They will reveal more in comparison to those measurements that follow.

73's
Richard Clark, KB7QHC

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

On May 14, 1:07 am, Richard Clark wrote:
On 13 May 2007 16:55:44 -0700, dykesc wrote:

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?

Sure, twist it candy cane (or barber shop pole) style and wind it
around a liter bottle with at least its width as separation between
windings.


Richard,

I wound the liter bottle choke as you suggested and do believe I'm
getting better results as follows:


1:1 Liter Bottle Choke 4:1 MFJ Balun (tuner
bypassed)

3.94Mhz 57 -j169 14 -j39

7.185Mhz 62 -j212 19 -j48

14.29Mhz 70 -j313 12 -j63

Appears to be a much better correlation to the expected 4:1. Meaning I
can "start" trusting my line input values, though I do believe I can
do better with a properly constructed 1:1 toroidal balun for my input
isolation. Got to order some toroids before I can do this however.

Looks like I'd be better off if I could just lower (zero out) the
capacitive reactance on the twin lead input leaving the resistive
terms alone. Sure wish there was a 1:1 current balun in the tuner. Its
tempting but I don't think I can bring myself to modifying the tuner.
My soldering / desoldering skills aren't the greatest. Its a nice
tuner and I'd hate to muck it up.

I found the thread on testing balun isolation. Still digesting it
though.

Thanks again and 73s
Dykes Cupstid AD5VS

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

On 14 May 2007 19:43:14 -0700, dykesc wrote:

1:1 Liter Bottle Choke 4:1 MFJ Balun (tuner
bypassed)

3.94Mhz 57 -j169 14 -j39

7.185Mhz 62 -j212 19 -j48

14.29Mhz 70 -j313 12 -j63


Hi Dykes,

This is what I meant about measurements made in isolation not being as
informative without other information.

Oddly enough, it looks like the 4:1 is mounted backwards.

However, I reserve making a final judgement pending review of my OCF
models (your results are just too luckily hitting the ham bands).

73's
Richard Clark, KB7QHC

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

On May 15, 1:21 am, Richard Clark wrote:
On 14 May 2007 19:43:14 -0700, dykesc wrote:

1:1 Liter Bottle Choke 4:1 MFJ Balun (tuner
bypassed)

3.94Mhz 57 -j169 14 -j39

7.185Mhz 62 -j212 19 -j48

14.29Mhz 70 -j313 12 -j63

Hi Dykes,

This is what I meant about measurements made in isolation not being as
informative without other information.

Oddly enough, it looks like the 4:1 is mounted backwards.

However, I reserve making a final judgement pending review of my OCF
models (your results are just too luckily hitting the ham bands).

73's
Richard Clark, KB7QHC

Richard,

I'm not following your statement that the 4:1 appears to be mounted
backwards. While the 1:1 values are not exactly 4 times the 4:1
values, they are at least "ballpark". Just to make sure you understand
my arrangement, when measured, the 1:1 values should "ideally"
represent the line input impedance without transformation. The 4:1
values (line on the high impedance side of the balun, analyzer on the
low impedance side) should be down by roughly a factor of 4, right?

Also I'm not sure what you mean by my results luckily hitting the ham
bands. I cut and fed the antenna to accomplish that. The OCF feedpoint
(at least by design) is just off the peak of a current loop on 80, 40
and 20 meters (even harmonics).

73s
Dykes AD5VS

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

On 15 May 2007 20:17:18 -0700, dykesc wrote:

I'm not following your statement that the 4:1 appears to be mounted
backwards. While the 1:1 values are not exactly 4 times the 4:1
values, they are at least "ballpark". Just to make sure you understand
my arrangement, when measured, the 1:1 values should "ideally"
represent the line input impedance without transformation. The 4:1
values (line on the high impedance side of the balun, analyzer on the
low impedance side) should be down by roughly a factor of 4, right?

Hi Dykes,

Look at your data comparison again and ask: Should it be 4:1 or 1:4?

Also I'm not sure what you mean by my results luckily hitting the ham
bands. I cut and fed the antenna to accomplish that.

No doubt, as that is everyone's goal.

The OCF feedpoint
(at least by design) is just off the peak of a current loop on 80, 40
and 20 meters (even harmonics).

I'm not arguing results, I am arguing common sense. Moving the feed
along a dipole does not change its resonances and anti-resonances
(some prefer the terms series and parallel resonances); it changes
their impedances (I will ignore slight reactances). A balanced 80M
dipole resonates on 40M and 20M (and 10M, and 5M....) too. However,
the balanced dipole shows low resonance (series) and high
anti-resonance (parallel) impedances. You are showing consistent low
resonant impedances.

Well, in my review of all of your correspondence, you neglect to tell
us just how far off from center the feed is, and how much slope there
is to the overall wire, and even how long the wire is. I originally
offered that these peculiarities will induce oddities and caught grief
(well, not actually, perhaps it was more like guff) from Tom for
noting it.

However, I have worked out OCDs in the past in response to other's
discussion and there are a world of results and I am going to attempt
to read tea leaves here to intuit the missing details:

The feed is roughly 15% to 20% from the end and there should be almost
as good a match somewhere between the 25M and 30M band. A flat OCD
will show a much poorer match in the 80M band (it will resonate
there), but sloping may introduce enough variation to pull it in
(where the ground is soaking up some of your power as sort of a Z
pad).

At 25% from the end, and there should be no 20M operation as you
describe.

There are possibilities at 35% to 40%.

Let me know about matches inbetween 40M and 20M.

73's
Richard Clark, KB7QHC

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

On May 16, 12:46 am, Richard Clark wrote:


Look at your data comparison again and ask: Should it be 4:1 or 1:4?


Richard, I guess I'm not seeing something obvious. Its a 4:1 balun
transforming the high side impedance down by a factor of 4. The 4:1
impedance measurements (line on the high impedance side of the balun,
analyzer on the low impedance side) should be down by roughly a factor
of 4, right?
I can't see anything wrong with how I presented the data.

Moving the feed along a dipole does not change its resonances and anti-resonances
(some prefer the terms series and parallel resonances); it changes their impedances

I agree

However, the balanced dipole shows low resonance (series) and high
anti-resonance (parallel) impedances.


By feeding off center my sloping dipole is not balanced.


You are showing consistent low resonant impedances.


The OCF feedpoint (at least by design) is near (but not on) the peak
of a current loop on 80, 40 and 20 meters (even harmonics). Don't
current peaks occur at points of low impedance along an antenna? My
EZNEC current traces confirm this. Shouldn't my even harmonics
impedance measurements all be low rather than high?

By the way Richard the frequencies my impedance measurements were
taken at are not "resonant" frequencies. The resonant frequencies
(zero reactance) occur at 3.56 Mhz, 8.05 Mhz, and 15.7 Mhz. A little
too low on 80M. Too high for 40M and 20M. The tuner gets me the match
in the 40 and 20 amateur bands.

I apologize for not stating that my sloping OCF is fed at 35% of its
total length from the high end. High end at a height of about 40 feet
and low end at a height of about 10 feet. Total antenna length is 136
feet.


73s
Dykes Cupstid AD5VS

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

On May 16, 12:46 am, Richard Clark wrote:

Look at your data comparison again and ask: Should it be 4:1 or 1:4?

I must be ovelooking something obvious Richard. Measuring through the
4:1 balun with my transmission line on the high side of the balun and
my analyzer on the low side, I obtain the values listed under the 4:1
MFJ Balun column in my earlier post. It doesn't look backward to me.
I'm getting lower impedances just as I would expect. What are you
trying to tell me?


Moving the feed along a dipole does not change its resonances and anti-resonances
(some prefer the terms series and parallel resonances); it changes their impedances

I agree

However, the balanced dipole shows low resonance (series) and high
anti-resonance (parallel) impedances. You are showing consistent low
resonant impedances.

My sloping dipole isn't balanced. Its being fed off center. The OCF
dipole (at least by design) is near (but not on) the peak of a current
loop on 80, 40 and 20 meters (even harmonics). Don't the lowest
impedances occur at current loops? Why are you surpised my impedances
are low rather than high on even harmonics?


Well, in my review of all of your correspondence, you neglect to tell us just how far off from center the feed is, and how much slope there
is to the overall wire, and even how long the wire is.

My apologies. Antenna is 136 feet long. Feedpoint is 35% from the end
that is the highest in the air. Height of high end is about 40 feet.
Height of low end is about 10 feet. Feeding with 300 ohm twin lead
that is 95 feet long (actual length, not electrical length),


Let me know about matches in between 40M and 20M.

The antenna is resonant (zero reactance) at 3.56 Mhz, 8.05 Mhz and
15.7 Mhz. My tuner is required for working in the Amateur bands.

73's
Dykes Cupstid AD5VS

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

On 16 May 2007 20:21:29 -0700, dykesc wrote:

On May 16, 12:46 am, Richard Clark wrote:


Look at your data comparison again and ask: Should it be 4:1 or 1:4?


Richard, I guess I'm not seeing something obvious. Its a 4:1 balun
transforming the high side impedance down by a factor of 4. The 4:1
impedance measurements (line on the high impedance side of the balun,
analyzer on the low impedance side) should be down by roughly a factor
of 4, right?
I can't see anything wrong with how I presented the data.

Hi Dykes,

Well then, your feed point Zs are inordinately low. (Get rid of the
idea of using the 4:1.)

The OCF feedpoint (at least by design) is near (but not on) the peak
of a current loop on 80, 40 and 20 meters (even harmonics). Don't
current peaks occur at points of low impedance along an antenna? My
EZNEC current traces confirm this. Shouldn't my even harmonics
impedance measurements all be low rather than high?

As OCF/OCD antennas have an infinite variety of feed points (where as
the balanced dipole has only one), there is nothing set in stone about
any of this until you define the degree of "off-center."

There are MANY OCDs that exhibit conventional Hi/Lo/Hi/Lo spectrums in
contrast to your Lo/Lo/Lo.... Certainly, they offer no advantage over
the conventional balanced dipole in this respect. Too often OCD
claims are made without corresponding supporting details.

By the way Richard the frequencies my impedance measurements were
taken at are not "resonant" frequencies. The resonant frequencies
(zero reactance) occur at 3.56 Mhz, 8.05 Mhz, and 15.7 Mhz.

You might note, then, that meaning of harmonics has been similarly
distorted in this thread.

A little
too low on 80M. Too high for 40M and 20M. The tuner gets me the match
in the 40 and 20 amateur bands.

I apologize for not stating that my sloping OCF is fed at 35% of its
total length from the high end. High end at a height of about 40 feet
and low end at a height of about 10 feet. Total antenna length is 136
feet.

Modeling against these criteria reveal nothing like your measurements
with:
(zero reactance) occur at 3.56 Mhz, 8.05 Mhz, and 15.7 Mhz.
(that is the short story)

However, modeling does suggest the antenna should perform for 80/40/20
in much the way your second set of data with the reactance driven out.
To say the least, you still have a hodge-podge of results probably
dominated by the contribution of unbalanced currents on the feed line
(a classic condition for this design that demands considerable
choking).

All that remains to confirm this last observation is to someway
determine the lobe patterns. If they exhibit weak nulls, then the
feed line is part of the radiator. Given the choke appeared to work
at the feedpoint (I assume this is what you did); then a second one is
warranted, and possibly a third. The usual placement advice is 1/4
wavelength from the feed point, but given this is a multi-band
antenna, that is out the window and you will have to experiment (I
would start with 1/4 of the shortest wavelength away).

However, if nulls are immaterial to the enjoyment of the antenna, then
theory has been satisfied and you can chalk that one up.

And to confirm my forecast of operation between 40M and 20M, it should
be exhibiting a significant SWR throughout.

73's
Richard Clark, KB7QHC

OCF Sloping Dipole Txmsn Line Input Resistance Measurement
 

Richard Clark wrote:
Look at your data comparison again and ask: Should it be 4:1 or 1:4?

Seems to me the convention for a BA-LUN is to put the balanced
number first followed by the unbalanced number.
--
73, Cecil, w5dxp.com