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[Articles Home]  [Add Article]  

Is Your Balanced Line Really Balanced?

Vito Chiarappa (W6TH) on December 8, 2004
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Is Your Balanced Line Really Balanced?

Years gone by when we used the open wire line feed systms on our ham radios, we had a system whereby we would check the open wire feed line for equal currents and balanced line. We used what was called the Letcher wire line system test. This test consisted of two wires and a rf ampere meter and would connect this test instrument across the balanced line and walk it up the line checking the rf current if to be equal.

A true balanced line should be equal in amplitude and opposite in phase for the proper balance. This will cancel any radiation from the line and the line would not radiate, just the flat top antenna.

You can make a simple test by taking one leg of your open wire and running it as a single random wire antenna. Lower your VSWR on a given frequency say on 3.555 Khz as I did with my check. On the first check with the single random wire, I had the wire test VSWR down to 1/1. I then went to the other line and found that my second line was 3/1 vswr. I then changed the frequency where the vswr would equal the same as the first wire. It so happens that the vswr on the second wire equalled the first wire at 3.658 Khz. Sure enough I did have a unbalanced line. This unbalance can be caused by several happenings:

The length of the flat top not being the same length, close proximity to another antenna or even a building or metal structure, different heights of each leg above ground. Knowing this and the unbalance, I now know my open wire feed line is radiating and can transmit vertical polorization as well as horizontal.

This test may not hamper your contacts or dx, but more or less to let you know how your antenna is going to perform. Yes, also to gain knowledge of what a balanced line can be and cannot be.

Have fun and enjoy the testing: you need not be a engineer or have expensive test equipment.

73, W6TH

Member Comments:
This article has expired. No more comments may be added.
 
Is Your Balanced Line Really Balanced?  
by KY6R on December 8, 2004 Mail this to a friend!
Thanks for some very interesting and useful information. I will try that out.
 
Is Your Balanced Line Really Balanced?  
by W5GNB on December 8, 2004 Mail this to a friend!
You can further balance the line by adding a 360-degree twist about every ten or twenty feet throughout the length of the line from the shack to the antenna. I have my antennas located nearly a Quarter mile from the shack and I have observed no radiation from the balanced line on any bands by being careful to ballance lengths and properly twisting the feeders...
 
Is Your Balanced Line Really Balanced?  
by WA6BFH on December 8, 2004 Mail this to a friend!
How about two RF Ammeters in each leg (or side) of the main feeder, out to the tuning network or antenna switcher?
 
Is Your Balanced Line Really Balanced?  
by NC9K on December 8, 2004 Mail this to a friend!
I use a multi-trace VHF scope to monitor my balanced line status and/or transmitted signal quality by clipping 10:1 probes over the the insulated line wires very close to my link coupled antenna tuner output. (I initially clipped directly to the link coupler output posts and set the scope to 50V/division, but high voltage flashed-over one of the probes and physically blew the 10:1 resistor pad right out of the end of the probe.) Anyway, I calibrate both probes next to each other on one insulated feed wire, and then invert the displayed polarity of one probe, separate the probes to the two wires equi-distant from the tuner output, and establish a third trace to display the sum of both probes. I achieve line balance when the "sum" goes to zero while individual line voltages go to maximum.

I have a "noisy" flourescent work light a few feet from the antenna feedline, and it is very easy to see the effects of tuner settings on the quality of my balanced line condition. I can have tuner settings that give perfect vswr readings ahead of the tuner, yet give poor line balance as indicated by the scope. And as to be expected, the "noisy" light produces noise in my receiver under the same unbalanced line conditions. When I set the tuner for good line balance, the noise from the light disappears from my receiver and my weak station reception improves considerably.

I applied the same test to a few high-dollar commercially made tuners that used output baluns, and as I discovered, these tuners had progressively poor line balance above 40M, and were useless as balanced line tuners at 20 through 10M. These tuners were still perfectly "matching" at 20 through 10M, but in reality were putting 80% of the power into resonating the antenna - feed system as an end fed wire, and 20% of the power between the balanced lines to feed the antenna proper. They also allowed severe received interference from the noisy light even though they had "tuned" my antenna. This effect could explain why so many people have trouble getting full TVI - RFI reduction and reduced received noise benefits from a "balanced" line feed system even though they have "tuned" their balanced antenna - feed system. These same commercial tuners received perfect or near perfect scores in reviews posted on eham.net.
 
Is Your Balanced Line Really Balanced?  
by NC9K on December 8, 2004 Mail this to a friend!
I have to add that my scope "sum" is of the two out-of phase line voltages - phase angles, and not of the "inverted" voltage vs. the non-inverted voltage.
 
Outta Whack in Da Shack  
by KA4KOE on December 9, 2004 Mail this to a friend!
I am inherent imbalanced, as Cal K4JSR and Mikee WA2JJH can heartily attest.

Why am I walking in circles with this buzzing in my ears?

How can we feed a fan dipole in this manner?

What does it all really mean, anyway?

PLEASE HELP ME THE VOICES ARE SCREAMING AGAIN!!!

Philip KA4KOE
Never "Amateur of the Year"
And Derned Proud of It
 
Is Your Balanced Line Really Balanced?  
by KA8VIT on December 9, 2004 Mail this to a friend!
In the "old" days... we would shunt a flashlight bulbs across each side of the ladderline. If there was an imbalance, the lights would not light equally bright.

A good reason for using a balance antenna tuner which allows you to tweak each side of the feedline.

Another reason for "twisting" the line from the tuner to the antenna is windloading.

72/73,

Bill KA8VIT
 
RE: Is Your Balanced Line Really Balanced?  
by KB9YZL on December 9, 2004 Mail this to a friend!
Thanks for an interesting read! We need more technical articles like this!

Now, …….If one of you guys would write an article entitled “A Beginner’s Guide to Antenna Analyzers and Their Use”, I would be eternally grateful. (As would many others like me, who are still on “The Lower Slopes” of the Learning Curve.)

Kent Carroll
KB9YZL
“Appliance Operator”

 
Is Your Balanced Line Really Balanced?  
by N4ZOU on December 9, 2004 Mail this to a friend!
I have an article waiting to be posted along the lines of this one. Stay "tuned" for it to appear on the front page soon!
 
RE: Outta Whack in Da Shack  
by K4JSR on December 9, 2004 Mail this to a friend!
Philip, I ain't touching that with a ten foot Pole,
much less a six foot Romanian! Besides, you left poor
old Charles out of the loop.
As far as being unbalanced, you'll just have to coax
yourself some serious questions.
Vito, I guess some folks just can't fathom the old
ways. I guess they are the "missing link" couplers.
Of course there are those of us who you can dress up,
but you dare not take us anywhere! ;-)
I enjoyed your recollections on testing balanced line,
Vito.
73, Cal K4JSR

PS. Philip has been running around with too many j and i operators. Poor boy cannot even get "normalized" on a Smith Chart! :-@
 
RE: Is Your Balanced Line Really Balanced?  
by KC8VWM on December 9, 2004 Mail this to a friend!
"Why am I walking in circles with this buzzing in my ears?"

I think it's the same shell shock they experienced in Vietnam when military personnel wore PRC-1099 HF man-pack radio's all day ?

I dunno, I could be wrong about this tho...

73

Charles - KC8VWM

"Amateur Of Radio"

 
RE: Is Your Balanced Line Really Balanced?  
by KA8VIT on December 9, 2004 Mail this to a friend!
PRC-1099... in Vietnam ??

In Nam there were PRC-25s and then later the solid state version.. the PRC-77.

72/73,

Bill KA8VIT
 
RE: Is Your Balanced Line Really Balanced?  
by KI7YY on December 9, 2004 Mail this to a friend!
Great article, thank you. 73, Kirk, KI7YY
 
RE: Is Your Balanced Line Really Balanced?  
by KC8VWM on December 9, 2004 Mail this to a friend!
PRC-1099... in Vietnam ??

Thank you for your corrective analysis.

(Note to self: o O strike out the word Vietnam and replace word with Antartica.)

"PRC 1099 Field Radios"

http://quest.arc.nasa.gov/antarctica/background/NSF/field-guide/manual8.html
 
RE: Is Your Balanced Line Really Balanced?  
by W3NRL on December 9, 2004 Mail this to a friend!
prc-25 and carried my prc-77

Happy Holidays to all
de
RTO 68-73
1ST LT 2/37a fa III
 
RE: Is Your Balanced Line Really Balanced?  
by W6TH on December 9, 2004 Mail this to a friend!

Is Your Balanced Line Really Balanced?


KA4KOE

K4JSR

KC8VWM

Thanks fellows for your interest in the post.

God bless you.


.:
 
Is Your Balanced Line Really Balanced?  
by VK1OD on December 9, 2004 Mail this to a friend!
An accurate SWR meter can only infer a specific load impedance (magnitude and angle) at just one value of VSWR.

When VSWR is 1, the load impedance is the impedance that the SWR meter was calibrated for, typically 50 ohms.

At any other VSWR, the load impedance could be any one of an infinite set of combinations of R and X.

If you are trying to tell us that your line is balanced if for example you read VSWR=2 on each side of the line at the same frequency, why does that imply balance when you have no assurance from the VSWR reading that both sides of the line are exhibiting the same impedance?

Owen
 
RE: Is Your Balanced Line Really Balanced?  
by N6AYJ on December 9, 2004 Mail this to a friend!
I liked your post, too, 'TH. Now we know why Riley suffered from excessive RF exposure the night before he decided that we weren't supposed to use phonetics.
 
RE: Is Your Balanced Line Really Balanced?  
by W6TH on December 9, 2004 Mail this to a friend!


If the feedline has no loss, and matches BOTH the transmitter output impedance AND the antenna input impedance, then - and only - then will maximum power be delivered to the antenna. In this case the VSWR will be 1:1 and the voltage and current will be constant over the whole length of the feedline. Any deviation from this situation will cause a "standing wave" of voltage and current to exist on the line.

You remember from elementary AC mathematics that a complex number has a "phase angle" associated with it. The phase of the reflected signal will be advanced or delayed depending upon whether the antenna appears inductive or capacitive to the feedline. If the antenna appears inductive the voltage will be advanced in phase, and if the antenna is capacitive, the voltage will be retarded. The reflective signal travels back to the transmitter and adds to the incident signal at that point.

.:
 
Is Your Balanced Line Really Balanced?  
by G0GQK on December 9, 2004 Mail this to a friend!
Don't know about that, but my wife says I've been unbalanced for years !
 
Is Your Balanced Line Really Balanced?  
by AI8H on December 9, 2004 Mail this to a friend!
(this ought to be good)
 
RE: Is Your Balanced Line Really Balanced?  
by KA4KOE on December 9, 2004 Mail this to a friend!
Is Your Balanced Line Really Balanced?


KA4KOE---You're welcome, and a Blessed Holy Christmas to you!

K4JSR

KC8VWM

Thanks fellows for your interest in the post.

God bless you.
 
Is Your Balanced Line Really Balanced?  
by W3ZD on December 10, 2004 Mail this to a friend!
"The reflective signal travels back to the transmitter and adds to the incident signal at that point."


Might try this and see if I can get a KW outa my 100 watt radio!. Hi.

Good article and to echo others, we meed more of this.

I remember an engineer friend of mine that had worked at Collins Radio who described another workers comment about VSWR circulating until it was disipated.

That cold be in heat at the tank ckt or into the air??? Oh well Merry Christmas to all

Clayton
W3ZD
 
Is Your Balanced Line Really Balanced?  
by W3ZD on December 10, 2004 Mail this to a friend!
"The reflective signal travels back to the transmitter and adds to the incident signal at that point."


Might try this and see if I can get a KW outa my 100 watt radio!. Hi.

Good article and to echo others, we meed more of this.

I remember an engineer friend of mine that had worked at Collins Radio who described another workers comment about VSWR circulating until it was disipated.

That could be in heat at the tank ckt or into the air??? Oh well Merry Christmas to all

Clayton
W3ZD
 
Is Your Balanced Line Really Balanced?  
by N6TZ on December 10, 2004 Mail this to a friend!
Here is the way I check for balance.

Just take a screwdriver and hold onto it with some of the metal making contact with your fingers.

Without changing your body position or the way you are holding the screwdriver, first touch one side of the line with the screwdriver tip and then the other side and note the difference in the amount of swr change.

If the change is about the same, then you probably have a balance.

Do this with only about 25 watts or so, and if you do not see enough change to note the difference, then use a five foot or so piece of wire clipped to the screwdriver instead of your body for the "unbalancing lead".

Hal, N6TZ@arrl.net
 
RE: Is Your Balanced Line Really Balanced?  
by N0TONE on December 10, 2004 Mail this to a friend!
These methods are all too complicated.

I squeeze the two wires close together, and clip an RF ammeter around them as a unit. The ammeter reads the difference current between the two wires. If it's zero, the line is balanced.

AM
 
RE: Is Your Balanced Line Really Balanced?  
by K4JSR on December 10, 2004 Mail this to a friend!
Vito, You date back to the days when radios either
had wind-up keys on the sides of them or either ran on kerosene! OK, so I exaggerate just ever so slightly! Seriously, I would really love to see you
come up with some articles on how radio was "back in
the day". Things like link couplers, real open wire
feedline, dynamotors, the golden age of military
surplus and hams. You da man on that as you lived and worked through all of that. Please share some more of your experirnces with us.
I think the ham radio community could well benefit from some history of how we got here.
I, for one, sit back in a state of awe and nostalgia
reading articles such as the one we are now commenting upon.
Many Thanks and have a Merry and Blessed Christmas.
73, Cal K4JSR
 
Is Your Balanced Line Really Balanced?  
by AI8H on December 12, 2004 Mail this to a friend!

Vito,

You are >offering< your knowledge and experience to others for use, vs those who try to >impose< theirs for self-esteem. That is the big difference between a critic and a fellow amateur. You are a humble fellow with the spirit of the hobby in mind and have considerable wealth of knowledge that we should all revere.

Thanks for a great article,

Merry Christmas!

Jeff
 
RE: Is Your Balanced Line Really Balanced?  
by N7DM on December 12, 2004 Mail this to a friend!
I, for one, consider my feedline balanced enough, when the 450 ohm twinlead into my house...past the TV...does not cause TVI !
 
Is Your Balanced Line Really Balanced?  
by WN9V on December 12, 2004 Mail this to a friend!
Many thanks for the original article and the added contributions. I learned a couple of alternative measurement methods from this discussion.

Ok, now I can determine that my antenna system is unbalanced. "Balance" being a condition of equal and opposite instantaneous currents so that the parallel style feeder does not radiate. An imbalance would not be a complete surprise. This doublet is off-center fed and part of it passes over the roof and other parts are near some tree foliage. Such lack of symmetry is probably more the rule than the exception for those of us who live on a city lot instead of an ideal antenna range.

Has anyone installed some remedies that can resolve the imbalance from the shack end of the feedline? That is, what can I add to the balanced feeder side of my matching device to bring about equal and opposite currents? This idea of forcing a balance brings up some questions:

Once I get the feeder to look balanced as it passes through the wall, is all the rest of the feeder balanced too? If balance at one point implies balance at all points along the length, then all is well, because I bet that if we measured right at the floating link coupled output of my matcher, we would see a balanced situation and I could stop worrying.

On the other hand, if a balanced condition at one point on the transmission line does NOT imply balance all along the length, then we better get a really long extension ladder to aid a more thorough survey of measurements up and down the feeder.

Looking for someone to restore balance to the system.

--Don WN9V

 
RE: Is Your Balanced Line Really Balanced?  
by W8AJU on February 14, 2005 Mail this to a friend!
W6TH/DEC.9/2004

I READ WITH INTEREST YOUR COMMENT ON PHASE ANGLE WITH BALANCED FEEDERS. DO TO THE FACT THAT FLAT TOP ON MOST ANTENNAS ARE SUBJECT TO MANY VARIABLES IN THE AREA OF THE ANTENNA WIRE EFFECTING THE REACTANCES,WILL THERE BE A DIFFERENT PHASE ANGLE INTRODUCED ON EACH SIDE OF THE LINE? IF SO THIS WOULD EFFECT THE BALNCE EVEN THOUGH THE CURRENTS ARE EQUAL, RIGHT OR WRONG?
W8AJU, WAYNE
 
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