Q about balanced feed line
 

Roy Lewallen wrote:
The value of Kelvin's contributions is unquestionable. But even he
didn't get it right all the time.

And Roy, allow me to point out, in that respect, you don't
get it right all the time either. I can prove to you that
reflected waves contain joules but you simply refuse to
listen and have "ploinked" me. What really aggravates me
is that when an internet guru, such as yourself (or W8JI)
appears to be on the verge of losing an argument, you simply
kill-file the opponent and refuse to continue the thread.
--
73, Cecil http://www.qsl.net/w5dxp

Q about balanced feed line
 

On Sat, 25 Feb 2006 21:31:17 GMT, The Benevolent dbu
wrote:

I am also concerned that the feedline may be causing unbalance condition
because it is routed straight down perhaps 30 feet from the feedpoint
then it makes a sharp turn to the shack and at that point it is parallel
with one leg of the antenna for about 30 feet.

Hi Al,

Too much worry can come from too little problem. You need only ask
yourself does the line inappropriately inject receive signal from the
nulls of your antenna; or do you get RF in the shack? If neither are
a concern, there is certainly nothing worse to worry about.

It's the only way I can
do it. I have thought of discarding the multiband doublet for a plain
dipole with 52 ohm coax. I do like the doublet and my Johnson matchbox,
besides I can use this antenna on 160 when I route the feedline via a
knife switch over to my MN2700 and configure it to a inverted L.

Nothing here suggests you change anything.

73's
Richard Clark, KB7QHC

Q about balanced feed line
 

If the antenna system can be satisfactorily matched to the transmitter
output impedance, it would seem to matter little whether the feed line
currents are balanced, or, if they are not, by how much.

If there are no obvious common mode currents causing problems in the
shack, then of what consequence would an imbalance be, other than to
modify the radiation pattern, perhaps even beneficially?

Chuck, NT3G

Cecil Moore wrote:
Big Endian wrote:

An unbalanced condition would have a meter indication, like current
flow? Balanced the meter needle would not move?


Yes, for a balanced condition, the meter needle should
not move.

Q about balanced feed line
 

chuck wrote:
If the antenna system can be satisfactorily matched to the transmitter
output impedance, it would seem to matter little whether the feed line
currents are balanced, or, if they are not, by how much.

If there are no obvious common mode currents causing problems in the
shack, then of what consequence would an imbalance be, other than to
modify the radiation pattern, perhaps even beneficially?

You have to remember that the common mode feedline current doesn't stop
at the rig. It continues to the Earth by whatever means are available.
So your house wiring, appliance cords, and other odd conductors often
become part of your antenna system. These aren't likely to be very
efficient radiators. People often go to a lot of trouble to put their
antennas high and in the clear. That doesn't make much sense if you're
going to have your house do a good part of the radiating.

But you can still talk to lots of stations even if some of your
radiating is being done by your feedline and house wiring. And that's
enough for a lot of folks.

Roy Lewallen, W7EL

Q about balanced feed line
 

If the antenna system can be satisfactorily matched to the
transmitter
output impedance, it would seem to matter little whether the feed
line
currents are balanced, or, if they are not, by how much.

If there are no obvious common mode currents causing problems in the
shack, then of what consequence would an imbalance be, other than to
modify the radiation pattern, perhaps even beneficially?

Chuck, NT3G
==========================================
I agree with what you say.

But antenna (or line) unbalance and line-to-antenna impedance mismatch
are not entirely independent of each other.

An unbalanced line or antenna causes a small impedance mismatch.
Because it is small is the reason why it very often happens it doesn't
matter very much whether or not a balanced feedline is used.

For example, a coax line can be used quite successfully to feed a
balanced dipole.

And, in practice, no antenna is perfectly balanced about ground.
----
Reg.

Q about balanced feed line
 

chuck wrote:
If there are no obvious common mode currents causing problems in the
shack, then of what consequence would an imbalance be, other than to
modify the radiation pattern, perhaps even beneficially?

The purpose of the antenna is to radiate. The purpose
of the transmission line is to transfer the energy from
the transmitter to the antenna with as little loss as
feasible. How much an antenna system is allowed to
deviate from its purpose is up to the individual. When
I was in high school, I didn't much care about the purpose
of an antenna system and burned a hole in my lip.
--
73, Cecil http://www.qsl.net/w5dxp

Q about balanced feed line
 

In article ,
Roy Lewallen wrote:

chuck wrote:
If the antenna system can be satisfactorily matched to the transmitter
output impedance, it would seem to matter little whether the feed line
currents are balanced, or, if they are not, by how much.

If there are no obvious common mode currents causing problems in the
shack, then of what consequence would an imbalance be, other than to
modify the radiation pattern, perhaps even beneficially?

You have to remember that the common mode feedline current doesn't stop
at the rig. It continues to the Earth by whatever means are available.
So your house wiring, appliance cords, and other odd conductors often
become part of your antenna system. These aren't likely to be very
efficient radiators. People often go to a lot of trouble to put their
antennas high and in the clear. That doesn't make much sense if you're
going to have your house do a good part of the radiating.

But you can still talk to lots of stations even if some of your
radiating is being done by your feedline and house wiring. And that's
enough for a lot of folks.

Roy Lewallen, W7EL

I'm always concerned about TVI and telephone I. and that is another
reason I hope to have my feeders balanced, so they radiate minimum RF.
I was using a field strength meter while I had the transmitter going the
other day and working the antenna along some table lamps and the
electrical wire I found the F.S. meter would jump up quite a bit. So
what you say about re-radiating house wiring is surely true.

Q about balanced feed line
 

Thanks for the responses.

Put differently, I guess the purpose of the entire station is to radiate
and intercept radiated waves containing information. I was trying to
explore the benefits and consequences of preventing transmission line
radiation as they relate to this more global purpose.

While it is clear that maintaining balance in the line will prevent
radiation from the line, some (maybe all) of the radiation prevented
might have contributed to the global purpose of the station. For
example, radiation from common-mode currents in a vertical transmission
line could produce beneficial low-angle, omnidirectional radiation, as
has been pointed out often on the group.

It would seem that for the common-mode transmission line currents the
antenna system would look like a top-loaded vertical, ignoring the
balanced line currents and their interaction with the horizontal portion
of the antenna.

The efficiency of the vertically polarized radiation from the line would
depend heavily on the station's RF ground system. But basically we would
have (for the common-mode currents) a conventional vertical antenna with
all its attendant plusses and minuses.

To the extent the AC grounding conductor in the house presents a lower
impedance than the station's RF grounding system, we would expect to see
displacement currents in the AC system, just as with an "ordinary"
vertical using a poor RF ground.

Coupling to the telephone wires also would seem to be a consequence of a
vertical radiator with a poor RF ground, rather than a consequence of
transmission line imbalance (which I understand is the cause of the
radiation in the first place).

So here is my main question: do we object to the vertical radiation per
se (i.e., if we wanted vertically polarized radiation, we would have put
up a vertical in the first place), or is radiation from an unbalanced
line somehow more insidious in that it causes other problems that
"ordinary" verticals do not cause? In other words, why do we really care
about imbalance?

Reg has called attention to another of my shortcomings: I have no idea
how the common-mode line currents that enter a link in the tuner are
seen and "processed" by the tuner. It would seem that the link appears
as one plate of a capacitor for those currents.

Thanks again for everyone's patience.

Chuck, NT3G






Cecil Moore wrote:
chuck wrote:

If there are no obvious common mode currents causing problems in the
shack, then of what consequence would an imbalance be, other than to
modify the radiation pattern, perhaps even beneficially?


The purpose of the antenna is to radiate. The purpose
of the transmission line is to transfer the energy from
the transmitter to the antenna with as little loss as
feasible. How much an antenna system is allowed to
deviate from its purpose is up to the individual. When
I was in high school, I didn't much care about the purpose
of an antenna system and burned a hole in my lip.

Q about balanced feed line
 

Please change my reference to a "link" in the tuner to the symmetrical
taps on the inductor in the tuner. Sorry. I still have the same
conceptual problem with common-mode currents entering that inductor.

Chuck, NT3G

Q about balanced feed line
 

chuck wrote:
So here is my main question: do we object to the vertical radiation per
se ...?

Maybe an example would help. I model a dipole until
I am happy with the results predicted by EZNEC. The
take-off-angle is perfect for my schedule to AZ.
EZNEC assumes no feedline radiation. I am sloppy
about putting my dipole in the air and lots of feedline
radiation results which goes off in directions not
predicted by EZNEC. Murphey's Law predicts that the
unknown directions will be bad (entropy never
decreases). Besides, half of my feedline is routed
horizontal under the eaves of my house.

So would you rather deal with the devil you know or
trust the angel that you don't know? Does the angel
that you are trusting really understand entropy?
--
73, Cecil http://www.qsl.net/w5dxp