"Kash J. Rangan" writes:

Is it advisable to use a combination of Coax and a ladder line to feed a
simple horizontal multiband dipole antenna?

In my new QTH it would be very easy for me to get a short run of coax out of
my shack window but I would like to use a low loss ladder line for the main
run up to the antenna feed point. Is it OK to place a 4:1 balun just outside
of the window for the transition?

I use a combination of window line and coax for my 80m antenna. I
don't have enough space for a full size dipole, so I had to shorten it
somewhat. From memory, about 6m of window line makes up for about 3m
of missing wire on each dipole leg. Easier to do than loading coils,
that's why. EZNEC claims that losses are negligible, don't know if
that's really so or a transmission line model is inappropriate here.

Totally by accident, the antenna also ended up with a resonance in the
30m band.

Jon LA4RT, Trondheim, Norway

Thanks for all your responses and ideas.

Yes, I do have an antenna tuner. The maximum length of the antenna I can
hope for can only be about 65ft because of the placement of trees in my back
yard and access to my shack. At this time I will be happy if I can tune to
some bands up to 40M. I did not want to drill any additional holes for
outside access if I can help it amd make use of the existing one. I also
wanted the option of total disconnect from the outside. My equipment has
been fried by lightning in my previous QTH.

I figure it would be about a 60 ft run to the feed point. I am aware that
certain feed line lengths are to be avoided to minimize transmission line
radiation and tuning problems. In addition to low loss I thought ladder line
would be much lighter than coax. I don't have any way to support my antenna
at the center so I am trying to keep it as light as possible. Not sure of
the wind loads though but I will have a modest workable antenna up soon.

You all have been very helpful in sharing your thoughts.

73

AG4EL, Kash

On Jun 11, 11:17*am, "Kash J. Rangan" wrote:
Thanks for all your responses and ideas.

Yes, I do have an antenna tuner. The maximum length of the antenna I can
hope for can only be about 65ft because of the placement of trees in my back
yard and access to my shack. At this time I will be happy if I can tune to
some bands up to 40M. I did not want to drill any additional holes for
outside access if I can help it amd make use of the existing one. I also
wanted the option of total disconnect from the outside. My equipment has
been fried by lightning in my previous QTH.

I figure it would be about a 60 ft run to the feed point. I am aware that
certain feed line lengths are to be avoided to minimize transmission line
radiation and tuning problems. In addition to low loss I thought ladder line
would be much lighter than coax. I don't have any way to support my antenna
at the center so I am trying to keep it as light as possible. *Not sure of
the wind loads though but I will have a modest workable antenna up soon.

You all have been very helpful in sharing your thoughts.

73

AG4EL, Kash

If it were me and I were using a tuner, I'd just run ladder
line the whole way. I've noticed that even if you pass
the line across a metal window frame, there is usually
no noticeable change to speak of. If you have to do that,
it's best to keep the line at right angles to the frame to
keep it as balanced as possible.
You could easily chunk the line outside during storms,
or you could rig up a way to disconnect by using
banana plugs, etc.. That way you can disconnect but
not have to fiddle with unplugging from the rig.
I would prefer to have those outside, so when
disconnected the line is totally out of the house.
It's probably quite well known on this group that
I don't like mixing feed line types in a case like this. :/

Running ladder line the whole way is the least lossy
vs mixing ladder line with coax, choke, etc..
Using G5RV type feeding schemes will work, but they
can take a decent hunk of your RF and turn it to heat
in many cases.
Even with a 80/1 mismatch, ladder line has low loss.
If the length of coax is short, the loss will be fairly low.
But.. many add a choke, etc, and I think the choke
is where a good portion of the loss is on these type
of feed systems. Some of these might use fairly long
coax lines, and the loss could add up vs ladder line.
BTW... Tune the tuner using the least inductance
needed to get a usable match whichever way you go.

Running ladder line the whole way is the least lossy
vs mixing ladder line with coax, choke, etc..

Often, but not always:

* Depending on the impedances, frequencies and lengths involved, the
loss in a coax section can be lower than in the equivalent length of
ladderline.
* Although there may be losses in a 1:1 current balun at the
ladderline/coax transition, don't forget that there will also be
losses in the tuner balun if ladderline is used all the way; if the
ubiquitous 4:1 tuner internal voltage balun is used, those losses
could be significant.

Steve G3TXQ

In message
,
steveeh131047 writes
Running ladder line the whole way is the least lossy
vs mixing ladder line with coax, choke, etc..

Often, but not always:

* Depending on the impedances, frequencies and lengths involved, the
loss in a coax section can be lower than in the equivalent length of
ladderline.
* Although there may be losses in a 1:1 current balun at the
ladderline/coax transition, don't forget that there will also be
losses in the tuner balun if ladderline is used all the way; if the
ubiquitous 4:1 tuner internal voltage balun is used, those losses
could be significant.

Maybe, instead of 'ubiquitous', read 'inappropriate' (at least on
certain occasions). I'm sure that, if you can't resist the urge to use
coax, a current balun / longitudinal choke (often wound from the coax)
could have much less loss.
--
Ian

wrote in
:

....
Even with a 80/1 mismatch, ladder line has low loss.

30m of Wireman 551 with a load of 5+j0 has VSWR=80 at the load end, VSWR=28
at the source end, and the transmission loss is 4.6dB... 65% of the input
power is converted to heat.

Speaks to your meaning of "low loss".

Mythical properties are ascribed to ladder line, some of attributable to
ARRL publications.

Owen

Owen Duffy wrote:
wrote in
:

...
Even with a 80/1 mismatch, ladder line has low loss.

30m of Wireman 551 with a load of 5+j0 has VSWR=80 at the load end, VSWR=28
at the source end, and the transmission loss is 4.6dB... 65% of the input
power is converted to heat.

Speaks to your meaning of "low loss".

Mythical properties are ascribed to ladder line, some of attributable to
ARRL publications.


Or, I think more properly, to statements in ARRL publications taken with
a different set of underlying assumptions..

For instance, ladder line between a tube amp output tank and a doublet
is probably "reasonably" low loss in most common practical applications..

And in an inappropriate application (reactive load with weird Z to 50
ohm transmitter) it's probably lower loss than RG-58.

Maybe it's that subjective term "low loss"???

Half a dB per foot is low loss at 32 GHz, but you'd be hard pressed to
find a commercially available transmission line with that kind of loss
at 7 MHz. (maybe that funky 1000 ohm Z delay line stuff?)


Ham applications in any case are kind of an odd thing, efficiency-wise,
since the limit is on RF power at the transmitter output connector.
Pretty much every other user of RF power amplifiers sets the system
measurement plane somewhere else.. in space (EIRP or ERP) or at the
power source (power budgets). For instance, you can trade increased
power consumption against lower feedline loss.

Jim Lux wrote in
:

....
Mythical properties are ascribed to ladder line, some of attributable
to ARRL publications.


Or, I think more properly, to statements in ARRL publications taken
with a different set of underlying assumptions..

The ARRL has long published characteristics of "Generic ladder line"
being #18 conductors spaced 1". They publish loss figures better than
theoretical loss for the same size copper conductors in a vacuum (eg at
10MHz, about 0.27dB/100m vs 0.47dB/100m).

The second factor is, I think, the notion that since one-way loss is
relatively low on open wire lines, that it is safe to consider it
*always* insignificant (irrespective of VSWR), then exagerate the point
by talking about it being essentially lossless at extreme VSWR.

I think that the best characterisation we have of ladder line is that of
Wes, N7WS. Similar measurements at lower frequencies might well reveal
whether the stranded copper clad steel versions have inadequate cladding
depth for copper-like performance at low HF.


For instance, ladder line between a tube amp output tank and a doublet
is probably "reasonably" low loss in most common practical
applications..

Perhaps a better concept is "acceptable loss" where acceptable is
influence by the application. The compromises accepted for multiband
operation might well include 3dB of line loss on the lowest band.

....
Ham applications in any case are kind of an odd thing,
efficiency-wise, since the limit is on RF power at the transmitter
output connector. Pretty much every other user of RF power amplifiers
sets the system measurement plane somewhere else.. in space (EIRP or
ERP) or at the power source (power budgets). For instance, you can
trade increased power consumption against lower feedline loss.

Actually, interesting you mention that.

I recently had cause to probe the meaning of the term "transmitter" in
our (VK) regulatory framework. Whilst we are limited in transmitter power
output, the meaning of transmitter is relevant.

From our legislation:

===quote

8 Definitions of radio emission and transmitter

(1) For the purposes of this Act, a radio emission is any
emission of electromagnetic energy of frequencies less than 420 terahertz
without continuous artificial guide, whether or not any person intended
the emission to occur.

(2) For the purposes of this Act, a transmitter is:

(a) anything designed or intended for radio
emission; or

(b) any other thing, irrespective of its use or
function or the purpose of its design, that is capable of radio emission.

=== end quote

It could be argued that an "emission" exists beyond the antenna ("without
continuous artificial guide"), and that everything up to an including the
antenna could be captured as part of a "transmitter" as defined.

Though there is a well understood ordinary meaning to the word
"transmitter", the drafters of the legislation have provided a definition
that should override any ordinary meaning in the context of that law.

Perhaps we (VK) are entitled to apply our limit to radiated power!

Owen

On Jun 13, 12:05*am, Jim Lux wrote:

Ham applications in any case are kind of an odd thing, efficiency-wise,
since the limit is on RF power at the transmitter output connector.

Jim,

That's not the case in the UK. The licence conditions specify "....
power supplied to the antenna by a transmitter ...."

Steve G3TXQ

On Jun 12, 5:43*pm, Owen Duffy wrote:
wrote :

...

Even with a 80/1 mismatch, ladder line has low loss.

30m of Wireman 551 with a load of 5+j0 has VSWR=80 at the load end, VSWR=28 *
at the source end, and the transmission loss is 4.6dB... 65% of the input
power is converted to heat.

Speaks to your meaning of "low loss".

Mythical properties are ascribed to ladder line, some of attributable to
ARRL publications.

Owen

I might have been a bit carried away with the degree of mismatch
and loss, but I still think running the ladder/window line the whole
way to the tuner will still be the best in most cases for "all band"
use.
If the major portion of the feed line will still be ladder line, even
with
the coax lead in, he will still deal with the same line losses for the
majority of the run with such a severe mismatch.
It won't be that bad most of the time.
With the coax and choke addition, even more loss is added to the
system. And if he saw an 80:1 mismatch, just 15 feet of RG-8
should cost you half your power at 14 mhz. That's more loss than 15
extra feet of the ladder line which at 80:1, should be about 1 db loss
or so.
I just find the addition of the coax and choke as totally unnecessary
unless there is no way at all to feed the ladder/window line through
to the shack.
Sure, there are losses with the balun used in most tuners, but I
consider that a price to pay for a multi band antenna.
Myself, I don't use many all band antennas..
Most of my dipoles are single band, and coax fed. :/
Here is one online calculator which seems to match your
numbers fairly close if set for 14 mhz. They include the
551 line as one of the choices.
I notice "generic" 450 line has less loss.. I don't know
what the difference is between generic and 551..
Maybe 551 has more plastic, and less open window..
I notice generic 600 ohm ladder line will show about 2.2 db
loss with an 80:1 mismatch. I'll agree.. Maybe not low loss,
but it's quite usable considering an ugly 80:1 mismatch.


http://www.qsl.net/co8tw/Coax%20Calculator.htm