Open wire feedline
 

I am feeding a 80 meter center feed with open wire, about 100ft feed-line.

Due to some new construction work that is going to start on the back of
our home this week I am forced to move the feed-line.

The original installation had about 50 ft vertical from the center of
the dipole and then across and under a raised wood porch and then up to
a second floor shack.

The porch is going and a new covered screened porch is replacing it.

I have three choices during construction, they a

1. Leave the 100' feed-line coiled out in the yard and not operate.
(Not a great idea)

2. Cut the feed line down to around 50' which would be temporary but
then I would have to splice it later after construction.

3. Coil about 40' near the 4:1 balun, however I am concerned that the
coiled feed line will act a one big inductor and change and or
significantly reduce the antenna efficiency.

#3 is the easiest but I am worried about open wire feed-line coiled,
thoughts please!

73 de
Ron W4LDE

Open wire feedline
 

Ron Walters wrote:
#3 is the easiest but I am worried about open wire feed-line coiled,
thoughts please!

Adjacent coils of parallel feedline should never be located
very close to each other. The minimum spacing should be a
few times the spacing between the wires.

What I do is use a dacron messenger line. For instance, if
a knot is tied in the dacron messenger line every two feet
and at each knot, the length of the parallel line is four
feet, a transmission spiral will result where 100 feet of
ladder-line can be spiraled into 50 linear feet of messenger
line. The ladder-line can be attached at the knots using
black nylon tie wraps. Hope this is understandable and helps.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

Open wire feedline
 

Ron Walters wrote in
t.net:

....
3. Coil about 40' near the 4:1 balun, however I am concerned that the
coiled feed line will act a one big inductor and change and or
significantly reduce the antenna efficiency.

#3 is the easiest but I am worried about open wire feed-line coiled,
thoughts please!

If you coil the transmission line so that the distance between turns is
much greater than the distance between the conductors, you will not
significantly alter its differential mode operation (which is its main
purpose in most antenna systems).

You will alter the common mode current distribution, probably for the
better. Remember that some folk use common mode chokes in systems using
open wire feeder, and you will create a common mode choke by coiling the
line as I described.

You could suspend the coil on a roughly horizontal span of nylon fishing
line to support and space the turns.

Owen

Open wire feedline
 

Wind 4 or 5 turns around an empty plastic water butt, and keep the
turns well separated. Like Owen said, it'll also serve as a nice
common-mode choke!

73,
Steve G3TXQ

Open wire feedline
 

On Sep 28, 2:44*pm, Ron Walters wrote:
I am feeding a 80 meter center feed with open wire, about 100ft feed-line..

Due to some new construction work that is going to start on the back of
our home this week I am forced to move the feed-line.

The original installation had about 50 ft vertical from the center of
the dipole and then across and under a raised wood porch and then up to
a second floor shack.

The porch is going and a new covered screened porch is replacing it.

I have three choices during construction, they a

1. *Leave the 100' feed-line coiled out in the yard and not operate.
(Not a great idea)

2. *Cut the feed line down to around 50' which would be temporary but
then I would have to splice it later after construction.

3. *Coil about 40' near the 4:1 balun, however I am concerned that the
coiled feed line will act a one big inductor and change and or
significantly reduce the antenna efficiency.

#3 is the easiest but I am worried about open wire feed-line coiled,
thoughts please!

#3 is less than optimal unless you actually want a big coiled piece of
feedline as part of your antenna setup. There are some folks that have
big coils of feedline just for impedance transformation purposes, I
always think it's odd but that's what they like.

Splicing parallel feedline (whether it be homebrew ladder line or
commercial window line) is not a big deal. The copper plated steel
stuff is hard to bend with your bare hands but is easy enough with
pliers. Splicing it with solder, and without a good mechanical twisted
splice, will mean that after some flexing it will be break at the
splice point. But make a good mechanical splice like in the handbook
and you'll do fine.

But if you don't really need that 50 feet of feedline then why keep
it? Straightest shot to the antenna will always be superior unless you
want that extra 50 feet for impedance transformation or something
else. Sounds like in most circumstances it'll be a win-win to keep the
shorter more direct routing.

Tim.

Open wire feedline
 

Tim Shoppa wrote:
But if you don't really need that 50 feet of feedline then why keep
it? Straightest shot to the antenna will always be superior unless you
want that extra 50 feet for impedance transformation or something
else.

100 feet of ladder-line with an 80m dipole is easy to understand.
The dipole is 1/2WL. The ladder-line is ~1/2WL. The low 80m
feedpoint impedance tends to be reproduced at the shack end
thus making for an easy match.

However, 50 feet of ladder-line is ~1/4WL. The low 80m feedpoint
impedance tends to be transformed to ~4k ohms. Most built-in
autotuners will not handle such impedances.

100 feet of ladder-line is also a good length for multiband
operation of an 80m dipole as can be seen from this chart:

http://www.w5dxp.com/pnts130.gif

50 feet of ladder-line seems to be a good length for HF amateur
frequencies above 10 MHz - not so good for 80m and 40m.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

Open wire feedline
 

On Sep 29, 10:07*am, Cecil Moore wrote:
However, 50 feet of ladder-line is ~1/4WL. The low 80m feedpoint
impedance tends to be transformed to ~4k ohms. Most built-in
autotuners will not handle such impedances.

I personally think it's unlikely that even if someone is trapped by
the fancy-pants autotuner they bought, that they probably don't need
an extra fifty feet of line to deal with it. In my experience even ten
extra feet of line at 80M can noticeably change the matching taps I
use on my tuner if you're working in the 1/4 WL 65 foot feedline
range. Of course that extra ten feet might make their fancy pants
autotuner crap out on 20M, etc. and I can see how someone might start
feeling like the old lady that swallowed the fly. I would rewrite the
song to "swallowed the autotuner".

Tim N3QE

Open wire feedline
 

Tim Shoppa wrote:
On Sep 29, 10:07 am, Cecil Moore wrote:
However, 50 feet of ladder-line is ~1/4WL. The low 80m feedpoint
impedance tends to be transformed to ~4k ohms. Most built-in
autotuners will not handle such impedances.

I personally think it's unlikely that even if someone is trapped by
the fancy-pants autotuner they bought, that they probably don't need
an extra fifty feet of line to deal with it. In my experience even ten
extra feet of line at 80M can noticeably change the matching taps I
use on my tuner if you're working in the 1/4 WL 65 foot feedline
range. Of course that extra ten feet might make their fancy pants
autotuner crap out on 20M, etc. and I can see how someone might start
feeling like the old lady that swallowed the fly. I would rewrite the
song to "swallowed the autotuner".


Wow, you do not like autotuners, eh?

I use both regular and autotuners, and both work pretty well for me.


Neither wear pants, fancy or otherwise 8^)

- 73 d eMike N3LI -

Open wire feedline
 

On Sep 29, 1:59*pm, Michael Coslo wrote:
TimShoppawrote:
On Sep 29, 10:07 am, Cecil Moore wrote:
However, 50 feet of ladder-line is ~1/4WL. The low 80m feedpoint
impedance tends to be transformed to ~4k ohms. Most built-in
autotuners will not handle such impedances.

I personally think it's unlikely that even if someone is trapped by
the fancy-pants autotuner they bought, that they probably don't need
an extra fifty feet of line to deal with it. In my experience even ten
extra feet of line at 80M can noticeably change the matching taps I
use on my tuner if you're working in the 1/4 WL 65 foot feedline
range. Of course that extra ten feet might make their fancy pants
autotuner crap out on 20M, etc. and I can see how someone might start
feeling like the old lady that swallowed the fly. I would rewrite the
song to "swallowed the autotuner".

Wow, you do not like autotuners, eh?

The autotuners that the neighboring hams have do not have knobs. They
just have a little button you push and then relays chatter and it
either succeeded or failed. There's a little LED idiot light to tell
you that it succeeded or failed.

I myself do not understand how a piece of radio equipment does not
have knobs. Or how it has little blinky LED's but no meters.

My homebrew tuner has alligator tips for selecting the turns on the
output link, as well as plug-in link-coupled coil sets for each band
and of course knobs on the variable caps. IMHO if a tuner has plug in
coil sets and alligator clips then you know you're cooking with gas. I
was looking a a picture of a station in the 1972 ARRL handbook last
night and realized that my tuner looks almost identical to the one in
the picture (which itself was probably 20 years old in 1972).

Tim.
Tim.

Open wire feedline
 

Tim Shoppa wrote:
On Sep 29, 1:59 pm, Michael Coslo wrote:
TimShoppawrote:
On Sep 29, 10:07 am, Cecil Moore wrote:
However, 50 feet of ladder-line is ~1/4WL. The low 80m feedpoint
impedance tends to be transformed to ~4k ohms. Most built-in
autotuners will not handle such impedances.
I personally think it's unlikely that even if someone is trapped by
the fancy-pants autotuner they bought, that they probably don't need
an extra fifty feet of line to deal with it. In my experience even ten
extra feet of line at 80M can noticeably change the matching taps I
use on my tuner if you're working in the 1/4 WL 65 foot feedline
range. Of course that extra ten feet might make their fancy pants
autotuner crap out on 20M, etc. and I can see how someone might start
feeling like the old lady that swallowed the fly. I would rewrite the
song to "swallowed the autotuner".
Wow, you do not like autotuners, eh?

The autotuners that the neighboring hams have do not have knobs. They
just have a little button you push and then relays chatter and it
either succeeded or failed. There's a little LED idiot light to tell
you that it succeeded or failed.

Those are simple indeed. My autotuner has channel memories, an analog
meter and a cool little lcd meter that tells me how much inductance and
capacitance are inserted in the circuit. plus I can manually adjust
both. It's pretty cool in fact.


I myself do not understand how a piece of radio equipment does not
have knobs. Or how it has little blinky LED's but no meters.

Majik? (grinning)

My homebrew tuner has alligator tips for selecting the turns on the
output link, as well as plug-in link-coupled coil sets for each band
and of course knobs on the variable caps. IMHO if a tuner has plug in
coil sets and alligator clips then you know you're cooking with gas. I
was looking a a picture of a station in the 1972 ARRL handbook last
night and realized that my tuner looks almost identical to the one in
the picture (which itself was probably 20 years old in 1972).

I certainly don't have anything against old school radios and tuners.
Dunno if you have yours this way, but I would be inclined to mount that
alligator clipped tuner coil on a nicely finished wood base, and go
really old school pretty with it. Maybe make the coil supports out of
the same type wood turned to a dowel or maybe even polished glass or
plastic. If yer going old school, flaunt it!

Anyhow, it's all good, old or new. Gives me a lot more to mess with
since I like both.


- 73 de Mike N3LI -