Coax + Ladder Line
 

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

Coax + Ladder Line
 

On Jun 13, 6:54*am, steveeh131047 wrote:
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

How interesting, so in both VK and UK (mixing abbreviations).. the
"reference plane" for the measurement is potentially "after" the
transmission line. The 5kW Active Antenna Tuner lives!

Here in the US, I'm sure the rule is interpreted the way it is because
of the heritage of "1kW DC power to the final stage" rule, which in
turn came from pre-ham radio rules for marine transmitters using
sparkgaps, etc... It was simple change from measuring plate current/
voltage to hooking a power meter at the output connector. I wonder if
anyone ever measured RF power on a non-50 ohm transmitter in an
enforcement action?

My father and grandfather both had stories, apocryphal perhaps, about
clever hams having very large "exciters" that fed through a relatively
low power "final stage"... using the final tube as a coupling
capacitor, perhaps, with unity gain.

Coax + Ladder Line
 

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

Coax + Ladder Line
 

Kash J. Rangan wrote:
Is it OK to place a 4:1 balun just outside
of the window for the transition?

Given the impedance seen by the balun, is a 4:1
transformation what you want?

If the impedance seen by the balun is 10 ohms,
for instance, do you think taking the impedance
down to 2.5 ohms is an improvement?
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

Coax + Ladder Line
 

Coax + Ladder Line
 

"Kash J. Rangan" wrote in
:

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?

If your antenna is balanced, it would probably be better to simply split
the ladder line onto the center conducters of two identical short coaxes
and then run ladder line inside to your tuner. If you MUST ground the
shields that's OK and you can use lightning arrestors on both coaxes. But
remember, no lighning arrestor is as good for protecting equipment as a
foot or two of air. Disconnecting during thunderstorms is solid policy!

--
Dave Oldridge+
ICQ 454777283

Coax + Ladder Line
 

"Dave Oldridge" wrote in message
0...
"Kash J. Rangan" wrote in
:

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?

If your antenna is balanced, it would probably be better to simply split
the ladder line onto the center conducters of two identical short coaxes
and then run ladder line inside to your tuner. If you MUST ground the
shields that's OK and you can use lightning arrestors on both coaxes. But
remember, no lighning arrestor is as good for protecting equipment as a
foot or two of air. Disconnecting during thunderstorms is solid policy!

--
Dave Oldridge+
ICQ 454777283

Sounds a little backwards. The Ladder Line should transition to coax
(balanced as you pointed out) inside to hopefully reduce RF in the shack.
An arrestor outside in addition to disconnecting from equipment will avoid
arcing in the shack at least. You have to be there to even remember to
disconnect.

Coax + Ladder Line
 

Mike Coslo wrote:
wrote:

Sure, there are losses with the balun used in most tuners, but I
consider that a price to pay for a multi band antenna.


Chiming in late on this one...


Mythical attributes aside, I believe the real reason that ladder line
has become more popular is:

1. Almost all rigs are All HF band these days.

2. Many people have just one antenna they can put up at any given time.
Whether it is space considerations, maintaining a low profile or
keeping the XYL happy I remember the discussions with my wife when I
wanted to put up the HF vertical. "Why do you need two antennas?" "Are
you going to transmit two signals at the same time?". Twasn't easy, and
a lot of Hams might lose that argument.

So assuming it is a doublet, and I wanted to run 80 to 10 meters, I'd
put up much wire as I could, not mess with coax, just run ladder line to
a window panel, then into the house, into a tuner that can handle
balanced line. And pay attention to the lengths that might make for
trouble in matching.


Or, put up as much wire as you can, put an autotuner at the feedpoint,
and run coax back to the shack.

probably a six of one, half dozen of the other, depending on what you
already have, what kind of support structures you have (if you are
putting up an inverted V, then supporting the weight of the tuner isn't
an issue..), etc.

lightning protection Coax + Ladder Line
 

Dave Oldridge wrote:
"Kash J. Rangan" wrote in


If your antenna is balanced, it would probably be better to simply split
the ladder line onto the center conducters of two identical short coaxes
and then run ladder line inside to your tuner. If you MUST ground the
shields that's OK and you can use lightning arrestors on both coaxes. But
remember, no lighning arrestor is as good for protecting equipment as a
foot or two of air. Disconnecting during thunderstorms is solid policy!


If you have a direct hit, a one foot air gap isn't necessarily going to
do you much good, unless the antenna end of the gap is on the ground
surface. (i.e. the wire going from where the coax ends to your
lightning dissipation ground has some non-zero inductance/resistance)

If you're worried about induced voltages from adjacent strikes, then a
good transient suppressor will help, but almost all suppressors have
"let through" voltage that is above the damage threshold for, say, a FET
front end. Depends on what your equipment sensitivity is.

Shorting the input of the radio and tying it to chassis ground.. that
WILL protect the radio.

Coax + Ladder Line
 

"Jim Lux" wrote in message
...
Mike Coslo wrote:
wrote:

Sure, there are losses with the balun used in most tuners, but I
consider that a price to pay for a multi band antenna.


Chiming in late on this one...


Mythical attributes aside, I believe the real reason that ladder line has
become more popular is:

1. Almost all rigs are All HF band these days.

2. Many people have just one antenna they can put up at any given time.
Whether it is space considerations, maintaining a low profile or keeping
the XYL happy I remember the discussions with my wife when I wanted to
put up the HF vertical. "Why do you need two antennas?" "Are you going to
transmit two signals at the same time?". Twasn't easy, and a lot of Hams
might lose that argument.

So assuming it is a doublet, and I wanted to run 80 to 10 meters, I'd put
up much wire as I could, not mess with coax, just run ladder line to a
window panel, then into the house, into a tuner that can handle balanced
line. And pay attention to the lengths that might make for trouble in
matching.


Or, put up as much wire as you can, put an autotuner at the feedpoint, and
run coax back to the shack.

probably a six of one, half dozen of the other, depending on what you
already have, what kind of support structures you have (if you are putting
up an inverted V, then supporting the weight of the tuner isn't an
issue..), etc.

for most people the feedline won't be that long so just put up the inverted
v, wind a coax choke at the feed point (or not) and just run it back to the
shack and use the tuner in the rig.