Ladder line Vs. Coax
Sonny Hood
system is RG-8X to my 75 meter inverted vee which is about 85 feet
away from the shack. I propose to replace some 88 feet of coax with
300 ohm window ladder line that is inserted into the coax run with 4:1
baluns to match the coax on each end. Also at the feed point of the
antenna switch from a voltage balun to a current balun (ferrite chock
type). By my calculations with a 98 watt generator I will increase
the power to the load by about 11-20 watts and with a 985 watt
generator, 117-210 more watts will reach the load. Figuring
theoretical total system (A) against total System (B) or by just the
difference in the 88 feet of ladder line versus coax. What do you
think the increase will be?
lt...@yahoo.com
- 'Doc
Highland Ham
Why not replace the complete coax feeder with twin lead feeder (if you
can keep it away from soil and/or metal) , and use a matching box
directly accepting the twin lead feeder ( without ferrite type balun),
be it 300 or 450 Ohms or approx 600 Ohms ladder line ?
It will improve efficiency and above all make the antenna multi-band.
Frank GM0CSZ / KN6WH
Tim Shoppa
I think you left out the losses in the balun. With a kilowatt even a
large (by ham standards) balun will get very warm if you leave the key
down... my guess is it's not quite as much as you're saving but
comparable. It all amounts to 10%, and that's such a tiny fraction of
a S-unit.
Now, if your antenna were an incredible mismatch to coax to begin
with, then ladder line makes good sense. Say you want to use your same
inv-V on 40M, then you'd run ladder line all the way to your tuner and
be in fat city.
Tim N3QE
John Passaneau
news:r6qq34tire06i75gm...@4ax.com:
One of the numbers that is hard to come up with is the loss through a
balun. The only number I could find for a voltage balun is a matched loss
of 0.075db, this would be times 2 in your setup. So there is loss, and it's
well known that the loss goes up with miss match. I think you are
neglecting the loss through the baluns and the miss match loss. Remember
your antenna will not be 50 ohms over a very wide frequency range.
Going open wire line all the way or changing to RG8 size coax will likely
work just as well and be simpler to do.
John W3JXP
Dieter Kiel
Hi,
> I think you left out the losses in the balun. With a kilowatt even a
> large (by ham standards) balun will get very warm if you leave the key
> down... my guess is it's not quite as much as you're saving but
> comparable. It all amounts to 10%, and that's such a tiny fraction of
> a S-unit.
The other side probably wouldn`notice the difference.
> Now, if your antenna were an incredible mismatch to coax to begin
> with, then ladder line makes good sense. Say you want to use your same
> inv-V on 40M, then you'd run ladder line all the way to your tuner and
> be in fat city.
I would not take TV ladderline if you have a high standing wave ratio,
and this will happen if you use the dipol for multiband purpose.
I`ve tested a dipol with about 20 m length (67 ft) for 80m.
At first I got almost the same s-meter report compared with a W3DZZ trap
dipol. But after a couple of month I noticed that the received signal
was up to 20 db down compared with the trap dipol. I only used 100 watts
but it broke the TV ladder line. Here I`ve learned what has happened:
http://www.w8ji.com/vswr_reactive_power.htm
I`m planning to build a new antenna with self built ladderline for
multiband purposes for one of the traps of my W3DZZ is broken. I扉e only
bought the spacers for the new ladder line.
--
73
DJ4PB
Cecil Moore
> Why not replace the complete coax feeder with twin lead feeder (if you
> can keep it away from soil and/or metal) , and use a matching box
> directly accepting the twin lead feeder ( without ferrite type balun),
> be it 300 or 450 Ohms or approx 600 Ohms ladder line ?
> It will improve efficiency and above all make the antenna multi-band.
Let's see how much improvement. Assuming a 50 ohm antenna,
3.8 MHz, and using Owen's xmission line calculator at:
http://www.vk1od.net/tl/tllc.php
85 feet of RG8x has a loss of 0.478 dB.
85 feet of 300 ohm twinlead has a loss of 0.424 dB.
How much will that 0.054 dB improve efficiency? 1%?
The coax has a 1:1 SWR. The 300 ohm twinlead has a
6:1 SWR. That makes the losses almost equal. If we
were talking about RG-213, the losses would be
0.308 dB, 0.116 dB better than the 300 ohm twinlead.
The following is becoming a myth: "One can ignore
the losses in twinlead and ladder-line."
Also - maybe he doesn't want to use a "matching box".
--
73, Cecil http://www.w5dxp.com
Tim Shoppa
> bought the spacers for the new ladder line.
I have a 135-foot dipole fed with approx 100 feet of home-made ladder
line and am incredibly happy with its performance from 80M all the way
to 15M.
Much of the joy of the ladderline was not in buying the parts to make
it, but making it from stuff on hand. I had a sheet of 1/8"
polycarbonate that I cut into 4"x3/8" strips, then drilled and
notched, to put a spacer every foot using tie-wires. Others boil
wooden dowels in paraffin for the spacers (the method recommended by
the 1930's ARRL Handbook). Seeing the ladderline go up 85 feet to the
middle of the dipole is a pure joy!
Tim N3QE
Roy Lewallen
discernible by the other station. As others have noted, even this
insignificant potential gain would be reduced by balun loss. But what no
one else has mentioned is that the ladder line loss can increase
significantly, possibly even dramatically, when it gets wet. Any
improvement you'll see from the proposed change will be due entirely to
placebo effect.
Roy Lewallen, W7EL
Cecil Moore
> I have a 135-foot dipole fed with approx 100 feet of home-made ladder
> line and am incredibly happy with its performance from 80M all the way
> to 15M.
Why those are good choices for lengths can be seen on
the following diagram:
http://www.w5dxp.com/pnts130.gif
You are relatively close to a low-impedance/current-
maximum point on all HF bands.
nm...@wt.net
If you switch from coax to ladder line and baluns or tuners, you are
going to lose a bit of efficiency I bet.
I always have when I've compared the two on that band.
You are converted from a pure and simple system which is a 50 ohm
radio, feeding 50 ohm line, which BTW at 75m is very low loss,
into an appx 50 ohm load. This "pure" system is probably 95%+
efficient on the 75m band as long as the coax is not junk.
In my opinion there is no better method of feeding a single band
dipole. Anything else is pretty much a step down as far as I'm
concerned. The *only* reason I would ever run that way is if I
wanted multi band use using ladder line and a tuner.
But in my case, I prefer multiple dipoles fed with a single coax.
The decrease in loss switching from coax to ladder line *on 75m*
is so small as to be nothing. But then you have baluns and tuners.
This is what is going to spoil the food. You will actually end up
with
a net loss at the end of the day. Maybe be a small loss, but I
bet it will be measurable on a meter if you used an A/B switch.
It was in my cases. Then you have the moisture issues, etc..
Do what you want, I prefer coax when feeding dipoles.
I usually use 213 on HF here at the house.
But at 3 mhz, even RG-58 is fairly low loss.
The mini 8 you are using should be a bit better than rg-58.
I think it's slightly larger and using foam if I remember right.
Owen Duffy
nos...@online.de:
> http://www.w8ji.com/vswr_reactive_power.htm
>
>
I assume Dieter that this is your recommendation of the article.
That article uses the term 'reactive power' in a non-conventional way,
though the term is a well known one (ie has a conventional meaning).
Conventional use is that the term 'apparent power' is applied to the
product of RMS voltage and current flowing into a two terminal load, and
the units are VoltAmps (VA), not Watts as used in the article.
Reactive power is the reactive component of apparent power, and expressed
in units of 'VoltAmpsReactive' (VAR).
'Real power' is the real component of apparent power and expressed in
units of Watts (W).
The relationship is that
apparentpower = (realpower^2 + reactive power^2)^0.5 .
This is all basic lumped component AC circuit theory, and holds at RF.
However, basic lumped component AC circuit theory is not a good way to
analyse antenna systems, expecially to determine transmission line losses
cause by highly reactive loads (which is what that article tries to do).
Owen
Owen Duffy
> I have an efficiency question concerning feed lines. My present
Sonny,
I have resisted the temptation to tell you that the question is wrong
rather than to answer the question... however...
You are trying to compare two configurations that are not optimal.
An optimal coax configuration would have a balun, usually at the antena
feed point so your coax loss budget is short changed a balun.
I assume from the fact that you have proposed coax that this is a one
band antenna. You haven't made it clear whether you can use an ATU to
transform the load to suit the tx, I will assume you can.
Why do you need two 4:1 baluns / transformers? The dipole is already an
approximately balanced load and loss on open wire line with a VSWR of 4:1
is still quite low. You could just attach the feedline directly to the
antenna, and use a 1:1 balun at the ATU. Alternatively, you could
lengthen the feedline a little so that it was an electrical half wave and
dispense with the ATU (still need the balun).
In the case of the latter (an electrical half wave of open wire line, 1:1
balun at the tx) you will achieve the lowest loss, but it is just a few
tenths of a db better than the balun/RG8X config if you work them
through.
The open wire line might not be as easy to route into and around the
shack, and depending on construction, more affected by water.
Owen
Sonny Hood
Thanks Guys, I got some good replies and it cause me to
reconsider the change. I find that the best and most simple change
will be to remove the RG-8X and it's high attenuation and install all
JT-2015 (RG-8 Type) from R&L Electronics. Also to put a good 1:1
balun at the feed point.
I have a 160M windom and a G5RV and will dedicate this
inverted vee antenna to 75M. This will be not used on 40M due to the
high resistance on the second harmonic with the current balun.
Yes the added baluns for the ladder line would increase the
insertion loss and yes the wet ladder line is a poor conductor. And
the cost will be spent for a more efficiency designed system.
K4WYS
Lisa
telling any difference.
Dave Oldridge
> I have an efficiency question concerning feed lines. My present
In one short word: imperceptible.
Using twinlead or ladder line is a good idea if you're feeding an antenna
that has a high SWR at the feedpoint on some of the frequencies you're
going to use it with, but at 75 meters, RG8X vs. ladder line will only
make a small difference if the SWR is at all close to 1. Less than half
a decibel, or a tenth of an S-unit!
Sure, it might make enough difference on very weak paths, but most of the
time nobody would be able to tell the difference on a direct on-air A-B
test!
And even that advantage almost disappears when the ladder line is wet.
Like I said, the picture is quite different at high SWR.
--
Dave Oldridge+
ICQ 1800667
Ralph Mowery
"Sonny Hood" <wrh...@cox.net> wrote in message
news:tk0s34557ge9q9nun...@4ax.com...
YOu have had many answers to your question, but have drawn the wrong
conclusion. If you replace the rg8x with some of the best low loss coax
(lmr400 for my example) you go from about .7 db to .2 db of loss on 80
meters. That is .5 db less loss. You will almost need an electron
microscope to see the s-meter move . Also 80 meters has so much noise on it
most of the time, you will not be able to hear the difference. I think it
was one db that was suppose to be the minimal detected difference in hearing
when the db scale was first put into use.
It may seem that if you have a 100 watt output transmitter you will go from
about 85 to 95 watts in a matched system. This may seem to be a lot , but
on the receving end it will not be noticed.
On maybe 20 meters and higher, especially 2 meters and up it does make good
use of the money to go to a higher grade of coax for weak signals.
Spend your money on something more productive.
Owen Duffy
> On Wed, 28 May 2008 10:16:45 -0400, Sonny Hood <wrh...@cox.net> wrote:
>
> Thanks Guys, I got some good replies and it cause me to
> reconsider the change. I find that the best and most simple change
> will be to remove the RG-8X and it's high attenuation and install all
> JT-2015 (RG-8 Type) from R&L Electronics.
Sonny, run the numbers at http://www.vk1od.net/tl/tllc.php before you
spend the money.
BTW, it will make NO difference on receive since S/N ratio on 80m is
almost entirely determined by band noise and small change in TL loss will
make no significant difference. Change in TL loss will affect the
strength of your transmitted signals.
> Also to put a good 1:1
> balun at the feed point.
Good move.
Owen
Ian White GM3SEK
>nos...@online.de (Dieter Kiel) wrote in news:1ihnz3n.wxm0z7nvxaivN%
>nos...@online.de:
>
>> http://www.w8ji.com/vswr_reactive_power.htm
>>
>>
>
>I assume Dieter that this is your recommendation of the article.
>
>That article uses the term 'reactive power' in a non-conventional way,
>though the term is a well known one (ie has a conventional meaning).
>
>Conventional use is that the term 'apparent power' is applied to the
>product of RMS voltage and current flowing into a two terminal load, and
>the units are VoltAmps (VA), not Watts as used in the article.
>
>Reactive power is the reactive component of apparent power, and expressed
>in units of 'VoltAmpsReactive' (VAR).
>
>'Real power' is the real component of apparent power and expressed in
>units of Watts (W).
>
>The relationship is that
>apparentpower = (realpower^2 + reactive power^2)^0.5 .
>
>This is all basic lumped component AC circuit theory, and holds at RF.
>
It's very misleading to quote "VAR powers" in the kilowatt range,
because the only power available to melt the feedline is 100W from the
transmitter. There is no magnification of real power.
The high value of "VAR power" is a theoretical result of the large RF
currents in the system. These result from an antenna feedpoint impedance
that has a very low resistive part and is almost entirely reactive. The
large RF currents are a genuine physical phenomenon, as also are the
high voltages a quarter-wavelength back along the feedline (if the
feedline is long enough, of course)... but if there were no losses in
the feedline, these would have no further effect. In spite of the wild
values of impedance, current, voltage, VSWR etc, if there were no losses
in the feedline then all of the RF power would still reach the antenna.
In a real feedline, the effect of the high currents is to divert almost
all of the available RF power away from the antenna and into the
feedline's own resistive losses - skin-effect losses in the copper
conductor, and dielectric losses in the plastic. Both of these result in
heating and softening of the plastic, which makes the dielectric loss
even higher. This tends to divert even more of the available power into
the weak spots, where the plastic finally melts.
But there is still only 100W available to do the damage.
No argument about the final conclusion - it ain't gonna work - but I
don't care for the explanation. There's no problem with "VAR power" for
anyone who already has a firm grip on the concepts, but it is not a good
way to explain those concepts to a newcomer.
--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek
Cecil Moore
... a very good posting with the exception (IMO)
of the choice of the word "magnification".
> There is no magnification of real power.
There is indeed no net increase in real average power.
However, "magnification" seems to be a poor choice of
words since its definition contains such words as
"apparent", "seems", "exaggerate", "overstate", ...
"magnify - to cause to *seem* greater" certainly describes
a feedline with 100W source power and 200W forward power.
> But there is still only 100W available to do the damage.
True, but a 100W laser can do a lot of damage. :-)
And a *magnifying* glass can start a fire.
Dieter Kiel
I think you are right, the referenced link of W8JI mixed up the
definitions. He used "kilowatts" instead of "1000 VAs". But for me the
text was very helpful. It also will give newcomers some information
about problems with short antennas. If you ask: What is responsible for
the losses of an antenna construction ? The answer would be: The losses
are proportional to the " Apparent Power VA" It`s "Scheinleistung" in
German language. I didn`t even know the term before it was mentioned
here.:(
I found this schematic in the wikipedia with the different terms
Real Power, Reactive Power, and Apparent Power:
http://en.wikipedia.org/wiki/Image:Power_Triangle_01.png
So if we use a short antenna, e.g. 20m for the 80m band or even the G5RV
we should use parts that can handle the "Apparent Power". I`ve seen
Sonny has already made up his mind using koax for the 80m Band. This
probably is a good idea, and I`m planning to build a monoband for my
favorite band and multiband antenna fed with a low loss ladder line to
cover all the bands. I`m not quite sure if a folded dipol as a monoband
antenna fed with ladder line would give better results as a coax fed
dipol. I have the equipment to match both kinds of feeding lines.
Michael Coslo
> I have a 160M windom and a G5RV and will dedicate this
> inverted vee antenna to 75M.
There's your answer. And here's the readers digest version of it.
As a rule of thumb, if you are going to use an antenna cut for a
specific band, cut it for that, and use coax, and a balun.
If you want to have multiple bands from one antenna without traps or
tricks, use ladder line and a tuner.
The ladder line can handle the wildly varying VSWR, and the tuner will,
well, allow the Xciever to see an impedence it likes.
- 73 de Mike N3LI -
Ian White GM3SEK
I have no intention of allowing *that* particular fire to start again!
Ed Cregger
"Sonny Hood" <wrh...@cox.net> wrote in message
news:r6qq34tire06i75gm...@4ax.com...
----------
In all likelihood, no one on the other end will ever be able to tell the
difference after you make the changes. Neither will you.
Ed, NM2K
nm...@wt.net
>
> ----------
>
> In all likelihood, no one on the other end will ever be able to tell the
> difference after you make the changes. Neither will you.
>
> Ed, NM2K
Maybe not from any practical standpoint, but I could see the
difference on a meter when I fed both a coax dipole, and a
ladder line dipole using the same tuner, which has antenna
switch, and meter built in.
So I could A/B real fast. I could see a slight difference on
receive switching between the two. And if it's enough to see
on a meter, I consider it a noticeable amount.
Most of the signals were in the 20-40 over 9 range being 75m,
and I'd see about 5 db worth of difference between the two
antenna/feed lines.
Course, I make no claim as to the exact DB amount of difference,
but I could see it on a meter.
After many years of 75 and 40 m operating using mostly NVIS
paths, I've come to the conclusion nothing will beat a dipole/loop/
turnstile fed with good coax for sheer system efficiency unless
say you had a run of several hundred feet or something...
Which of those three doesn't really matter much, although I
prefer the turnstile over the other two if I had a choice.
Nothing wrong with a loop, but in my cases, some sections
end up sagging closer to the ground, and you are often a
bit more prone to ground losses, and also overall performance
if sections of heavy current are low to the ground.
With a dipole or turnstile, max current is at the feed point, so
the ends of the wires height above the ground is often not quite
as critical.
As far as I can think of, only Cecil's no tuner/no choke system
would let a ladder line fed dipole equal or slightly beat a coax
fed. And in that case, I'm not sure how noticeable it would be,
being as the 213 I use is quite low loss at 3-4 mhz.
But like you say, for on the air, many would probably not
notice much. #1, you would have to do quick A/B transmit
tests for them to notice any difference, and also make sure
fading doesn't skew the results. It would be best to test with a
stable ground or space wave signal.
But... I still prefer coax.. I want every drop out I can get, and
I also much prefer the convenience of coax. IE: with most
antennas, no tuner required. And really not even a "balun"
required if you roll a choke out of the feed line itself and tie
wrap it. Weather is no issue with coax. I can have it sitting
in standing water with no problems.
The only time I use ladder line is mostly experimental
antennas where the feed point impedance is not the usual
50 ohms. If the mismatch to coax is high, ladder and the
tuner makes sense.
Ralph Mowery
<nm...@wt.net> wrote in message
news:805ed22e-e45f-48be...@b1g2000hsg.googlegroups.com...
> On May 30, 6:46 pm, "Ed Cregger" <ecreg...@bellsouff.net> wrote:
>
>>
>> ----------
>>
>> In all likelihood, no one on the other end will ever be able to tell the
>> difference after you make the changes. Neither will you.
>>
>> Ed, NM2K
>
> Maybe not from any practical standpoint, but I could see the
> difference on a meter when I fed both a coax dipole, and a
> ladder line dipole using the same tuner, which has antenna
> switch, and meter built in.
> So I could A/B real fast. I could see a slight difference on
> receive switching between the two. And if it's enough to see
> on a meter, I consider it a noticeable amount.
> Most of the signals were in the 20-40 over 9 range being 75m,
> and I'd see about 5 db worth of difference between the two
> antenna/feed lines.
> Course, I make no claim as to the exact DB amount of difference,
> but I could see it on a meter.
Most of it had to be the antennas. Going from almost no loss open wire to
much higher loss rg58 would be only 1 db at the most on 75 meters.
You still need a magnifing glass to see the smeter move this much on a ham
receiver.
nm...@wt.net
>
> Most of it had to be the antennas. Going from almost no loss open wire to
> much higher loss rg58 would be only 1 db at the most on 75 meters.
> You still need a magnifing glass to see the smeter move this much on a ham
> receiver.
What about the tuner loss? And.. I was using the least amount
of inductance needed to tune.. The difference was noticeable on a
meter.
So that would tend to indicate the difference was more than 1 db.
The 213 I use at the house would be even lower loss than the 58,
but I do use rg-58 sometimes when portable, etc..
Doesn't do any good to use a slightly lower loss feed line, if the
tuner
needed to match causes more loss than the feed line saves vs coax.
And tuners will vary also. Also setting the tuner itself can lose even
more power if the minimum inductance is not use. It's not too hard
to lose up to 20% of your power if the inductance settings are wrong.
I'll still stick with coax and no tuner. :)
Bob Miller
<sho...@trailing-edge.com> wrote:
> Seeing the ladderline go up 85 feet to the
>middle of the dipole is a pure joy!
>
>Tim N3QE
Having a dipole at 85 feet would be a joy :-)
bob
k5qwg