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eHam Forums => Antenna Restrictions => Topic started by: KJ4TRI on July 09, 2012, 01:38:12 PM



Title: Ladder Line question
Post by: KJ4TRI on July 09, 2012, 01:38:12 PM
Hello all,

I picked up an FT-817ND as my first “shack” radio (yea, yea bad first choice with QRP, but I am looking forward to the challenge). I do not have an auto tuner but plan on picking one up. The long term goal is to become familiar enough with the 817 to turn it in to a pack radio and eventually “upgrade” to something slightly more powerful (for this layout no more than 200 watts).

Due to HOA I have to go stealth in the attic.

I want to conceal the ladder line between the wood and corner molding of the plastic siding. This would run, approximately, 3 stories from a walk out basement to the soffit where I can handle any stand offs that may be needed once it enters the attic. My question is, how much heat/interference (radiated or inducted interference) will I have to be concerned with.  I am still not sold on the ultimate attic design but it will probably be a dipole.

Again the question is, can I run Ladder Line, up to 200W in such close proximity to vinyl siding and wood or is my shack location a no-go from the start.

Any advice would be appreciated.

Tim
KJ4TRI


Title: RE: Ladder Line question
Post by: K5LXP on July 09, 2012, 02:20:36 PM
I picked up an FT-817ND as my first “shack” radio
...
Due to HOA I have to go stealth in the attic.

Yeah,  you'll have a challenge alright.


Quote
My question is, how much heat/interference (radiated or inducted interference) will I have to be concerned with.

Heat won't be a problem.  Interference is another question and depends a lot on your specific installation.  It could be totally quiet or RFI hell.  No way to know until you try it.


Quote
I am still not sold on the ultimate attic design but it will probably be a dipole.

Consider a loop too.


Quote
can I run Ladder Line, up to 200W in such close proximity to vinyl siding and wood

Feedline should never get hot.  The energy is delivered to the load and radiated.  (Ideally) nothing will even get slightly warm and if it does, it will be a lumped component and not the wire.

At high voltage nodes there is an opportunity for arcing.  The fix for that is to keep conductors a safe distance from combustibles.

Another option is to put a remote ATU in the attic and use coax from your shack to the attic.  I think it would be easier to mitigate common mode that way.


Mark K5LXP
Albuquerque, NM



Title: RE: Ladder Line question
Post by: N4UM on July 09, 2012, 03:31:36 PM
I like K5LXP's suggestion about running coax to the attic and having a remote autotuner close to the antenna feedpoint. 

If you're really set on the ladder line idea, consider whether or not you can run it inside PVC conduit up the side of the house.

I have a dipole in my attic and it really picks up a lot of electrical noise on 80 and 40 meters.

My main antenna is a 23 foot "flagpole" in my back yard with 50 20-foot radials that works well on 40 thru 10.  I feed it thru 13 feet of buried coax going to an autotuner inside a Rubbermaid cabinet on my back porch with about 75 feet of coax going from my rig to the autotuner.


Title: RE: Ladder Line question
Post by: KJ4TRI on July 10, 2012, 03:27:45 AM
Thank you both for your opinions and help.

Am I missing something with the coax? I thought the point of ladder line was for low loss? Is the loss factor somehow negated between the auto tuner and the radio (yes the auto tuner adjusts for the overall length but why make it work harder)? I was going with a 5W output and approximately 50 feet from the station to the antenna. I do data cabling (fiber and copper) design and installation, so I have no problem picking up some LMR400 (not sure about adequate pathway but that is my problem).  Even with LMR400, it was my understanding that I was looking at between 0.35db and 1.35db of loss. Granted not much but again if I am starting with 5W I will be looking to make the system as efficient as possible.

It never occurred to me to place the tuner at the antenna location, just one of those “should have been obvious” brilliant ideals. Now you’re going to make me consider a radio with a separation kit and research the maximum separation distance.

Thank you both for your input on this.

Tim
KJ4TRI



Title: RE: Ladder Line question
Post by: N3WAK on July 10, 2012, 04:16:46 AM
Jim--I like the idea of coax to a remote tuner, with ladder line from there to your dipole. 

If you run coax, even excellent, low loss coax like LMR 400, to an antenna that is not resonant on the frequency on which you want to operate, you'll have an elevated SWR, as you know.  So, feeding a 20 meter dipole with coax will work great on 20 meters, but there'll be a lot of signal loss on 17 or 15 meters, for example.  However, as you know, ladder line is very low loss, so if you run a length of coax from your transceiver to a tuner (whether manual or automatic), and use ladder line from your tuner to your antenna, you need to realize that you have two discrete parts to your antenna feedline.  The part from your transceiver to your tuner is coax, but there's relatively very little loss in the transmitted and received signal between the two because the SWR is low (your tuner sees to that).  The second part is the ladder line from the tuner to the antenna.  The SWR is high on the ladder line side, but that doesn't matter (relatively speaking) because even with high SWR your loss will be miniscule at HF. 

A lot of people feed their resonant dipoles with coax because the SWR that the transmitter sees is low.  With a low SWR, on HF with a reasonable length of good coax, feeding a 40 meter dipole with coax will work great--as an example.  But because you can't use a 40 meter dipole on 20 meters if you're feeding it with coax (or, more aptly, you wouldn't want to because of horrendous losses in the coax even if you were using a tuner to make the transmitter happy), people instead feed their 40 meter dipole with ladder line and, with a tuner, happily use it between 40-10 meters. 
You just have to locate a tuner somewhere between the transmitter and the antenna. 

Some people use a 3' coax jumper from their transmitter to a manual tuner located in the shack, with LL from there.  Others use a 50' length of coax to a remote, autotuner, with LL from there.  It makes no difference in your signal--it's all up to you how you want to arrange your shack and antenna system.  The nice thing about a remote autotuner is that it gives one a lot of flexibility, since it is easier for most people to run coax into their shack than ladder line--but either way works fine. 

One last thing--as a general rule, because LL has lower losses at HF than coax, it's better in a technically pure sense to have more ladder line and less coax as your antenna feedline.  However, in the real, every day world, using coax at HF if your SWR is less than 3:1 (decent coax of a reasonable length--say, less than 100'), you'll be fine.  You'll have next to no losses on 160 meters even with a 5:1 SWR (IMHO), but you'll have higher losses on 10 meters since coax loses more signal (even with a low SWR) the higher you go in frequency.

So, keep your SWR <3:1 at HF if your antenna feedline is all coax.  (Often, by the way, your 40 meter 1/2 wave dipole will work fine on 15 meters as a 3/2 wave dipole, with a low SWR, even with coax.)   If you're using a tuner and feeding your antenna with LL, don't worry about SWR.  Relax and be happy. 

Good luck and 73!  Tony


Title: RE: Ladder Line question
Post by: WB6BYU on July 10, 2012, 05:05:57 AM
Quote from: KJ4TRI

Am I missing something with the coax? I thought the point of ladder line was for low loss? Is the loss factor somehow negated between the auto tuner and the radio (yes the auto tuner adjusts for the overall length but why make it work harder)?



The loss depends on the SWR on the line.  If you are feeding a single antenna on multiple bands,
likely the SWR will be high on some bands, which increases the losses in the coax.

The ladder line has lower losses, especially when operated at high SWR.  (Usually, but not always.)
So if you have to use an antenna that isn't matched on some bands with a tuner in the shack,
ladder line is often a good choice.

But if the SWR is low, most sorts of coax will have reasonably low losses at HF.  By putting your
tuner in the attic, it should provide a good match to the coax.

Here is a great calculator to see the relative losses of various sorts of cables:

http://www.vk1od.net/calc/tl/tllc.php

For example, even using RG-58 coax on 10m, the loss in 50' is just over 1dB when the coax has
a low SWR, and it will be less on the lower frequencies).  It is only 0.34dB using LMR-400 if you
can run that without it being too noticeable.  Those losses will hardly be significant on HF.



Title: RE: Ladder Line question
Post by: KG4NEL on July 10, 2012, 11:47:19 AM
Icom's integration with the AH-4 tuner sounds like it would work perfectly for you :) I used a 706MKIIG for a while with an attic loop - tough going with an indoor antenna, definitely. Using Morse or a digital mode would be a huge advantage under these compromises.

If you don't want to be tied down to a single brand of transceiver, SGC would be one to look at too.


Title: RE: Ladder Line question
Post by: AB4D on July 10, 2012, 03:30:45 PM
As others have suggested, use a tuner at the antenna feed point and feed it with coax. I did this for several years to feed a delta loop antenna with an SGC 239 auto tuner. The antenna worked great for what it was.  However, I mounted my antenna outside with the tuner and feed line contained out of sight inside the attic. I used 18 gauge copper weld for the antenna, extended out to each corner and across of the back yard, which was nearly invisible.  A next door neighbor once asked what it was for, I told him SW reception.  He indicated that he used to listen to short wave too when he was a teenager. I never heard another word about it from anyone else for the 5 years I was there.

73


Title: RE: Ladder Line question
Post by: W5DQ on July 12, 2012, 02:36:11 PM
At high voltage nodes there is an opportunity for arcing ---- FT-817ND ???

Now chew on that for a minute  ;D


Title: RE: Ladder Line question
Post by: K5LXP on July 13, 2012, 07:20:52 AM
At high voltage nodes there is an opportunity for arcing ---- FT-817ND ???    Now chew on that for a minute  ;D

Per the original question:

eventually “upgrade” to something slightly more powerful (for this layout no more than 200 watts).


Title: RE: Ladder Line question
Post by: W5DQ on July 13, 2012, 08:43:03 AM
At high voltage nodes there is an opportunity for arcing ---- FT-817ND ???    Now chew on that for a minute  ;D

Per the original question:

eventually “upgrade” to something slightly more powerful (for this layout no more than 200 watts).

I know that ... where's your funny bone ... it was just funny hearing it said in a thread about a FT-817  ;D


Title: RE: Ladder Line question
Post by: KC4MOP on July 14, 2012, 03:56:57 AM
The Ladder Line will not like being run near any electrical wiring or passing near metal objects. You mentioned plastic siding, but what is behind this wall as you run the OWL??
OWL is better coming out of the shack and going directly to the antenna.

Here is a boring link to a Youtube movie of my mess............but it works!!
http://www.youtube.com/watch?v=95goqNmJFTQ

In my new QTH , I thought I could run OWL over the drop ceilings in the basement to the shack and was disappointed with S-9++ of trash from the fluorescent lights. So a re-design of coax to the tuner mounted on the basement wall and the OWL goes out through a hole in the wall to the antenna.

Your situation seems better for the coax and auto tuner at the antenna.

Fred


Title: RE: Ladder Line question
Post by: KC4MOP on July 14, 2012, 07:21:31 AM
I went past the time to edit my previous.
I think I know where you are trying to go with the OWL and antenna, and your attic antenna.

The OWL will have to be spaced away from any part of the structure about 6 inches. Entering into the attic will be the same hassles of clearances. Window line might be a little easier than the OWL. But still needs to be spaced away from other objects. I would not know how you can test to be assured of no metal whatsoever near the Ladder line. I realize that the vinyl siding will not bother the ladder line, and you hope that there is nothing behind the vinyl that will induce noise into your antenna system (RX) or cause imbalances.
Once in place you hope that the tuner can handle the wide range of impedances involved. I'm assuming 40M and up?? 80M is going to be a lot of problems, but as long as the wire is up there and doesn't double back on itself too much, it might work. 
Good luck
Fred


Title: RE: Ladder Line question
Post by: KH2G on October 28, 2012, 01:24:48 PM
Running ladder line flat on the side of a building is never good at best. I suggest you snake some coax up a rain gutter and pull out and under the eaves to your attic. Get matching paint to coat the visible under eave part.
Good luck
Dick KH2G


Title: RE: Ladder Line question
Post by: K1ZJH on October 31, 2012, 09:56:36 AM
The SWR at the FEEDPOINT is the critical issue, and determines which feedline will work the best, under ideal conditions.

Pete


Title: RE: Ladder Line question
Post by: N4VNV on November 01, 2012, 07:19:11 AM
When I used ladder line it transmitted RF just like the antenna wire did. As a result RFI got into my house wiring. It was a nightmare. I feed with coax to a remote auto-tuner at the feed point, work 6 thru 160M bands and everything is hunky-dory.


Title: RE: Ladder Line question
Post by: WV4L on November 01, 2012, 08:02:55 AM
Using coax to an auto tuner at the feed point of the antenna is a workable solution. The caveat to a ladder line/coax combination is to keep the coax short. I use an tuner in the shack that has a 18 foot run of coax to a balun and then the needed length of ladder line to the feedpoint of the antenna. Any losses on the short run of coax from the tuner to the balun are nominal at best. Loss from the balun using ladder line to the feed point-very, very little if any.


Title: RE: Ladder Line question
Post by: W8JI on November 01, 2012, 08:55:35 AM
When I used ladder line it transmitted RF just like the antenna wire did. As a result RFI got into my house wiring. It was a nightmare. I feed with coax to a remote auto-tuner at the feed point, work 6 thru 160M bands and everything is hunky-dory.

If you had significant radiation from the ladder line, you had an installation or design issue in the system. Perhaps a poor balun, or a grossly unbalanced antenna.

Some antenna tuners and some baluns actually force ladder line into UNbalance. A friend of mine had severe RFI, and it turned out to be the balun design he was using. The balun was actually designed in a way that forced gross unbalance!!

That aside, antenna tuners generally do NOT transform common mode. There is a false idea that common mode disappears, or is easier to handle, on the input side of a tuner. You can read about that here:

http://www.w8ji.com/tuner_baluns.htm






Title: RE: Ladder Line question
Post by: K1DA on December 04, 2012, 10:14:53 AM
I run 300 ohm twin lead through a hole which carries two RG 8 leads and a rotor cable.  The 100 foot flat top to which it is  connected works on 80 through 10, including 60 meters.  So far, a pair of 3-500s amp  hasn't caused any problems.  I don't think 200 watts will cause you a problem.  My exciter runs that much.


Title: RE: Ladder Line question
Post by: W2WDX on December 05, 2012, 09:06:00 PM
Most times there numerous factors that lead to RF radiation from ladder-line. Most times its not understanding how it works and installing it poorly.

Some things you should be aware of:

  • Pay attention to the length of the feedline. Resonant lengths are bad and that is dependant also on the type of antenna being fed.
  • Make sure you have true balance in the entire system. This can done buy measuring both legs on an oscilloscope at low power and using the add function to measure for amplitude and phase being equal. You can also use two RF ammeters, one for each leg. Balance in the entire antenna system is crucial.
  • Use a balanced tuner that does not use a balun on the output. Most modern tuners are very poor in this regard.
  • Do not run the feed-line near metal objects. This throws off the balance in the feedline.

If you use balanced feedline properly, and everything is in balance, you will have very little feedline radiation and much, much lower loss over coax. Less than a dB even under a severe mismatch condition. With coax you will have significant losses if the mismatch is even at 2:1; on the order of 5dB or even higher depending on frequency, type of cable, length and amount of mismatch. That pretty much cancels any gain you may have in your antenna.

For instance, take a 100' length of Belden 9913 with a loss figure of about .38dB at around 7mHz, feeding an antenna with 1.4 SWR. In this case you lose about 9% of power to losses in the cable. So 100W in and you radiate 91W from the antenna, the rest is lost. If your SWR climbs to let's say 3, the loss goes up to 13.5%. So 100W in and you radiate about 87W.

Now lets say you use some RG174 with loss figure of about 2.50dB/100'. (Similar to RG-58 with RG8X only slightly better) The power loss is about 45% with an SWR of 3. So 100W in means you radiate about 55W.

Add a zero to the above figures and you see how much you lose on your Killowatt amp. Now these loss figures are at about 40M. The losses go up even higher as you go up in frequency. For instance at 50mhz the loss in RG174 is now at about 6.6dB/100'. That's about 75% loss with a perfect match at the feedpoint. And 9913 gets up to 1.1dB.

Now remember, this is with a tuner. The mismatch between your feedline and antenna still exists, the tuner is only cancelling the reactance at the coax-tuner connection point, not the antenna feedpoint. Basically, with a modern transistorized radio you're putting back the Pi-network not used in your radio, allowing the transistors to run at nominal current levels and not burn up. You are not really correcting the mismatch between the coax and the antenna, you are just tuning the entire system to resonance (not the same thing). Now the same thing mentioned above happens with balanced feeders like ladder-line. But because the loss figures are so low (with losses as low or lower as .02dB at 100'), the actual radiated energy is much much higher even with sever mismatch.

Sidenote: As far as losses in coax goes... I had a friend who was complaining he didn't "get out" as well on his 2m rig as I did, even though we had the same antenna and power levels. So I went to his house to see what the problem was. The difference was I was using LMR600 into my 2m loop array, and he was using RG-8X. We both had fairly good matches at an SWR of about 1.2. However, due to coax losses, my cable loss was about 16% and his was about 60%. Nuff said.

John W2WDX


Title: RE: Ladder Line question
Post by: K1DA on December 10, 2012, 09:17:33 AM
W2WDX about sums it up.  The materials don't cost much, most tuners have a balun built in for the balanced/50 ohm unbalanced conversion, and a  center fed  wire dipole is a simple antenna.  You can make your own  center insulator. Chances are it will work very well on a number of bands.  If it doesNOT t, you'll find yourself learning a lot about balance/unbalance and impedance transformations, the inpedance of a particular center fed wire length on different bands, what 1/4 wave and half wave lengths of line do to inpedances, and the radiation patterns of a particular length of wire on different bands.  You'll    be the better for it.  If you want plug and play....a  center fed dipole, open wire line  to a remote auto tuner with a proper balun, and hope the tuner likes what it sees. 


Title: RE: Ladder Line question
Post by: W5WSS on February 10, 2013, 04:26:03 AM
The routing of twin balanced transmission line directly flat against any solid mass will shear half the transmission off along the line.

During receive the induced voltage from the antenna to travel back towards the rig is not effected by the proximity of the line to solid mass.

Use coaxial cable for the antenna feedline.

Place a tuner at the antenna or as close as you can to allow the coax to operate in a matched state allowing full delivery, full or almost so delivery of the transmitter power to the load avoiding the high losses of a mismatched line.


Title: RE: Ladder Line question
Post by: K0ZN on February 12, 2013, 09:00:35 PM
Here is why they call it AMATEUR Radio..... you probably need to experiment with your set up to see what works best in your situation. That is pretty common
in this game! Sometimes stuff that looks ugly works quite well and the reverse.....you just gotta try it!

My take would be that if the plastic you mention is NOT a type of plastic that would attenuate RF (You would have to put a small piece in your
microwave and see if it gets warm or not....warm is bad...no temp rise is good!) and the wood is/stays DRY, you likely are OK to run it that way at
lower power levels. This assumes there is no metal/conductor/sheet metal otherwise close to the line. (Close would be < 6" ). You need to know what
material is just behind that wood.

I don't know if it would take or adhere, but you could spray paint coax to a color that matches the siding. I would not do this with ladderline. That way
you could run coax up to an autotuner if you want to go that route.

It is likely that a decent manual tuner to ladderline to a balanced antenna (center fed dipole or loop) would be the most flexible antenna you could
put up in terms of frequency coverage and likely have the fewest problems. That said, I think too many hams try to get something up that will work "all bands" where in reality, sticking with two or maybe three bands in a coax fed situation may yield better results. I would suggest you concentrate your antenna efforts on
40, 30 and 20 M if you are QRP and using CW; that will likely give you the best bang for the buck.

Good luck.  73,  K0ZN


Title: RE: Ladder Line question
Post by: AC4RD on February 13, 2013, 04:33:50 PM
If you use balanced feedline properly, and everything is in balance, you will have very little feedline radiation and much, much lower loss over coax. Less than a dB even under a severe mismatch condition.

John is a wise man.  :-)  There are people who don't like balanced feeder lines, but I sure don't understand why.  You can run it for LONG lengths with very little loss, you can feed an antenna with it and use it for lots of bands with virtually no loss, and it's inexpensive besides. 

Now, yeah, it takes a little work to run it away from metal and things that can interfere with it.  And for some hams, that makes it unworkable.  But if you CAN feed an HF antenna with balanced line (twinlead, window line, 300-ohm line), it's a great solution for most people.


Title: RE: Ladder Line question
Post by: N0NZG on February 28, 2013, 07:06:39 PM
In response to your query of running ladder line in very close proximity to vinyl siding.  PVC pipe and vinyl siding in very close proximity to you ladder line will cause some additional loss.  These plastics have metal-based “ plasticizers” in them that I suspect cause the extra losses. If you take an antenna and put it inside a PVC pipe you will see a change in resonate frequency.  This same effect can be seen winding a loading coil on a PVC form vs air or cardboard for a form.  Lastly look at the difference in loss between “TV” type twin lead vs open window ladder line vs home brew ladder line with little spacers every 4 inches or so. The loss goes down as you remove these so called dielectrics from the feed line. This is also why a foam dielectric coax has less loss than a solid core coax. If this was a length critical application your velocity factor will also change.   Food for thought. In your situation I would go with a remote tuner.

73, Jeremy


Title: RE: Ladder Line question
Post by: W1JKA on March 01, 2013, 06:09:56 AM
  First of all there is nothing wrong about starting off into the hobby with QRP, after all most OT hams started off with small one or two tube homebrew qrp power xtmrs.,some stayed qrp like me and many have returned back to it. As K0ZN says you will most likely find 20/30/40m your most used qrp bands.Until such time that you get your ladder  line question resolved and purchase a tuner please consider that many qrp ops both CONUS and DX use simple no tuner frequency cut coax fed attic dipoles with very satisfactory results.


Title: RE: Ladder Line question
Post by: N0NZG on March 01, 2013, 11:59:01 AM
That is so true. I use a tuned 20 meter dipole in the attic with my Bitx20 with great results.  Make the most of what you can as any antenna is better than NO antenna.


Title: RE: Ladder Line question
Post by: WB6BYU on March 04, 2013, 11:49:38 AM
Quote from: N0NZG
...PVC pipe and vinyl siding in very close proximity to you ladder line will cause some additional loss.  These plastics have metal-based “ plasticizers” in them that I suspect cause the extra losses...




Actually, if you look at the physics involved, the feedline losses tend to be
more in the conductor resistance rather than the dielectric characteristics, at
least though the VHF range.

For example, foamed dielectric coax has lower loss than solid polyethylene, but
that is primarily because the conductors have to be larger to maintain the same
characteristic impedance when the dielectric constant of the insulation changes
due to the presence of more air in the mix.  TV twinlead has relatively small
conductors compared to typical ladder line, which accounts for most of the
difference in loss, rather than the dielectric surrounding it.

While it is true that putting a J-pole inside a length of PVC pipe shifts the tuning,
in my experience the change is much less for a normal dipole.  It isn't the antenna
itself that is detuned, but primarily the velocity factor of the matching stub
(especially if the antenna lays against the inside of the pipe rather than hanging
straight down the middle.)  You can test this by inserting the radiator of the J-pole
inside a pipe, measuring how much the SWR changes, then pushing the rest of
the matching stub inside to see the difference.

Open wire line has a relatively high impedance (though it is possible to make
lower impedance lines using multiple wires).  That helps to keep the impedance
high along the length, which minimizes the current, reducing resistive losses.

But when open wire line runs at a high SWR, so there are points of relatively
low impedance with high current, the losses can be quite higher than expected.
For example, using VK1OD's transmission line loss calculator here:

http://vk1od.net/calc/tl/tllc.php

The losses in 20' of Wireman 551 on 80m (so a short line on a low frequency
where we expect feedline to be low) is about 0.85dB with a load impedance of
10-j200 ohms, and 1.5dB at 5-j200 ohms.  In fact, this is a convenient tool to
look at the losses in partial wavelengths of feedlines, which don't always behave
as the textbook loss tables might suggest based on SWR.  That's because the
tables assume the loss is averaged over the whole wavelength when operated
at a high SWR, while in practice the lower impedance portions will have the
highest losses, consistent with our observation that loss is more due to conductor
losses rather than dielectric losses.