Very long ladder line runs...
What is considered a "long" run of ladder line. Most folks with doublets or loops fed with ladder line have runs anywhere from 50-60 feet to maybe 120 feet. How about 300 feet? Maybe a little more...
This would feed a 160m or 80m horizontal loop back to my tuner in the shack. I know a better solution might be a good remote tuner then low loss coax back to the shack. Right now, 450 ohm ladder line is what I need to use. I've fed all sorts of antennas with the stuff, all runs of 100' or less. I have a great location, tall trees, etc. but it's on the other side of the house. I would pay attention to how the line is run with respect to other objects. Thoughts???
If you are concerned with minimizing feedline loss for a given feedline length, increase the size of the conductors. VK1OD's online calculator can help you get a feel for your situation.
Please note that some commercially available 450 ohm ladder line is constructed with copper clad steel conductors that may have inadequate copper thickness for low loss on 160 or 80.
For long runs and low loss, consider making your own feedline with "large" copper conductors. The working definition of "long" and "large" is connected with your definition of tolerable loss (as well as mechanical concerns).
Last edited by NW2K; 04-17-2012 at 02:17 AM.
There have been longer runs than 300 ft and they worked. It does depend on the quality of the ladder line. If you make it yourself and use wire spaced 6 inches apart you can have some very long runs. A run of 150 ft of ladder line will not have that much loss. The amount of loss depends on the SWR the frequency and the IR losses of the line. Coax can have very high loss again depending on the SWR and the frequency. Either one of them in the high range and you will probably have problems.
I have heard of one amateur that lived in a valley and ran his ladder line up to the top of a ridge. Don't recall the distance but it was extremely long. It worked for him.
Ladder line needs to be suspended away from anything that can conduct. This includes wet wood.
If your area is prone to ice storms that will make the ladder line very high in loss if it gets coated with ice. Rain causes some problems too.
Hope this helps
Last edited by KO6WB; 04-17-2012 at 03:52 AM.
There have been articles in QST and the Antenna book about hams running open wire lines up the sides of mountains to reach good antenna sites. For extreme performance "4 or 5 wire lines" can be constructed as are used at some commercial broadcasters.
Author of: Mr. Fred, Nuke This Forum (Danger Close)
Thanks for your post Milt, my question if you don't mind me asking is on the opposite, can i successfully run a very short length of ladder line (20 feet from indoor to attic) to feed a 40 to 10 mtrs doublet? I'm concerned about high RF in the shack
73 de Rod 2E0RPS
Your RF problems won't have anything to do with the transmission line, whether it is ladder line or coax. The RF level in the shack will be a function of the proximity to the antenna mostly.
Originally Posted by 2E0RPS
Common mode issues would result in RF in the shack, but you are only 20 feet away from the antenna which is probably a much bigger issue. A common mode current problem might be better or worse with a given distance. The "shortness" is only a factor because you are next to an antenna.
Probably not a problem if you aren't using an amplifier.
It depends on the impedance match between antenna, transmission line, and transmitter.
Originally Posted by WA4FNG
1000 feet of Wireman 551, copper clad 18g, is 1dB if the system is matched. However, the loss goes to over 3dB if it is wet. (80m)
The losses get higher with a mismatch (such as if you are tuning from the shack).
You can get an idea by using Owen's TLLC calculator: http://vk1od.net/calc/tl/tllc.php You'll want to know the impedance of the antenna feed point on each frequency. (Zload) in this format: R+jX Alternately you can make estimates with only the source side SWR, but they are subject to error.
Here is a DOS program I wrote that predicts where the differential voltage nodes (minimum voltage) will fall. It runs under XP (or DOSBox on the later operating systems). 20' of ladder-line is a pretty good length for a 66' dipole on 20m, 15m, and 10m but not for 40m where the ideal ladder-line length (for minimum differential RF voltage in the shack) would be 1/2WL, i.e. 62'.
Originally Posted by 2E0RPS
73, Cecil, www.w5dxp.com
The maximum power transfer theorem works just as well for a non-resonant antenna as it does for a resonant antenna.
Many thanks Cecil, that answers what i wanted to know, i guess i may have to sacrifice the 40 mtrs band that said i prefer to have one or two working bands at his full potential than a compromise multi band aerial. Your answer also confirms that it's not always correct what is said on the wide web and that's any length of ladder line would work ok
Originally Posted by W5DXP
Originally Posted by K1DNR
I will be using max 50 watts for the reasons explained on your post