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Author Topic: ladder line laying on the roof.  (Read 2885 times)
KK4MYT
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Posts: 14




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« on: February 06, 2013, 11:22:03 PM »

I am planning to build a G5RV junior. But the length of the ladder is going to cause it to lay on my roof. Will that be a problem?
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AA4HA
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Posts: 1368




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« Reply #1 on: February 07, 2013, 12:38:32 AM »

If it is conventional roofing materials (wood, tar shingles) not really. If it is a metal roof then yes indeed.

Ideally you do not want it just laying on anything. Roofs collect snow, rain, etc.
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
KC4MOP
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Posts: 706




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« Reply #2 on: February 07, 2013, 03:21:24 AM »

It's best to keep the ladder line in the clear for two feet, maybe less, all around if it is 600 ohm, 6 inch spacing. That's the only thing bad about ladder line.
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K1CJS
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« Reply #3 on: February 07, 2013, 06:11:22 AM »

You can lay the ladder line directly on a non-metallic roof surface.  There will be no problem at all--providing that the run is straight down the angle of the roof.  If you try to lay it along a down pitching roof surface and there is any amount of snow or ice on the roof that would tend to slide off during a thaw, it may just take the ladder line with it.

In other words, for RF purposes, no, there would not be a problem, but for other reasons, (physical strain to the ladder line) there may be.
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AA4PB
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« Reply #4 on: February 07, 2013, 06:24:52 AM »

The problem is that you never know how conductive your roofing surface is. Typical roofing has metal flashing, nails, and clips under some areas of the shingles. In addition, new anti-mildue shingles have pieces of copper imbedded into them. I'd suggest that it is better to provide some type of support to keep the ladder line spaced away from the roof by at least 6-inches.
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KC4MOP
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« Reply #5 on: February 07, 2013, 06:59:36 AM »

The problem is that you never know how conductive your roofing surface is. Typical roofing has metal flashing, nails, and clips under some areas of the shingles. In addition, new anti-mildue shingles have pieces of copper imbedded into them. I'd suggest that it is better to provide some type of support to keep the ladder line spaced away from the roof by at least 6-inches.

I do not want to be a needle in this thread, but I agree with AA4PB about the unknown part of the materials in the shingles, etc etc. We ALL know there are numerous nails tacked into the shingles to attach to the plywood, whatever is underneath.
Pick a point in your antenna layout and install a 4:1 balun and make a transition from Ladder Line to coax, to the antenna feed point; then the coax can lay on the roof and RF will be happy.
Any way to re-position the antenna so that the ladder line can be hung in the clear?
Fred
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KK4MYT
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« Reply #6 on: February 07, 2013, 09:18:20 AM »

Since I am going to build the whole thing I could make the ladder line shorter so it doesn't lay on the roof. I was just going off the demensions I see on the web. Just not sure about how shortening the ladder will effect the performance versus laying on the roof. I have no where else to string the antennae to get it off the roof that's why I am asking.
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N6AJR
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« Reply #7 on: February 07, 2013, 09:28:41 AM »

G5RV's are actually a 20 meter antenna that will work on other bands as well, and the section of laddwe line is actually a part of the antenna. Idealey you want that up in the air as well.  It may or may not work so put it up and give it a try
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W5WSS
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« Reply #8 on: February 07, 2013, 09:42:33 AM »

Two points:

I would not change the line length because The ladder line dropping straight down from the inverted legs of a G5rv antenna is part of the antenna designed to radiate and contribute to the antenna pattern.

The clearance around the entirety of a balanced transmission line regardless of the composition of any nearby material should be about 4" 360 degrees around the line.

Strive to install the antenna high enough for the balanced line portion to be in the clear and free of routing issues.



 
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K5LXP
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« Reply #9 on: February 07, 2013, 01:08:17 PM »

I would not change the line length because The ladder line dropping straight down from the inverted legs of a G5rv antenna is part of the antenna designed to radiate and contribute to the antenna pattern.

What about a G5RV would suddenly make the feedline radiate?

In order for that to happen with balanced line, there would need to be a current imbalance.  The G5RV is a symmetrical doublet.  There is no "third wire" as there would be with a coaxial feed.  The currents are balanced, and there is no radiation.

Nothing about the length of the feedline has anything to do with the radiation characteristics of a 3/2wl doublet.  It only influences the Z you see at the input of the feedline at any given frequency.


Mark K5LXP
Albuquerque, NM
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KC4MOP
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Posts: 706




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« Reply #10 on: February 07, 2013, 01:57:14 PM »

oops forgot about the G5RV and ladder line being part of the antenna.
Looks like it cannot be on the roof for sure.
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K1CJS
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Posts: 5525




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« Reply #11 on: February 07, 2013, 03:30:36 PM »

I can see the point about metal imbedded in the shingles--if the roof is fairly new.  Yes, flashing can also affect it too, but when someone says the nails holding the shingles are going to affect the ladder line---give me a break!

Jason, see if there is someway that you can support the ladder line at the feedpoint and at the edge of the roof--and put enough tension on the ladder line to keep it clear of the roof--if you're worried about it.  You can also find a way to keep the ladder line at the recommended length, even if you come down off the roof somewhere other than above where the shack cable entry is then string it along the eaves till you get it to the entry or transition it to co-ax.  That will solve all your problems.  

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N4CR
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« Reply #12 on: February 07, 2013, 05:20:02 PM »

I have no where else to string the antennae to get it off the roof that's why I am asking.

Tie a messenger line off between two points, run it through several holes in the ladder line, zip tie it to the string. It can look like a roller coaster, but you can't coil it up or lay it on things.

A roller coaster of ladder line in the air works just fine.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
KB6HRT
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Posts: 63




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« Reply #13 on: February 07, 2013, 06:34:32 PM »

Have installed many a G5RV when I was in my testing period, found as others have said the ladder line radiates, so I have had the best results with the G5RV when I treat the ladder line as a legs of the antenna, I add a messenger to the ladder line and secure the ladder the same as one of the legs of the antenna, the G5RV will radiate better an hear better as well, if you can adjust the height up and down and find the sweet spot where the antenna receives best for your setup then lock it in there, this will also help, also on 75m I rag chewer an stay on a given frequency, you can also add or subtract feeder coax to bring you SWR down where it low on a frequency you may talk on most, Have my current G5RV setup that way so am around 1.3 SWR at the feed end of the coax with out the tuner engaged and of course flat when its engaged but that will makes the G5RV some higher on 40m at the feeder end but don't talk there much. There is one more little tid bit that I have learned over the years, you can experiment with wire size of the two legs and it will change the tone of your receive some a larger wire will accent Base or tones an number 16 AWG will accent midrange tones an small sizes will change the pitch some more, but if you go for smaller than 16AWG wire use steel core wire so you still have some strength in the wire and it won't stretch, hope this is of some help to ya, this is such a FUN hobby.......73s.........KB6HRT
 to see what works best for radio and station setup. The guy that came up with the G5RV spent his hole life playing with it and bet ya he know a lot more thing than I have pasted on to ya..........73s...........KB6HRT
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W5LZ
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Posts: 459




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« Reply #14 on: February 08, 2013, 04:24:01 AM »

Luis Varney(sp), the former G5RV, made the thing as a 20 meter antenna.  It only incidentally works harmonically on other bands.  He made no claims for it as a multiband antenna and disputed those claims fairly often (look it up it's bound to still be available on the internet).
On 20 meters that ladder line is only part of the impedance matching necessary for it to be 50 ohms at the transmitter end, and it doesn't radiate significantly.  On harmonically related frequencies it does radiate.  The feed line on any harmonically related antenna radiates, it's normal.
Putting that ladder line near anything will affect how it operates, interfere with it's impedance transforming.  Laying it on a roof is probably possible under some conditions, band of use, etc, but it's definitely not a good idea.  Try it, see what happens.  If it's 'livable' for you, then enjoy it.  If it's not, then don't be surprised.  I hope you plan on using a tuner, you'll need one.  Think of it as a double Zepp fed with coax...
 - 'Doc
« Last Edit: February 08, 2013, 04:29:51 AM by W5LZ » Logged
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