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Author Topic: Roof Antenna  (Read 1463 times)
KA4NMA
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Posts: 348




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« on: June 06, 2013, 08:30:13 PM »

I live in an no antenna apartment complex.  I presented a proposal for an outside antenna and it was approved.  Unfortunately, the antenna did not work out as during the remodel, metal flashing was placed in the way.  So on to plan b.  I have 2 ideas and would like input from everybody!  Please help me out.  I am good at regular antenna's but stealth presents a few problems.  Additional info is that I live in a 4pex and no trees are bushes are close by.  The only tree is across the driveway from my apartment.  Bands of interest 75m (state nets) - 6m.  I will be using a SGC 237 antenna coupler.  Both antenna's would be facing west and go onto the neighbors apartment.  Power output would be less than 100 watts or less.  Most likely I would use 50 watts to reduce any RFI and for RF exposure limits. Also I have no balcony.  I do have a front porch nearby.  All lengths are an  estimate (guess).  A antenna on my truck and using a long coax is not possible.  I also do not have access to the attic.  I have not learned how to model antenna's but I would like to learn sometime.

1. The rain gutter is "L", which is a horizontal run and a downspout. It is also brand new.  It appears to be a continuous run or else I cannot see any joints. I am guessing that the horizontal run is about 20 to 25 feet and the downspout about 8 feet.  I could feed it with a single wire at the end of the horizontal run, which would give me an elevated feed point.   I could lay 2 buried random length radials or use several inside the apartment.   I am not sure about installing a ground rod.  The electrical service ground is on the other side of 4plex.

2.  The roof is steep pitched, and has new asphalt shingles.  The new shingles are placed on wood.  During installation, I saw not metal.   Antenna 2 would be a loop a short distance about the roof.  Instead of using traditional window line, I would use coax to form a shielded line (due to having to go over the rain gutter to get into my shack.  I am looking at The Wireman 177, Dual coax for balanced lines or make my own out of rg8x.  How close could I place the loop above the shingles? With rules saying no attachments allowed to the building, how would I mount the loop?  Could the loop be placed directly on the shingles?

3.  Another idea is a vertical compact loop, run around the inside of the outside wall.  It would be small, maybe 8ft or so per side. I found a website that the ham used a 2.4m per side loop with a 1:1 balun used with an antenna tuner.  The problem is a window would be in the middle and the window has a metal window screen and it would be close to my operating position.

4.  Another idea is a loop run around the ceiling of my shack.  It would also be smallsmall.  I have also considered adding a switch at the far side to make it a broken bent random dipole or a loop.  I wonder what power rating the switch should be? It would be rectangle about 13x9 feet

I have also considered magnetic loops inside my apartment, but my disability and funds prevent building or buying one.  I have also looked into some commercial antenna's such as Isotron, hamsticks, screwdriver antenna, and a Transworld vertical antenna.  I really like the Transworld vertical dipole.  I wonder how the Transworld antenna structure without the tuning modules, would work if feed with regular 450 ohm ladder line? Must are out of  budget or not to efficient.

One good note is that my doctor wrote a "prescription" for an outside antenna.  He believes that if I got back into ham radio, it will help with my disabilities.

I know they are a compromise.  The main thing is I need a Goto antenna.  That is Get On the Air antenna.

If you made it this far, please leave a comment.  I am looking for any advice!
« Last Edit: June 06, 2013, 09:15:59 PM by KA4NMA » Logged
WX7G
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Posts: 6128




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« Reply #1 on: June 07, 2013, 06:00:08 AM »

Any antenna worked against ground is a recipe for RFI in a fourplex.

Balanced Line made with two coaxial cables can still have common-mode current and is no better than regular balanced line. Balanced line can be run over small metallic objects (such as the rain gutter) with no ill effects.

For 80-6 meters this is what I would do:

Dipole 90' long laying on the roof - it can be bent as needed to fit
Feed with 300 ohm TV Twin Lead or Ladder Line
Tuned with an MFJ-969, 80-6 meter tuner; this tuner has balanced outputs
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AD4U
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« Reply #2 on: June 07, 2013, 06:17:22 AM »

In addition to what WX7G suggested.......If you lay your dipole on the shingled roof, I would use insulated wire for the dipole which MAY insulate it from a wet roof.  With uninsulated wire a wet roof MAY cause problems - and it may not.

Dick  AD4U
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K9RCM
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Posts: 17




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« Reply #3 on: June 07, 2013, 07:25:53 AM »

Would an EH antenna be an option. I never used one and I know a lot of folks say they can't possibly work, but there is a lot of info on the web about them. Check yahoo groups for the EH group. Also check out http://www.wb5cxc.com/
Just a thought. You'll probably have all the usual forum nay Sayers tell you that they don't work, but it might be worth looking into.
Good luck....Bob K9RCM
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WX7G
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« Reply #4 on: June 07, 2013, 08:09:06 AM »

The EH antenna is a "common-mode current excitation device." It is not the main radiator, the outside of the coaxial cable shield is. It is much like the Isotron antenna that turns your coax into a random length top loaded vertical. If that is what you want, the EH is one way to do it.
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KA4NMA
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Posts: 348




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« Reply #5 on: June 07, 2013, 08:23:37 PM »

WX7G - Thanks for your input.  I have a SGC-237 tuner that I will be using.  I already have ladder line.   I am not sure of the building length.   Living in a end unit, I would have a run of cable - whether twin lead or window. I wonder what the RFI situation would be.  The apartment complex wants the antenna to be discreet.  How would I mount a dipole along the roof peak?  I cannot do anything permanent.   I was thinking of the screw in tv twinlead holders or an adhesive backed hooks as antenna supports.  Life was much simpler with trees and no antenna restrictions!

Randy ka4nma
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WB6BYU
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« Reply #6 on: June 07, 2013, 08:29:51 PM »

I just tucked my wire antenna under the corners of the shingles.  You can choose
an insulation color that matches the roof, but the natural discontinuity right along
the edge of the shingles tends to make it hard to see anyway.  (#24 or #26 magnet
wire is pretty hard to see from a distance.)
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WX7G
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« Reply #7 on: June 08, 2013, 04:36:21 AM »

It's time to experiment. Wire antennas aren't forever and with your tuner you can quickly try several.

The SGC-237 will need a 1:1 or 4:1 current balun when used with a balanced antenna.

The single-ended antenna (rain gutter or single wire) will tend to light up the AC wiring in all units with RF and you may or may not have to use QRP to keep the RFI down. To comply with the FCC RF Exposure rules you can restrict power to 50 watts on 12, 10, and 6 meters.

The quick way to get on the air is to use the rain gutter or put up a length of thin insulated wire tucked under the shingles as WB6BYU describes. A couple of radial wires laying on the ground or buried and you are on the air. If the RFI situation is ok you are finished with the antenna and on the air. That should take you an hour to try out.



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