View Full Version : Roof Mount Vertical Antenna
07-30-2003, 07:44 PM
I am thinking of mounting a vertical antenna on the roo. We have a large gable roof and I was wodering if i did not mount the Ant on the prak of the roof but on the back side of the gable, how will the performance be affected?
I need to do this to hide the antenna.....
07-30-2003, 07:50 PM
If mounting the antenna down from the peak of the roof will hide it, I'm assuming it's a VHF and/or UHF vertical.
You may experience some "shadowing" effect, but you should still be able to hit your local repeaters with little or no more difficulty than if it were mounted on the peak.
No, I am not so sure that is correct. If you turn a vertical on its side, it becomes a horizontal antenna. There is a little problem with a phenominum called "cross polarization" . This effect can cause as much as a 20 db loss in signal strength between the vertical and horizontal stations. It is for this reason that VHFers using vertical antennas hardly ever hear any local SSB/CW activity until they get some form of horizontally polarized antenna set up.
Now if it is an HF antenna, the previous answer would be correct, since the ionosphere tends to scramble all the polarization up, anyway.
Let us know what band(s) you are considering setting up for.
73 from Jim AG3Y
07-30-2003, 08:49 PM
Sorry for the spelling errors. I mean by not mounting the antenna on the "peak" of the roof....
07-30-2003, 08:56 PM
It would be an HF Antenna. I still plan on mounting it vertically but it will be mounted on a mast close to where the gutters are, or alternatively, there is a second story deck that is close to the roof that I can mount a mast on. Either way it will be "shadowed" by the slope of the roof....
07-31-2003, 01:37 AM
Mike, it will certainly work on a mast close to the gutters or on the second story deck. Maybe not quite as well if mounted on the roof peak. Possibly other factors may be of more concern, such as will you have radials?
#Tell us more about the actual antenna and feedline.
# # # # # # # # # # # #John #K5CEY
07-31-2003, 02:45 AM
Well I am thinking of a Hustler 4BTV or 6BTV with a 50 ohm coax for the feedline...
I wonder what it would take to actually support the mast that holds one of these also....
07-31-2003, 05:16 PM
The Hustler 4BTV-5BTV-6BTV have only one real serious requirement, that is they must be used with a good radial system in order to work -- that is much more important than the actual mounting location of the antenna.
The BTV family work very well in any elevated installation (elevated meaning "above the ground," and not mounted "on the ground"), and the peak of your roof won't effect performance to speak of. But, you need to have tuned, cut radials for each band. Having installed a lot of these antennas (I have a 6BTV on my roof, myself, right now), I've found it only takes four (4) radials per band to work well.
The 4BTV requires radials only for 10-15-20-40 meters; the 5BTV requires radials for 10-15-20-40-80 meters, and the 6BTV requires them for 10-15-20-30-40-80 meters. That's the one I have, so I have 24 radials total, four per band, for six bands.
Each radial should be cut to 234/f feet, where "f" is the frequency in MHz; e.g., the 10m radials are 8.21' long each; the 20m radials are 16.5' long each, etc. It's best to use insulated wire for the radials, for a few good reasons, and make sure the radial ends (tips) are well insulated from everything, including your roof. As such, end insulators (ceramic, plastic, glass -- anything that's a good insulating material) really must be used, with non-conductive (rope or string) leads tied to those, and then anchored to the roof.
As long as you have a good radial system, be assured your BTV series vertical will perform well. Without the radials, it won't perform at all, so it doesn't really matter where you put it.
05-29-2004, 04:10 AM
My house has a metal roof....
Can I mount a 4BTV on the roof and use the roof as a ground plane instead of using wire radials