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Author Topic: Antenna flat on roof.  (Read 2057 times)
KD7TWI
Member

Posts: 21




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« on: August 19, 2006, 10:42:54 PM »

Greetings all,

I built a new home and there are restrictions of course.  I thought of putting a rectangular loop wire around the edge of my roof, flat on the asphalt shingles.  A full loop would be about 240'.  It is a pitched roof so only two 40' legs would be horizontal (about 10' off the ground) the the other ends would be on the order of an inverted V (top of V about 30' off the ground) but paralell to one another.  The wire would almost have to be laying on the roof to avoid detection.  Would it work?  How well?

Thx

KD7TWI
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WB6BYU
Member

Posts: 18460




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« Reply #1 on: August 21, 2006, 12:16:07 PM »

Yes it will work.  I've done that a number of times, either
tucking the wire under the corners of the shingles to hold
it in place (choosing a wire color that blends in) or
stapling it to the back side of the facia board - or both.
In one case we put up the wire while the ham's wife was
out shopping and 3 months later she hadn't noticed the
antenna, even though it ran in the air between two parts
of the roof in a couple places.

Is it the best way to put up an antenna?  Probably not.
But it may be the best option in some cases.  Performance
will depend a lot on your roofing material: wood shakes
probably are best, composite shingles are kinda lossy and
metal is bad news.  Tile roofs aren't too bad until it
gets wet.  The higher you can get it up above the roof the
lower the losses, but this isn't always compatible with
concealment.

The house itself will also have a large effect on the
antenna, and vice versa.  (This will be true of attic
antennas as well.)  I've found such loops tend to resonate
about 10 to 20% lower in frequency than the typical
formula 1005/f would suggest - the loop above dipped at
5.8 MHz when cut for 7.1 MHz.  It can take several
attempts to tune the antenna to resonance, so it is
usually easier just to install whatever size loop will
fit and use a tuner to make it work.  Also there will
be more opportunity for RFI to alarm systems, telephones,
etc. than there would be if the antenna were installed
10 or 20 feet from the roof, but given the other
limitations you may have to live with that.

Some practical pointers:  If possible, put the center
of the wire (opposite the feedpoint) at the highest
point of the roof - this will be a high current point
on all bands.  If you can put the feedpoint under the
eaves it will be protected from the weather - and there
often is a screened attic vent near the peaks.  I ran
two separate wires from the feedpoint down through the
holes in the vent screen then through the attic to a
convenient point where I could splice them to twinlead,
which then dropped through the ceiling into the radio
room.

I like the type of insulators that don't need to be
threaded onto the wire from one end - they make it much
easier to install.  When I've tied a corner of a loop to
a tree I usually use the sort of plastic egg insulator
where the backs of the holes are open - this lets me
slip it around the wire and tie it off.  Have a look at
the electric fence supplies at the local farm and ranch
store - they should have some small clips that go around
the wire and snap closed.  (Also some insulating tubing
if needed.)  You don't need to pull up much tension on
the wire - just enough to keep it from hanging down
where it may be noticed.  I've been known just to staple
the wire to the back of the fascia board with a staple
gun, but a purist might add some insulation - perhaps
a short piece of nylon rope or a tie-wrap around the
wire that is stapled down.

You should end up with good coverage around the Pacific
NW on 40 and 80m, with occasional further contacts.  With
enough height you should get reasonable performance on
the higher bands - it won't beat a beam up high in the
clear, but you should still be able to make contacts.
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W9WHE-II
Member

Posts: 1




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« Reply #2 on: August 23, 2006, 07:30:44 AM »

I have confirmed 256 countries using a fan dipole laying flat on the peaked roof of a 2 story home. The wire lays flat on my asphalt shingles. Works freat for me, although a wer roof changes the swr....but its not a huge problem.

W9HWE
Proud to have CANCELLED my arrl membership!
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AH6FC
Member

Posts: 117




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« Reply #3 on: October 12, 2006, 11:00:41 AM »

Perhaps not ideal but will work.  Give some thought to a SteppIR dipole.  Place it either on the roof or a couple of inches above the roof.  It will likely work well, probably better than a wire.

Also consider a SteppIR vertical or 5BTV.  You can erect it at night and lay it down during daylight.  Both are lightweight and work quite well.

I live in similar area, using the Steppir Vertical, have about 150 confirmed in past 2 years.

73, Bill
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