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Author Topic: Vertical in the trees  (Read 2786 times)

Posts: 1

« on: November 24, 2001, 02:15:57 PM »

I am planning on installing a Hustler 6-BTV in my back yard which is in a woods.  Restrictions prevent me from placing it anywhere else on my property. The antenna will be surrounded by large trees  The closest will be a 60 ft. pine about 8 feet away.  Limbs from this tree and others will over reach the 24 ft. antenna.  I have been unable to find information in any publication which tells me what the effect of trees will have on my signal. Any thoughts will be appreciated.

Posts: 17479

« Reply #1 on: November 26, 2001, 11:28:25 AM »

If that is the only option for an antenna, then it certainly will work
better than no antenna!

Some folks have reported signal absorbtion from surrounding trees,
and others haven't noticed any difference.

If you want to test the performance before purchasing a vertical,
you can use a vertical quarter wavelength wire in the same location
and see how well it works.  Tie a string to the end of the wire, throw
a rock (with the other end of the string attached) over a convenient
branch, and pull the wire into a somewhat-vertical position.  You
may need to do this for each band, but it wil give you a chance to
see how well it will work in your specific location.

Posts: 21764

« Reply #2 on: November 26, 2001, 12:41:35 PM »

If you truly have no other options, then it doesn't matter much to know what effect the trees will have...unless that information would lead you to begin cutting down trees.

Use a lot of ground radials under that 6BTV, and try to keep the tree limbs from knocking the vertical over, and I think you'll see the antenna works well.  30-40 radials, about 20' long (or longer), for a ground-mounted 6BTV work well.  The entire secret to that antenna is its radial system.  Hustler includes a note in the directions, advising that if you mount the vertical on a 4' pipe inserted into the ground, the antenna will work without radials.  That depends on your definition of "work."  It may load up, but it works a whole lot better with lots of radials.

73 de Steve WB2WIK/6

Posts: 10

« Reply #3 on: November 27, 2001, 02:47:43 PM »

Im Mounting my 5-BTV on a 15' steel mast will I need to use radials? the 5BTV kit does include them. I figure the top of the antenna will be around 35' in the air. DP

Posts: 21764

« Reply #4 on: November 28, 2001, 12:33:29 PM »

Of course it needs radials; how the 5BTV is mounted is irrelevant, it always needs radials.  You definitely don't want to use a 15' mast without radials, or the 15' mast will become part of the antenna and completely knock the 5BTV out of resonance: The antenna will try to resonate at 15.5 MHz, due to the resonance of the mast.  Very bad idea.  Use sufficient radials, and all will be well.

73 de Steve WB2WIK/6

Posts: 984

« Reply #5 on: November 30, 2001, 02:19:06 AM »

I guess I have just been lucky. In all the years I have used the 4BTV and the 5BTV I NEVER used radials. I used a MFJ tuner and it always loaded okay and got out just fine. I even used it on the top of the ladder of my 5th wheel travel trailer. I believe the manual says radials are not necessary but the antenna should be mounted on a mast that is in the ground and NOT concrete. I now have a 66 foot length of wire running around my yard to see if it will make any diffence, but since I did that 2 weeks ago; I see no difference. But then, maybe I am just lucky.

Posts: 17479

« Reply #6 on: December 13, 2001, 08:00:07 AM »

There have been a lot of previous posts on radials.  Here is a
summary of my suggestions:

1) if the antenna is ground mounted, the radials don't have to be
resonant lengths, but you need to have enough of them.  As a
minimum, consider 8 radials at least 20' long.  Having more short
ones is better than a few long ones.  This reduces the ground
losses so the antenna is more efficient.

2) if the antenna is mounted in the air, then the radials need to be
resonant for the desired bands, but it doesn't require as many of
them.  With a base height over 1/4 wave, two radials per band will
probably be adequate, or four at lower heights.  (Though it may
still work with half as many.)  Remember, with a multi-band vertical,
this means radials for EACH band you are going to use.  Since the
radials provide the "missing half" of the antenna, their length will
affect the resonant frequency in the same way that changing the
antenna length does.

Posts: 135

« Reply #7 on: August 18, 2002, 07:13:06 AM »

Wow! You could not cover vertical antenna and radial requirements, and effects thereof, in a month of Sundays on this forum. Anyone that really wants to better understand this complex topic should at least read 'Vertical Antenna Handbook' by Orr/Cowan, if not the ARRL antenna handbook. This also applies to HF mobile ops, where verticals are always used.

Many factors should be considered, including ground conductivity, upright length vs 1/4 wave, height above ground (RF) of feedpoint, and radial angle to upright at feedpoint. As these factors get further from optimum, so does efficiency of the antenna system, which can easily be less than 10%. At least a basic 'antenna analyzer', for use at the antenna feedpoint, is must have gear for multiband vertical antenna systems. Remember, in shack tuners serve to match the radio to the transmission line, and have no effect on the match between the transmission line and the antenna, save the false sense that all is well with the latter, and with the effectiveness/efficiency of the antenna system!!

For low angle DX work, properly designed verticals are the way to go for those of us unable to put up a horizontal directional gain antenna at sufficient height to be effective.
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