Couple of thoughts here.
1. <RANT> Coax-seal is evil and messy.
</rant>
2. For short-term protection against the elements, I recommend Scotch
23 or 130 rubberized splicing tape plus or minus ScotchKote.
3. If you were to expand the braid and double it back over the jacket
of the coax, you'd achieve the decoupling you're trying to get with the
(effectively HF) choke. A similar decoupler can theoretically (meaning,
I've not tried this yet) with a piece of 1/2 in pvc and aluminum or
copper tape bonded (electrically) to the shield and also .52 wave long.
This is a good idea for a short-term, temporary, quickie antenna.
gerry
Richard Polivka, N6NKO wrote:
Here is a quick and dirty one. We all have coax, wire ties, and a good
pitching arm.
Sometimes a mast is not the easiest thing to install but if you have
tall overhanging objects, this helps. I always carry a spool of mason's
twine (either pink or electric green/yellow). The antenna is made out of
RG-58. I strip back about 22 inches to expose the center conductor,
making sure that the outer shield does not short against the exposed
center conductor. I also put a little coax-seal at that point to seal
the cable against the elements. I form a loop at the end of the center
conductor so the length is .52 meters. At the same distance down the
coax from the strip point, I put about six-eight turn coil about 3-4
inches in diameter, straight wind, not scatter wind. I hold the
inductor together with the plastic wire ties. I have just now created a
vertical 1/2 wave dipole. I tune it with an MFJ box. Tuning is
accomplished with it hanging in an accessible spot off the ground and
adjusting where the coil is and the length of the exposed copper center
conductor.
The antenna works either inside or out. It may not be a gain antenna,
but it is simple, easy to store, easy to use, and costs are just for the
coax, connector and wire ties. A nice safety aspect of this is that
there are no radials sticking out. It can be used inside in a building (
a pin in the wall to hang it on or in a suspended ceiling from a
paperclip) or outside from a tree or lamp post. Don't use power lines as
a hanger. You could get away using a cable TV cable or phone cable, but
not power lines.
73 from 807,
Richard, N6NKO
Gerry Creager wrote:
Steve Friis wrote:
Jim Tolbert wrote:
When considering adding a portable digipeater to a kit, what does an
antenna mast buy you and what is the relationship between height and
effectiveness?
What is antenna height & specifications and equipment specifications
that should be considered for a permanent antenna, centrally located
in the county?
We are in Burnett County, Wisconsin ..... according to the U.S.
Census Bureau, the county has a total area of 2,280 km² (880 mi²).
2,128 km² (822 mi²) of it is land and 152 km² (59 mi²) of it (6.69%)
is water. There are small elevation changes in the county (800
feet to 1440 feet above mean sea level) and the land is largely
forested.
Many thanx ............. jt
My experience shows that doubling the height is equal to multiplying
the power by 4. This is especially true if you can get above the
tree-tops. Here in the desert, you can really increase the range by
adding height. I bring a 25' pole to mount both the HF antenna on
plus the dual band VHF/UHF antenna.
My portable repeater exploits suggest that an antenna should be
between 20-40 feet as a minimum... or else just left on the car. You
see benefits with antenna height above local terrain that cannot be
compensated for by either power or preamplification.
I tend to shoot for one of several 30 foot portable masts I have
available. One of the simplest is a "bull-float" handle available
from concrete supply stores (but probably not Home Depot). they're
~1-3/4" diameter threaded poles, 10 ft long. I've put up to 4
together with 3-way, single level guying and had the antenna up for as
long as a week. Easy to carry and handle, and total cost of the mast
was less than $80. Very rugges... they have to be to survive the
concrete business.
gerry
--
Gerry Creager -- [EMAIL PROTECTED]
Texas Mesonet -- AATLT, Texas A&M University
Cell: 979.229.5301 Office: 979.458.4020 FAX 979.862.3983
MAIL: AATLT, 3139 TAMU
Physical: 1700 Research Parkway, Suite 160,
College Station, TX 77843-3139
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