[Xastir] Portable Digipeater Antenna?

[Gerry Creager]

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 -- gerry.creager at tamu.edu
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