[time-nuts] GPS antenna installation problem

Mark Spencer mspencer12345 at yahoo.ca
Mon Mar 2 12:19:11 EST 2009


Quote:

Some antennas are setup with the coax connector on the inside of a place with
>> threads where the pipe attaches.  The coax has to go up the inside of the
>> mounting pipe.  

Just a data point.   I have installed numerous 2 way radio antennas over the years that use this mounting method.    As far as I can recall I have never used a mast longer than 5 feet and I have never had any issues with the coaxial cable or connectors.     I'm not sure I would want to use a mast longer than five feet in this application but I don't have any real evidence to support my oppinion.

In a few weeks I hope to mount my first home GPS antenna using this mounting method (:

I have also been involved in a project where long lengths of free hanging cable were required.    (ie. hanging inside the towers of a suspension bridge.)    Special cables were used in this application.    Sorry I don't know what the height limit is for free hanging conventional coaxial cable is but I'd hesitate to have more than 5 feet or so free hanging.

Regards
Mark Spencer

VE7AFZ



 


----- Original Message ----
From: Steve Rooke <sar10538 at gmail.com>
To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
Sent: Monday, March 2, 2009 8:27:03 AM
Subject: Re: [time-nuts] GPS antenna installation problem

Just as a followup, here's some other ideas:

When I worked for British Telecom (it was called Post Office
Telephones then) as an apprentice I woked on undergroud work for a
while. Telephone cables were lead sheathed and the joints were made in
a shoth lenght of large diameter lead pipe. A lot of these joints were
lead soldered but some were sealed by a compressible gland at each
end. The gland was made of a thick disk of black rubber which would
fit snugly but freely inside the joint sleeve. Either side of the
rubber disk was a brass blate slightly smaller in diameter than the
rubber. There were holes through the gland to allow the cables to
enter and this was a snugh but free fit on the cable, and with the
brass plate holes being a bit larger than the cable holes. The two
brass plates were held either side of the rubber by brass bolts which
went through clearance holes on the outside and were threaded in the
rear brass plate. The idea is that the cables went through the glands
were they were jointed. The joint then went into the joint sleeve and
the gland was pushed just inside the sleeve. The bolts were then
tightened to compress the rubber gland which then made a tight
mechanical and waterproof (hopefully) seal to the joint. You could do
something similar with a gland fitted into the antenna support pole
which would grip the cable firmly in place but allow it to be removed
easily. A bit of engineering, I know, but an idea.

Another option would be to find a piece of bamboo or doweling which
would fit inside the antenna post along with the cable. The cable
could then the cable tied to this stick and run up the inside of the
antenna support with the base of the stick fixed to the bottom of the
antenna pole.

And while I'm at it, how about some builders expanding foam. You could
hold the cable in the pipe and squirt the foam into the pipe where it
would expand to grip the sides of the pole and the cable as well. A
cable tie round the coax should stop the cable falling down in the
event of shrinkage. Bit messy though.

As the pipe being mentioned was plastic plumbing supplies, you could
find a flat piece of the same plastic and using a hole cutting saw,
cut out a disk with a tight fit into the pipe. Make the hole in the
middle to fit the cable and glue it a few inches down the pipe with
the pipe sealing glue for plumbing. Just need to put a cable tie on
the coax for cable relief to stop it dropping down and attach it to
the antenna.

You could also find a wood plug the same size as the inside of the
antenna pipe. Make a hole through the middle , lower it into the pipe,
drill a small hole through the side of the pipe and secure the wood
plug with a short wood screw. Just need to use the same old cable tie
strain relief again.

Just some random ideas, sorry for taking you time on an off topic subject.

73, Steve.

2009/3/3 Steve Rooke <sar10538 at gmail.com>:
> 2009/3/2 Hal Murray <hmurray at megapathdsl.net>:
>>
>>> Gaffa tape the cable to the supporting pipe with a small drip loop
>>> into the connector.
>>
>> That assumes the cable gets to the outside of the pipe.  I was interested in
>> the case where the antenna sits directly on the top of the pipe (not a
>> bracket off to the side).
>
> Find a rubber cork, or something which will not deteriorate, that is a
> tight fit for the inside of the pipe. Drill a hole in it to pass the
> coax through. Leave enough coax  out of the cork to attach to the
> antenna and then press the cork into the pipe. The short length of
> coax at the top will not be a strain on the connector and the action
> of squeezing the cork into the pipe will further grip the coax to stop
> it travelling downwards. You can also add a cable tie round the cable
> just above the cork to stop it slipping down.
>
> Just an idea.
>
> 73, Steve
>
>> Some antennas are setup with the coax connector on the inside of a place wiIn th
>> threads where the pipe attaches.  The coax has to go up the inside of the
>> mounting pipe.  You can also use a bracket, but it's setup for the
>> inside-the-pipe approach.
>>
>> Here is a drawing:
>>  http://www.synergy-gps.com/images/stories/pdf/anttiming3000_tn888.pdf
>>
>> For a setup like that, I don't see how to get tape or anything else inside
>> the pipe, so the coax will end up hanging from the connector.
>>
>> So the question is how much coax can you hang from a connector?
>>
>> Clearly a foot or 3 is reasonable because you need that much for a drip loop.
>>  How about 6 ft?  20 ft?
>>
>>
>>
>>
>> --
>> These are my opinions, not necessarily my employer's.  I hate spam.
>>
>>
>>
>>
>> _______________________________________________
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>> and follow the instructions there.
>>
>
>
>
> --
> Steve Rooke - ZL3TUV & G8KVD & JAKDTTNW
> Omnium finis imminet
>



-- 
Steve Rooke - ZL3TUV & G8KVD & JAKDTTNW
Omnium finis imminet

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