But not the black pipe owing to the carbon content.

73


David W Wood

Ham call - G3YXX
FOC # - 1685
Licensed - 1969
 
-----Original Message-----
From: For blind ham radio operators [mailto:[log in to unmask]] On Behalf Of Howard Kaufman
Sent: Saturday, September 01, 2012 7:48 AM
To: [log in to unmask]
Subject: Re: Description of a J Pole antenna

Other uses?
Never thought of it, but you could make a UHF water pipe j-pole into an 
effective bong!!!  Nice way to hide a pipe!  LOL!!!
----- Original Message ----- 
From: "John Miller" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, August 27, 2012 8:02 PM
Subject: Re: Description of a J Pole antenna


>I had a real nice one made out of water pipe, I built it when I was in
> college to use in the dorm, then it found various other uses, like as a
> scanner antenna for a long time but it was stolen at my last apartment. I
> had it in the storage unit and the first time it was broken in to that was
> stolen. One of those things I know who did it but couldn't prove it. Then
> people wonder why I'm so anal about locking everything up since then. when
> my room for ham radio is built over here, that will be locked as well.
> ----- Original Message ----- 
> From: "Ronald E. Milliman" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Monday, August 27, 2012 8:49 PM
> Subject: Description of a J Pole antenna
>
>
>> Howard,
>>
>> several days ago you asked if one of us could describe a J Pole antenna 
>> to
>> you in enough detail so you could build one.  Well, I will try.  Here it
>> goes...
>>
>>
>> construction for a 2 meter J Pole :
>>
>> First, imagine the print letter J . This represents the shape of the
>> antenna. It has one long side and one short side all connected at the
>> bottom or said another way, one continuous length of conductor shaped 
>> into
>> a J.
>>
>> Now turn or flip the J backwards as if you were writing it with the short
>> side on the right rather than on the left.  I say this simply because 
>> this
>> is the way it is usually shown in the ham mags and on most web pages.
>>
>> The J is one single "conductor" in the shape of a J.
>> From the top of the long side of the J to the bottom, for 2 meters, is
>> about 58 inches long before it turns horizontally a couple of inches and
>> then goes vertical for about 19 1/4 inches. So you have a total length of
>> about 77 1/4 inches forming a single J shape.
>>
>> The center conductor of the coaxial feedline is attached to The long
>> section of the J Pole and the braid or shield of the feedline is attached
>> to the short section.  These feed points for the coax are spaced up from
>> the bottom of the J or antenna about two inches, and they need to be,
>> initially, adjustable , until you find the optimum tap or feedpoint that
>> gives minimum SWR. So, do not make a permanent feedline connection yet.
>> Once you have these feedpoints adjusted to produce minimum SWR, you can
>> solder them for a permanent connection.
>>
>> Again, the shield of the 50 ohm coax is attached to the short section
>> about
>> 2 inches up from the bottom.
>> The center conductor of the 50 ohm coax is attached to the long section
>> about 2 inches up from the bottom. Both the center conductor and the
>> shield
>> should now be side by side on the vertical elements equal distance from
>> the
>> bottom. One on one vertical side and the other on the other vertical 
>> side.
>> BOTH are connected equal distance from the bottom of the antenna and are
>> adjusted up or down equally for lowest swr. This is the tricky part. Some
>> method of making temporary connections for tuning will be needed or they
>> can just be tack soldered for testing and tuning.=20
>>
>> For tuning, you can mount the J Pole on top of a short pole, a length of
>> PVC, a push-pole, etc., or you can mount it on a temporary support like a
>> wooden ladder.
>>
>> Then, once you have it tuned, you will need some method of mounting the
>> antenna to a mast, pole, etc in your final installation.
>>
>> Most builders just add about 15 to 20 inches to the long side at the
>> bottom
>> for mounting.
>> This extra length becomes invisible to the operation of the antenna; 
>> thus,
>> not effecting its operation.  So, it can be metal tubing for a J pole.
>> Adding this length would make the long side about 58 plus 15 inches =3D 
>> 73
>> inches...or
>> 58 plus 20 inches =3D 78 inches.
>> =20
>> Of course, you want to mount the antenna in a location about 1/2 wave
>> length away from any metal surface near the antenna in any direction
>> except
>> the bottom of the antenna.
>>
>> The lengths and spacing of the J element is not very critical due to the
>> variable tuning section. The main thing is to get the final swr down as
>> low
>> as possible.
>>
>> Also, it is recommended to add about 4 or 5 turns of coax in a neat coil
>> with coils side by side at the bottom of the antenna making an air
>> choke=9D
>> out of it to keep stray rf off of the coax outer conductor.
>>
>> It is a challenge to describe something like this, but there you have it.
>> I hope you are able to visualize it well enough to take a shot at 
>> actually
>> building one.  Alternatively, they are available to purchase either fully
>> assembled or the parts that you can put together yourself. =20
>>
>> Ron, AC4HM 

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