Dual Band J-Pole

[N8BMB]

I got a set of plans for a Dual-Band J-Pole that works AWESOME!! I use the antenna listed in the plans and Get EXCELLENT SWR and TX/RX.

If you are interested in a copy, send me an e-mail!

[va3css]

Hey stranger! ;D

Are those plans in Text form? Can you copy / paste them here?

[N8BMB]

Unfortunately, the plans are in MS Publisher format. Therefore, I do not think I can post them here. But will e-mail to anyone who would like them. If you do not have publisher, Will try to accomodate!

[va3css]

Well, along the same lines, here's a FAQ about antenna design that is a darn good read!

It's lengthy, but it's got a ton of great info:
www.qsl.net/aa0ni/antennafaq.html

Here's also an online Jpole calculator:
www.hamuniverse.com/jpole.html

If you want the Jpole to be dual-band, (2m and 70cm) then simply calculate with a 70cm center frequency as well as 2m center frequency. You'll see the dimensions are multiples of each other.

[va3css]

Once again, Ed Humphries, N5RCK, delivers...

I have recently been searching various sources for easy-to-understand designs for J-pole antennas for my 2-meter radio and finally found what I consider to be the best. They were posted on an obscure "Pirate Radio" website on the Internet... Anyway, the credit goes to Mr. Ed Humphries - N5RCK, who is the original source.


A Copper Tube J-pole
by Ed Humphries - N5RCK
[e-mail]

The following is a description of a J-Pole antenna made from copper pipe. You can use 1/2 inch to 1 inch pipe (wall thickness will affect stiffness/stability AND price, but not performance). Larger diameter pipe increases bandwidth, but 1/2 inch is fine for amateur frequencies. Start with a 10 foot (standard) length of pipe, 1 90 degree (right angle) fitting, 1 "tee" fitting, 2 end-caps, 2 hose clamps (worm-gear adjustable of the appropriate diameter), and your coax (end stripped, braid separated, center conductor stripped, and coax sealant to close opening in coax to keep water out). Use a tube cutter (for best/easiest results) and cut the 10 foot pipe according to the dimensions needed following the diagram below:

__
| <=endcap
|
|
5/8 | for 146 MHz
|
|
wave |
|
|
|
-- | | <=endcap
| | 1/4
| | wave
| |
coax ctr conductor=>* *<= coax shield
| |
@ 5"-->| |
tee => --- <= elbow
|
| < "leftover" pipe
|

For best general purpose use, the 5/8th wave version should be used. The dimensions to cut are: 66 1/2 inches (5/8 + 1/4 matching section), 19 inches (other half of 1/4 matching section), 3/4 inch (joins the tee and the elbow), and the "leftover" 33 3/4 inches that forms the base. Use standard plumbing solder methods to join main section to base using the tee. Use the 3/4 inch piece and the elbow to attach the 19 inch piece. Be careful to keep pieces parallel.

This will give you a center frequency of 146 MHz. Attach the coax as shown using the hose clamps. Adjust the swr at 146 MHz by sliding the connections up or down as needed -- you should be able to reach very close to 1:1 (best to do this in approximately where you intend to use the antenna - the base can be attached directly to a mast by two hose clamps). Try not to be standing right by the antenna!

It has been noted that this design can lead to rf coupling onto the feedline. To avoid this, put a ferrite on the coax at the feedpoint, or use 3 turns (@1") of the coax taped together at the feedpoint.

Other center freq. dimensions: (adjust 5/8 section accordingly).
144 =19.25 inches, 145 =19.12, 146 =19, 147 =18.86, 148 =18.73.



TV Twin-lead J-pole
By Ed Humphries - N5RCK
[e-mail]

The following is a description of a J-Pole antenna made from 300 ohm TV twin-lead. They have quite a few advantages which include improved performance for 2-meter HTs, portability, and low cost.

| | do not short this end.
| | (when trimming for vswr, cut both sides)
| |
| |
| |
3/4 | | Technically-speaking, this is a 1/2
wave | | wave end-fed antenna with a 1/4 wave
| | matching section.
| |
| 1/4" gap
| | (trim for vswr _below_ gap)
| | 1/4
| | wave
| |
coax ctr conductor=>* *<= coax shield
1 1/4"-| |
-*- solder the twin leads together at bottom

1. Start with @54" of TV twin lead (flat, NOT foam core)
2. Strip 1/2" of insulation at bottom and solder wires together.
3. Measure 1 1/4" from soldered wires and strip insulation on both sides. This is the solder point for a coax feedline.
4. Measure 16 3/4" from coax shield solder point and cut out 1/4" notch.
5. Measure 50 1/3" from coax center conductor solder point and trim off twin lead at that point.
6. Feed with a length of RG58U coax. Tape coax at feedpoint to the twin lead for strength and seal coax for weather protection.

It has been noted that this design can lead to rf coupling onto the feedline. To avoid, put ferrite beads on the coax at the feedpoint, or use 3-5 turns of coax (1"-2") taped together at the feedpoint.

You may attach an alligator clip to the plastic on the top of the antenna in order to easily hang it. Alternately, punch a hole near the top and use a length of fishing line to hang.

This design appears on many BBSs, in club newsletters, and in books; the earliest reference that I know of is a Jan. 1984 D.A.R.C. antenna article by James Burks, KA5QYV.

FYI, the 1/4 wave sections for other center frequencies are:
144 MHz =17 inches
145 =16.88
146 =16.75
147 =16.65
148 =16.54

I usually just go ahead and solder the coax in place and trim down to as close to 1:1 vswr as I can get. I use the MFJ vhf antenna analyzer and a frequency counter then afterwards test with a radio and in-line swr/power meter. When done, the antenna should also present 1:1.2-3 vswr in the center of 444MHz band as well (demonstrated on my dual-band meter and Alinco DJ-580). You will need to trim in a 3:1 ratio to maintain the 3/4 to 1/4 wave.