Open Stub J-Poles

RadioChief55 · Mar 10, 2018

I'm thinking of building an Open Stub J-Poles VHF UHF antenna to put in my attic and using it on the Uniden BCD996P2. But I have a few questions.

1) Anyone use one and does it work well?
2) If I build it, can I use threaded rod and angle iron? Does it matter if the elements are solid or do they have to be hollow?
3) Can I solder the coax directly to the metal or do I need a filter?

Attached is a picture of whet I'm thinking of building.

Thanks

ipfd320 · Mar 10, 2018

That Design is an----arrow J-Pole--I Had 1 I Borroewd from a Friend---Works Great on the VHF (146.00) with a 1.2 to 1 SWR / as for the UHF Side Not So Good--had SWR at 2.6 to 1 and Couldnt get it low at all on UHF (440 to 470)---I was Feeding it with LMR 400 25 Feet in Length

http://www.arrowantennas.com/osj/j-pole.html

RadioChief55 · Mar 10, 2018

I mainly scan VHF 154 to 160 and UHF 460 to 501. with about a 25 foot run with coax. IDK what kind it is though.

prcguy · Mar 10, 2018

The Arrow antenna pictured is not a J-pole, its something else. The coax connects to an element that is 1/4 wavelength on 2m and 3/4 wavelength on 440Mhz providing a good match and ok pattern on 2m. They add a 1/2 wave "sympathetic radiator" for 2m and a 1/4 wave stub for 440Mhz that resonate and re-radiate some of the signal present on the driven element.

A J-pole is a 1/2 wavelength radiator with a 1/4 wavelength matching transformer that you tap for the best match to 50 ohms. The 1/4 transformer would allow matching to 10 ohms or 100 ohms or most anything between a few ohms and a few thousand ohms. The Arrow antenna does not have that. What it does to is make the coax and mast part of the antenna and the mast and coax will radiate on the Arrow, which is one of many reasons I would never buy or make one. For Arrow its a gimmick to manufacture antennas that work well enough for a cheap price.
prcguy

cmdrwill · Mar 10, 2018

prcguy said:
The Arrow antenna pictured is not a J-pole, its something else.
prcguy

That is correct, it IS an Arrow antenna.

NOT a Open Stub J-Pole either. Or even a J-Pole.

popnokick · Mar 10, 2018

Isn't the Arrow antenna pictured in this thread rather narrow-banded to be used as a wide ranging VHF / UHF scanner antenna? Wouldn't an Off-Center Fed Dipole (OCFD) like this provide a much broader receive range? Homebrewed Off-Center Fed Dipole - The RadioReference Wiki

RadioChief55 · Mar 10, 2018

Thank you for all the feed back. I just want a good all around antenna to hook up to my scanner. I thought it would be a fun project to build on. So, my question is, what indoor scanner antenna is good for when I want to do? I'd still like to build one, it's going in my attic in the rafter above the ceiling, The coax will run down between the roof and drywall and come out the wall, about a 20 foot run. The antenna height will be around 45 feet off the ground and I'm on top of a hill.

Thanks

ipfd320 · Mar 10, 2018

Just Posting what he Has There and what i had and Used thats all---the pic is an arrow j-pole same pic same design--as for Scanner recieve I Like the Ol T.V. Log Periodic Antenna Myself---But Everyone has there own opinion with a million different answers to meet there needs---good luck chief

majoco · Apr 17, 2018

Deleted

barrylewis1234 · May 23, 2018

If making a 1/2 Wave J pole look at these on ebay:
https://www.ebay.co.uk/itm/DIY-J-PO...2M-4M-6M-AMATEUR-HAM-RADIO-JPOLE/332659591355

Great for a waterproof connection and easy adjustment on tuning. Im currently making a j pole so ill post some pics when complete

ko6jw_2 · May 24, 2018

prcguy said:
The Arrow antenna pictured is not a J-pole, its something else. The coax connects to an element that is 1/4 wavelength on 2m and 3/4 wavelength on 440Mhz providing a good match and ok pattern on 2m. They add a 1/2 wave "sympathetic radiator" for 2m and a 1/4 wave stub for 440Mhz that resonate and re-radiate some of the signal present on the driven element.

A J-pole is a 1/2 wavelength radiator with a 1/4 wavelength matching transformer that you tap for the best match to 50 ohms. The 1/4 transformer would allow matching to 10 ohms or 100 ohms or most anything between a few ohms and a few thousand ohms. The Arrow antenna does not have that. What it does to is make the coax and mast part of the antenna and the mast and coax will radiate on the Arrow, which is one of many reasons I would never buy or make one. For Arrow its a gimmick to manufacture antennas that work well enough for a cheap price.
prcguy

I'm sure the engineers at Arrow are thrilled that you set them straight about their antenna. False advertising.

Oh wait, it is a j-pole. It is direct fed which is a very tried and true method of making j-poles. I've been doing it for years. I talked to a friend who has been licensed for well over 50 years and has a Phd in electrical engineering. He uses the direct fed method. It used to appear in the ARRL Antenna handbook. I guess the people at Arrow read about it too.

These threads contain more disinformation about j-poles than any other forum I've ever seen.

The j-pole is, in fact, an end fed Zepp. This type of antenna is direct fed and always has been. It does not use a shunt feed. It works on HF and it works on VHF/UHF.

By the way, I've had one of these antennas for many years and it works very well. Measures 50 ohms and has good bandwidth.

KC4RAF · May 24, 2018

RadioChief55, the J-Pole antenna is one of the most controversial antenna design, at least here on the RR forums. There's many who say that it is not a J-Pole but of some other design. It IS a "J-Pole" antenna; and for your needs, it don't matter what it's called.
I've built a couple of these and bought one. They all worked great.
For your needs for scanning, it will do quite nicely in your attic. VHF will be received very well; but UHF may, and I say may be slightly less received.
If you build it to specs, you should be quite happy with your work.
And:
the metal can be iron, copper, or aluminum. Aluminum is lighter and easier to work with and hang.
It can be tube or solid. Tubing is much lighter weight.
And yes you can solder your joints. BUT, by using an SO239 connector, you will be farther ahead should changes need be done.
KO6JW_2 gave a great description of the J. That made me happy to read his post.

majoco · May 24, 2018

Why not read the original article instead of all the 'chinese whispers'.....

https://en.wikipedia.org/wiki/J-pole_antenna

Interesting that the Corps of Signals book pages 163 and 164 feed the j-pole with 600 ohm open line, not coax and the airship HF version feeds the bottom of the J through a transformer - perhaps the bars across the stub are insulators just to hold them apart or one might be a matching piece. I'd like to experiment but my airship is away for maintenance......

prcguy · May 24, 2018

Still not a J pole but maybe a 3rd cousin. A J pole is a very specific design using a tapped 1/4 wavelength line section as a 50 ohm to high impedance transformer to match an end fed 1/2 wave radiator. The Arrow does not specifically have that. A Cushcraft Ringo is a 1/2 wave radiator with a tapped 1/4 wave tuning thing but that doesn't make it a J-pole either.

An end fed zep is simply a balanced feedline ending at a 1/2 wavelength radiator only connected to one side of the feedline and there is no impedance matching because you feed it with a high impedance tuner. That is not a J-pole.

Arrow is clever but also cheap and they are simply using a very cheap, no factory tuning required way to mfr antennas. And don't make me get my Phd's, Senior Staff Scientists and Fellows friends on a bus to your house to debate your Phd friend.....

ko6jw_2 said:
I'm sure the engineers at Arrow are thrilled that you set them straight about their antenna. False advertising.

Oh wait, it is a j-pole. It is direct fed which is a very tried and true method of making j-poles. I've been doing it for years. I talked to a friend who has been licensed for well over 50 years and has a Phd in electrical engineering. He uses the direct fed method. It used to appear in the ARRL Antenna handbook. I guess the people at Arrow read about it too.

These threads contain more disinformation about j-poles than any other forum I've ever seen.

The j-pole is, in fact, an end fed Zepp. This type of antenna is direct fed and always has been. It does not use a shunt feed. It works on HF and it works on VHF/UHF.

By the way, I've had one of these antennas for many years and it works very well. Measures 50 ohms and has good bandwidth.

barrylewis1234 · May 27, 2018

I have to agree that that arrow antenna does NOT look like a traditional J POLE

This is a great video explaining how a J pole works:

https://www.youtube.com/watch?v=GRJw3SCBGfA

Also there are very nicely priced J poles on ebay from this seller who i purchased the jpole connector from.
Im sure they will ship across the pond if you ask:

https://www.ebay.co.uk/itm/AirBand-...tary-J-Pole-RTL-SDR-Aerial-Jpole/332663737501

Open Stub J-Poles

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