J-Pole Ant. ?

[Hardchargers]

I've noticed a few references lately for the homemade J-pole antennas made of the copper pipe tuned(sized) for the frequencies one would listen to.

My question is would this type of antenna work as well in an attic? I can get away with using a lot less coax if I use my attic as opposed to running it the length of my house to get to the t.v. tower. I realize the height of the tower would be great, but if the attic will suffice then so be it.

TIA

 

[Mike-KC8OWL]

I used a copper pipe J-pole for 2m in my attic for years and it worked great.

 

[kb0nly]

The construction of the attic space is a factor also, what do you have for insulation, foil covered? Lots of wires? Any plumbing? Just think anything metal that would be near the antenna.

A J-Pole is basically a 1/2w antenna, about 3dB of gain, though some will argue that its less or more. Either way, i consider a J-Pole to be a compromise, for the price in copper pipe to make one now days you can buy a better antenna.

 

[Hardchargers]

The construction of the attic space is a factor also, what do you have for insulation, foil covered? Lots of wires? Any plumbing? Just think anything metal that would be near the antenna.

A J-Pole is basically a 1/2w antenna, about 3dB of gain, though some will argue that its less or more. Either way, i consider a J-Pole to be a compromise, for the price in copper pipe to make one now days you can buy a better antenna.

Virtually nothing in this attic as my house had an original flat tar/gravel roof and subsequent to my purchase a previous owner put a traditonal shingled hip roof overtop of that. Great spot for storage as it's strong and you don't need to balance on any trusses, just walk around as you please.

If there are better options please suggest away. I didn't realize copper had increased that much that a 10' length would epual the cost of a commercially made antenna

 

[kb0nly]

Virtually nothing in this attic as my house had an original flat tar/gravel roof and subsequent to my purchase a previous owner put a traditonal shingled hip roof overtop of that. Great spot for storage as it's strong and you don't need to balance on any trusses, just walk around as you please.

If there are better options please suggest away. I didn't realize copper had increased that much that a 10' length would epual the cost of a commercially made antenna

Oh man thats awesome for attic space!!! Can't beat that. I have crawled around some attics in my day, yours is a wonderland compared to those.

Right now a length of 3/4" copper pipe costs me $18, and 1/2" runs about $15, then the elbows are $1.50 each, the T is $1.75, a couple caps are $1 each.. I'm looking at spending about $20-$30 on materials alone for an 1/2w antenna with only so-so performance.

For my money, if you wanted a short antenna for say VHF/UHF get a ham band dual band antenna. I used a Jetstream JTB3 for my scanners right now. About $50 shipped and more gain. I could step up to a Jetstream JTB2 which costs about $68 shipped and gives me 6db on VHF and 8db on UHF, about twice the price but also twice the gain.

I guess the big question is what bands are you going to monitor? If your primarily VHF there is so many choices. Now days for about $50 you can get a good antenna. You mentioned a tv antenna tower outside, if you went with a higher gain antenna and a good quality coax your going to see a lot better performance then a high gain antenna in the attic and less coax, just something to consider. Sounds like you could easily run the coax across the attic and go out the wall near this tower perhaps?

 

[Hardchargers]

Oh man thats awesome for attic space!!! Can't beat that. I have crawled around some attics in my day, yours is a wonderland compared to those.

Right now a length of 3/4" copper pipe costs me $18, and 1/2" runs about $15, then the elbows are $1.50 each, the T is $1.75, a couple caps are $1 each.. I'm looking at spending about $20-$30 on materials alone for an 1/2w antenna with only so-so performance.

For my money, if you wanted a short antenna for say VHF/UHF get a ham band dual band antenna. I used a Jetstream JTB3 for my scanners right now. About $50 shipped and more gain. I could step up to a Jetstream JTB2 which costs about $68 shipped and gives me 6db on VHF and 8db on UHF, about twice the price but also twice the gain.

I guess the big question is what bands are you going to monitor? If your primarily VHF there is so many choices. Now days for about $50 you can get a good antenna. You mentioned a tv antenna tower outside, if you went with a higher gain antenna and a good quality coax your going to see a lot better performance then a high gain antenna in the attic and less coax, just something to consider. Sounds like you could easily run the coax across the attic and go out the wall near this tower perhaps?

Yeah right now strictly VHF.
Was trying to keep the cost down that's why I was thinking straight up into the attic instead of the much longer run with good($$) coax over to, then up the tower.
Got any suggestions on a basic VHF ant.? I'm real new to this stuff.

 

[jackj]

Why not use a 1/2 wave, center fed antenna. You could use either copper pipe or a wire on plastic pipe. Then again, fasten one end of the wire to a roof rafter and the other to a weight and let it hang. Use good quality coax and you should be good to go. You would get about 3 dbi of gain.

 

[majoco]

TV antennas can provide all sorts of Aluminum tube, insulators, nuts & bolts for making J-poles. Now that you guys have gone to UHF digital, there must be a heap of old Band 1 antennas being taken down.

Cheers - Martin ZL2MC

 

[kb2vxa]

As long as you have enough vertical room for one it will work in the attic. Since where VHF is concerned height is might so the obvious choice for the best you can get is the tower. I'm stating the obvious that has been stated time and time again but one more time couldn't hurt. Don't overlook low loss coax, you can't do it on the cheap and expect good reception when you get too little signal out for what you put into it.

 

[kb0nly]

Your looking at $50-$60 for a good vertical VHF base antenna if you want just a plain single band VHF antenna. Go on ebay, type in VHF Base Antenna and have a look. Always plenty new and used to look at, even if you dont buy from ebay it will let you do some research, look at pictures, check out measurements.

kb2vxa points out one other very good point, height! How much height do you have in your attic? At VHF the bigger the better. I know your trying to save money also, and i feel your pain there. But look at it this way. Do you want to spend the money on a run of feedline to the attic, some cheaper stuff, and put up a cheap antenna or even just a homebrew antenna and then a few months from now realize you want more? Then you just wasted money taking one more step to your goal. I think most of us have done it, so if you do i don't blame you, but if instead you spent a couple months more saving up some money for good coax and a better antenna and got it out on the tower your going to be much happier in the end!

 

[LtDoc]

'J'-pole antennas work. They may not be the 'best' antenna for particular things, but they are a pretty good general antenna. They can certainly work in an attic. Not as well as if they were outside at the same height etc, but oh well. Would one work acceptably in your attic? Probably. Just depends on what's 'acceptable' to you. It also makes a big difference if that attic is insulated with metal backed insulation, you know?
Any benefits to the thing being copper rather than some other metal? Not really. Copper tends to be easier to work with, solder to, etc. It isn't necessarily cheaper, but most plumbing supply houses tend to have all sorts of fittings, sizes, what-not, so it's fairly easy to find 'stuff' to make an antenna.
Antenna height at VHF/UHF does make a big difference! You have to be practical about that though. I'd love to have a 'J'-pole at 1/4 mile high, but how would you feed the @#$ thing, the feed line losses get sort of big at that height.
In general, it'd probably work just fine...
- 'Doc

 

[majoco]

One of the advantages of a J-Pole is that it doesn't require a ground plane. Be wary of quarter and 5/8 wave antennas designed to be mounted on a vehicle or a mast - you'll need to add radials in your attic if you use one like that.

Cheers - Martin ZL2MC

 

[nanZor]

If you do decide on the J-pole, be sure to use an rf-choke near the feedpoint. This prevents the common-mode of the coax braid (outside skin depth) from becoming part of the antenna, and destroying the radiation pattern.

Although $$, Radio Shack has the type-43 snap-on chokes that are good from about 25mhz to 300mhz - RS model 273-105. At a minimum, you'd need about 4 to do any good, 6 would be my minimum. And then skip lunch.

 

[N5JBD]

JPole info

There is some good info on the J Pole antenna on this thread so I wont go into that. They are very cheap to build, each year I build a dozen or so to sell at one of the local "hamfests" in the area.

I wanted to comment about a RF choke. If you decide that you need one making one is very simple. All that you need to do is take your extra coax and roll it up near the feed point and walk away. If you want to you can go on line and search "ugly balun" and it will show you how to make one. I use the "ugly balun" on all of my ham radio antennas. I use a plastic 1# coffer can and wrap 20' of coax around it right at the feed line.

Good luck
Terry
N5JBD