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Homemade dual band....


74IN,
The cheapest and 'dirtiest' answer I can think of for a dual-band VHF/UHF antenna is a simple 'J'-pole for 2 meters. It'll work fine on '440. And unlike HF (as you probably know, or will find out), higher means more than any 'gain'.
'J'-pole's aren't that 'picky' about what you make them from, size wire/tubing. If it'll hold it's self up, and it's shape, it'll work just fine. Same goes for any antenna.
That's just one solution, there are as many as you want to try.
- 'Doc
 
I saw one that used twinlead with a piece of RG-174 in the upper section. It seemed like one of the best designs I'd seen.

I think it was on the ARRL...

yes, here it is: http://www.arrl.org/tis/info/pdf/0302038.pdf

If someone could help explain the RG-174 a bit more clearely, I'd like help understanding it better.

I intend to build this one, two of them actually. One in a PVC pipe for permanent install and the other for portable use.
 
C2,
That piece of RG-174 coax is used as a 1/4 wave phasing section on 440. At 145 Mhz it acts just like a plain piece of wire, but at 440 Mhz it acts as a timing or phasing section to make the 17" above and below it into a two section vertical array. Nothing wrong with doing that, but I have 'qualms' about using RG-174 for anything (just a personal thingy, not very important).
- 'Doc
 
C2,
That piece of RG-174 coax is used as a 1/4 wave phasing section on 440. At 145 Mhz it acts just like a plain piece of wire, but at 440 Mhz it acts as a timing or phasing section to make the 17" above and below it into a two section vertical array. Nothing wrong with doing that, but I have 'qualms' about using RG-174 for anything (just a personal thingy, not very important).
- 'Doc


Would love to hear about those qualms...is there a higher performing solution?

I do recall a copper cactus j-pole that had another J pole as the upper section of the 2-meter j-pole and used multiple feeds for each j-pole, similar to this:

The Copper cactus antenna by dxzone.com

and actually the tri-band above seems like a good concept.
 
How about this one?

dualband_j-pole.gif
 
I've made a few Jpoles for vhf/uhf.

They work just fine, I'm looking to build something else.

Dunno what, so I ask.

I made a couple of 2M groundplanes, they seemed to work better.

I think I've seen dual band ones that had two vertical radiators.

Do they work?
 
I was also going to try and duplicate a Larsen dual band mobile. I believe it is a 1/2 wave on 2m and 5/8 over 1/2 wave collinear on 70cm.
 
How about this one?

dualband_j-pole.gif

These a.k.a. the Arrow J-pole work very very well and they are indestructable.

The club built several and I've been rather amazed at how well they work as a field antenna stuck up on a PA speaker tripod.
 
About those 'qualms'.

It has to do with RG-174 being a terrible feed line, at any frequency, especially the higher ones, lots of loss. As it's used in this application, that just doesn't apply much. ( Just something to keep in mind, but don't let it worry you much.) I also have my doubts as to it's power handling abilities. No idea what it's rated for, but I'd certainly think twice before putting much through it.
A lot of reason for these 'qualms' is that I just don't know much about the stuff, never had need of it.

One thing about the gain of a 'J'-pole antenna. When you get right down to it, One 'style' is going to be very similar in performance to a different 'style' 'J'-pole. Mechanically it might make a difference if it's made of copper tubing, or wire. Electrically, ain't enough difference to make much difference at all. One or two dB gain over a 'whats-it's-name' antenna may look good on paper, but it doesn't mean much on the air.
Which should you try -first-? Whichever one you want, and that you think you can put together. Wonder about that "-first-" thingy? Cuz if you make one and it works, tell me you ain't gonna try something different. I dare you. :)
- 'Doc
 

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