Homebrew Quad antenna

[n4yek]

Here is an antenna I had drawn years ago when I was playing around with Autocad.
I never built it so I don't know how it performs, but again I was just playing.
Basically you have coax going up the center pipe and branching off to each band.
The design is basically a vertical dipole for each band, utilizing the coax itself by
pulling the center out of the shield. Having the center on the top side and the
coax shield going down the bottom side.

What do you think?
Comments welcome.

 

[zz0468]

What do you think?
Comments welcome.

1. Use schedule 40 PVC, not 80.

2. Configure the individual antennas as coaxials, not dipoles.

3. Make no attempt to diplex them to a single coax. Oh, it can be done, but you'll be happier if you don't.

4. I wouldn't be happy with the aesthetics of the contraption, but if it works for you... *shrug*

5. Call it something else. A quad antenna is a completely different animal.

 

[n4yek]

3. Make no attempt to diplex them to a single coax. Oh, it can be done, but you'll be happier if you don't.

You didn't look close enough, there are 4 connectors at the bottom, for four coax cables inside. I should have been a bit more clear on that aspect.

1. Use schedule 40 PVC, not 80.

Explain why? just curious as to your point of view.

2. Configure the individual antennas as coaxials, not dipoles.

Isn't that what a coaxial antenna is? A vertical dipole made from coax, center up in the air and coax shield hanging down?
http://en.wikipedia.org/wiki/Coaxial_antenna

Thanks for your comments.

 

[zz0468]

You didn't look close enough, there are 4 connectors at the bottom, for four coax cables inside. I should have been a bit more clear on that aspect.

Ok. I missed that little detail.

Explain why? just curious as to your point of view.

Schedule 80 is very thin walled and won't hold up under that kind of use. Schedule 40 has thicker walls, and is a great deal stronger. I've successfully used schedule 40 PVC on many antennas. I wouldn't even build a sprinkler system with schedule 80 pipe, which is it's intended purpose.

Isn't that what a coaxial antenna is? A vertical dipole made from coax, center up in the air and coax shield hanging down?

Well... **I** know what a coaxial antenna is. The PVC piping in your drawing is configured to appear like a center fed dipole, which would be impractical if you were to enclose a coaxial antenna in there. In a coaxial, although center fed, the coax cable actually comes out one end of the antenna, not the center. It's not merely an antenna made from coax. It describes a particular configuration. What you're describing doesn't quite cut it. Did you look at the PDF diagram on the wiki link you posted?

 

[n4yek]

Schedule 80 is very thin walled and won't hold up under that kind of use. Schedule 40 has thicker walls, and is a great deal stronger. I've successfully used schedule 40 PVC on many antennas. I wouldn't even build a sprinkler system with schedule 80 pipe, which is it's intended purpose.

I believe you have this backwards, Schedule 80 has thicker walls than 40.

Well... **I** know what a coaxial antenna is.

ok, I can redraw it to look like a bunch of 'J' antennas

But if you just use this antenna for receive purposes only, current build up won't be a problem. So a vertical dipole would be just fine.

 

[zz0468]

I believe you have this backwards, Schedule 80 has thicker walls than 40.

You're right. What's that paper thin stuff? That's what I've had fixed in my mind as schedule 80 all this time.

 

[n4yek]

You're right. What's that paper thin stuff? That's what I've had fixed in my mind as schedule 80 all this time.

It's called 'Eggshell', I'm not sure why they make it but I would say it has it's purpose, maybe for electrical usage.
Possibly to save money, but I wouldn't trust the stuff.

 

[zz0468]

It's called 'Eggshell', I'm not sure why they make it but I would say it has it's purpose, maybe for electrical usage.
Possibly to save money, but I wouldn't trust the stuff.

I think it's for sprinklers.

Another thought on your PVC antennas... With all those 'T' connectors in there, it' probably wouldn't be a great idea to to mount it on the end of a pipe. Maybe clamp it in a couple of places further up. Those 'T's will be a weak link.

 

[Bill_White]

I think you should be using antenna modeling / analyzing software instead of Autocad.
Go here and get a free copy of MMANA-GAL:
http://mmhamsoft.amateur-radio.ca/
Let us know how your design performs.

 

[prcguy]

It looks like the center support will have coax inside and that will turn all the dipoles into a 2 element beam pointing in various directions. If this is the intent the spacing from the dipole to the coax "reflector" looks wrong for the different bands. If you want omni coverage you will have to separate all the antennas many wavelengths apart.
prcguy

 

[zz0468]

It looks like the center support will have coax inside and that will turn all the dipoles into a 2 element beam pointing in various directions. If this is the intent the spacing from the dipole to the coax "reflector" looks wrong for the different bands. If you want omni coverage you will have to separate all the antennas many wavelengths apart.
prcguy

I'm thinking that the "reflector" is non resonant, it wouldn't act so much like a yagi reflector as it would just a long conductor, like you'd find side mounting a dipole on a mast. So, the pattern might be more cardioid shaped, not beam-like.