1/4 wave coax vertical dipole

[sharky]

No worries, i was interested on the performance

[pjeva]

Regarding performance, it's very good for double stacked dipole. Good match to 50ohm output. Bad side of this, it is more complicated for installation, since it must be insude pvc pipe and isolated from boom and lambda section or mast. Not very rugged construction i must say. This goes in favour of gamma match since it is fully grounded (only gamma match part is "hot").
Word of advice, if you have good quality cable (like i used) and you know exact velocity factor, this is very easy-build antenna

[Dan]

Sharky if i remove the folded back sheath and replace with a copper tube, can it be the same length as the center core, like on a center fed dipole ? and does the tube go over the coax to act like the reversed sheath ?

[teckniqs]

Yes it can, the bottom element of an end fed unipole isn't so critical, it's the top element that is. I've messed around with bazooka end fed dipoles many years ago and I found it didn't matter too much on the length of the ground element.

[Dan]

ok cool, so should i cut the sheath off and replace with a copper element ? and then use the same measurement for center fed on the top half, or is the measurement slightly different ?

[teckniqs]

I found the top element to vary slightly from the calculated length, start with it a little longer and work your way down.

[Dan]

can I use an aluminium tube or does it have to be copper ? cant find any 12mm copper tubes to fit perfectly over the coax. RG213

[teckniqs]

You can use either.

[pjeva]

I'm not sure what design we are talking about, but i think that sleeve should not fit perfectly over coax. It should be wider

And aluminium cannot be soldered to coax, so it is better to use copper

Sent from my iPhone using Tapatalk

[Dan]

talking about the first design (sharky). Iv left the braid on and just slid the element over the entire bottom half, would this work the same or would the braid need to be removed?

[sharky]

Sorry for the late reply, I ve been dodging redundancy at work, just !!

talking about the first design (sharky). Iv left the braid on and just slid the element over the entire bottom half, would this work the same or would the braid need to be removed?

Should be fine as long as you have a good connection between the two..
I used RG213 for the last one, and 28mm copper slid over the bottom element.
For the complete build I used a 2m length of overflow ( 21.5mm ) ran the cable through it, folded the braid over the top then the 28mm over the top.. Very tight fit!!
I'm off on Wed & Thurs so i'll post a few pics up with the parts i used.

I might have got the pipe diameter out slightly, i'll have to check.
Working in a plumbers merchant helps !!