5/8 vertical

[kevycorsa]

Ok so I'm trying to tune up a 5/8
I'm waiting for a antenna analyzer to turn up but I'm impatient
What should the vertical element length be for 87.5 to 108.
Does 80 inches for 87.5mhz to 65 inches for 108mhz sound about right ?
The one i got was marked at 88mhz but when i measured the length it was over 82 inches and i couldn't get a good swr reading.
Also would i need a balun choke turns of coax?
How many turns and what diameter?

[radionortheast]

running the calculator 80 and 65 are fine, i’ve never managed to get 5/8 to work on 88, the lenght is too long, always favours the half wave at 88, i’ve managed to get verticals all the way from 120cms to 165cms less than a half wave and up to 5/8 to load at 108.

i've also never been able to get end fed aerial to work without coiling the coax, i've found its 2 turns of 10 cms

[Albert H]

My ⅝-wave vertical uses four ¼-wavelength groundplane elements, bent down to (approx) 60° from horizontal (I usually use welding rod or zinc-coated studding for the groundplanes). The feeding coax is coiled around a 2" diameter piece of drainpipe - usually five turns at the bottom of the band and 4 turns at the top end. The ⅝-wave vertical radiator calculates at 6' 7", and I usually start slightly longer than that. I have a test jig that is (basically) a short flagpole in the garden. When the aerial is raised, it's several wavelengths away from anything around it.

This is crucial!

I fire about 1 Watt (with a very accurate 50Ω output impedance) up the feeder, and measure the SWR at the transmitter end. I usually expect to see around 2.5 : 1 to begin with. I drop the aerial and cut a few inches off the radiator, raise and re-test. The SWR will have come down to under 2 : 1 (unless something's really wrong!). It cut and re-try several times, and - according to the thickness of the radiator - the final length will be 95 - 97% of the calculated length. I almost always cut slightly too much off, so add length by screwing in either a coach-bolt or a piece of studding.

The ⅝-wave is a bit unwieldy, but the gain and low radiation angle make it an excellent omni-direction choice for high sites.

[kevycorsa]

Ok, well I'm going to have a mess about this weekend and try and get it tuned up, hopefully my antenna analyzer turns up by then aswell.
I might have a go at making a couple antennas in next couple of weeks if anyones got any ideas floating about or step by step guides ?
5/8 seems easy just thinking how you would attach the vertical element to a so239 socket.
Slim jim and j pole also look pretty easy to make.
Well lets see aye

[kevycorsa]

Ok so my antenna analyzer has come.
Antenna is about 6meters up away from anything.
Fed with rg213
set freq on analyzer and tuned to lowest swr.
But its telling me resistance is only 30ohms.
What obvious things could cause this
Would a choke change the resistance?

[radionortheast]

think it depends on the frequency your trying to tune it to, off frequency its problaly going to be higher or lower impedance, if you where using a ground plane you could problaly tilt the radials up or down to get the right impedance, think the swr is the most important thing, if its near 2 you've got a problem

I always tend to use rg6 when i'm messing, its 75 ohms rarely see a difference with low power, its rare to get it bang on 75.

[Albert H]

As an aside - for years I mostly used 75Ω feeders. It's not difficult to make (or buy) 75Ω dummy loads, and a Breune Bridge will still work very accurately for measuring VSWR if you have the right 75Ω characteristic connectors. 75Ω low-loss VHF / UHF coax was much cheaper than the 50Ω variety, so if you had gear being taken several times a week (as happened when Brian Gotts was being enthusiastic), it saved a lot of money!