102" whip as base antenna on a metal post questions..

[loosecannon]

K3ACZ, remember that a quarter wave radiator will have an impedance around 36 ohms, so don't go trying for a 1.1:1 SWR or you are going to end up cutting too much off of your antenna.
get it down to 1.4:1 at the center of your SWR curve and call it good. (50 / 1.4 = 35.7)
LC

 

[CB590]

After fine tuning the Firestik II I got 1.1-1 on ch. 1 and 1.4 on ch. 40 and 1.2 on ch.20.

When I get up $80 I will more than likely by the A99 to cover 10 & 11m.

 

[543_Dallas]

K3ACZ, remember that a quarter wave radiator will have an impedance around 36 ohms, so don't go trying for a 1.1:1 SWR or you are going to end up cutting too much off of your antenna.
get it down to 1.4:1 at the center of your SWR curve and call it good. (50 / 1.4 = 35.7)
LC

How does he know he should stop trimming at 1.4 or trim to a 1.1:1 and then trim some more to hit 1.4 again? Same swr different impedance.

For maximum band coverage I'd shoot for 1.1 at the center of the frequencies he plans to use. Without an analyzer at the feedpoint or a carefully measured length of coax its a shot in the dark.

 

[loosecannon]

It's an excellent question 543, and one I hadn't really considered, but only because i've just never had to.

first, i don't tune 102" whips. i install them correctly and then check the SWR curve and call it done.

when they are installed correctly (in my experience) you will find a 1.4:1 SWR at the middle of the curve, which will gradually rise to a 2:1 SWR at the ends.

that range is usually quite broad enough for most people, but for those who need it shifted up or down a bit, that's exactly what i do, shift the curve up or down by adding or subtracting length from the system.
obviously subtracting is easier LOL.

LC

 

[543_Dallas]

Putting one on a vehicle can be different game for sure. I've used them as a base antenna on a few occasions. It was only on 11 meters and I never cut the whip or added any kind of extensions. I did use a spring when one was handy and it wasn't a stealth operation. I just trimmed the ground radial(s) to get a good match and talked on it.

 

[Heavy Metal]

I always thought of two 102" or 108" as a dipole and small rotor a half in thick pale of plexiglass and an SO-239 connector, connecting them. simple

 

[Paul-W5lz]

This is a little late, so for what it's worth...
That vertical part is -half- of the antenna. There has to be another half for it to work. that other half can be a couple of radials of the right length, or just a wire of the same length of the vertical thingy, making the whole thing a 1/2 wave instead of a 'groundplane' thingy. Hang a 1/2 wave dipole vertically, same difference. Got a chain-link fence with a tree limb hanging over it? Suspend the whip from the tree limb and use the fence as the 'groundplane'. It works.

 

[Slowmover]

Bump. (102” on metal roof thread relation)

 

[groundwire]

Just connect three 1/4 wave ground radials drooping at a 45 deg angle, that should bring up the feedpoint impedance close to 50 ohms, and wind an rf choke to get rid of any common mode current that may exist. Use wire radials, cheap. And remember to keep your expectations within reason, it is only a 1/4 wave vertical after all.