UHF CB antenae

if you had a head like mine...and you do....you'd have a headache too..

Hahahaha If I had a head like yours (and I don't)I'd give up drinking!!!!

lol

VK3CAT

bang another dead vk3cat

thanks Tony, I knew there was an expert somewhere on this site..

I was thinking of a really long wire ..like 40metres or what ever length it needs to be....just to see what it can do???

Why don't you just try it & see what happens. Don't transmit on it unless you have some means of monitoring the SWR.

Antenna theory 101.

To the some of the others that replied to the question, No1 asked if a longwire was possible on UHF & not what the simplest or best antenna was.
Note that a 1/4 wave groundplane is not an endfed antenna as the missing 1/4 wave is represented by the groundplane - giving it a low input impedance (50 - 70 ohms) making it a reasonable match to a 50 ohm feedline. By adjusting the angle of the ground plane radials, the input impedance may be altered to give the best impedance match & SWR ((assuming that the antenna and radials are resonant (correct length) .))
An example of an endfed antenna is the 27mHz 1/2 wave station master. The input impedance is altered by changing the tapping point on the coil at the base of the antenna.
A centre fed antenna will have a low input impedance. The feed point is a high current & low voltage point. A 1/4 wave out from the feed point of a centre fed antenna (the end of a dipole) will be a low current & high voltage point.
If the feed point is taken away from the middle & placed at the end, then this will be at a high voltage / low current point (high input impedance) and a matching network will be required.
By saying that adjacent 1/2 wave segments of a longwire antenna will not be in phase it is meant that the direction of current flow in the wire will be opposite to that of the 1/2 wave segments on either side. A collinear antenna (Commercially made high gain UHF) will use matching segments (1/4 wave stubs) to keep the antenna currents in phase.
Cheers again, Tony VK3CAT

Thanks again Tony

am I correct...the longer the wire, the less it matters to transmission problems?

and why would I need to watch the swr...surely if it was that far out i'd have one stoofed set anyway?

This may be so, as the antenna currents will decrease due to reactive losses in each 1/2 wave segment as the length of the wire increases.
A short test transmission on a high SWR antenna might be OK but a long one could cause problems in the PA stage of the transmitter. If the antenna receives well, then the impedance & SWR might be OK.
Tony.
www.qsl.net/vk3cat

I was gunna say that too......but as I asked an intelligent question i thought i'd better play dumb

Watt is "power flow"?

I thought it would be more meaningful to the non-technical person than "SWR" or "Forward Power".

Fair enough.