Help With Homebrew Diplole

[Fdtrucker]

I have a homemade dipole that has been giving me some trouble. No matter how I add or subtract lengths on either side I still have high swr. Tried 2 different feed lines (rg58) still not down where I want it. It gets 1.5 with the amp off and 3.0 with the amp on. It talks all over. Good contacts all over the continent.. Any suggestions?

 

[Sonwatcher]

I use an antenna tuner with mine. I just made a Hamstick dipole for 11 meters and had some problem. I made a choke at the feedpoint and it is working great !

 

[W5LZ]

Fdtrucker,
Is your dipole a 'flattop' or does it sort of 'droop' a little? An SWR of around 1.5:1 for a 'flattop' isn't really bad at all. You might lower that a bit by 'drooping the ends a bit.
Going to a high SWR, or around 3:1 when the amplifier is turned on means that the amplifier's output impedance isn't very close to 50 ohms. Not the dipole's fault, now is it...
A 'flat top' dipole's input impedance is something close to 70 ohms, give or take a little. If you 'droop' the legs, the input impedance lowers a bit. Doesn't take a whole lot of 'droop'. Not the easiest thing to do if it's supported on the ends instead of in the middle.
- 'Doc

PS - Just curious, is the truck pictured a 'quad' or a 'quint'?

 

[Fdtrucker]

Yes the ends are drooping down at both ends. It is supported in the middle. will try messing with the angles a little when condions drop off later today.

The truck in the picture is a Ward Lafrance pumper. Cant remember what year it is, early 70's maybe..

 

[W5LZ]

Then it's a 'quint'. My last one was a '95 'Pierce'. Mostly had 'Boardmans' till about '91 - '92.
- 'Doc

 

[Master Chief]

It gets 1.5 with the amp off and 3.0 with the amp on.

Where are you checking the SWR, or should I say, where is the SWR meter located when taking measurements?

IF the SWR meter is between the radio and the amplifier, you have issues with the input section of the amplifier. When an amp is switched on, the radio thinks the amplifier IS the antenna.

IF the SWR meter is between the amplifier and the antenna, the extra output is magnifing an existing problem.

Have you tried using a dummy load at the end of the coax and testing SWR with the amp on and off. If you have high SWR with the dummy load, you have COAX issues (connectors, bad coax, water intrusion, etc).

 

[Fdtrucker]

Cool Doc, I like the old Ward and Americans. Nothing like the bark of a Detroit diesel winding up with a Federal Cue wining out on the way to a fire!!
And to Master Chief, I have it on the antenna side of the amp. I will have to get a dummy load. I have been wanting to get one for a while now anyway. Thanks..