Dual Band (6m/10m) helically wound antenna

[tahrens]

Hi Folks,

I'm trying to build a mobile dual band antenna for 6 & 10 meters.

I read an article back from a year ago in QST where the author
started with a full size CB whip, cut it half, and used a polycarbonite
coupler (with a trap built on it for 10m).

Sounded ok, but I neither had a CB whip, nor did I have a way to
make the coupler.

I did have one of those helically wound HF mobile antennas for 20m
that I could sacrifice to the project.

Got the base all wound & had an excellent match on the 6m FM
frequency that I wanted (had to add about 47pF to the base to
make it happy). Then I made the trap at the top of the whip
for 10m (with the whip attached to the top).

When I checked for the 10m resonance, I found it to be a little lower
than I needed, so I decided to pull a couple of turns from the trap.

Before I did that, I re-checked the 6m resonance point, and it had gone
up to 60mHz!

Anybody have a clue what's going on here, & why it jumped up?

Thanks,

Tim W5FN

 

[Moleculo]

My shot in the dark guess is that you should do the matching for 6m after you've got the trap set for 10m. Are you able to get a good match on both 10m and 6m if you change the capacitance at the base?

 

[tahrens]

dual band antenna

Hi Mole,

I got a good match on 6 (without trap or top whip), but when I tried to add anything at the top, the resonant frequency went really wierd.

I'm getting a 'regular' whip to put on the spring tomorrow. I might play
with adding something to top with it. (more like the original plans spec'd).

I'll keep you posted.

Thanks!

Tim W5FN