[TowerTalk] Fwd: FW: Adding 160 to an 80M dipole?

[Jim Brown]

On Wed,12/17/2014 9:13 AM, Hans Hammarquist via TowerTalk wrote:
> The solution for this is to place the capacitor outside the coil instead of inside.

There's another solution, a very good one, that's been around for a 
while. W9INN (SK) used it in many of the antennas he sold; Barry at 
Hypower Antenna Company has been using it for at least 10 years. Barry 
has a 2x1 3-call, but I always forget it. :)  We've worked several times 
in contests.

The solution is to add an inductor that is NOT a trap to each leg of a 
dipole, carefully tweaking the design so that the antenna resonates on 
two or more bands. I used an 80/40 version of this design in Chicago to 
fit 80 into about 100 ft between supports, have used a 160/80 version 
with a 40M fan element at three different QTHs with good results. The 
only negative is that it's usually impractical to get it high enough to 
have a good vertical pattern on 160M.

I've measured the traps for both of these antennas with a Vector Network 
Analyzer, and they are NOT functioning as traps -- their stray C is 
small enough that they resonate FAR above the bands they cover. I've 
also plugged the loading coils into NEC and confirmed the design.

The 80/40 version has the loading coil approximately a quarter wave from 
the feedpoint, and there's a relatively short section perhaps a 1/10 
wavelength after the coil. The 160/80 version is built the same way.

The SWR bandwidth of these antennas is roughly comparable to a half wave 
dipole on the higher band, and significantly narrower on the lower band. 
It is VERY sensitive to the length of the short section on the other 
side of the coils, so is very tricky to tweak. My experience, as well as 
predictions of the NEC model, are that it radiates as well as any other 
dipole at the same height.

BTW -- I told Larry about this yesterday in private email.

73, Jim K9YC