Denny wrote:

On Jan 30, 10:19 pm, wrote:
I recently built a modified vertical dipole
from wire and using a pole and trees as supports.
I had hoped it would work on 2 bands 75 and 40 but it only
works on one 75 where the VSWR is 1.3:1 and the bandwidth is 85 khz
for the 2:1 points.

On 40 meters the VSWR is over 10:1 so I thought I could use a 1/4 coax
matching section 50 ohms but this doesnt solve the problem either as the
VSWR doesnt change much with the extra coax section.

I did cut the section properly as the velocity factor for the coax is
.78% which gave me 26.825 ft.

Not sure what I am doing wrong or assuming - but looks like I could
use some input.
--
I SPILLED SPOT REMOVER ON MY DOG..............AND NOW HES GONE!!


What do you mean by "modified"?

looks like the letter "H" on its side "normally" but modified
the feed is asymmertical about 5 ft off the gound.

similar to Force 12 Sigma 80


it looks like this

|
|
| abot 56 ft high
|
|
|
|

feed here has 2 loading coils

|
___________|____________ both sides approx 17 ft
|

base insulator here

_|_ base mount

ground

feed point impedance is supposed to be very low - maybe 12 ohms

We will need antenna dimensions,
where the feed point is, overall height, height above ground, is it
straight or bent, etc., in order to give you any advice...

The only immediate comment I can make is that any 'dipole' that is
near 50 ohms at the feed point is going to be several thousand ohms at
double the frequency... A matching section of coax will not help...


denny / k8do

--
I SPILLED SPOT REMOVER ON MY DOG..............AND NOW HES GONE!!