"Owen Duffy" wrote in message
...
"826" wrote in
:

Hi. Have a new Hustler 6 band vertical. Installed the radials and also
buried 75 foot of RG213 coax between shack and antenna. I used a 6
foot peace of coax connected to adjust the antenna with a MFJ-259.
Every band was tuned to the middle and SWR was lower than 1.7:1 at the
edges. After the adjustments, I reconnected the buried coax to the
antenna and on all bands everything had shift up by any where from 200
to 400 khz. Now the rig is seeing greater than 2:1 SWR.
Should I retune the antenna with the MFJ 259 in the shack?

Vern,

An oft asked question, and there are usually emphatic answers readily
proffered.

You might find my article at http://www.vk1od.net/VSWR/displacement.htm
relevant to understanding what goes on 'within' the transmission line,
and the 'Traps for players' heading offers reasons why behaviour that is
inconsistent with transmission line behaviour may be observed.

In your case, one of the things you appear to have done is the change the
thing that was measured. You adjusted the antenna with the shield of the
main feedline disconnected. This is discussed under the heading
'Disturbing the thing being measured'.

Owen

Hi,
Sorry I didn't rely sooner. The weather hasn't been too good hear. This
morning I disconnected the coax from the shack and measured the antenna with
the six foot length of coax. It looked OK. I then connected just the shield
of the long coax going to the shack and still measuring with the short coax
it shifted just like measured before in the shack. I have then made up a
choke balun and installed it at the base of the antenna and it improved
everything by about 60%. I will now make another one for the shack end. I
think everything is under control now. Thanks to all for heading me in the
right direction.
Vern M0WQR

"826" wrote in
:

Hi,
Sorry I didn't rely sooner. The weather hasn't been too good hear.
This
morning I disconnected the coax from the shack and measured the
antenna with the six foot length of coax. It looked OK. I then
connected just the shield of the long coax going to the shack and
still measuring with the short coax it shifted just like measured
before in the shack. I have then made up a choke balun and installed
it at the base of the antenna and it improved everything by about 60%.
I will now make another one for the shack end. I think everything is
under control now. Thanks to all for heading me in the right
direction. Vern M0WQR

Vern, whilst the choke made a difference, the fact that there remains a
difference in the feedpoint impedance with the shield connected and
disconnected, even when using the choke, indicates that there is some
effects observable from common mode feed line current in your scenario.

If you want a measurement of the antenna as it would be used, measure it
as it would be used... make sure the shield current path is as it would
be used.

Owen

"Owen Duffy" wrote in message
...
"826" wrote in
:

Hi,
Sorry I didn't rely sooner. The weather hasn't been too good hear.
This
morning I disconnected the coax from the shack and measured the
antenna with the six foot length of coax. It looked OK. I then
connected just the shield of the long coax going to the shack and
still measuring with the short coax it shifted just like measured
before in the shack. I have then made up a choke balun and installed
it at the base of the antenna and it improved everything by about 60%.
I will now make another one for the shack end. I think everything is
under control now. Thanks to all for heading me in the right
direction. Vern M0WQR

Vern, whilst the choke made a difference, the fact that there remains a
difference in the feedpoint impedance with the shield connected and
disconnected, even when using the choke, indicates that there is some
effects observable from common mode feed line current in your scenario.

If you want a measurement of the antenna as it would be used, measure it
as it would be used... make sure the shield current path is as it would
be used.

Owen
Hi all,
The antenna is now working very well on all bands. After installing both
choke baluns at the antenna base and in the shack, the resonant points
measured from the shack end were the same as with the short coax at the
antenna without the longer coax shield connected. Everything is OK now. All
it needed was the two baluns.
Regards
Vern M0WQR

826 wrote:

...
Owen
Hi all,
The antenna is now working very well on all bands. After installing both
choke baluns at the antenna base and in the shack, the resonant points
measured from the shack end were the same as with the short coax at the
antenna without the longer coax shield connected. Everything is OK now. All
it needed was the two baluns.
Regards
Vern M0WQR



Your path sounds very similar to mine. At first, unless the plans/specs
called for a balun/choke, I ignored the need. Now I use one, or more,
no matter what ... I picked up that knowledge here. At first, the loss
of the balun/choke made me hesitant--I no longer worry about those
trivial matters. :-)

Regards,
JS