Vertical problem
 

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?
Thanks Vern M0WQR

Vertical problem
 

826,
My first thought is that the feed line has become 'part' of the
antenna and has changed the antenna's characteristics accordingly. My
second though, if that 6 foot of feed line was connected directly to
the antenna when measurements were taken, is that you being that close
to the antenna changed it's characteristics.
So, what to do? How about doing that checking from the end of the
feed line that will normally be used? Make any antenna adjustments
accordingly. Don't want that feed line to be 'part' of the antenna?
Well, how about using a feed line to do the checking that's of an
appropriate length to sort of 'cancel' it's self out, to do the
checking?
Doing all that checking will also give you some idea as to the
accuracy of your measuring device, and the characteristic values of
the feed lines, etc, sort of.
That's the 'long' version. The 'short' version is that you're
probably doing something wrong, re-do it.
- 'Doc

Not much of an answer, huh?

Vertical problem
 

wrote in message
...


826,
My first thought is that the feed line has become 'part' of the
antenna and has changed the antenna's characteristics accordingly. My
second though, if that 6 foot of feed line was connected directly to
the antenna when measurements were taken, is that you being that close
to the antenna changed it's characteristics.
So, what to do? How about doing that checking from the end of the
feed line that will normally be used? Make any antenna adjustments
accordingly. Don't want that feed line to be 'part' of the antenna?
Well, how about using a feed line to do the checking that's of an
appropriate length to sort of 'cancel' it's self out, to do the
checking?
Doing all that checking will also give you some idea as to the
accuracy of your measuring device, and the characteristic values of
the feed lines, etc, sort of.
That's the 'long' version. The 'short' version is that you're
probably doing something wrong, re-do it.
- 'Doc

Not much of an answer, huh?


Surprise!

It is turning out that coax isn't what you thought it was, is it?

Lots of folks think that coax is some miracle device that absolutely
contains all of the RF until the RF reaches (poetic license please) the
termination point. In truth, no such creature exists in any form of
transmission line.

What you are trying to do is to make the transmission line the worst
possible radiator and the antenna the best possible radiator. There are
gazillions of possibilities somewhere betwen those two potentials.

Run the full length of transmission line into your shack and then tune the
antenna based upon the data gathered in the shack. Yes, it is a PITA, but it
is the only way to do it, if you want the best tuning.

Every antenna system is just that, a system. It cannot be tuned piecemeal to
obtain the best end result. Welcome to the world of radio.

Oh, it isn't so bad once you get used to it. Now you have an excuse to
invite a ham over to help you by reading the analyzer while you are outside
making adjustments to the antenna.

Wait until you discover, if you haven't already, that adjusting one part of
the antenna will cause you to readjust another part of the antenna, probably
the one that you adjusted before the last part that you adjusted. Hang in
there. It is doable. Good luck with your project.

Jack

Vertical problem
 

On Fri, 25 Jul 2008 18:44:46 +0100, "826" wrote:

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?
Thanks Vern M0WQR

I have a 5BTV with buried radials. Works and tunes like crap without
the radials. Tune the antenna with the 259 connected to it with the
shortest piece of coax you can work with, like 1 foot. If you're a
purist - which I advise - lie down so you're as much out of the
antenna field as possible when taking readings. Or back way off and
read with binoculars. (Just don't let your body affect the antenna
tuning.) When that's done, coil the main coax or use a common mode
choke where the coax connects to the antenna to prevent the coax
shield from acting like a radial. Forget that nonsense of adjusting
SWR by adjusting coax length unless you're prepared to use a different
length for every band.

The MFJ 259 reads SWR with respect to it's own 50-ohm nominal
impedance so if you can adjust to a very low SWR (and you can with a
5BTV or 6BTV), it should read the same at the radio end of a longer
50-ohm coax.

Vertical problem
 

Hi, Thanks for all your input. Hustler recommended using 5-6 foot of coax in
there manual. This I did follow and the antenna tuned very nice. When I
connected the 75 ft buried coax it threw me because the resonance frequency
on each band went higher. I do not have a balun at the base of the antenna.
I thought that after connecting the buried coax the frequency would go down
because of the capacitance of the longer coax. After rethinking this I can
see that adding a balun may help. Thanks for your help and will let you know
how things turn out.
Vern M0WQR

"Jim Higgins" wrote in message
...
On Fri, 25 Jul 2008 18:44:46 +0100, "826" wrote:

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?
Thanks Vern M0WQR

I have a 5BTV with buried radials. Works and tunes like crap without
the radials. Tune the antenna with the 259 connected to it with the
shortest piece of coax you can work with, like 1 foot. If you're a
purist - which I advise - lie down so you're as much out of the
antenna field as possible when taking readings. Or back way off and
read with binoculars. (Just don't let your body affect the antenna
tuning.) When that's done, coil the main coax or use a common mode
choke where the coax connects to the antenna to prevent the coax
shield from acting like a radial. Forget that nonsense of adjusting
SWR by adjusting coax length unless you're prepared to use a different
length for every band.

The MFJ 259 reads SWR with respect to it's own 50-ohm nominal
impedance so if you can adjust to a very low SWR (and you can with a
5BTV or 6BTV), it should read the same at the radio end of a longer
50-ohm coax.

Vertical problem
 

Funny, I've seen no one recommend addition of a 1:1 choke balun near the
antenna feedpoint. If RF is flowing back down the shield of his feedline,
that surely could cause some incorrect readings on SWR in the shack,
wouldn't it?

Ed K7AAT

Vertical problem
 

On 27 Jul 2008 23:26:04 GMT, Ed wrote:


Funny, I've seen no one recommend addition of a 1:1 choke balun near the
antenna feedpoint. If RF is flowing back down the shield of his feedline,
that surely could cause some incorrect readings on SWR in the shack,
wouldn't it?

And, how well would rf flow back down the shield of
"buried 75 foot of RG213..." ? :-)

Jonesy
--
Marvin L Jones | jonz | W3DHJ | linux
38.24N 104.55W | @ config.com | Jonesy | OS/2
*** Killfiling google posts: http://jonz.net/ng.htm

Vertical problem
 

Funny, I've seen no one recommend addition of a 1:1 choke balun
near the
antenna feedpoint. If RF is flowing back down the shield of his
feedline, that surely could cause some incorrect readings on SWR in
the shack, wouldn't it?

And, how well would rf flow back down the shield of
"buried 75 foot of RG213..." ? :-)



About as well as it flows up the center conductor, possibly. You
don't think that just because the cable is buried that RF flow on the
shield conductor is prevented, do you?

Ed

Vertical problem
 

Ed wrote:

...
About as well as it flows up the center conductor, possibly. You
don't think that just because the cable is buried that RF flow on the
shield conductor is prevented, do you?

Ed

I sure can imagine one heck of a "capacitive load" on that outer
conductor to ground! What, thousands/tens-of-thousands of pf?

Regards,
JS

Vertical problem
 

On 28 Jul 2008 04:03:29 GMT, Ed
wrote:

About as well as it flows up the center conductor, possibly. You
don't think that just because the cable is buried that RF flow on the
shield conductor is prevented, do you?

Hi Ed,

I think Jonesy is fairly safe in his presumption. The classic work
performed by Brown, Lewis, and Epstein pretty conclusively reported
the nearly complete attenuation of direct driven RF currents in ground
radials at 3MHz.

75 feet of buried shield would seem to be quite snubbed by the
proximity of earth over much of the range of frequencies reliably
operated from a multi-band HF vertical.

Of course, adding a choke can't hurt.

73's
Richard Clark, KB7QHC