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

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

...
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


I was not aware of the depth, length, and other specifics of the
buried coax installation as I jumped into the thread a bit late. Sorry.
Here where I'm located we have nothing but sand, which doesn't really
provide much of a ground. I forget other people have real dirt! :^)

Ed

Hi,
Here is some more info. The depth of the coax is 6". Its length is 75 foot
of RG-213. The ground here is below sea level (3 ft). It was reclaimed from
salt water by wind driven pumps in the 14th and 15th century. The
conductivity of the ground is great for antennas. But not sure about buried
feed lines.
I tested the antenna with the MFP-259 and 6 ft of cable on the ground. Yes
the first thing I checked was if the reading changed if I backed off from
the instrument and antenna.
I have tried buried coax one other time with a 2m vertical and thought the
coax was bad because it was used before. It also gave bad reading but can
remember the details. Do remember running another peace of coax back to the
shack overhead and everything was OK.
Now I wondering if it is something to do with the installation. The coax is
new and inside of a garden hose for protection. I did check the hose to make
sure it was dry before it was used.
I know that the antenna is adjusted correctly and have taken an FT-817 and
SWR meter to the antenna and it also indicated good readings.
Now something tells me not to tune the antenna with the instruments locate
in the shack because it will not be curing the problem. It will just hid it
until I start running some power. Then I would think something would start
to get hot in the field. Like the traps.
Because the antenna no longer wants my power because its no longer tuned to
the ham bands.
Regards
Vern

"Ed" wrote in message
92.196...
...
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


I was not aware of the depth, length, and other specifics of the
buried coax installation as I jumped into the thread a bit late. Sorry.
Here where I'm located we have nothing but sand, which doesn't really
provide much of a ground. I forget other people have real dirt! :^)

Ed

826 wrote:
Hi,
Here is some more info. The depth of the coax is 6". Its length is 75 foot
of RG-213. The ground here is below sea level (3 ft). It was reclaimed from
salt water by wind driven pumps in the 14th and 15th century. The
conductivity of the ground is great for antennas. But not sure about buried
feed lines.
...

I, like Richard C., would like to encourage you to the use of a 1:1
current-choke/balun, either of a toroid core of proper material--or even
a ferrite rod, beads, etc. -- and installed at the antenna feed point or
both ends of the coax (xmitter also) ...

I would have to install software and check out a couple of things. But,
I suspect, and especially at ~28+ mhz, that capacitive load on the outer
conductor can't help look like anything other than/near a direct short.
Even the rf down the inside of the braid/shield must be tempted to
that path if it nears or is less than ~50 ohms (well, some
possible/noticeable effect/affect.)

The coax I have buried, I always encased in ~1 inch PVC--possibly an
overkill ... but hey, it was cheap when I bought it--I ran the UNUN
(unbalanced-to-unbalanced current balun), just don't remember if I had
to, or not ...

Just my two cents worth--feel free to disregard if someone ventures
better/more-accurate data or proofs ... but then, you already knew that.
;-)

Regards,
JS

One other thing comes to mind: When you measured the antenna through the
short piece of coax, was the shield of the long buried piece connected
to the antenna's ground system? If not, you might try that. It would act
as an additional radial, which would have some affect on the antenna's
impedance.

Roy Lewallen, W7EL

On Mon, 28 Jul 2008 19:55:16 +0100, "826" wrote:

Now something tells me not to tune the antenna with the instruments locate
in the shack because it will not be curing the problem. It will just hid it
until I start running some power. Then I would think something would start
to get hot in the field. Like the traps.

Hi Vern,

You DO want to tune the antenna with instruments located in the shack.
You are tuning an "antenna system" and the complete system should
appear to be resonate to both the instruments AND the transmitter.
More power (or less power) should have nothing to do with the state of
tune - unless you have an intermittent. If you have an intermittant,
this is a failure, not a mis-adjustment.

From other indications you have shared, your problem is a
comparatively subtle error, not a major failure.

73's
Richard Clark, KB7QHC

On Sun, 27 Jul 2008 21:07:25 -0700, John Smith
wrote:

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

95% plus of the transmitter or received energy is safely contained
between center conductor and shield. That is how the physics works
out. All of the feed line center conductor current is pretty well
matched by the same current in the shield. It is the closely coupled
concentric magnetic fields that make coax work so well.

JosephKK wrote:

...
95% plus of the transmitter or received energy is safely contained
between center conductor and shield. That is how the physics works
out. All of the feed line center conductor current is pretty well
matched by the same current in the shield. It is the closely coupled
concentric magnetic fields that make coax work so well.


Or, simply put, for ever action, an equal and opposite reaction occurs
.... yes, basic physics ... however, what is in question--since the other
braid has and "inside" and an "outside", where does that equal opposite
reaction occur ...

Regard,
JS

John Smith wrote:
JosephKK wrote:

...
95% plus of the transmitter or received energy is safely contained
between center conductor and shield. That is how the physics works
out. All of the feed line center conductor current is pretty well
matched by the same current in the shield. It is the closely coupled
concentric magnetic fields that make coax work so well.


Or, simply put, for ever action, an equal and opposite reaction occurs
... yes, basic physics ... however, what is in question--since the other
braid has and "inside" and an "outside", where does that equal opposite
reaction occur ...

Regard,
JS


Gawd, I am getting hasty in my old age ...

No electrical field can occur without a magnet field, no magnetic field
can occur with out a corresponding electrical component, again, basic
physics; you are attempting to say the magnetic component of the
current on the outside of the braid is NOT SEEN by the center conductor
.... that may be in error ... but, I would be willing to listen how
tinned copper (the braid) is some sort of shield to magnetic fields ...

Regards,
JS