Thanks to all the many respondents to my question! The good news is, that
following the general concensus that the coax length does not matter I
pursued the shorter length again today, resited the wire antenna (G30JV
80plus2) to another location, and the analyer I have now indicates a
distinct improvement. What was throwing me was some stuff I read somewhere
about using odd halfwave length multiples for coax runs - but perhaps this
was another myth!

Thanks Guys

Keven

Harold Burton wrote:

SNIP

Careful, one of the local Ham "Channelmasters" will dub you a
CBPlusser for using the term "contact". It's a pet peeve of his.

Harold Burton
KD5SAK



It may be a 'pet peeve' but what do you call:

"T40E 599 TU de W1MCE"

For me it's a contact! It is not a QSO. It is not a Rag Chew. It's the
minimum requirement for a DXCC type CONTACT.

BTW: is it Harold Burton or HALLIBURTON?? Hmmm ... ???

For my own take on it I would say

1) You are in the near field of the antenna

2) The fact that the coax is, by own admission "bad"
would indicate there is sumpin' is up as old ratty coax
*can* actually appear to be good by giving a false SWR
indication.

I think this is where CBers get that old "18 feet of coax" thing so many
believe firmly. The thing to do is to use the
shortest run of coax you can, set the antenna by adding or
removing length and keep the thing out of the way of nearby objects (people,
cars, towers, fuel tanks. If you
re-resonate the antenna and re-attach the shorter line, it shouldn't make
any difference.


Jerry
K4KWH
"Keven Matthews" wrote in message
...
I recently moved my shack from an upstairs room to downstairs, much
closer
to the garden and antennas. All the antennas previously had a long run of
coax to the old shack. The obvious thing was to have a nice new short
run
of coax to my HF vertical which is now only 15' away. So I cut the coax
and
since then the antenna is no longer resonant on 40 Metres. Also this week
I
was putting up a new HF wire antenna, it was getting dark and raining by
the
time I was hoisting it up but so I could just have a listen that night a
grabbed an old (15 years) large coiled up of quantity RG213 coax
complete
with rotten oxydized pl259 plugs on each end which had just sat on the
garage wall for years. I just slung the coil down and plugged in at each
end. The plugs looked so rotten it was shameful but it pitch dark by
then!
However The SWR was pretty good across the band. Regardless I started my
evening doing a tidy job with some of that nice 5DFB japanese coax all
ready
for the following day. Guess what ? I put on the nice new cable and
plugs
and the antenna is no longer anywhere near resonant on 80M. So why am I
getting a better result with a long length of still coiled cable sitting
on
my patio rather that a much shorter brand new piece. Please could some
one
explain to me if the coax length does matter, it has certainly never been
a
problem for me in the past on VHF and Six but I am new to HF frequencies.
If you do need to have a certain size run, what can you do with the cable
if
you phisically dont need it ?


Many Thanks & 73 for 2004

Keven G7UUD

Handle was used on the HF ham bands before most of the readers were born.

Steve

K;9;D;C;I

"w4jle" W4JLE(remove this to wrote in message
...
Just like I had some "newby" attempt to chastise me on a 2 meter repeater
for using "handle". He told me that that word was only used on 11 meters.

I had to admit, I did use it on 11 meters when it was a ham band. But
thanks
for the lesson Good Buddy!

I would add only one thing to this. The thing used to measure the SWR can
also be responsible for strange results when the SWR is not low. Don't
always assume that the thing used to measure something is exact all the
time.
Steve
K:9:C:I

"Dave Shrader" wrote in message
news:biGJb.213249$8y1.750188@attbi_s52...
Keven Matthews wrote:

I recently moved my shack from an upstairs room to downstairs, much
closer
to the garden and antennas.

SNIPPED

Kevin, there have been numerous responses to your original post. Let me
be an Elmer for a short moment.

An example of antenna resonance and VSWR follows.

In my mobile I have a resonant 40 meter Hamstick. Resonance means there
is NO Reactance in the antenna impedance. My antenna analyzer indicates
approximately 12 + j0 ohms at 7.225 MHz. This is almost a 5:1 VSWR and
that's what a meter indicates. Now, I added an ICOM AH-4 automatic
antenna tuner at the antenna. The antenna is still 12 + j0 ohms but the
tuner transforms the impedance to 50 + j0 ohms. So, the VSWR from the
antenna/tuner to the 706, approximately 16 feet of coax, is now
approximately 1:1.

Since the length of coax in your installation changes the measured VSWR,
the coax is part of the antenna system and is radiating. So, you need to
isolate the coax from the antenna. There are several ways to accomplish
this. The most direct way is to make a coil of coax about 4 to 6 inches
diameter and having 8 to 10 turns and install it directly at the base of
the antenna. If you have a ground radial system make sure the coax is
underneath [lower] than the radial system. Finally, install some clamp
on ferrites, available from Radio Shack for less than $10, at the 1/4
and 1/2 wavelength on the coax from the antenna feedpoint.

Hopefully this will clean up the RF on the coax.

With a vertical antenna a reasonable VSWR at antenna resonance should be
somewhere between 1.5:1 and 2.0:1.

Deacon Dave, W1MCE

Crazy George sed:

"At 15', you are in the near field of any HF antenna. You do not want your
station to be in the near field of the antenna. All kinds of undesirable
and often unpredictable things happen."
---------------------------------

Kind of rules out mobile operation.

Of course the metal body of the vehicle probably shields the station from the
effects of the near field.

73 de Jack K9CUN

I would venture to say we all operate in the near field. How does one avoid
it, particularly on 160 meters?

"JDer8745" wrote in message
...
Crazy George sed:

"At 15', you are in the near field of any HF antenna. You do not want
your
station to be in the near field of the antenna. All kinds of undesirable
and often unpredictable things happen."
---------------------------------

Kind of rules out mobile operation.

Of course the metal body of the vehicle probably shields the station from
the
effects of the near field.

73 de Jack K9CUN

On Tue, 6 Jan 2004 13:14:01 -0500, "w4jle" W4JLE(remove this to
wrote:
I would venture to say we all operate in the near field. How does one avoid
it, particularly on 160 meters?

Hi OM,

The greater part of risk is in the wavelength compared to body height.
Sitting down obviously lowers risk.

Now, for the standing individual of average size, that person is
approaching a quarter wave at 10M (especially if you are a fat
conductor). If you were the standard 1 wavelength away from a 100W
transmission, then the standard 22dB down would be your exposure and
you would experience something less of 1 watt of heating throughout
your body. Touch a christmas tree bulb (7.5W) and ask yourself how
uncomfortable that feels, then average that over your 2M² surface
area.

At 160M, you certainly stand the risk of being much closer than 1
wavelength, but you also stand less risk of being a quarter wave tall
(towering egos do not conduct). In any event, you are probably
sitting down anyway. Your radiation resistance in that band makes you
nearly invisible to the power emitted. Those standing next to VOA
half megawatt towers need to check their insurance clauses covering
acts of incipient stupidity.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
Now, for the standing individual of average size, that person is
approaching a quarter wave at 10M ...

Unless the individual is grounded at one end, that 1/4WL is
non-resonant. :-) Richard, what is your velocity factor?
--
73, Cecil http://www.qsl.net/w5dxp



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On Tue, 06 Jan 2004 14:28:06 -0600, Cecil Moore
wrote:
Unless the individual is grounded at one end, that 1/4WL is
non-resonant. :-) Richard, what is your velocity factor?

I can see why you ask about velocity if you are not on ground.