Cecil Moore wrote:
jawod wrote:

Yep, too LONG.
Egg on MY face. In my defense, it was late and I was working all day
getting the G5RV up in the trees.


The dipole should be 102 feet for bare wire. Maybe 99
feet for insulated wire. That's 1.5WL on 20m. The
series section should be 1/2WL on 20m. With a VF = 0.9,
that's a little over 31 feet.

According to EZNEC, here are the optimum lengths for
the series section:

3.8 MHz 30.5', 7.2 MHz 34.5', 10.125 MHz 20.7',
14.2 MHz 33', 18.14 MHz 12.5' or 37',
21.3 MHz 29.5', 24.95 MHz 30.5', 28.4 MHz 23.4'

It's easy to see why 31' doesn't work well on
30m, 17m, and 10m.
Yep, that's about right. I cut it at 51 x2 = 102 feet but I used
insulated wire...so if I want to bring down the antenna to correct it, I
should remove about 18 inches per side, right?

Pretend, for a minute, that I am NOT an antenna "purist" (not too hard a
task, you say?)

....Do I want to go out and correct it or just let the ATU compensate?

jawod wrote:
...Do I want to go out and correct it or just let the ATU compensate?

I once made a 2000 mile QSO on a light bulb.
--
73, Cecil http://www.w5dxp.com

On Wed, 27 Sep 2006 21:04:42 -0400, jawod wrote:


...Do I want to go out and correct it or just let the ATU compensate?

Can the ATU "compensate" for feedline loss?

Owen
--

Owen Duffy wrote:
On Wed, 27 Sep 2006 21:04:42 -0400, jawod wrote:



...Do I want to go out and correct it or just let the ATU compensate?


Can the ATU "compensate" for feedline loss?

Owen
--
My initial question related to a dipole 3 feet too long, no change in
feedline was/is contemplated...consider that a constant.

On Wed, 27 Sep 2006 22:09:20 -0400, jawod wrote:

Owen Duffy wrote:
On Wed, 27 Sep 2006 21:04:42 -0400, jawod wrote:



...Do I want to go out and correct it or just let the ATU compensate?


Can the ATU "compensate" for feedline loss?

Owen
--
My initial question related to a dipole 3 feet too long, no change in
feedline was/is contemplated...consider that a constant.

The length of feedline(s) may be constant, but the losses in the
feedline(s) depend on VSWR, and nothing you can do with an ATU changes
the loss in feedline(s) beyond the ATU.

I note that you have figured that the dipole is 3' too long, that is
about 3% too long, but the antenna resonance appears about 6% low at
14MHz. Are those two pieces of information consistent?

Owen
--

My initial question related to a dipole 3 feet too long, no change in
feedline was/is contemplated...consider that a constant.


The length of feedline(s) may be constant, but the losses in the
feedline(s) depend on VSWR, and nothing you can do with an ATU changes
the loss in feedline(s) beyond the ATU.

I note that you have figured that the dipole is 3' too long, that is
about 3% too long, but the antenna resonance appears about 6% low at
14MHz. Are those two pieces of information consistent?
Should they be consistent?

Owen
--
Owen,

I get about 4% at 14 MHz, 3.5% at 7 MHz, next to zero on 80M...these are
all relative to the low CW portion of the band where I "live".

I understand your point. VSWR at the XMTR as lowered by the ATU makes
the transmitter happy but the antenna may not be happy or as efficient.

Being a pragmatist and the wet season about to arrive, I just want a
handle on whether, all things considered, it is worthwile to shorten the
antenna or leave it alone.

I've got to start using EZNEC.


John
AB8O

On Wed, 27 Sep 2006 23:36:33 -0400, jawod wrote:



My initial question related to a dipole 3 feet too long, no change in
feedline was/is contemplated...consider that a constant.


The length of feedline(s) may be constant, but the losses in the
feedline(s) depend on VSWR, and nothing you can do with an ATU changes
the loss in feedline(s) beyond the ATU.

I note that you have figured that the dipole is 3' too long, that is
about 3% too long, but the antenna resonance appears about 6% low at
14MHz. Are those two pieces of information consistent?
Should they be consistent?

Yes, the length of open wire section of the feedline influences the
frequencies at which the RG8 VSWR is low, near as much as the dipole
itself.

The band where the "tuning" of the radiator and openwire line section
(together) is most critical is 80m, the optimal bandwidth (from a feed
loss point of view) is narrowest, and has the steepest sides.

However, the place where the VSWR looking into your RG8 is most
predictable is at 20m (typically 14.2MHz) where the common form of the
G5RV should have a three half waves resonant dipole and half wave
electrical open wire section. The Z at the dipole centre will be
around 90+j0, and if the loss on the open wire line is low, the Z into
it will be 90+j0, for a VSWR on the RG8 of just under 2, a little
lower at the tx end.

If you were to find that the VSWR minimises higher or lower than 14.2,
it is a sign that the combination of the dipole length and open wire
section are too long or too short.

If you objective was resonance of the dipole + open wire section at
14.2 (and I now understand that is not your objective), you would be
6% low with your stated observations.

If you are happy with the location of the VSWR dip on 80m, leave it
all alone because the VSWR dip results in the least losses in your
RG8, and if that is of significant length, then the additional losses
are significant. Most other bands are less sensitive than 80m, but
note that a G5RV is not efficient on "all" bands, and so should not
qualify as an all band antenna.

Owen
--

Owen Duffy wrote:
On Wed, 27 Sep 2006 23:36:33 -0400, jawod wrote:


My initial question related to a dipole 3 feet too long, no change in
feedline was/is contemplated...consider that a constant.


The length of feedline(s) may be constant, but the losses in the
feedline(s) depend on VSWR, and nothing you can do with an ATU changes
the loss in feedline(s) beyond the ATU.

I note that you have figured that the dipole is 3' too long, that is
about 3% too long, but the antenna resonance appears about 6% low at
14MHz. Are those two pieces of information consistent?

Should they be consistent?


Yes, the length of open wire section of the feedline influences the
frequencies at which the RG8 VSWR is low, near as much as the dipole
itself.

The band where the "tuning" of the radiator and openwire line section
(together) is most critical is 80m, the optimal bandwidth (from a feed
loss point of view) is narrowest, and has the steepest sides.

However, the place where the VSWR looking into your RG8 is most
predictable is at 20m (typically 14.2MHz) where the common form of the
G5RV should have a three half waves resonant dipole and half wave
electrical open wire section. The Z at the dipole centre will be
around 90+j0, and if the loss on the open wire line is low, the Z into
it will be 90+j0, for a VSWR on the RG8 of just under 2, a little
lower at the tx end.

If you were to find that the VSWR minimises higher or lower than 14.2,
it is a sign that the combination of the dipole length and open wire
section are too long or too short.

If you objective was resonance of the dipole + open wire section at
14.2 (and I now understand that is not your objective), you would be
6% low with your stated observations.

If you are happy with the location of the VSWR dip on 80m, leave it
all alone because the VSWR dip results in the least losses in your
RG8, and if that is of significant length, then the additional losses
are significant. Most other bands are less sensitive than 80m, but
note that a G5RV is not efficient on "all" bands, and so should not
qualify as an all band antenna.

Owen
--
Thanks Owen, for your good advice

John
AB8O