Feedline suggestions?
 

I am using a whip antenna mounted on a metal patio cover. Results are good
on 10 and 12 meters, and contacts have been made down to 40 meters.
(Matches were not obtained on 15 or 30 meters) The whip is 8.5 ft long (a
longer whip is under consideration). It is fed through an antenna tuner and
about 25 feet of RG-58. I'm about to replace that with RG-8.

Any comments on how to hold down feedline losses. One suggestion is to use
two parallel lengths of RG-8 so that half the current runs through each.
Also, site geometry would allow open wire feed.

Possibilities?

Feedline suggestions?
 

On Mon, 5 Dec 2011 09:01:15 -0800, "Wayne"
wrote:

I am using a whip antenna mounted on a metal patio cover. Results are good
on 10 and 12 meters, and contacts have been made down to 40 meters.
(Matches were not obtained on 15 or 30 meters) The whip is 8.5 ft long (a
longer whip is under consideration). It is fed through an antenna tuner and
about 25 feet of RG-58. I'm about to replace that with RG-8.

Any comments on how to hold down feedline losses. One suggestion is to use
two parallel lengths of RG-8 so that half the current runs through each.
Also, site geometry would allow open wire feed.

Possibilities?

Sorry, Parallel cables would give you twice the losses. Also, what it
would do for matching will vary by frequency but not likely anything
you want. Lower loss coax is always a good idea but with only 25 feet
total your losses may not be enough to notice. Vertical antennas are
usually at their best at 1/4 wave length long for the purpose of
radiation. In practice, if you get it tuned up well enough to take
power, it will work!

I have a 28 foot vertical antenna that sometimes outperfoms my 3
element beam. It is tuned with an SGC autotuner.

There is a lot of information on the internet for free, Google a bit
and keep at it. I seem to enjoy working on antennas more than using
them.

BTW, Check out the ARRL.NET site. There is a 10 meter contest in a
week or so that your antenna will around the world...
John Ferrell W8CCW

Feedline suggestions?
 

"Wayne" wrote in message
...
I am using a whip antenna mounted on a metal patio cover. Results are good
on 10 and 12 meters, and contacts have been made down to 40 meters.
(Matches were not obtained on 15 or 30 meters) The whip is 8.5 ft long (a
longer whip is under consideration). It is fed through an antenna tuner
and about 25 feet of RG-58. I'm about to replace that with RG-8.

Any comments on how to hold down feedline losses. One suggestion is to
use two parallel lengths of RG-8 so that half the current runs through
each. Also, site geometry would allow open wire feed.

Possibilities?

As John mentioned, 25 feet of coax is too low of a loss to worry about
especially below 30 Mhz. The other best bet is to use a remote antenna
tuner at the antenna. A longer antenna should work much beter on 80 and 40
meters.

Feedline suggestions?
 

Dear Wayne (no call sign given): The use of "it" causes an ambiguity. If
the antenna tuner is "at" the antenna feed point, then 25 feet of RG-58
running to the shack will contribute very little to the overall loss of the
system.

A colleague has had success with an insulated wire on his roof fed in the
middle with an auto-tuner. The coax from the tuner has several type 31
chokes to kill common mode and the coax itself contributes very little to
the performance of the system.

On the other hand, such a short antenna as you are using (on the lower
bands) fed with RG-58 from a tuner in the shack is expected to have
significant losses. If this is the case, moving the tuner outside should be
tried.

73, Mac N8TT

"Wayne" wrote in message ...

I am using a whip antenna mounted on a metal patio cover. Results are good
on 10 and 12 meters, and contacts have been made down to 40 meters.
(Matches were not obtained on 15 or 30 meters) The whip is 8.5 ft long (a
longer whip is under consideration). It is fed through an antenna tuner and
about 25 feet of RG-58. I'm about to replace that with RG-8.

Any comments on how to hold down feedline losses. One suggestion is to use
two parallel lengths of RG-8 so that half the current runs through each.
Also, site geometry would allow open wire feed.

Possibilities?


J. C. Mc Laughlin
Michigan U.S.A.
Home:

Feedline suggestions?
 

"Wayne" wrote in
:

I am using a whip antenna mounted on a metal patio cover. Results are
good on 10 and 12 meters, and contacts have been made down to 40
meters. (Matches were not obtained on 15 or 30 meters) The whip is 8.5
ft long (a longer whip is under consideration). It is fed through an
antenna tuner and about 25 feet of RG-58. I'm about to replace that
with RG-8.

Taking this to mean that the ATU is at the tx end of the 25' of RG58...

It is challenging with that topology get get good antenna system
efficiency when the monopole is less than about 17% of a wavelength.
Working that backwards, your 2.6m whip is 17% of a wavelenght on 15m
wavelength or 20MHz.

The contributions to poor efficiency are feed line loss under standing
waves, ATU loss, and if the whip is magnetic stainless, conductor losses
in the whip.

RG8 will have lower losses, but the result will be a more challenging
load for the ATU and its losses will increase, consuming some of the
benefit.

You really need to take a system perspective because there is a complex
interaction of the system components.


Any comments on how to hold down feedline losses. One suggestion is
to use two parallel lengths of RG-8 so that half the current runs
through each. Also, site geometry would allow open wire feed.

Paralelling two cables reduces Zo to one half, but the matched loss per
metre is the same. The loss under standing waves depends on the actual
load impedance which you probably don't know.


Possibilities?


A remote ATU, a longer monopole.

Owen

Feedline suggestions?
 

"J. C. Mc Laughlin" wrote in message
...

Dear Wayne (no call sign given): The use of "it" causes an ambiguity. If
the antenna tuner is "at" the antenna feed point, then 25 feet of RG-58
running to the shack will contribute very little to the overall loss of the
system.

A colleague has had success with an insulated wire on his roof fed in the
middle with an auto-tuner. The coax from the tuner has several type 31
chokes to kill common mode and the coax itself contributes very little to
the performance of the system.

On the other hand, such a short antenna as you are using (on the lower
bands) fed with RG-58 from a tuner in the shack is expected to have
significant losses. If this is the case, moving the tuner outside should
be tried.
73, Mac N8TT

-
Yes, the wording is confusing. The antenna is fed with about 25 feet of
RG-58 with the tuner next to the rig in the shack. The cable will be
changed to RG-8 tomorrow assuming that the winds finally die down here in So
Cal.

On 10 and 12 meters the performance is quite acceptable. I'm not the big
signal on the band, but it works well.

I'm hoping to slightly lengthen the antenna and get performance from 17 to
10 meters. Since the tuner to antenna VSWR will be very high, I'm pondering
ways of lowering the loss.

A separate loaded whip is used on 20 and 40 meters.

So far, the experiment has been good, and it is one of the few antenna
configurations that meet the established requirements. (established by the
xyl) :)

Thanks
Wayne
W5GIE /6








"Wayne" wrote in message ...

I am using a whip antenna mounted on a metal patio cover. Results are
good
on 10 and 12 meters, and contacts have been made down to 40 meters.
(Matches were not obtained on 15 or 30 meters) The whip is 8.5 ft long (a
longer whip is under consideration). It is fed through an antenna tuner
and
about 25 feet of RG-58. I'm about to replace that with RG-8.

Any comments on how to hold down feedline losses. One suggestion is to
use
two parallel lengths of RG-8 so that half the current runs through each.
Also, site geometry would allow open wire feed.

Possibilities?

Feedline suggestions?
 

In message , John Ferrell
writes










Vertical antennas are
usually at their best at 1/4 wave length long for the purpose of
radiation. In practice, if you get it tuned up well enough to take
power, it will work!

Actually a 5/8 wavelength is what gives the most poke in the horizontal
direction.




--
Ian

Feedline suggestions?
 

In message , Owen Duffy
writes
"Wayne" wrote in
:

I am using a whip antenna mounted on a metal patio cover. Results are
good on 10 and 12 meters, and contacts have been made down to 40
meters. (Matches were not obtained on 15 or 30 meters) The whip is 8.5
ft long (a longer whip is under consideration). It is fed through an
antenna tuner and about 25 feet of RG-58. I'm about to replace that
with RG-8.

Taking this to mean that the ATU is at the tx end of the 25' of RG58...

It is challenging with that topology get get good antenna system
efficiency when the monopole is less than about 17% of a wavelength.
Working that backwards, your 2.6m whip is 17% of a wavelenght on 15m
wavelength or 20MHz.

The contributions to poor efficiency are feed line loss under standing
waves, ATU loss, and if the whip is magnetic stainless, conductor losses
in the whip.

RG8 will have lower losses, but the result will be a more challenging
load for the ATU and its losses will increase, consuming some of the
benefit.

You really need to take a system perspective because there is a complex
interaction of the system components.


Any comments on how to hold down feedline losses. One suggestion is
to use two parallel lengths of RG-8 so that half the current runs
through each. Also, site geometry would allow open wire feed.

Paralelling two cables reduces Zo to one half, but the matched loss per
metre is the same. The loss under standing waves depends on the actual
load impedance which you probably don't know.


Possibilities?


A remote ATU, a longer monopole.

The OP seems to be doing what I did for many years, ie feed an endfed
monopole antenna (of undefined length) with coax, and force match it, as
required, at the shack end. [I believe it was you, Owen, who pointed out
my error in trying to use the graphs showing loss vs SWR when the coax
is electrically short (less than a wavelength.]

Although I now have a remote tuner at the antenna feedpoint, I can't say
I've noticed an outstanding improvement in performance (although, to be
honest, I really haven't really done a lot of operating since I
installed the tuner).

If you don't want use a remote tuner at the antenna feedpoint, the
impedance at the shack end of the coax will be the antenna feed
impedance, transformed by the length of the coax, and also altered by
the loss in the coax. Provided the shack-end tuner can be persuaded to
match the impedance seen looking into the coax, the system will work
tolerably well with low-loss coax.

It is obviously advantageous to use the lowest loss coax you can lay
your hands on. As, in cable TV systems, long coaxial trunk lines have
now been superseded by optical fibers, I would suggest that a cable TV
operator might be persuaded to donate some nice chunky coax (preferably
"as thick as a horse's prick", as one of my bosses once described it).
Failing that, just go for the best you can get.
--
Ian

Feedline suggestions?
 

On Mon, 05 Dec 2011 18:50:53 -0800, Wayne wrote:

"J. C. Mc Laughlin" wrote in message
...

Dear Wayne (no call sign given): The use of "it" causes an ambiguity.
If the antenna tuner is "at" the antenna feed point, then 25 feet of
RG-58 running to the shack will contribute very little to the overall
loss of the system.

A colleague has had success with an insulated wire on his roof fed in
the middle with an auto-tuner. The coax from the tuner has several type
31 chokes to kill common mode and the coax itself contributes very
little to the performance of the system.

On the other hand, such a short antenna as you are using (on the lower
bands) fed with RG-58 from a tuner in the shack is expected to have
significant losses. If this is the case, moving the tuner outside
should be tried.
73, Mac N8TT

-
Yes, the wording is confusing. The antenna is fed with about 25 feet of
RG-58 with the tuner next to the rig in the shack. The cable will be
changed to RG-8 tomorrow assuming that the winds finally die down here
in So Cal.

On 10 and 12 meters the performance is quite acceptable. I'm not the
big signal on the band, but it works well.

I'm hoping to slightly lengthen the antenna and get performance from 17
to 10 meters. Since the tuner to antenna VSWR will be very high, I'm
pondering ways of lowering the loss.

A separate loaded whip is used on 20 and 40 meters.

So far, the experiment has been good, and it is one of the few antenna
configurations that meet the established requirements. (established by
the xyl) :)

Thanks
Wayne
W5GIE /6








"Wayne" wrote in message ...

I am using a whip antenna mounted on a metal patio cover. Results are
good
on 10 and 12 meters, and contacts have been made down to 40 meters.
(Matches were not obtained on 15 or 30 meters) The whip is 8.5 ft long
(a longer whip is under consideration). It is fed through an antenna
tuner and
about 25 feet of RG-58. I'm about to replace that with RG-8.

Any comments on how to hold down feedline losses. One suggestion is to
use
two parallel lengths of RG-8 so that half the current runs through
each. Also, site geometry would allow open wire feed.

Possibilities?

If its an autotuner, best place for it is at the base of the vertical.

Feedline suggestions?
 

"Ian Jackson" wrote in message
...
In message , Owen Duffy
writes
"Wayne" wrote in
:

I am using a whip antenna mounted on a metal patio cover. Results are
good on 10 and 12 meters, and contacts have been made down to 40
meters. (Matches were not obtained on 15 or 30 meters) The whip is 8.5
ft long (a longer whip is under consideration). It is fed through an
antenna tuner and about 25 feet of RG-58. I'm about to replace that
with RG-8.

It is obviously advantageous to use the lowest loss coax you can lay your
hands on. As, in cable TV systems, long coaxial trunk lines have now been
superseded by optical fibers, I would suggest that a cable TV operator
might be persuaded to donate some nice chunky coax (preferably "as thick
as a horse's prick", as one of my bosses once described it). Failing that,
just go for the best you can get.
--
Ian

Way too much time and money is being wasted in the change over from the rg58
coax. Even with a 20 to 1 SWR the rg-58 will loose about 3 db of signal due
to the large mismatch. the rg-8 will still loose atleast 1 db. This 'big'
gain of 2 db is hardly worth it. More time and money should be put into a
beter antenna. Maybe one of the trap type verticals that is 30 or more feet
tall. You gain by a beter radiation efficency and at the same time cut the
loss in the coax due to the beter match. Even the screwdriver type antenna
would probably be much beter. With that you get rid of the losses in the
antenna tuner.