nbr wrote:
1) How to feed the antenna and be able to run legal limit, all bands?

Put your matching network at the base of the antenna. Feed your matching
network with coax.
--
73, Cecil http://www.qsl.net/w5dxp



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On Sun, 27 Jul 2003 19:50:04 -0500, W5DXP
wrote:

nbr wrote:
1) How to feed the antenna and be able to run legal limit, all bands?

Put your matching network at the base of the antenna. Feed your matching
network with coax.

Thanks for your reply to my message, but this is not feasible. The
antenna is 120' from the shack, unblanaced transmatch in the shack.
Looking for matching network at the base of the antenna (or apex,
maybe), perhaps balun (???), but needs to be broadband so antenna can
operate multiband.
Thanks and 73
dan

hey there
i am planning on a similar antenna here is the website for it
http://www.bloomington.in.us/~wh2t/invertedl.html

according the the person who did this website if you feed it at the
ground you can feed it with 50 ohm coax
good luck and let me know how it turns out

nbr wrote:
On Sun, 27 Jul 2003 19:50:04 -0500, W5DXP
wrote:

nbr wrote:
1) How to feed the antenna and be able to run legal limit, all bands?

Put your matching network at the base of the antenna. Feed your matching
network with coax.

Thanks for your reply to my message, but this is not feasible. The
antenna is 120' from the shack, unblanaced transmatch in the shack.
Looking for matching network at the base of the antenna (or apex,
maybe), perhaps balun (???), but needs to be broadband so antenna can
operate multiband.

Cecil's right - it can't be done without a matching network at the base,
because the feedpoint impedance varies too much between bands.

Your antenna is about a twice-size version of mine. I have a 35ft
vertical, with a 35ft horizontal section followed by a "switch" that can
connect another 65ft (all dimensions approximate). It's fed through
matching networks at the bottom of the vertical, against a large number
of radials.

The extra length of horizontal is only used for Top Band
(quarter-wavelength, low Z, needs those radials) and for 80m short-skip
(half-wavelength, mostly horizontal, voltage fed so doesn't use the
radials much).

With the "switch" open, it's simply a 35ft vertical, 35ft horizontal
inverted-L.

Top Band: 1/8-wave, inefficient but long enough to be usable for easy
QSOs.

80m: bent quarter-wave, surprisingly effective for DX, but low-Z feed
and needs those radials.

40m: voltage-fed half-wave, half vertical and half horizontal - from the
UK it's good for mixed European/DX working, but obviously receives the
European signals even when you don't want them. High-Z feed.

Higher bands: too long - wastes power in lots of little lobes pointing
in useless directions. Gets worse and worse as the frequency goes up,
and even a simple dipole is better. Mostly high-Z feed.

As Cecil says, there's no choice but to feed it at the base through
matching networks on most bands. Trying to feed it from the shack end
through the long run of coax is a non-starter, except on the bands where
it's a low-Z feed. On all the other bands the SWR is too high and the
losses in the coax are crippling.

For many years I used a conventional T-match ATU out there in a
waterproof box. Band-changing was possible, but a chore. Then I tried
custom switchable networks, but that became too complex. At present I'm
using a military auto-ATU that is 1kW rated and works like a dream.

I would certainly recommend the 35+35ft along inverted-L with an
auto-ATU for any small backyard. The extra horizontal length is fine if
you can get it - and the advantage of using the auto-ATU is that it can
be *any* practicable length; you don't have to worry about matching any
more. The only problem is that amateur auto-ATUs are limited to medium
power.

Your system is twice as big as mine, so you can shift all the above
comments down one band. It should go like a rocket on Top Band, but even
on 40m it's getting over-long. If you have other antennas for the higher
bands, think of the inverted-L only as your "low-band special" - then
two or three remotely switched, pre-tuned matching networks will be all
you need.

In your situation I would also consider a remote switch at the top of
the vertical, to disconnect the horizontal part completely. You'll then
have a very effective DX antenna for 40m. Take a look at N6RK's site,
which has some information about switching out the upper sections of
antennas for the bands where they are "over-tall".


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek

Put an SGC at the base and feed it with 12 volts and RF via Co-ax.

Nick

On Mon, 28 Jul 2003 02:47:19 GMT, Dennis Kaylor
wrote:

hey there
i am planning on a similar antenna here is the website for it
http://www.bloomington.in.us/~wh2t/invertedl.html

according the the person who did this website if you feed it at the
ground you can feed it with 50 ohm coax
good luck and let me know how it turns out

This was an easy experiment...tried it and couldn't load the antenna
from the shack. Put an MFJ analyzer on it, and the impedance was all
over the place. I got the sense that while my trasnmatch might make my
transceiver happy, there was very little RF radiation going on. I've
seen the article you mention...in my case, my INV-L dimensions were
different, I am trying to operate multiband, plus 120' of buried coax
to the shack had us comparing apples to oranges.
Thanks for your comments...stay tuned!
73
Dan (K0DAN)

On Mon, 28 Jul 2003 13:53:51 +0100, "froggers"
wrote:

Put an SGC at the base and feed it with 12 volts and RF via Co-ax.

Nick


Yes I have considered this. However my original post says that I wish
to be able to run legal limit. No such SGC matching network.
73
Dan (K0DAN)

On Sun, 27 Jul 2003 19:19:26 -0500, nbr
wrote:

I've put up an inverted-L, which consists of approx. 135' horizontal
leg, and approx. 70' vertical leg. I can shorten the overall length of
the antenna, but cannot lengthen it. There are about 4 ground rods
within about 10' of the base ofthe vertical element, plus about 25
square feet of chickenn wire to serve as a ground plane. I can feed
the antenna right at ground level, or can arrange to feed it up to
6-10' above ground. There is about 120' of buried coax to the shack,
which must feed this antenna. I'd like to use this inverted-L on
160-10M (will settle for 80-10M).
1) How to feed the antenna and be able to run legal limit, all bands?
Current or voltage balun? Won't a balun disspiate power and decrease
efficiency? WIll a balun at ground level increase ground losses?
2) How is the inverted-L said to be a vertically polarized antenna,
when a major portion of its radiating element is horizontal?
3) For Field Day we added another vertical leg to this antenna to make
it into a half-square, and had decent results on 40M/20M. How is the
half-square described as "two verticals in phase", when again, there
is a major part of the antenna (the so-called "phasing element") which
is horizontal?
Thanks and 73
Dan (K0DAN)


Thanks for the recent comments on my previous post. They have been
interesting and informative.

The "antenna voodoo" is still bothering me about the theory of some of
these antennas (e.g. inverted-L, half-square, etc.). I understand that
the horizontal leg of the "L" is considered an "inductor at the top of
the vertical" element, but why not the reverse? Why is this not a
"bent horizontal" with segments which radiate both in the horizontal
and vertical planes? Why is the horizontal sengment of a 1/2-square
considered a "phasing line" and not a radiator?

73
Dan (K0DAN)

On Mon, 28 Jul 2003 09:57:42 -0700, W5DXP
wrote:

nbr wrote:
Why is the horizontal sengment of a 1/2-square
considered a "phasing line" and not a radiator?

The center of the "phasing line" on a half-square is a
maximum voltage point but there is nothing to keep that
horizontal wire from radiating. At a TOA of about 65 degrees
the broadside horizontal radiation and vertical radiation of
a half-square are about equal at about -9 dBi.

I don't think you're suggesting the horizontal component is cancelled
out??? So in truth the 1/2-square may perform DX best at low angle TOA
broadside to the two verticals, but may also have high angle lobes
from the horizontal wire (effective close-in cloud-warmer)?

nbr wrote:
On Sun, 27 Jul 2003 19:50:04 -0500, W5DXP
wrote:


nbr wrote:

1) How to feed the antenna and be able to run legal limit, all bands?

Put your matching network at the base of the antenna. Feed your matching
network with coax.

Thanks for your reply to my message, but this is not feasible. The
antenna is 120' from the shack, unblanaced transmatch in the shack.
Looking for matching network at the base of the antenna ...

This is what I suggested but it will have to be switchable or tunable
for each band, maybe a stub for each band. There is no single fixed
network or balun that will do the job. The impedance on some bands
will be sky high and cause sky high SWRs on your coax.

(or apex,
maybe), perhaps balun (???), but needs to be broadband so antenna can
operate multiband.
--
73, Cecil, W5DXP