[Antennas] 160 Inverted L 160 Radials

Thu Nov 17 14:16:56 EST 2005

I am not really some sort of antenna guru but IMHO this antenna will work
somehow. There are a lot of IMHO wrong statements in the article. First if
you have non conductive mast the model that I have made shows that the
impedance of the antenna is around 18 ohms. Therefore if the author got 50
ohms impedance there is 32 ohms impedance of losses (ground losses, linear
loading losses etc. Therefore the efficiency is way off of the claimed 85%
and more like 30%. The fact that the author claims 300 kHz bandwidth
confirms that the efficiency of the antenna is pretty low. Its broad
bandwidth is mainly determined by the impedance of losses. I did the model
with 20m tall mast. That is the best case out of the choice suggested by the
author. If your mast is not that high the efficiency will drop even more.
You will also need to address the problem of decoupling the shield of the
coaxial feeder from the radiator.It may prove to be not that simple because
of very heavy interaction between the two. Still the antenna will work.
There will be more high angle horizontally polarized radiation and it will
be good for local or medium distance communication.
Secondly if you change to metal mast say 40mm in diameter your impedance
will go up somewhat reaching 28 ohm but you get then completely different
antenna with more vertically polarized radiation. Of course metal mast will
detune the antenna and you will have to adjust the length of the linear
loading but still it looks better to me. Besides you can route your feeder
through the metal mast and decouple it that way from high current running in
the vertical radiator. Still as with any vertical both the efficiency and
performance of such a system will greatly be dependant of the properties of
the ground.
Anyway usually verticals are build for DX on 160m and horizontal
polarization that makes antenna collect local QRM is not desirable.
Therefore I would rather use 20m tall conducting radiator, add T shaped
capacitive hat (just 2 horizontal wires instead of 1) and probably would get
even better results especially on RX.
73, Igor UA9CDC
----- Original Message -----
From: "W3OA" <w3oa at adelphia.net>
To: "Jerry Forwood" <e.j.forwood at juno.com>
Cc: <antennas at mailman.qth.net>
Sent: Thursday, November 17, 2005 5:41 AM
Subject: Re: [Antennas] 160 Inverted L 160 Radials
> Jerry -
>> Sorry you were offended by the grammatical errors in the description at
> http://members.tripod.com/~KE4UYP/80m_160m_Antenna.html.
> I was aware of the grammatical errors (at least some of them) and agree
> that their presence detracts from the author's credibility. In spite of
> this, I think the idea of a 160 antenna with essentially the same foot
> print as an inverted L without radials is very attractive. I don't have
> enough experience/knowledge to evaluate the technical merits of the
> antenna and I haven't seen similar antennas described elsewhere. So I
> came to this list for help.
>> Did you get a chance to evaluate what the author said as opposed to how
> he said it? What do you think? Is it reasonably good for my first 160
> antenna?
>> Thanks for your interest. Dick, W3OA
>> Jerry Forwood wrote:
>> >Frankly, I have a problem with people that post websites where they don't
even know the difference between the words to and two! As in 2 two 1 SWR!
:0(
> >Learn to proof read before you post! You are showing your intelligence ,
or lack of it, to the world!
> >
> >73 de Jerry, KØEJF
> >E.J.(Jerry) Forwood
> >
> >-- W3OA <w3oa at adelphia.net> wrote:
> >I'd like to put up a 160 antenna. I'm thinking of an inverted L. The
> >vertical section would be 54 feet and I have room for a horizontal
> >section up to 157 feet long. I am concerned about the radial field -
> >it's approximately square, about 90 feet on each side. Is this
> >hopelessly small? Should I try something like KE4UYP suggests at
> >http://members.tripod.com/~KE4UYP/80m_160m_Antenna.html? I'd like to
> >hear of peoples success, or failure, trying his design.
> >
> >Thanks for any suggestions - Dick, W3OA
> >
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> >
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> >
> >
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