[TowerTalk] Smart antennas

[Michael Tope]

Seems like an EIRP scheme would take away incentive
to make ones antenna better. Why put up a 4-square to get
5dB of extra TX gain, when you would have to derate your
transmitter power by that same amount for a zero net gain.
Right now the FCC gives you 1500 joules/second to work
with. You are then free to distribute them across the heavens
any way you see fit (in keeping with safety limits of course).
If you want to spray them all in one direction with a high
gain antenna or distribute them uniformly with a omni, you
are free to do so. Other services have EIRP limits because
they have frequency reuse concerns that we don't have
(except for repeater service where we do have EIRP
constraints).

Sorry, Jim, but I like big transmitters AND big antennas :):)

73 de Mike, W4EF..............................

----- Original Message -----
From: "Jim Lux" <jimlux at earthlink.net>
To: <va3pl at cuic.ca>; <towertalk at contesting.com>
Sent: Tuesday, September 02, 2003 2:03 PM
Subject: Re: [TowerTalk] Smart antennas


> This is an area of great interest to me, both professionally and as an
> amateur in a fairly rigidly controlled HOA.  In fact, I think that
adaptive
> antennae and phased arrays are a reasonably practical way to deal with HF
> communications in "tough" environments.
>
> While you're not necessarily going to be able to beat the huge antenna on
> the huge tower, an adaptive phased array can do the following:
> 1) Form nulls on intefering signals
> 2) Form the main lobe on the signal of interest, and, with sufficient
> sophistication, actually coherently combine the skywave from more than one
> angle and polarization.
> 3) Move the pattern in the "blink of an eye"
>
> If you are cursed by geography, nothing's going to help (say your QTH was
> at the bottom of a big pit... no amount of gain or Tx power will help you
> get sufficient signal out at low angles)
>
>
> Interestingly, on receive, because you're normally atmospheric and
> environmental noise limited, you can tolerate a low gain (in absolute
> terms) antenna, as long as you have directivity, which is easy to come by
> in a phased array.
>
> On transmit, it's a bit tougher, because you have the 1500W limitation on
> transmitted power, and a physically low and small antenna is going to put
> more of that power into the dirt or the clouds overhead.  In pretty much
> the rest of the radio world the licensing and power limits is in terms of
> ERP.  Maybe we should push for the FCC to do the same for hams?  It's not
> that different than how RF exposure is handled, or the limits on the 5 MHz
> band.  You can either guarantee compliance by an antenna of known gain
> (i.e. a dipole) and limited transmit power, or by analysis/measurement of
> actual field strength.
>
> In reality, the rule requires use of the least power to communicate, and
> from a theoretical standpoint, that's the radiated far field.  If you use
a
> 1000W transmitter and a dipole or a 100W transmitter and a 12 dBi
directive
> antenna, the field strength is the same.  Philosophically, I should be
able
> to allocate my resources how I see fit, subject to the radiated power
> limit.. If I want to invest in big high gain antennas and small
> transmitters or small antennas and big transmitters, that should be my
> choice (subject to safety rules, etc.)
>
> Of course, there are those who run big antennas AND big transmitters who
> may not agree.
>
> Jim, W6RMK
> (http://home.earthlink.net/~w6rmk/antenna/phased/index.htm)
>
> At 03:19 PM 9/2/2003 -0400, VeeAthreePL wrote:
> >There is interesting article by Martin Cooper in July 2003 issue of
> >Scientific American pages 49 to 55. He is talking about Smart and
> >Adaptive antennas. This basically is aimed at cell phones but who knows.
> >Worth the reading.
> >73 de Andy - VA3PL
> >
> >_______________________________________________
> >
> >See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless
> >Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with
> >any questions and ask for Sherman, W2FLA.
> >
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> _______________________________________________
>
> See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
>
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