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Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff

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Well, you are just doing what you always have done and the rest of the 'scientific community' does, Cut-and-Paste Science.
http://www.northcountryradio.com/Articles/Construction%20of%20AM88%20Antenna.htm

I suspect most homework turned in class today is Cut-and-Paste Science.


Then they graduate with Cut-and-Paste Science Thinking.


and you're part of the 100%...














Serg Io wrote:
> 
> Is sci.physics now 100 % clutter ?
> 
>         any real physics at all being posted ?
> 
> At present, FCC restrictions require the use of an antenna with Part 15
> transmitters to be either 10 feet or less, or limit field strength to
> 2400 / f in kHz. This applies in the the top of the AM broadcast band
> and certain other frequencies. Consult current FCC rules. However, as
> long as you are using 100 milliwatts and a 10 foot antenna, there is no
> specific limit on range. Typical antenna efficiencies at 1.6 MHz are
> about 0.5 to 1 percent. This limits effective radiated power to 1
> milliwatt or less. This sounds discouraging, but it is not really bad.
> If an antenna radiating 1 milliwatt is placed at the center of a sphere
> of 1 mile in diameter, all this power is still present at the surface,
> less any losses inside the sphere (very small in most cases can be
> considered zero as in free space). The following is a mathematical
> demonstration of this but you can skip it and take our word for it
> should you not care for the details.
> 
> The surface area of a 1 km (1000 meters) radius sphere is 4 x pi x r
> squared, where pi = 3.14159 and r squared = 1,000,000
> 
> Surface Area = 12.56 x 10 exp 6 (12.56 million square meters)
> 
> Dividing 1 milliwatt (1/1000 of a watt) by this figure, we get the power
> per square meter as (79 x 10 exp -12 watts)
> 
> The signal in volts per meter can be calculated by realizing that free
> space has an impedance of 377 ohms
> 
> The signal strength in volts/meter is equal to the square root of the
> power/sq meter x the impedance in ohms
> 
> multiplying power/sq meter by 377 ohms and taking the square root we get
> 172.5 microvolts/meter at 1 kM (1000 meters or 0.62 miles)
> 
> At 1 mile this would be 107.15 microvolts/meter (uv/meter or uv/m)
> 
> Now, 107 uV/meter is a fairly good signal level. As signal levels of 50
> uV/m are still useable a range of over 2 miles should be obtained with a
> properly tuned antenna and 100 milliwatts. A decent AM receiver with a
> ferrite loop antenna can easily pick this up. A good AM receiver with a
> sensitivity of 10 uV per meter might hear this signal at several miles.
> However, ambient noise and interference will be the limiting factor.
> Using similar antennas (8 foot whip with loading coil), Amateur radio
> operators have operated transmitters from automobiles on the nearby (in
> frequency) 160 meter ham band (1800-2000 kHz) and with 10 watts, two way
> contacts of 25 to 50 miles are possible. This would correspond to 2.5 to
> 5 miles range with 100 milliwatts. Typical AM receivers equipped with
> the usual ferrite rod or loop antennas have sensitivities ranging from 5
> uV/meter for excellent receivers with large loop antennas, to as poor as
> 2000 uV/meter for cheap small AM portable sets. 50 to 300uV / meter is
> typical for average AM BC receivers. This depends on antenna size,
> receiver gain, and bandwidth. Note that this figure includes the loop
> antenna and is not the same as that would be measured at the 50 to 600
> ohm input terminals of the receiver (if so equipped). In this case, in
> order to get usable radiation, the antenna must take as much power from
> the transmitter as possible and radiate it with maximum efficiency. This
> requires a reasonable ground system and an antenna that is properly
> matched to the transmitter. A 10 foot vertical or whip antenna has an
> impedance of about 3000 ohms capacitive reactance in series with about
> 0.1 ohm radiation resistance. The trick is to get as much current
> flowing in this 0.1 ohm resistance as possible. For 1 milliwatt radiated
> power this would be 100 milliamperes (0.1 ampere). To force this much
> current through the impedance of the antenna, an RF level of 300 volts
> is needed. This can be done by using a series inductance to cancel out
> the capacitive reactance of the antenna. A simple indoor 3 foot whip
> plugged into the transmitter, with no matching network, would look like
> about 0.007 ohm in series with 8000 ohms capacitive reactance. About
> 3000 volts of RF signal would be needed to have this antenna radiate 1
> milliwatt. Since 100 milliwatts. A 100 milliwatt transmitter would
> supply about 2.3 volts of RF into 50 ohms. Open circuit or the level
> delivered into this antenna would be around 4.5 volts. The radiated
> power would be around 2 nanowatts. This would produce a very weak signal
> barely detectable at more than a few feet from the transmitter.
> 
> These high RF voltages appear on the antenna as a result of using a
> loading coil to get a series resonant circuit together with the self
> capacitance of the antenna. This capacitance depends on the antenna
> dimensions and will be around 30 pf for a 10 foot vertical, depending on
> its configuration and diameter. This capacitance can be calculated from
> electromagnetic theory or inferred from an antenna analysis program such
> as ELNEC. For frequencies in the 1.6 MHz region, around 350 to 400 uHy
> will be needed. At 530 kHz around 3000 uHy will be needed.
> 
> This inductance can be reduced by using a "capacity hat" on the top of
> the antenna. This is made up of 4 or 6 lengths of wire (12 inches)
> arranged horizontally like the spokes of a wheel, with one end connected
> to the top of the antenna (see fig). The calculated capacitance of this
> short vertical antenna is 36.3 pF and is fairly constant over the entire
> AM broadcast band. This allows a coil of 220 to 2400 microhenries to
> make this antenna resonant from 1700 to 530 kHz. The exact inductance
> will be affected by antenna location, height above ground, length of
> ground lead and size of ground plane, proximity to other objects, and
> other environmental factors. Therefore it is best to start off with a
> coil of somewhat higher inductance than actually needed, and adjust the
> number of turns experimentally. Best radiation efficiency is at the
> higher frequencies.

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Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff Serg Io <invliad@invalid.com> - 2017-02-12 21:12 -0600
  Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff noTthaTguY <abu.kuanysh05@gmail.com> - 2017-02-12 19:31 -0800
  Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff The Starmaker <starmaker@ix.netcom.com> - 2017-02-13 09:46 -0800
    Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff James McGinn <jimmcginn9@gmail.com> - 2017-02-14 07:32 -0800
    Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff noTthaTguY <abu.kuanysh05@gmail.com> - 2017-02-14 10:19 -0800
  Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff moroney@world.std.spaamtrap.com (Michael Moroney) - 2017-02-13 22:07 +0000
    Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff The Starmaker <starmaker@ix.netcom.com> - 2017-02-13 18:45 -0800
      Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff moroney@world.std.spaamtrap.com (Michael Moroney) - 2017-02-14 12:49 +0000
      Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff James McGinn <jimmcginn9@gmail.com> - 2017-02-14 07:38 -0800
    Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff Poutnik <poutnik4nntp@gmail.com> - 2017-02-14 06:27 +0100
      Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff john <johnsefton288@gmail.com> - 2017-02-14 02:31 -0800
        Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff Serg Io <invliad@invalid.com> - 2017-02-14 07:57 -0600
          Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff john <johnsefton288@gmail.com> - 2017-02-14 07:28 -0800
    Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff Mahipal <mahipal7638@gmail.com> - 2017-02-14 05:23 -0800
      Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff Serg Io <invliad@invalid.com> - 2017-02-14 08:22 -0600
        Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff john <johnsefton288@gmail.com> - 2017-02-14 07:18 -0800
          Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff Serg Io <invliad@invalid.com> - 2017-02-14 09:49 -0600
            Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff James McGinn <jimmcginn9@gmail.com> - 2017-02-14 08:04 -0800
        Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff Mahipal <mahipal7638@gmail.com> - 2017-02-14 07:29 -0800
        Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff James McGinn <jimmcginn9@gmail.com> - 2017-02-14 07:41 -0800
          Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff edprochak@gmail.com - 2017-02-14 11:48 -0800
            Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff James McGinn <jimmcginn9@gmail.com> - 2017-02-15 09:03 -0800
      Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff benj <benj@nobody.net> - 2017-02-14 18:52 -0500
        Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff Mahipal <mahipal7638@gmail.com> - 2017-02-14 21:14 -0800
    Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff James McGinn <jimmcginn9@gmail.com> - 2017-02-14 07:36 -0800
      Re: Is sci.physics now 100 % scrap ? and AM transmitter antenna stuff noTthaTguY <abu.kuanysh05@gmail.com> - 2017-02-14 13:26 -0800
    Michael Moroney can't/won't read me properly. Jeff-Relf.Me <@.> - 2017-02-14 18:18 -0800
      The inmates always hate their description moroney@world.std.spaamtrap.com (Michael Moroney) - 2017-02-15 04:28 +0000

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