Re: long antenna

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From	jimp@specsol.spam.sux.com
Newsgroups	sci.physics
Subject	Re: long antenna
Date	Thu, 26 Nov 2015 20:05:37 -0000
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Sender	Jim Pennino <jimp@mail.specsol.com>
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gilber34 <fafa@invalid.com> wrote:
> On 11/26/2015 9:21 AM, gilber34 wrote:
>> On 11/24/2015 2:12 PM, benj wrote:
>>> On 11/24/2015 02:39 PM, RichD wrote:
>>>> On November 17, Timo wrote:
>>
>>>> Sometimes, the cord gets wrapped into a loop, how does
>>>> that affect the physics?
>>>
>>> Of course it does! The rule in EM is that inductance is determined ONLY
>>> by geometry (and material properties, natch) Same goes for capacitance.
>>> These are two key parameters in antennas.
>>>
>>> And you may recall I talked about antenna "aperture".
> <snip>
>  It's in effect representing a
>>> hole the size of which admits the energy that the given antenna collects.
>>>
> 
>>> And I should point out that a larger dish may NOT collect more energy.
>>> Hence the aperture could be much smaller than the dish size. If part of
>>> the dish is out of phase with the other part the collected waves may
>>> cancel. Hence the signal out is reduced. That is why I said above a
>>> "perfect" dish.
>>
>> note:
>> the dish has to "roll off" the edge away from parabolic shape, to
>> diminish the back lobe.  if you keep parabolic to the edge, it will
>> cause a large back lobe in the antenna pattern where the edge
>> diffraction adds in phase, and then you will pick up the temperature of
>> the ground (which is quite warm) as noise into your LNA on the dish.
>> (looking at cold sky dish application, sattilites etc)
>>
>>
>>>
>>> Same thing can happen if the wire is too long. Since the signal travels
>>> DOWN the wire to the radio, there is a delay. And that delay together
>>> with the geometry of the wire can result in the same kind of phase
>>> cancellation that reduces the signal rather than increases it.
>>
>> there is freewhere somewhere on internet for antennas, very easy to see
>> this effect on long wires, the antenna pattern splinters up very badly.
>> (EZnec ??)
>>
>>
>>>
>>> In general, the phrase "long wire antenna" really means: We didn't
>>> bother to put a real antenna on it, but just attached a piece of wire we
>>> had available and hoped it worked and it sort of does.
> 
> mostly shortwave radio and ham radio stuff.   ham radio transmitters 
> have to tune up to match the long wire usally by a pi network, two 
> adjustable Cs and a coil w multiple taps on it in the middle.

If you actually knew anything about antennas, you would know why long
wire antennas fell out of favor a very long time ago.

> I used a long wire antenna on a shortwave halecrafters radio, the long 
> wire was a fence, worked just excellent, then lightning  hit the fence, 
> and rearranged parts in the radio. (those radios had a ac hot chassis, bad)

You know nothing about antennas and your results are hardly surprising.

You did not have a long wire antenna, you had a random wire antenna.

A long wire antenna is at least one, and to be effective, several 
wavelengths long.

https://en.wikipedia.org/wiki/Random_wire_antenna


>>> A long wire traveling wave antenna is a different animal and usually
>>> isn't a long wire, though traveling waves do travel down a wire. A true
>>> antenna of that type will be terminated on one end like say a rhombic
>>> antenna so it really consists of just a terminated transmission line.
>>
>> terminated to eliminate waves going in a direction on the wire
> 
> which changes the pattern to have gain in a direction.

Actually long wire antennas are generally not terminated.

Rhobic antennas are terminated.


>>> The whole subject is quite complex and very much dependent upon the
>>> exact details of the system. Quick rules of thumb can easily be quite
>>> wrong.
>>
>> and the ground reflection is bigtime consideration up past FM, EZNEC
>>
> http://eznec.com/
> i think older versions are free, and they have demo,
> even used by ARRL

And again you are wrong.

The free demo version is the current version with limited capabilities.

 

-- 
Jim Pennino

Thread

long antenna RichD <r_delaney2001@yahoo.com> - 2015-11-17 10:42 -0800
  Re: long antenna Odd Bodkin <bodkinodd@gmail.com> - 2015-11-17 12:46 -0600
    Re: long antenna Poutnik <poutnik4nntp@gmail.com> - 2015-11-17 20:10 +0100
    Re: long antenna jimp@specsol.spam.sux.com - 2015-11-17 20:28 +0000
      Re: long antenna benj <nobody@gmail.com> - 2015-11-17 16:59 -0500
    Re: long antenna Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-11-18 22:56 +0100
      Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-18 16:57 -0600
        Re: long antenna jimp@specsol.spam.sux.com - 2015-11-18 23:15 +0000
          Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-18 20:42 -0600
            Re: long antenna jimp@specsol.spam.sux.com - 2015-11-19 05:29 +0000
              Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-19 08:54 -0600
                Re: long antenna jimp@specsol.spam.sux.com - 2015-11-19 18:44 +0000
                Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-22 15:32 -0600
                Re: long antenna jimp@specsol.spam.sux.com - 2015-11-22 23:16 +0000
            Re: long antenna HVAC <mr.hvac@gmail.com> - 2015-11-19 06:59 -0800
              Re: long antenna benj <none@gmail.com> - 2015-11-19 20:02 -0500
      Re: long antenna benj <none@gmail.com> - 2015-11-19 01:36 -0500
  Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-17 13:28 -0600
  Re: long antenna "reber g=emc^2" <herbertglazier0@gmail.com> - 2015-11-17 14:04 -0800
    Re: long antenna jimp@specsol.spam.sux.com - 2015-11-17 22:35 +0000
      Re: long antenna benj <nobody@gmail.com> - 2015-11-17 19:28 -0500
        Re: long antenna Timo <timo@physics.uq.edu.au> - 2015-11-17 17:18 -0800
          Re: long antenna RichD <r_delaney2001@yahoo.com> - 2015-11-24 11:39 -0800
            Re: long antenna benj <none@gmail.com> - 2015-11-24 15:12 -0500
              Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-26 09:21 -0600
                Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-26 10:05 -0600
                Re: long antenna jimp@specsol.spam.sux.com - 2015-11-26 20:05 +0000
                Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-26 18:39 -0600
                Re: long antenna jimp@specsol.spam.sux.com - 2015-11-27 01:46 +0000
                Re: long antenna jimp@specsol.spam.sux.com - 2015-11-26 19:55 +0000
            Re: long antenna jimp@specsol.spam.sux.com - 2015-11-24 20:04 +0000
              Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-24 16:33 -0600
                Re: long antenna jimp@specsol.spam.sux.com - 2015-11-24 22:58 +0000
                Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-26 09:11 -0600
                Re: long antenna jimp@specsol.spam.sux.com - 2015-11-26 19:42 +0000
                Re: long antenna "Ross A. Finlayson" <ross.finlayson@gmail.com> - 2015-11-26 11:57 -0800
                Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-26 14:52 -0600
                Re: long antenna jimp@specsol.spam.sux.com - 2015-11-26 21:12 +0000
                Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-26 18:58 -0600
                Re: long antenna jimp@specsol.spam.sux.com - 2015-11-27 01:37 +0000
                Re: long antenna benj <none@gmail.com> - 2015-11-26 23:45 -0500
                Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-27 01:01 -0600
                Re: long antenna "Ross A. Finlayson" <ross.finlayson@gmail.com> - 2015-11-26 23:31 -0800
                Re: long antenna benj <nobody@gmail.com> - 2015-11-27 11:34 -0500
                Re: long antenna "Ross A. Finlayson" <ross.finlayson@gmail.com> - 2015-11-27 09:58 -0800
                Re: long antenna benj <nobody@gmail.com> - 2015-11-27 11:46 -0500
                Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-28 16:42 -0600
                Re: long antenna jimp@specsol.spam.sux.com - 2015-11-28 22:58 +0000
                Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-30 07:46 -0600
                Re: long antenna jimp@specsol.spam.sux.com - 2015-11-30 19:01 +0000
                Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-30 14:12 -0600
                Re: long antenna jimp@specsol.spam.sux.com - 2015-11-30 20:43 +0000
                Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-30 17:41 -0600
                Re: long antenna jimp@specsol.spam.sux.com - 2015-12-01 00:15 +0000
                Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-30 20:23 -0600
                Re: long antenna jimp@specsol.spam.sux.com - 2015-12-01 06:21 +0000
                Re: long antenna benj <none@gmail.com> - 2015-11-30 15:22 -0500
                Re: long antenna jimp@specsol.spam.sux.com - 2015-11-30 20:48 +0000
                Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-30 17:16 -0600
                Re: long antenna jimp@specsol.spam.sux.com - 2015-11-30 23:52 +0000
                Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-30 19:59 -0600
                Re: long antenna jimp@specsol.spam.sux.com - 2015-12-01 02:16 +0000
                Re: long antenna benj <none@gmail.com> - 2015-11-30 19:20 -0500
                Re: long antenna jimp@specsol.spam.sux.com - 2015-11-27 18:53 +0000
              Re: long antenna benj <none@gmail.com> - 2015-11-25 00:08 -0500
                Re: long antenna jimp@specsol.spam.sux.com - 2015-11-25 06:13 +0000
  Re: long antenna "reber g=emc^2" <herbertglazier0@gmail.com> - 2015-11-18 16:25 -0800
  Re: long antenna "reber g=emc^2" <herbertglazier0@gmail.com> - 2015-11-19 16:08 -0800
    Re: long antenna jimp@specsol.spam.sux.com - 2015-11-20 00:40 +0000
      Re: long antenna "reber g=emc^2" <herbertglazier0@gmail.com> - 2015-11-20 15:51 -0800
        Re: long antenna jimp@specsol.spam.sux.com - 2015-11-21 00:34 +0000
          Re: long antenna jmfbahciv <See.above@aol.com> - 2015-11-21 14:37 +0000
            Re: long antenna jimp@specsol.spam.sux.com - 2015-11-21 19:32 +0000
              Re: long antenna jmfbahciv <See.above@aol.com> - 2015-11-22 14:50 +0000
                Re: long antenna "reber g=emc^2" <herbertglazier0@gmail.com> - 2015-11-22 11:27 -0800
                Re: long antenna jimp@specsol.spam.sux.com - 2015-11-22 19:44 +0000
                Re: long antenna jimp@specsol.spam.sux.com - 2015-11-22 19:40 +0000
                Re: long antenna jmfbahciv <See.above@aol.com> - 2015-11-23 14:13 +0000
                Re: long antenna benj <none@gmail.com> - 2015-11-23 13:00 -0500
                Re: long antenna jmfbahciv <See.above@aol.com> - 2015-11-24 13:20 +0000
                Re: long antenna benj <none@gmail.com> - 2015-11-24 13:40 -0500
                Re: long antenna jmfbahciv <See.above@aol.com> - 2015-11-25 13:44 +0000
                Re: long antenna jimp@specsol.spam.sux.com - 2015-11-23 18:47 +0000
                Re: long antenna jmfbahciv <See.above@aol.com> - 2015-11-24 13:20 +0000
                Re: long antenna jimp@specsol.spam.sux.com - 2015-11-24 19:49 +0000
                Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-24 16:36 -0600
                Re: long antenna jimp@specsol.spam.sux.com - 2015-11-24 23:00 +0000
                Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-26 16:17 -0600
                Re: long antenna jimp@specsol.spam.sux.com - 2015-11-26 23:35 +0000
        Re: long antenna benj <none@gmail.com> - 2015-11-20 20:58 -0500
    Re: long antenna benj <none@gmail.com> - 2015-11-19 20:09 -0500
  Re: long antenna "nuny@bid.nes" <Alien8752@gmail.com> - 2015-11-24 12:51 -0800
    Re: long antenna benj <none@gmail.com> - 2015-11-25 00:01 -0500
  Re: long antenna "reber g=emc^2" <herbertglazier0@gmail.com> - 2015-11-25 15:36 -0800
    Re: long antenna jimp@specsol.spam.sux.com - 2015-11-25 23:51 +0000

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