Re: Einstein's Doppler equation wrong?

From: jahn (suzysewnshow_at_yahoo.com.au)
Date: 11/08/04 

Date: Mon, 8 Nov 2004 12:35:12 -0500

"Paul B. Andersen" <paul.b.andersen@hia.no> wrote in message news:cmo15b$b2c$1@dolly.uninett.no...
>
> "jahn" <suzysewnshow@yahoo.com.au> skrev i melding news:2v9b5mF2j4onoU1@uni-berlin.de...
> >
> > "Paul B. Andersen" <paul.b.andersen@hia.no> wrote in message news:cmnmkt$kgk$1@dolly.uninett.no...
> > >
> > > "jahn" <suzysewnshow@yahoo.com.au> skrev i melding news:2v1iekF2ers21U1@uni-berlin.de...
> > > >
> > > > "Paul B. Andersen" <paul.b.andersen@hia.no> wrote in message news:cmg1k9$n7a$1@dolly.uninett.no...
> > > > >
> > > > > "sal" <pragmatist@nospam.org> skrev i melding news:pan.2004.11.03.16.29.21.640648@nospam.org...
> > > > > > Question, Paul.
> > > > > >
> > > > > > On Wed, 03 Nov 2004 16:30:27 +0100, Paul B. Andersen wrote:
> > > > > >
> > > > > > > If we have a mismatch between the antenna and the 50 ohm transmission
> > > > > > > line, then we will have a specific SWR which is independent of the length
> > > > > > > of the line, and there is not possible to "make the generator see a god
> > > > > > > match" by adjusting the length of the line. The matching impedance of the
> > > > > > > CB transceiver is 50 ohm, and there is no way to make the impedance "seen
> > > > > > > into" the line equal to 50 ohm if the SWR is different from 1. We can
> > > > > > > however make the impedance resistive by adjusting the length of the line.
> > > > > >
> > > > > > (My knowledge of amplifiers is limited to relatively low-power audio stuff
> > > > > > so this may be a dumb question.)
> > > > > >
> > > > > > Does the _transmitter_ care what the impedance of the line is?
> > > > >
> > > > > Yes, very much so.
> > > > > It will care what impedance it "sees" into the line.
> > > > > All transmitters are made to work with a specific load.
> > > > > If the transmitter is loaded with an impedance different from
> > > > > the specified one, you can safely assume that it will not be
> > > > > able to transmit the rated power, and it may even be damaged
> > > > > if the mismatch is too severe.
> > > > >
> > > > > > Unless this is a tube set, isn't the impedance of the transmitter's
> > > > > > output stage roughly zero? Certainly if the output stage consists of
> > > > > > something like a pair of power transistors with bases nailed to the last
> > > > > > voltage amp stage, it'll be acting as a voltage source. (Stray current in
> > > > > > the load won't affect the transmitter output voltage in that case, so its
> > > > > > impedance must be zero.)
> > > > >
> > > > > You seem to be thinking of a low frequency amplifier, like an audio
> > > > > amplifier. They will usually have a very low output impedance,
> > > > > but not even those can be allowed to be loaded with zero impedance.
> > > > >
> > > > > An RF-transmitter will usually be tuned, that is, there is a resonance circuit
> > > > > at the output. (Usually called a "tank circuit" because it "stores" energy).
> > > > > These transmitters are most often C-amplifiers. The "tank circuit" is
> > > > > tapped in some way (a capacitor or a transformer), and fed into
> > > > > the load. The load impedance will affect the output stage, and a wrong
> > > > > load may well bring the amplifier elements (transistors or whatever)
> > > > > outside of their "safe operating area."
> > > >
> > > > What impedance is an inverting op-amp designed to drive and
> > > > what terrible things happed if you drive 75 ohm line with it?
> > > > http://www.hobby-toy.com/29/am-transmitter-schematic.html
> > > >
> > > > RF DAC's are used these days with LC components only needed to filter the switching transients.
> > > > << When there is no modulation (silence), 48 modules will be turned on simultaneously to generate approximately 55 KW (5 KW
is
> > > lost
> > > > on the way to the antenna). To modulate the transmitter, modules are turned on and off. As you turn more modules on, you
have
> > more
> > > > RF carrier and when you turn more off, you have less RF carrier. >>
> > > > http://hawkins.pair.com/wabcnow.shtml#digmodsect
> > > >
> > > > http://hawkins.pair.com/wabcnow/wabcn10.jpg
> > > > http://hawkins.pair.com/wabcnow.shtml
> > > > ;-) Sue...
> > >
> > > What is your point?
> > > Are you trying to say that that a transmitter doesn't care
> > > what the load impedance is?
> >
> > Some don't. Norton amplifiers for example.
> > >
> > > Of course the 55 kW transmitter above will work according
> > > to spec only if it is loaded with the specified impedance.
> > >
> > > Here are the specs for a 100kW Harris LW transmitter
> > > of the kind as the one above:
> > > http://www.broadcast.harris.com/extremedigital/pdf/dx100.pdf
> > > From where I quote:
> > > | RF Output:
> > > | 4 1/16" EIA flange (female), 50 ohms unbalanced.
> > > | Other impedances available upon request per quotation.
> > > | RF Load:
> > > | 50 ohms, nominal. Front panel matching adjustments.
> > > | Antenna matching range 1.2:1 VSWR minimum.
> > >
> > > Do I have to explain what it means?
> > No.. but I would be interested in seeing some of you designs for filters and combiners that don't use standing waves.
> > Sue...
>
> This is getting to bloody stupid.
> Of course transmission line sections with a high SWR
> are used in a number of different applications when the frequency
> is so high that lumped components will give excessive loss.
> When did I ever say otherwise?
>
> For your information I have designed and built microwave
> bandpass filters (L-band, microstrip, golden lines on alumina).
> In bandpass filters, you use resonators, and a resonator
> at these frequencies is always a half wavelength transmission line.
> The SWR in a resonator is obviously very high.
> (Depending on the loaded Q.)
>
> So what?
> All I have claimed is what should be an obvious triviality, namely
> that you don't want a high SWR in the transmission line from
> the transmitter to the antenna, and that you must ensure that
> the transmitter will see the load impedance it is designed for.
I think you were claiming dipoles couldn't have standing waves
or modeled as impedance invering line sections to the 377 ohm
radiation resistance of free space but I leave that search to your
prowess at advesarial process.
>
> Do you disagree?
Only so your day isn't spoiled. :-)
Kind regards,
Sue...
>
> Paul
>
>

Relevant Pages

  • Re: Standing Waves (and Impedance)
    ... I will modify my earlier position that High SWR causes TVI to Roy's ... I used to operate ATV on 440mhz with a 48 element collinear antenna. ... >> A matched transmission line behaves like the theory books say it does. ... >I deleted only "with the lowest possible loss" because increased SWR ...
    (rec.radio.amateur.antenna)
  • Re: Einsteins Doppler equation wrong?
    ... >> Of course transmission line sections with a high SWR ... >> at these frequencies is always a half wavelength transmission line. ... >> The SWR in a resonator is obviously very high. ... >> the transmitter will see the load impedance it is designed for. ...
    (sci.physics.relativity)
  • Re: Standing Waves (and Impedance)
    ... A matched transmission line behaves like the theory books say it does. ... Power loss will be at its worst for a given line. ... Solid state rigs don't tolerate a high SWR. ...
    (rec.radio.amateur.antenna)
  • Re: Transmission line ?
    ... Rene Tschaggelar wrote in news:413b01c4$0$704 ... > transmission line not intended as resonator. ... Standing waves need not have nothing to do with resonance. ...
    (sci.physics)