Not considering losses, there are only 2 conditions were no changes in
impedance occurs between antenna and transmitter :
1 ) Source, line and load have the same impedance
2 ) The line is half wavelenght
73,
Mauri I4JMY
-----Messaggio Originale-----
Da: Gilmer, Mike <mgilmer@gnlp.com>
A: 'AMPS' <amps@contesting.com>
Data invio: martedì 28 settembre 1999 21.02
Oggetto: RE: [AMPS] Re: swr
>
> I'll ignore all the imperfection problems (line bumps, poor directivity
> of meters, etc.)
>
> If the antenna/load impedance (at the far end) in question here doesn't
> match the line impedance, then the line will transform the impedance,
> and the SWR will vary (as seen at the near end) depending on the cable's
> length, correct?
>
> Nowhere does it say what the antenna impedance measured WITHOUT any coax
> in series.
>
> Am I missing something?
>
> 73
> Mike
> n2mg@contesting.com
>
> On Tuesday, September 28, 1999 2:50 PM, Richard W. Ehrhorn
> [SMTP:w4eto@rmi.net] wrote:
> >
> > Hi Pat...
> >
> > If the transmission line were ideal (lossless), actual SWR would NOT
> change regardless of its length or the point of SWR measurement. With
> real (lossy) transmission lines, actual SWR decreases with distance from
> the load - due to the loss of the transmission line.
> >
> > In most real-life cases at HF, (with up to a hundred feet or so of
> RG-8A/u or better coax transmission line having loss typically << 1 dB),
> actual SWR does not change very greatly from one end to the other.
> Significant point-to-point variations in SWR along the line, as
> indicated by most common SWR meters, are due to either (a) imperfect SWR
> meters (which virtually all are, from slightly to outrageously!) or (b)
> impedance variations in the line itself and/or introduced by connectors,
> other in-line devices, etc. Such line "lumps" generally are much less
> relevant and noticeable at lower frequencies, more significant at higher
> freqs.
> >
> > Such SWR and related line-loss issues are discussed in reasonably
> understandable fashion in, e.g., the 1995 ARRL Handbook, pgs. 19-4
> through 19-6.
> >
> > 73, Dick W0ID
> >
> > > -----Original Message-----
> > From: PD W [SMTP:w0opw@yahoo.com]
> > Sent: Tuesday, September 28, 1999 11:12 AM
> > To: amps@contesting.com
> > Subject: Re: [AMPS] Re: swr
> >
> >
> > > Using my Autek RF1 analyst, I get different Swr values and
> > resonance at various places in the shack. Every
> > connector/coax cable changes Swr and resonance, including
> > before and after the MFJ 2 pole antenna switch. Finally,
> > measuring Swr right at the coax end at the transceiver, I
> > get a different value and resonance on the RF1 compared to
> > the Yaesu rig. All cables are 50 ohms cuz I checked them
> > too. A note that any cables not 50 ohms will exacerbate
> > the problem. So, what indeed is true resonance/Swr but in
> > the eye of the beholder ??
> > > Pat W0OPW
> >
> >
> >
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>
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