[AMPS] Re: swr

[Gilmer, Mike]

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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