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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