I'm sorry if this is a repeat, but it never appeared with me
from the reflector.
Steve
-----Original Message-----
From: Steve Thompson <g8gsq@txrx.demon.co.uk>
To: amps@contesting.com <amps@contesting.com>
To: <amps@contesting.com>
Date: 06 October 1999 08:13
Subject: Re: [AMPS] Re: The Worldwide, No Holds Barred, SWR
Quiz.
>
>-----Original Message-----
>From: measures <measures@vcnet.com>
>To: AMPS <amps@contesting.com>
To: <amps@contesting.com>
>Date: 06 October 1999 05:52
>Subject: Re: [AMPS] Re: The Worldwide, No Holds Barred, SWR
>Quiz.
>
>
>
>>
>>measures wrote:
>>
>>>? I'm trying, I'm trying. . I thought I recalled
>reading that you
>>>supported the theory that the placement of the SWR meter
>would make no
>>>difference in the SWR reading. I was wrong. Sorry,
Jon.
>>
>>Only, if the transmission line was 50 Ohms and the load
was
>of a different
>>impedance (ie: a 100 Ohm load on a 50 Ohm transmission
line
>measured with
>>a 50 Ohm instrument).
>>
>>A half wave transmission line with a load at end A,
repeats
>the impedance
>>of that load at point B (end of the line).
>>
>OK
>
>>For your specific case, you are correct. So one cannot
>always say that
>>placing an SWR meter at different points in a line will
not
>change the
>>SWR. But if the characteristic impedance of the line and
>the SWR meter is
>>the same, it will always read the same SWR.
>>
>? With this I do not agree. Only when there are no
>reflected waves
>does the SWR meter read the same everywhere on the line.
>
>>In your example, if we used a 93 Ohm SWR meter the SWR
>would measure 1.86
>>not matter where it was placed along that transmission
>line.
>>
>
>? . It seems to me that a 93-ohm SWR meter would read 1:1
>at the center
>of the halfwave section and 1.55:1 at the ends -- i.e.,
the
>50-ohm
>points.
>
>- Rich..., 805.386.3734, www.vcnet.com/measures.
>
>Sorry, Rich but you are wrong on both points and the quoted
>text is correct. In a 93 ohm line, a 93 ohm meter with
>decent directivity will indicate constant reverse power
>regardless of position along the cable - inline meters
>sample both voltage and current on the line, otherwise they
>can't tell forward from reverse. VSWR is calculated from
the
>power measurement. I think we use VSWR as a indicator of
the
>match because the voltage peaks and troughs can be measured
>using a slotted line, as was the case in the early days. We
>could just as (un)easily use ISWR, which would be easier to
>measure on open wire feeders.
>
>It's power that travels along transmission lines, both
>voltage and current are needed. If a line isn't terminated
>in a resistance equal to its Zo, the voltage, current and
>impedance vary along the line, but the power doesn't.
>
>
>Steve
>
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