Cathy,
I have an entire YouTube channel with over 30 videos to date showing how
the free program SimSmith can calculate these types of problems very
easily. The graphical output of SimSmith makes understanding a huge
number of amateur radio and RF topics much easier.
https://www.youtube.com/channel/UCKSyLSu4fm_1RHoO3Jvk4YQ
or go to YouTube and search for my call sign.
To answer your question 25+j0, 100+j0, 40+j30, 40j30 all are exactly
2:1 SWRs.
73,
Larry, W0QE
On 6/11/2017 8:27 AM, Catherine James wrote:
Bill,
I'm puzzled at the idea that changing "the impedance the transceiver sees"
wouldn't affect SWR. Isn't SWR the ratio between the impedance seen at the measurement
point vs. the desired impedance at that point? I must not be understanding your comment.
Anyway, you can certainly change impedance by changing the length of coax,
provided that the coax used does not have the same impedance as the impedance
at the termination point. So if you have a 50 ohm load fed with 50 ohm coax,
it does not matter how long the coax may be, but if you use 75 ohm coax for
part of the feedline, the impedance seen at the transmitter will vary with the
length of the 75 ohm section.
The matching section does not have to be a quarter wavelength long.
73,
Cathy
N5WVR

On Sat, 6/10/17, Bill Turner <dezrat@outlook.com> wrote:
>Tried different lengths of coax between the amp and the radio and still no
better.
REPLY:
The length of coax does not affect SWR unless it is extremely long,
where line loss comes into play. Even then, the effect is to reduce
SWR, not increase it.
It does affect the impedance the transceiver "sees", but not SWR.
73, Bill W6WRT
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