"Reg Edwards" wrote in message
...
Let's do what nobody has ever done before, not even in the ARRL handbooks
or
in Terman, and get an idea of the magnitudes involved.

Examine two cases over a range of frequencies.

Case (1). In a 50-ohm system, use of a poor connector having an impedance
deviating 10 percent from its nominal value of 50 ohms.

Case (2). Making the mistake of using a 75-ohm connector in a 50-ohm
system.

In both cases the connector, plug and socket, is 1" (25.4mm) long.

We first calculate the input impedance of a 75-ohm transmission line, 1"
long, terminated with 50 ohms. Zin will not be very much different from
50
ohms.

We then calculate the SWR on a 50-ohm line which is terminated by the
afore-mentioned input impedance.

RESULTS of calculation

MHz SWR Case 1 SWR Case 2
------ ----------------- ----------------
2 1.0002 1.0009
30 1.0028 1.0146
150 1.014 1.073
300 1.029 1.145
1000 1.105 1.524

It is seen that results do not become significant to a radio amateur, and
almost everybody else, until he has made the serious mistake of using the
wrong impedance connector, and the frequency has risen to 1000 MHz for
which
he hasn't an SWR meter anyway.

Below 300 MHz the results are submerged well beneath the uncertainty of an
SWR meter. Now we can take a balanced view of the situation.
----
Reg, G4FGQ


Reg,

I suspect your 1 inch length is overly pessimistic. Clearly, for an F
connector, it is more like 1/2 inch. Lastly, if the load at the end is not
50.0, then any small deviation in the feedline could just as well improve
things, as make it worse; this is probably not true for pulses or video.
Think of an antenna tuner. It does nothing to the SWR on the main piece of
line.

Tam/WB2TT