In message , Channel Jumper
writes

W5DXP;799379 Wrote:
On Friday, December 7, 2012 9:17:13 AM UTC-6, JIMMIE wrote:-
I am looking for tutorial information on cutting coaxial cables to
various electrical phase lengths.-

Do the cables always have an SWR of 1:1, i.e. are they always flat? If
not, the cable will also transform impedances which adds another
dimension to the complexity.

You are over thinking the problem at hand.

The purpose of the phasing cables is to put the two antenn'a in phase
with each other.

You may not want the two antennas to be in phase. It would be more
generally correct to say that a phasing cable puts the phase of one
antenna to what it needs to be with respect to another.

You don't tune the antenna with the coax - you tune it with the antenna
matching unit.

If the feed impedance of the antenna itself is not the same as the coax,
the length of the coax will affect the tuning of the 'antenna system' -
ie antenna plus feeder - ie what the transmitter sees.

Once the antenna is tuned - the length of the coax is the matching unit.

Only if 'tuned' equals 'matched' - otherwise the length of the coax will
affect the impedance seen at the transmitter end (or at some
intermediate point, if that is relevant to what you're doing). And, of
course, regardless of matching, the length of the coax will also affect
the phase of the RF reaching the antenna.

To answer the question, except for very low frequencies, the
characteristic impedance of coax itself should be 'flat' (having a
constant characteristic impedance at all frequencies). If it is
terminated by its characteristic impedance, it will have no standing
waves on it. Usually, standing waves are considered a 'bad thing', but
if a short length of coax is used to transform one impedance to another,
there are bound to be standing waves on that particular piece of coax.
However, as the length of the transforming coax is typically a
quarterwave, mismatch losses are pretty negligible.





--
Ian