David first let me comment that using lossy coax to make the results
look better is muddy thinking at best... Use the lowest loss feed line
you can get, period!

Next, check the ARRL Antenna Handbook for a diagram of the equipment
and layout for cutting coax to resonance at a given frequency... I have
not worked at GPS frequency but the basics are the same at 435 mhz -
just harder at the higher frequencies...
A signal generator for driving the coax... Put a 3dB pad on the output
of the generator to stabilize the impedence it sees... At the load end
of the coax is a resistive load for terminating the coax in its
characteristic impedence... An oscilloscope pick up across the load for
seeing amplitude and phase... I normally drive the coax at a frequency
that makes that coax length an odd 1/4 wave at the test frequency...
Then I trim the coax for the voltage minimum...
As far as phase batching the the individual coax pieces after they are
cut to frequency I would pick one coax piece as the master..
I would put a splitter on the output of the generator and drive this
master coax from one side of the splitter and also drive a test coax
off the other side of the splitter... At the load ends of the of the
coax pair I would use a dual channel oscilloscope. or vector meter,
etc., to compare phase between the load on the end of the master coax
and test coax, repectively......

Now, having said that let me comment that unless you are using hard
coax, I suspect at GPS frequencies just routing two flexible coax
cables around the innards of a piece of electronic gear will introduce
enough internal mechanical distortion to cause phase variations at the
load ends... I may be wrong but that is my suspicion..

denny / k8do


David wrote:
Can anyone post any informationon or web addresses on phase matching and
batch / set matching of coax cables? I am interested in principles and
procedures to phase match coax cables. Phase matching involves cutting coax
cables to the same electrical length. The phase matched cables can then be
analysed and put into batches or sets i.e. cables with similar
characteristics and frequency response are put into a set. What would be
analysed to form a set?

This practice is used on coax cables that feed antennas for satellite
systems. For example, if several antennas receive GPS signals, to
triangulate position, the GPS signals must all arrive at a particular point
at exactly the same time.

It also appears that going for the best quality low loss cable can actually
be worse, because using lower quality coax cable with some loss can dampen
the reflections from in-line connectors.

Stages are 1) phase matching 2) batch matching 3) assemble cables chosen by
batch matching process onto RF system and perform vector generation. A
vector gen file is created which is a calibration snapshot of the system
i.e. records the RF performance in the form of a signature or footprint.

Measuring instrument is a Network Analyser HP8753.