Building phased cable
 

I am looking for tutorial information on cutting coaxial cables to various electrical phase lengths. I have directional couplers for the VHF and UHF bands I am concerned with and also access to a vector voltmeter. I am proficent in terminating cables with connectors but realizing there is more than one way to skin a cat and would also welcome input on assembling the cables..I am not looking to open a discussion on this but discussion would be welcome. Instead I am desiring direction to a website that has a tutorial on the subject.

TIA
Jimmie

Building phased cable
 

On Fri, 7 Dec 2012 07:17:13 -0800 (PST), JIMMIE
wrote:

I am looking for tutorial information on cutting coaxial
cables to various electrical phase lengths.

http://www.belden.com/pdfs/Techpprs/Wireless%20Market%20Web%20Phase%20Paper.pdf

I also used to use a slotted line for generating a phase reference at
RF frequencies. It's then just a matter of comparing your cut coax
phase shift with that from the slotted line. A telescoping coax cable
section might also work, but I've never tried it. Accuracy was kinda
low, but good enough for what I was doing.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Building phased cable
 

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 don't tune the antenna with the coax - you tune it with the antenna matching unit.
Once the antenna is tuned - the length of the coax is the matching unit.

Building phased cable
 

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

Building phased cable
 

On Friday, December 7, 2012 10:17:13 AM UTC-5, JIMMIE wrote:
I am looking for tutorial information on cutting coaxial cables to various electrical phase lengths. I have directional couplers for the VHF and UHF bands I am concerned with and also access to a vector voltmeter. I am proficent in terminating cables with connectors but realizing there is more than one way to skin a cat and would also welcome input on assembling the cables.I am not looking to open a discussion on this but discussion would be welcome. Instead I am desiring direction to a website that has a tutorial on the subject. TIA Jimmie

OK, the best info I got was to play with a few cable samples and test equipment like I was going to use before building the cable. See how phase changes responds to trimming. There doesnt seem to be as much "magic" and "art" to it as some have claimed. Heliax with compression fittings make the job easy.

Jimmie