Callsign

1. Ham Member
Join Date
Apr 2009
Location
Clearlake Oaks, Ca
Posts
3

## stacking harness info

A need to construct a stacking harness for 2 horizontally stacked Cushcraft A449-11 yagis separated by 1 wavelength at 445 Mhz. Can anyone give me the lengths and type of coax for the harness I will need to match to 50 ohm coax? Thanks ( the antennas are vertically polarized.)

Bill WA7FBU

2. Ham Member
Join Date
Jan 2000
Posts
33,395
You are going to have to use 75 ohm coaxial cable as the harness. Because of the spacing they are going to have to be 3/4 wavelength long. I would suggest using RG59/U cable and true RG59/U has a velocity factor of 0.66. Thus, calculate the wavelength at the desired frequency and then multiply by 0.75. This will give you the length of the 3/4ths wavelength. Then multiply by the velocity factor which, in the case of true RG59/U coax is 0.66. This will be the length of the phasing lines. If that is too short to go between the antennas then use 5/4ths wavelength lines. Start with the same figure as the wavelength above but multiply by 1.25. Then multiply by the velocity factor.

Connect the phasing line directly to the driven element and then connect the other end to a "T" connector. Basically, the phasing line converts 50 ohms at the driven element to 100 ohms. Then, when you put the two 100 ohm lines in parallel you get back to 50 ohms.

Glen, K9STH

3. Ham Member
Join Date
May 2007
Location
Etna PA
Posts
2,858
There is an easier way than cutting all those wavelengths of 50 and 75 Ω cable.

Build yourself a 2 way power divider out of Tubing. Then, the 2 coax cables to the 2 antennas can be ANY EQUAL length.

Phasing errors in a horizontal stacking arrangement will skew the radiation pattern left or right. Errors in a vertically stacked array will skew the pattern up into space, or down into the ground.

Rege

4. Ham Member
Join Date
Jan 2000
Posts
33,395
3V:

The lengths of the 50 ohm cables still have to be of equal length. That is from the power divider to the antennas. Otherwise, you will have variations in the phasing and that will skew the pattern just as errors in the phasing lines.

Phasing lines are, in general, easier for the average amateur radio operator to construct as well as generally being less costly.

Glen, K9STH

5. If WA7FBU is still reading and interested, I have a 2-way 70cm power divider that covers 430-470 MHz perfectly and is 50 Ohms per port, already built and tuned. Insertion loss measures 0.0 dB at 450 MHz. It's aluminum outer tubing and copper inner conductor, with three type N connectors.

If you use something like this, all you need to do to feed each antenna is cut two pieces of 50 Ohm coax that are exactly the same length, and reach from the divider to each antenna connector.

BTW, optimum spacing for the A449-11 is more than one wavelength. I'd use 40" separation to achieve maximum gain, if that's the goal.

WB2WIK/6

6. Good article on Power Dividers. Thanks for posting that link.

Speaking of links, does anyone have any links to companies that sell small quantity copper or brass that would be used in a project such as this?

7. Ham Member
Join Date
Jan 2000
Posts
33,395
Yep! McMaster-Carr sells such and, frankly, the metal that I purchase from them costs less including shipping than purchasing it locally in small quantities.

http://www.mcmaster.com/#

Glen, K9STH

8. Ham Member
Join Date
Apr 2009
Location
Clearlake Oaks, Ca
Posts
3
WB2WIK - I would be interested in your power divider, although funds are pretty tight for me right now. I had planned to build the coax type phasing harness as I have some of the parts I need. Thanks for the info. If you like, you could email me at bnj@kozt.com

73's
Bill WA7FBU
Last edited by WA7FBU; 05-01-2009 at 06:09 PM.

9. Ham Member
Join Date
Jan 2000
Posts
33,395
HDU:

I ordered the aluminum square stock and a section of 1/4th inch OD copper pipe from McMaster Carr this afternoon. They are in 6 foot lengths. The cost for the pipe was \$5.94 and for the 1 inch by 1/8th inch thick square stock was \$16.83. Unfortunately, they don't stock tubing with a 11/32 OD.

Glen, K9STH

10. Originally Posted by K9STH
Yep! McMaster-Carr sells such and, frankly, the metal that I purchase from them costs less including shipping than purchasing it locally in small quantities.
Thanks, Glen. Good link to keep in the bookmarks.

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