|Stacking with Coax||Stacking with Power Splitters|
Stacking with Coax Cables as Transformation Lines (DK7ZB)
The stacking cables are made of odd multiples of λ/4-coax-cables (3/4-, 5/4- or 7/4-λ). They use the transformation attribute of an electrical quarterwave-line. This can be a coax-cable or power splitter. Here we work with the simple method (a good way for shortwave, 6m and 2m), described below:
ZE = Z2 / ZA
ZE = Impedance of the output
ZA = Impedance of the antenna, in most cases 50 Ohm
Z = Impedance of the matching line with a length off odd multiples of λ/4
Example for stacking two Yagis:
The pieces L1 and L2 are the quarterwave matching section, they must rise the 50 Ohm of each antenna to 100 Ohm at the connection point, because both resistances in parallel give the wanted 50 Ohm for the coax to the station.
With the formula above, the matching line must have an impedance of 70,7Ohm. There is no cable with that impedance, therefore we use 75Ohm-coax, which is customary at the trade. The additional SWR for the mismatch is < 1,15,
V=Velocity of propagation, depends on the dielectric attribute of the cable, e.g.
PTFE V = 0,71
Foam-PE V = 0,8-0,85
In the upper picture both lengths l1 and l2 must have exactly the multiples of 3/4-, 5/4- or 7/4-lambda*V. If the V is not correct, the failure will be multiplied.
If you use longer stacking cables for Longyagis, it is better to use the method shown right. Two cables l1 and l2 with any but same length of 50Ohm coax will give a Z=50Ohm at the connection point. One piece of lambda/4-75Ohm-cables will give the 50Ohm for the feeding.
Martin, OK2FKF has stacked his 2x7-El.-28Ohm-group with this principle. Picture at Czech VKV activity 10/07 in JO70UQ in 1370m ASL. Jim, OK2GTI winning this competition with these antennas and stacking method. Congratulation!
Waterproof mounting of the stacking cable for 2x2m-Yagis (2x9-El.-28Ohm)
by Mark, CT1FJC
The white cables are 75-Ohm-CATV-coax, the black coax has 50Ohm to the station
Stacking cable for portable use with BNC-connectors
2x103,5cm RG-59B/U (MIL)
2 x 3/4-λ for 144,3 MHz
2 x 9/4-λ for 432 MHz
suitable for both bands!
Stacking of 4 Yagis
The first example is a method for a stacked array of 4 Yagis in the vertical plane.
All cables are of 75-Ohm-coax, which has lower losses than 50-Ohm-coax with the same diameter. All impedances at the connection points are marked blue.
L1 = 5/4-λ*V
L2 = 5/4- or 7/4-λ
The "plumbers delight"-construction of the connection point for high power. Simple, but electrical with high efficiency. The braid is sold together with copper fittings, the inner conductors have short leads.
This is a picture of the stacking harness by
in his EME-Yagi-array
The best method for combining 4 Yagis in a H-configuration
L1 = any length 50-Ohm-coax (recommended: λ/2 * V)
L2 = λ/4 * V 50-Ohm-coax
At the points X we have an impedance of 25 Ohm (2x50 Ohm parallel)
At Y the quarterwave matching line tranforms the 25 Ohm at X to 100 Ohm at Y, in parallel = 50 Ohm