Stacked 5-El.-2-m-Yagi, 25 Ohm

Two Versions of stacked 25-Ohm-Yagis (1,80 m and 2,00 m Boom)

The picture left shows shows the 4x5-Element-25-Ohm-Yagis with 2-m-boom and a stacking distance of 2,30 m. Two Yagis are connected together with Aircell-5 transformations lines, the two groups are coupled with a power-splitter as described on the "stacking page".

The Yagi-array handles 1 KW HF without any problems and was used for a test in the Alpe-Adria-Contest 2010. The array works excellent with a very good antenna pattern. The measured SWR of the complete group in the common feeding point is <=1,1 beween 144,0 and 144,8 MHz.

At not very good band conditions QSOs from central Germany (450 m ASL) to middle Italy were possible, distance 800- 1000 km.

The Yagis on the picture are built with 8-mm-elements.

The lowest antenna is 6 m above ground, with groundgain you can get 20 dBd gain! The Elevation angle is only 3°, the 3-dB-angle vertical is also only 2,8°. Plots below!

Version 1:

The stacked

5-Element- 25-Ohm-

2-m-Yagi, Boom 180 cm

Gain of each Yagi is 8,8 dBd, F/B 23 dB

3-dB-angles hor = 49,6°, ver = 61,6°

Gain of the stacked array 11,5 dBd

3-dB-angles hor = 50,0°°, ver = 25,4°

Stacking distance is 2,20 m

With two Yagis of 25-Ohm-impedance an easy stacking is possible. We need two pieces of 5/4-λ-coax-cable with 50 Ω. The 25 Ω at XX are transformed to 100 Ω at XX.

With both cables L1 and L2 parallel we get the 50 Ω for the cable to the TRX. The first 45 cm of the 175,5 cm long pieces are wound to a coax-choke for surpressing common mode currents. The two chokes are in the radiator-box, we do not need coax sockets and connectors.

The left picture shows the choke,here are 45 cm of the coax wound on a 25-mm-PVC-tube. The right picture shows the 2x50-Ohm resistors (1/2%) parallel. With both chokes and two resistors of 25 Ohm, length of 2x2,04 m Aircell-5 the SWR is 1,0. Between 144,0 and 144,5 MHz the impedance is 50 +/- j 0 Ohm.

First I started with a length of 213 cm (5/4-lambda * V = 0,82). But this was to long (frequency to deep below 144 MHz). Then I cut the ends in the connection box until the resonance is exactly as you see in the picture of the analyzer. It may be that the individual coax cables differ from the calculated length, therefore a preliminary measurement is very important!

On 143 MHz R= 49 - j 5 Ohm, on 146 MHz R= 51 + j 5 Ohm, the impedance with an analyzer is shown down:

Element	Position	6 mm	4 mm	3,2 mm	2,4 mm
Reflector	0 mm	1032 mm	1034 mm	1037 mm	1040 mm
Radiator	355 mm	993 mm (6 mm)	998 mm	998 mm	998 mm
Director 1	640 mm	950 mm	959 mm	963 mm	968 mm
Director 2	1240 mm	929 mm	939 mm	944 mm	949 mm
Director 3	1780mm	896 mm	907 mm	912 mm	919 mm

Version 2:

The stacked 5-Element- 25-Ohm-2-m-Yagi, Boom 200 cm

Gain of each Yagi is 9,1 dBd, F/B 27 dB

3-dB-angles hor = 47,2°, ver = 56,8°

Gain of the stacked array 12,1 dBd

3-dB-angles hor = 47,8°, ver = 24,2°

Stacking distance is 2,30 m

Element	Position	8 mm	6 mm	4 mm	3,2 mm	2,4 mm
Reflektor	0 mm	1036 mm	1040 mm	1040 mm	1042 mm	1044 mm
Radiator	345 mm	978 mm	982 mm	989 mm	988 mm (4mm)	988 mm (4 mm)
Direktor 1	735 mm	926 mm	934 mm	945 mm	948 mm	953 mm
Direktor 2	1410 mm	922 mm	930 mm	942 mm	944 mm	950 mm
Direktor 3	1970mm	891 mm	898 mm	908 mm	914 mm	920 mm

Details	2-El.-2m	3-El.-2m	4-El.-2m	5-El.-2m	6-El.-2m
7-El.-2m	7-El.-70cm	9-El.-70cm	10-El.-70cm	12-El.-70cm	14-El.-70cm