Saturday, January 4, 2014

2m Lightweigth 4 Element Yagi

Lightweight 4 Element Yagi for 144.3MHz


Materials and description

The choice of the materials used should be a compromise between weight and robustness. So this ended up at 1.4mm stainless steel rods and 11mm PE installation tubing as used by electricians. For the beam to be portable, it is convenient to spit the boom into two pieces. The ideal solution (in my mind) is to used the ends for the middle of the boom, as they are already made to stick into eacs other. I drilled a whole through the joint boom at the overlapping region. One now can kill two birds with one stone by impaling the yagi at this specific drilling to hold the boom parts together and the antenna to the sky (see sketch). The elements sticked through drillings in the boom and fixed by hotglue. The driven element is tuned by sliding the rods in and out, until matched. Fixed then by luster terminals. The driven element is built similarly to the 3-element-yagi presented in the ARRL handbook 2000.


Dimensions

 
 Element  Material  Dimensions   Dist. to reflector 
 reflector  1.4mm steel rod  1035mm  0mm
 driven element   1.4mm steel rod  2x50mm  416mm
 1st director  1.4mm steel rod  936mm  831mm
 2nd director  1.4mm steel rod  926mm  1290mm
 boom 1  11mm PE tubing   700mm     --
 boom 2  11mm PE tubing   700mm     --

Simulation

The dimension of the driven element was measured after SWR-tuning. The construction allows easy tuning as the element is fixed using a luster terminal. -------------------------------------------------------------------------------
YAGIMAX 3.0 CALCULATION OF 4 ELEMENT YAGI
ULTRA LIGHT YAGI AS BUILT
07-20-2000
13:37                                                      FILE: DL1GSJ_R.INP
-------------------------------------------------------------------------------
ELEMENT:      LENGTH (Cm.)  SPACING FROM REF. (Cm.)     ELEMENT DIA. (Cm.)
Reflector:        103.5000                   0              0.14000
Driven Ele.:       99.0000             41.6000              0.14000
Director #: 1      93.6000             83.1000              0.14000
Director #: 2      92.6000            129.0000              0.14000
-------------------------------------------------------------------------------
Normalized Radiation Resistance at 144.300 mHz is  55.71 Ohms
-------------------------------------------------------------------------------
FREQ (mHz)    GAIN (dBi)     F/B (dB)      IMPEDANCE (ohms)       VSWR
144.000         9.09          12.04         49.69+j14.17          1.04
144.050         9.09          12.07         49.89+j14.43          1.03
144.100         9.09          12.09         50.09+j14.69          1.03
144.150         9.10          12.12         50.29+j14.94          1.02
144.200         9.10          12.15         50.48+j15.19          1.01
144.250         9.10          12.17         50.67+j15.44          1.01
144.300         9.10          12.20         50.86+j15.68          1.00
144.350         9.10          12.23         51.05+j15.92          1.01
144.400         9.10          12.25         51.24+j16.15          1.01
144.450         9.10          12.28         51.43+j16.38          1.02
144.500         9.10          12.31         51.61+j16.61          1.02
144.550         9.10          12.33         51.79+j16.83          1.03
144.600         9.10          12.36         51.97+j17.05          1.04
144.650         9.10          12.39         52.15+j17.26          1.04
144.700         9.10          12.42         52.32+j17.47          1.05
144.750         9.11          12.45         52.50+j17.68          1.05
144.800         9.11          12.48         52.67+j17.88          1.06
144.850         9.11          12.51         52.83+j18.08          1.06
144.900         9.11          12.54         53.00+j18.27          1.07
144.950         9.11          12.57         53.16+j18.46          1.07
145.000         9.11          12.60         53.32+j18.64          1.08
-------------------------------------------------------------------------------

Photo

Yagi-Uda antenna held in the evening sky of Hamburg

yagi in operation

Experience

Immediately after tuning the antenna went into the sky. Fortunately it was weekend, so that a few station were operating 2m SSB. Good reports and a good directional effect made me believe the antenna is worth to be presented. Without having planned to do so, I made several QSOs during the scandinavian activity contest with 10W pep RF output. Like the magnetic loop for 2m the beam is lifted in a hight of 3-4m above the roof. For sure this does only work when there is no wind, as the beam sticks to the telescopic mast where this is 4mm in diameter only.

No comments:

Post a Comment