DG7YBN / 144 MHz / GTV 2-8w
  Last Update July 04th 2016




.......

     

Performance Data and Geometry
Pattern and VSWR
Download as File
Crossyagi - xpol configuration
Stacking


GTV 2-8w Yagi   with bent Driven Element

Wide-band version ... a "unconditionally stable" yet high G/T Yagi that shows least
degradation with wet elements or snow on and thus easy to reproduce parameters.

Yagis generally show a degradation in performance with wet elements. Which is due to
water film or drops hanging on the elements. Thus they appear thicker when wet. Which detunes
the Yagi both in gain and pattern as in SWR. The GTV 2-8w shows very little degradation for
its G/T. If you are looking for a Yagi suitable for worst weather condx ... this one might be it.

GTV 2-8w xpol built by Peter, DJ4TC, coaxes fed from rear

Return Loss plots of both planes with Yagi elevated by 30 degrees


→ Place mouse over images to enlarge

 

 
GTV 2-8w by Peter, DL1RPL and VNA plot on low pole; Geometry per table 2

Frequency modified GTV 2-8w (102-106 MHz) built by Hossein Khamooshi from the city of Gorgan, Iran for FM reception.
Boom and element holders are made from a wooden lace. Below: comparing against a 5 element design





This medium length Yagi is anchored around 144.3 MHz to produce guaranted G/T at a moderate
T_ant from 144.0 to 145.0 MHz. The bent DE (K6STI style) transforms from low impedance to 50 ohms
at feed point for direct feed.

An easy to reproduce Cross Yagi:
2 x or 4 x GTV2-8wx will do for even EME expeditions which may benefit from the Yagis stability if
mounted on a short mast with the reflectors only a few feet above ground.

Wet weather degradation analysis by courtesy of UR5EAZ:

1). G/T DRY (40.8 deg x 46.6 deg; 2.98m x 2.63m; DielC=1; Thk=0mm).
Results of Tant: 233.9K; 3.6K; 234.6K; -4.45dB

2). G/T WET Degradation: (2.98m x 2.63m; DielC=8; Thk=0,1mm).
Results of Tant: 233.3K; 4.0K; 234.3K; -4.4dB (!)

- Very good stab.[ility] of the antenna!
- Very good pattern!
- Good VSWR.

Владимир UR5EAZ.



Performance Data

                     Elem. 8 mm
Gain vs. isotr. Rad.  13.4 dBi
Gain vs. Dipole       11.2 dBD
-3 dB H-plane         40.8 deg.
-3 dB E-plane         46.6 deg.
F/B                  -27.8 dB
F/R                  -22.8 dB
Impedance               50 ohms
VSWR Band Width     1.12:1 *
Mechan. Length        3696 mm
Electr. Length        1.78 λ

Stacking Dist. h-pol.
top-to-bottom         2.63 m
side-by-side          2.98 m

*) as in VE7BQH G/T table = at 145.00 MHz


Geometry


4 mm elements - without BC, SBC added        
       Refl.    DE       D1       D2       D3       D4       D5      D6
Pos.   0        275      431      819      1466     2198     2984    3696
Lgth.  1030.2   992.2    973.6    953.8    930.2    914.6    898.0   868.2

4 mm elements insulated through boom BC:
Use DJ9BV BC numbers and nylon rivets on square boom as shown on BC-page

Corr. Tab. 2015-07-23
8 mm Elemente - without BC, but with SBC of 3.2 mm        
       Refl.    DE       D1       D2       D3       D4       D5      D6
Pos.   0        275      431      819      1466     2198     2984    3696
Länge  1023.2   989.2    958.2    937.2    910.2    893.2    875.2   845.2
	  
8 mm elements - on 20 x 20 mm boom with suitable BC and SBC
       Refl.    DE       D1       D2       D3       D4       D5      D6
Pos.   0        275      431      819      1466     2198     2984    3696
Lgth.  1027.1   993.1    962.1    941.1    914.1    897.1    879.1   849.1	  

Applies to all diameters				
SegmentationBC = +3.2 mm = (144.9 MHz - 144.35 MHz) * 5.85 mm/MHz
BaseBC (20x20) = +3.9 mm for semi-insulated on boom
Total          = +7.1 mm				
Note: element lengths for Ø 8 mm fit 5/16" too
The Drivers diameter is 10 mm for all examples. Use EZNEC's Auto-Segmentation at 380 MHz.

Sketch of Driver Cell



Note: The tips of the bent dipole in many cases have to be brought more straigth, towards D1, by up to approx. 20 ... 30 mm.
Connect the Yagi to a VNA or SWR meter and adjust bending angle for best Return Loss.

  • Bent DE Online Calculator as web app



Table 1: "Ready to saw and drill" data for mounting 4 mm elements insulated through 20 x 20 mm boom using DL6WU including a 30 mm offset from booms end:

Table 2: "Ready to saw and drill" data for XPOL Yagi - mounting 8 mm elements on 25 x 25 mm boom with insulators as sold by Konni, Nuxcom, WiMo using DG7YBN BC:








Pattern and VSWR Plots

Elevation and Azimuth plot at 144.1 MHz

 


RL and SWR plot - simulated / 144 - 145 Mhz


RL and SWR plot - simulated / 140 - 150 Mhz


Gain, F/B and F/R plot - simulated










Downloads

EZNEC file of this Yagi with 4 mm elements  

EZNEC file of this Yagi with 8 mm elements  

EZNEC file of this Yagi as xpol with 8 mm elements on boom 25 x 25 mm  

EZNEC file of the 4 Yagi Bay  


An array of 8 x GTV 2-8wx for tropo and EME  









Cross Yagi / X-Pol = GTV 2-8wx

on boom 25 x 25 mm: offset of element plane from centre is:

25 mm x 0.5 = 12.5 mm
plastic insulator clearance is 1.7 mm
half element diameter = position of wire in NEC = 8 mm x 0.5 = 4 mm
=> total offset = 12.5 + 1.7 + 4 = 18.2 mm => simulation carried out with 20 mm


on boom offset: second (vertical plane) = -80 mm



Performance Data

Gain vs. isotr. Rad.  13.36 dBi
Gain vs. Dipole       11.2 dBD
-3 dB H-plane         43.6 deg.
-3 dB E-plane         43.6 deg.
F/B                  -27.8 dB
F/R                  -25.5 dB
Impedance               50 ohms
VSWR Band Width     1.11:1 *
Mechan. Length        3776 mm

Stacking Dist.
top-to-bottom         2.80 m
side-by-side          2.80 m

*) as in VE7BQH G/T table = at 145.00 MHz

Pattern plot SWR plane 1 and SWR plane 2

  This array is 7.50 x 2.50 m in summed up stacking distances. Gain = 21.8 dBi ex. phasing lines. See Download Area









Stacking



Stacking Dist.    DL6WU Formula
H-plane               2.630 m
E-plane               2.984 m


Elevation and azimuth plot and data of 4 Yagi bay using DL6WU stacking distances

 

TANT screenshot


Gain vs. isotr. Rad.  19.3 dBi
Gain vs. Dipole       17.1 dBD
-3 dB H-plane         18.2 deg.
-3 dB E-plane         21.0 deg.
F/B                  -30.5 dB
F/R                  -28.9 dB
T_los                  3.4 K
T_ant                234.6 K*
G/T                  -4.45 dB*
Theoretical numbers, no phasing line losses
nor imperfections caused by H-frame included
*) T_sky = 200 K, T_earth = 1000 K as in VE7BQH G/T table





73, Hartmut, DG7YBN


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