Performance Data and Geometry
Pattern and VSWR
Download as File
Crossyagi - xpol configuration
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, rebuilt to route the 1/4 wl lines out rearwards which results in clearer VSWR
Return Loss plots of both planes with Yagi elevated by 30 degrees
GTV 2-8w by Peter, DL1RPL
→ Place mouse over images to enlarge
Philippe, F4GRT built a GTV 2-8w self modified to 145 MHz with polarisation rotator
See the mechanism in action:
GTV 2-8w modified for FM Radio built by Hossein Khamooshi
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.
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
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" tooThe 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
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
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
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 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
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