Performance Data and Geometry
Details of GTV70-19 by ZS6JON
Pattern and VSWR
GTV 70-19m Yagi with bent Driven Element
EME + SSB band, with some loss usable for FM up to 435 MHz
Slideshow: 4 x GTV 70-19m 'Blade Dipole' built by John, ZS6JON
as a vertical polarised 4 Yagi bay for EME
'Blade' Dipole (basically K6STI style but modified with straight middle section and 2 dimensional geometry)
Ele. 8 mm Ele. 6 mm Gain vs. isotr. Rad. 17.8 dBi 17.8 dBi Gain vs. Dipole 15.7 dBD 15.7 dBD -3 dB H-plane 25.0 deg. = -3 dB E-plane 26.0 deg. = F/B -31.9 dB -31.5 dB F/R -29.6 dB -29.4 dB Impedance 50 ohms = Mechan. Length 4116 mm = Electr. Length 5.94 λ = Stacking Dist. h-pol. top-to-bottom 1.54 m side-by-side 1.60 m
The 6 mm and 8 mm element fit On-Boom-with-Standard-Insulators style of building.
Segmentation BC and Base BC (see below) must be added.
A simple symmetrising member may be made from a 3 x 1/4 Lambda line grounded at the far side with
N-flange-bushing and an aluminium plate and ferrite added as close as possible to the DE, see below.
An Imperial Measures Version
<= NEC Geometry for elem. mounted through boom builds
3/16 in = 4.763 mm ele. insulated through boom with SM5BSZ BC:
"Ready to saw and drill" data for mounting elements on boom with standard insulators on 1 x 1 inch boom including a 40 mm offset from boom ends:
Further details: boom thickness = 1/16 in = 1.6 mm, holes in boom Ø 7.5 mm, added SBC = 1.83 mm (real SBC plus 0.7 mm for insulators)
Metric Measures Versions for On-Boom-Insulators
<= NEC Geometry 6 mm ele. semi-insulated on boom ex. BC
"Ready to saw and drill" data for mounting elements on boom with standard insulators on 20 x 20 mm boom including a 30 mm offset from boom ends:
<= NEC Geometry 8 mm ele. semi-insulated on boom ex. BC
The Drivers diameter is 10 mm for all examples.
Use EZNEC's Auto-Segmentation at 1050 MHz.
Sketch of Bent Dipole
Details and Return Loss plot of the GTV 70-19m built by ZS6JON
see how the Blade Dipole and its mounting plate are milled
Return Loss without any fine tuning -40 dB @ 432.14 MHz = VSWR = 1.02, Z = 51.0 + 0.2 ohms
and falling towards 432.40 exactly as simulated. Well done John, ES tnx for the photos!
VE7BQH comments: "I certainly am pleased with the confidence factor both in BC.exe and use of the correct segment ratio".
Steps to this achievement:
(1) the application of the through Boom Correction BC.exe, which is SM5BSZ's work,
(2) the YBN Segementation Correction (SBC) is in place,
(3) the plastic insulators influence is taken into account,
(4) the elements are cut to the 10th of a millimetre with help of a calliper gauge,
(5) the 3/4 λ line is trimmed accurately using a VNA
(6) the tolerant 'Blade Dipole' - here we go ...
And with a little honing: Return Loss (S11) - 51 dB @ 432.07 MHz on an Anritsu S332E Sitemaster
Smith Chart of Impendance full 70 cm band 10 MHz sweep: Z = 49.8 + 0.07 ohms @ 432.07 MHz
Pattern and VSWR Plots
Elevation and Azimuth plot at 432.1 MHz
SWR and Return Loss plots - simulated with 4nec2
Real Return Loss plot (Planar TR1300 VNA - Yagi by DG7YBN with 'Blade Dipole')
Elem. 4 mm: EZNEC file of this Yagi
Elem. 6 mm: EZNEC file of this Yagi
Elem. 8 mm: EZNEC file of this Yagi
4nec2 file of this Yagi as a 4 bay (8 mm) copy nec table from page using CTRL + A, save as .nec and open in 4nec2.
Drawing of this Yagis 'Blade' Dipole in 2 mm aluminium sheet metal
Sketch of Blade DE on Boom
a = 30; b = 104.5; c = 48.5; d = 93 mm
As on the 432 MHz Band the Y-factor = T_earth / T_sky is that high I see little chances in
bettering an array's RX performance by using "Over Stacking" distances. However, depending
the level of local QRM it might be worthwhile to try less distance, especially in H-plane.
Stacking Dist. h-pol. DL6WU top-to-bottom 1.54 m side-by-side 1.60 m
Elevation and azimuth plot and data of 4 Yagi bay using DL6WU stacking distances
Gain vs. isotr. Rad. 23.7 dBi Gain vs. Dipole 21.5 dBD -3 dB H-plane, appr. 11.5 deg. -3 dB E-plane, appr. 12.1 deg. F/B -37.7 dB F/R -29.6 dB T_ant 29.5 K* G/T 8.98 dB* Theoretical numbers, no phasing line losses nor imperfections caused by H-frame included *) T_sky = 20 K, T_earth = 350 K as in VE7BQH G/T table
Symmetrising 50 to 50 ohms Feedline to 432 MHz Bent DE
The principle is similar to the 1/4 Lambda coax. Adding 2 x 1/4 Lambda or a half wave line does not change anything but allows
to form a gentle bow below the boom or until behind the Reflector. Follow practical construction hints on "Building a Yagi" page.
Attenzione! Take care when lengthening the coax, measure the right length instead of refering to given v-factors only.
A good choice may be the diam. 5 mm PTFE coax RG-142 B/U: real resonate length (432.2 Mhz as 3/4 Lambda) shield-shield is around 348 mm
Find more information on Phasing & Matching Lines page
73, Hartmut, DG7YBN