DG7YBN / 432 MHz / GTV 70-18m
  Last Update Aug 27th 2021




.......



Performance Data and Geometry
Pattern and VSWR
xpol
Stacking
Matching


GTV 70-18w Yagi   with bent Driven Element

Wideband version covering the full 70 cm band with nice G/T at EME & SSB part of band


This Yagi has very low back lobes for its length. It may serve as single antenna for portable
use and certainly make a useful 4 x vertical stack. It makes a quiet contest antenna due to its
high F/B. The bent DE (K6STI style) transforms from approx. 17 ohms to 50 ohms at feed point.
This Yagi is based on the GTV 2-18w design. Date of issuing this design: 22nd of Aug. 2021

Current distribution

3D Pattern








Performance Data

Specs: with 8 mm elements @ 432.1 MHz

Gain vs. isotr. Rad.  17.6 dBi
Gain vs. Dipole       15.4 dBD
-3 dB E-plane         25.8 deg.
-3 dB H-plane         26.8 deg.
F/B                  -33.5 dB
F/R                  -30.1 dB
Impedance               50 ohms
Mechan. Length        3969 mm incl. 2 x 40 mm stand off
Electr. Length        5.61 λ

VSWR Bandwidth        1:1.08 (as in VE7BQH Antenna Table)

Stacking dist. h-pol.
top-to-bottom         1.51 m or 4.95 ft
side-by-side          1.57 m or 5.14 ft


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Geometry



Ø8 mm Elements - On Boom - Dimensions (BC acc. DG7YBN)

Ele. 8.0 mm
DE 10 mm
Boom 20 x 20 mm


"Ready to saw and drill" data for mounting elements on boom with BC according DG7YBN for standard insulators as sold by WiMo, Tino's Funkshop, 7arrays, HF-Kits.nl:

Includes an SBC of 1.14 mm





Ø8 mm Elements - On Boom - Dimensions (BC acc. DG7YBN)

Ele. 8.0 mm
DE 10 mm
Boom 25 x 25 mm


"Ready to saw and drill" data for mounting elements on boom with BC according DG7YBN for standard insulators as sold by WiMo, Tino's Funkshop, 7arrays, HF-Kits.nl:

Includes an SBC of 1.14 mm






        

Table 2: GTV 70-21n, 4 mm elements through boom:




"Ready to saw and drill" data for mounting elements through boom with BC according SM5BSZ's BC.exe:
Note: with through Boom BC it is important to stick to the boom end offsets given below!




Metric Boom 20 x 20 x 2 mm

Boom shape: square
Boom dim: 20 x 20 mm
Wall thickn.: 2.0 mm
Holes in boom: 6.0 mm
Offset rear: 40 mm
Offset front: 40 mm
 



Note: with through Boom BC it is important to stick to the boom end offsets given below!






Metric Boom 25 x 25 x 2 mm

Boom shape: square
Boom dim: 25 x 25 mm
Wall thickn.: 2.0 mm
Holes in boom: 6.0 mm
Offset rear: 40 mm
Offset front: 40 mm
 



Note: with through Boom BC it is important to stick to the boom end offsets given below!






Imperial Boom 1"

Boom shape: square
Boom dim: 1 x 1 inch
Wall thickn.: 1.6 mm
Holes in boom: 6.0 mm
Offset rear: 40 mm
Offset front: 40 mm
 


Note: All the above include a "Segmentation Density Correction" (SBC) of 1.14 mm plus an offset of 0.70 mm per element = 1.84 mm
for compensation of the insulators (7arrays.com ) as shown above in combination with SM5BSZ'S BC.exe values.

Note: with through Boom BC it is important to stick to the boom end offsets given below!

Read abt. the SBC here .







For making of a 'Blade Dipole' which I recommend for elements through boom builds

Sketch of Bent Dipole










Radiation Pattern and VSWR Plots

Elevation and Azimuth plot at 432.1 MHz (8 mm ele.)

 



Elevation and Azimuth plot at 435 MHz (8 mm ele.)

 



Elevation and Azimuth plot at 439 MHz (8 mm ele.)

 


VSWR and Return Loss plots - simulated with 4nec2

Wide Return Loss plot of 4 mm version - simulated with 4nec2










This Yagi as XPOL 435 MHz Version



EZ/AZ Plot (4 mm ele.):



h/v-plane offset = 680 mm,
Stacking per DL6WU h/v mean dist. = 1.54 m



This Yagi with 4 mm elements through a 25 x 25 mm boom Metric Boom 25 x 25 x 2 mm

Boom shape: square
Boom dim: 25 x 25 mm
Wall thickn.: 2.0 mm
Holes in boom: 6.0 mm
Offset rear: 40 mm h-plane,720 mm v-plane
Offset front: 720 mm h-plane, 40 mm v-plane
 



Note: with through Boom BC it is important to stick to the boom end offsets given below!

Includes an SBC of 1.84 mm








Stacking

As on 432 MHz the Y-factor = T_earth / T_sky is so high, I see little chances to
improve an array's RX performance by using "Over Stacking" distances. However, depending on
the level of local QRM it might be worthwhile to try a decreased distance, especially in the H-plane.

Stacking Dist.    DL6WU Formula
H-plane               1.51 m or 4.95 ft
E-plane               1.57 m or 5.14 ft


A 4 Yagi bay



Elev. Plot


Azim. Plot


4 bay data (8 mm ele.):

Gain vs. isotr. Rad.  23.5 dBi
Gain vs. Dipole       21.3 dBD
-3 dB H-plane, appr.   5.8 deg.
-3 dB E-plane, appr.   5.8 deg.
F/B                  -34.0 dB
F/R                  -30.1 dB
T_ant, total          61.8 K*
G/T                   5.56 dB*

at Tsky = 27 K, Tearth = 1800 K as in newer VE7BQH Antenna Table


3D pattern plot with 4nec2's 3D viewer


Antenna G/T with AGTC lite VBA-version:

at Tsky = 27 K, Tearth = 1800 K as in newer VE7BQH Antenna 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 actual electrical length instead of considering v-factors specified in a catalogue 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


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