DG7YBN / 432 MHz / GTV 70-8n
  Last Update Jan. 06th 2016




.......



Performance Data and Geometry
Pattern and VSWR
Download as File
Stacking
Diamond Stagger Stacking Crossover
Matching


GTV 70-8n Yagi   with bent Driven Element

EME + SSB narrow bandwidth version ... strictly G/T breeding


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.

Current distribution

3D Pattern




Performance Data

Specs: with 4 mm elements @ 432.1 MHz

Gain vs. isotr. Rad.  13.6 dBi
Gain vs. Dipole       11.5 dBD
-3 dB H-plane         38.8 deg.
-3 dB E-plane         44.0 deg.
F/B                  -24.9 dB
F/R                  -27.9 dB
Impedance               50 ohms
Mechan. Length        1334 mm incl. 2 x 30 mm stand off
Electr. Length        1.84 λ

Stacking dist. h-pol.
top-to-bottom         0.93 m or 3.04 ft
side-by-side          1.04 m or 3.43 ft


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Geometry





        

Table 1: GTV 70-8n, 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

This table is only valid for:
Boom shape: square
Boom dim: 20 x 20 mm
Wall thickn.: 2.0 mm
Holes in boom: 6.0 mm
Offset rear: 300 mm
Offset front: 40 mm

With 300 mm offset on rear boom end for effective formast mounting






Imperial Boom 5-8"

This table is only valid for:
Boom shape: square
Boom dim: 5/8 x 5/8 inch
Wall thickn.: 1.6 mm
Holes in boom: 6.0 mm
Offset rear: 300 mm
Offset front: 40 mm

Note: All the above include a "Segmentation Density Correction" (SBC) of 1.28 mm plus an offset of 0.70 mm per element = 1.98 mm.
for compensation of the insulators shown with the GTV 70-19m website. Note: Other insulators will need other offset,
with their length being probably the most important parameter for this. Thus I advise to cut other plastic insulators
to 7 mm each to match at least the length of the pilot insulators.

Read abt. the SBC here .




Same with 300 mm offset on rear boom end for effective formast mounting



In the download section you find a CSV file for the Yagi Element Configuration Tool of this Yagi with 4 mm elements
with you can use for own adaptions to variations of boom dimensions etc.

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 (4 mm ele.)

 


SWR and Return Loss plots - simulated with 4nec2
(I have settled the best Retrun Loss a bit higher for giving headroom in wet weather)



Gain, F/B and F/R 431 to 434 MHz










Downloads

EZNEC file of this Yagi with Ø 4 mm ele.  

EZNEC file of a 4 Yagi Bay with Ø 4 mm ele.  


CSV file of this Yagi with Ø 4 mm ele. for the BC-Excel









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               1.04 m
E-plane               0.93 m


A 4 Yagi bay




Elev. Plot


Az. Plot


Gain vs. isotr. Rad.  19.53 dBi
Gain vs. Dipole       17.38 dBD
-3 dB H-plane, appr.  17.4 deg.
-3 dB E-plane, appr.  19.8 deg.
F/B                  -28.9 dB
F/R                  -26.0 dB
T_ant                 41.9 K
G/T                   3.30 dB


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













A Crossover between Diamond and Stagger Stacking

This stacking scheme is performed at stacking at DL6WU Distances plus 40 Percent
for both E and H plane.

Due to the larger stacking distances and hence a larger effective Aperture Area Diamond Stacking results in higher gain
at more modest side lobes with same Aperture Area used with the classical stacking scheme. However the rear lobes
grow as gain grows. I added Stagger Stacking as a proven tool to reduce the amount of rear lobes for arrays
formed of small Yagis.

Note that the mid pair of Yagis must be feed with a phase lag of 90 degrees by using
feedlines that are 0.25 wave length longer than the ones for the upper and lower Yagi.

Stacking Dist.    DL6WU Formula x 1.40
H-plane               1.46 m
E-plane               1.30 m
mid Yagis in x        171 mm


Find a link to more information about Stagger Stacking down the page.

  Attenzione! Viewing and judging Patterns of Diamond Stacks by Azimuth and Elevation Plots leads to wrong conclusions according their amount of front-, side- and rear lobes suppression. As the Diamond Stackings wave interference pattern runs the most characteristic lobes by a 45 degree shift to the ordinary stacking scheme. So they do not show in the ordinary Azimuth and Elevation plots. Which is the reason why many rumors about the marvels of Diamond Stacking are to be heared. Hence I show a 3D plot here.

The above is the reason why I implemented Stagger Stacking into the Diamond Stacking, as that usually
decreases rear lobes by a signifcant amount. And so it does in practise here.


Antenna Temperature and G/T produced with beta version of AGTC by F5FOD

The AGTC (Antenna G/T Calculator) is a shared development of F5FOD and myself, DG7YBN, that will be available
with full open source code. Background of the AGTC is scheduled to be published in Dubus 1/2017

Antenna Temperature and G/T produced with TANT


Read more about Stagger Stacking and feeding such arrays here









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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