DG7YBN / 432 MHz / GTV 70-21n
  Last Update Aug 22th 2019




.......



Performance Data and Geometry
Pattern and VSWR
Stacking
Matching


GTV 70-21n Yagi 'Voskhod'   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.
It is another Yagi that needs to be built in a very accurate way.


How to pronounce? Voskhod means sunrise



With spacecraft Voskhod 2 the first spacewalk of mankind was achieved:

  

Above: Cosmonaut Alexei Arkhipovich Leonov, first spacewalk ever, March 18th, 1965 and clip of Russian Poststamp
As I understand it, re-entering the capsule was a tight affair but
nevertheless it was the first time a human was out in space.

Current distribution

3D Pattern


GTV 70-21n built by Thomas, M0ABA

   

The GTV 70-21 Voskhod attracted a bright and shiny aeronaut!
And a quick first EME QSO dated 2019-09-01: MX0CNS < > DL7APV with no good Farady Rotation







Performance Data

Specs: with 4 mm elements @ 432.1 MHz

Gain vs. isotr. Rad.  18.2 dBi
Gain vs. Dipole       16.1 dBD
-3 dB E-plane         23.8 deg.
-3 dB H-plane         24.6 deg.
F/B                  -40.5 dB
F/R                  -32.4 dB
Impedance               50 ohms
Mechan. Length        4775 mm incl. 2 x 40 mm stand off
Electr. Length        6.77 λ

VSWR Bandwidth        1:1.48 (as in VE7BQH Antenna Table)

Stacking dist. h-pol.
top-to-bottom         1.63 m or 5.34 ft
side-by-side          1.68 m or 5.52 ft


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Geometry

        

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 1.1 mm plus an offset of 0.70 mm per element = 1.8 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 (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)










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               1.68 m
E-plane               1.63 m


A 4 Yagi bay



Elev. Plot


Azim. Plot


Gain vs. isotr. Rad.  24.1 dBi
Gain vs. Dipole       22.0 dBD
-3 dB H-plane, appr.  17.4 deg.
-3 dB E-plane, appr.  12.0 deg.
F/B                  -44.8 dB
F/R                  -33.1 dB
T_ant                 52.7 K*
G/T                   6.89 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:

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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