DG7YBN / 432 MHz / GTV 70-23m
  Last Update Apr. 24th 2017




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Performance Data and Geometry
Pattern and VSWR
Download as File
Stacking
Matching


GTV 70-23m Yagi   with bent Driven Element

EME + SSB band, with some loss usable for FM up to 435 MHz

This Yagi has very low back lobes for its length. It may serve as single antenna for Tropo or make a nice 4 Yagi EME array.
It also 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


2015-04-17: Nice photo of a GTV 70-23 m over GTV 2-16w at SP8MRD on qrz.com

GTV 70-23m built on 20 x 20 mm boom by Rickus, ZS4A

Following the building samples given on my web closely he reports a VSWR of 1.2 mid band without any tuning done.
Note the boom to mast mounting plate as described here arranging the pole to be underneath the boom in a symmetrical way




Performance Data

Gain vs. isotr. Rad.  18.7 dBi
Gain vs. Dipole       16.5 dBD
-3 dB E-plane         23.0 deg.
-3 dB H-plane         23.6 deg.
F/B                  -34.9 dB
F/R                  -32.3 dB
Impedance               50 ohms
Mechan. Length        5240 mm
Electr. Length        7.55 λ

Stacking Dist. h-pol.
top-to-bottom         1.70 m
side-by-side          1.76 m
Geometry

The 8 mm element geometry data are to fit On-Boom-with-Standard-Insulators style of building.
Segmentation BC and Base BC (see BC page) must be added. "Ready to saw" data will follow shortly.

    <=   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.

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.


"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 booms end:





    <=   NEC Geometry for 4 mm ele. insulated through boom excluding BC


Ø 3/16 inch (4.763 mm) Elements - Through Boom - Dimensions (BC acc. SM5BSZ's BC.exe)



"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!

This table is only valid for:
Boom shape: square
Boom dim: 20 x 20 mm
Wall thickn.: 1.5 mm
Holes in boom: 7.5 mm
Offset rear: 40 mm
Offset front: 40 mm

Note: This does include a "Segmentation Density Correction" (SBC) of 1.98 mm.
Which does include a correction for the insulators, which is 0.7 mm as a fix offset.
Read abt. the SBC here .








Ø 4.0 mm Elements - Through Boom - Dimensions (BC acc. SM5BSZ's BC.exe)

"Ready to saw and drill" data for mounting elements through boom with BC according SM5BSZ's BC.exe:

This table is only valid for:
Boom shape: square
Boom dim: 20 x 20 mm
Wall thickn.: 1.5 mm
Holes in boom: 6.0 mm
Offset rear: 40 mm
Offset front: 40 mm

Note: This does include an SBC of 1.98 mm plus a correction of 0.7 mm





Sketch of Bent Dipole










Pattern and VSWR Plots

Elevation and Azimuth plot at 432.1 MHz

 


SWR and Return Loss plots - simulated with 4nec2










Downloads

EZNEC file of this Yagi with 4 mm elem.  

EZNEC file of this Yagi with 8 mm elem.  










Stacking

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.    DL6WU Formula
H-plane               1.70 m
E-plane               1.76 m

Elevation plot and data of 4 Yagi bay using DL6WU stacking distances


Gain vs. isotr. Rad.  24.51 dBi
Gain vs. Dipole       22.36dBD
-3 dB H-plane, appr.  10.2 deg.
-3 dB E-plane, appr.  10.5 deg.
F/B                  -32.6 dB
F/R                  -32.3 dB
T_ant                 27.8 K*
G/T                  10.08 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


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