DG7YBN / 432 MHz / GTV 70-17m
  Last Update Nov. 04th 2017




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


GTV 70-17m Yagi   with bent Driven Element

EME + SSB to mid of band Longyagi

This Yagi has very low back lobes for its length. It may serve as single antenna for Tropo or make quiet 4 Yagi EME array.
It also makes a quiet contest antenna due to its very high F/B and clean rear pattern. The bent DE (K6STI style) transforms from approx. 17 ohms to 50 ohms at feed point.

Another first built by Thomas, M0ABA: GTV 70-17m ready for the ARRL EME Contest

Final Blade Dipole shape (on left) and adjustable experimenters blade to find the shape needed (on right), far right: simple elevation mount by M0ABA

       

Boom is 1 x 1 inch, elements 4.0 mm, insulators by 7arrays.

How Thomas, M0ABA feeds these Yagis: self engineered coax hardline stub, the base plates are sawn from kitchen plastic boards(!)
A smart idea to access plastic sheets in the right thickness in small quantites at a reasonable price.

Feasible Return Loss: > -50 dB at 432.8 MHz


And this how the Yagi performs:

WSJT Screenshot QSO NC1I <> MX0CNS with GTV 70-17m and 60 W at Feed


    2017.11.03: DL7APV <> EME with single GTVV70-17m and just 10 W at feed

2017.11.04: 8 Yagi station ON4GG received with single GTVV70-17m during ARRL EME Contests 2nd leg

2017.11.04: 4 x 21 ele. Tonna station FR5DN received with single GTVV70-17m during ARRL EME Contests 2nd leg



Current distribution




Performance Data

Specs: with 8 mm elements @ 432.1 MHz

Gain vs. isotr. Rad.  17.3 dBi
Gain vs. Dipole       15.1 dBD
-3 dB E-plane         26.6 deg.
-3 dB H-plane         27.8 deg.
F/B                  -38.3 dB
F/R                  -31.5 dB
Impedance               50 ohms
Mechan. Length        3628 mm
Electr. Length        5.23 λ

Stacking Dist. h-pol.
top-to-bottom         1.51 m   or  4.95 ft
side-by-side          1.44 m   or  4.74 ft


Geometry



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.

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Geometry for 8 mm elements     



Using a large calliper gauge to control lenghts to the 10th of a millimeter is a must.




Geometry for 4 mm elements     


"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: 1 x 1 inch
Wall thickn.: 1/8 inch (3.175 mm)
Holes in boom: 6.0 mm
Offset rear: 40 mm
Offset front: 40 mm

Note: This includes a "Segmentation Density Correction" (SBC) of 0.90 mm plus an offset of 0.70 mm per element = 1.60 mm.
for compensation of the insulators shown with the GTV 70-19m website. Note: Other insulators will need slightly 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 .




Using a large calliper gauge to control lenghts to the 10th of a millimeter is a must.







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 elements 

EZNEC file of this Yagi with 8 mm elements 










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               1.44 m
E-plane               1.51 m

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

  


AGTC_lite screenshot of this Yagi with 8 mm elements


Gain vs. isotr. Rad.  23.20 dBi
Gain vs. Dipole       21.05 dBD
F/B                   33.6 dB
F/R                   32.8 dB
T_ant                 28.5 K*
G/T                   8.65 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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