DG7YBN / 432 MHz / GTV 70-30m
  Last Update Nov. 2nd 2017




.......



Performance Data and Geometry
Pattern and VSWR
Folded Dipole Version
Download as File
Stacking
Matching


GTV 70-30m Yagi   with bent Driven Element

EME + SSB band Longyagi

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.

Look at this: A close to 8 m long GTV 70-30m Rope Yagi built on Kevlar Kite lines,
4 mm elements and a 1/4 λ sleeve with Pawsey symmmetrising ... built by Thomas, M0ABA at MX0CNS

Click here to see the full frame photo
There are details and all the news to be posted shortly about this antenna on the MX0CNS facebook

M0ABA at MX0CNS: Screenshot of WSJT of first QSO with the Rope Yagi, beam slightly off the moon still,
60 W at feed at MX0CNS <> DL7APV



GTV 70-30m built by Chris, PA2CHR with 8 mm Elements on Boom, BC acc. DG7YBN




Current distribution



Short Screenshot Movie showing rotating 3D Pattern



To watch the rotating 3D Pattern movie by F5JM click here pse





Performance Data

Specs: with 4 mm elements @ 432.1 MHz

Gain vs. isotr. Rad.  19.7 dBi
Gain vs. Dipole       17.6 dBD
-3 dB E-plane         20.6 deg.
-3 dB H-plane         21.2 deg.
F/B                  -33.8 dB
F/R                  -33.8 dB
Impedance               50 ohms
Mechan. Length        7276 mm
Electr. Length        10.48 λ

Stacking Dist. h-pol.
top-to-bottom         1.89 m
side-by-side          1.94 m


Geometry

Geometry for 4 mm elements     



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



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

Note: This includes a "Segmentation Density Correction" (SBC) of 1.10 mm plus an offset of 0.70 mm per element = 1.80 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 .




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






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

Actual BC for on a 25 x 25 mm Boom with standard insulators is 11.0 mm, SBC is 1.10 mm,
total length to add is ~ 12.10 mm



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

Sketch of Bent Dipole










Pattern and VSWR Plots

Elevation and Azimuth plot at 432.1 MHz

 


SWR and Return Loss plots - simulated with 4nec2










GTV 70-30 with Folded Dipole

The straight split bent dipole can be replaced with a bent folded dipole like in any non-bent Yagi design.
In doing so the transformation ratio of 1:4 remains. The bent folded dipole versions impedance is 200 ohms.

The folded dipole itself is of Ø 8 mm; I recommend an 'elements through boom' built.
So that the folded dipole is centered in the element plane for best symmetry in the elevation pattern.
For building with elements on boom see second sketch.

Geometry of the Folded Dipole

In the model we use the center of the tube, regardless of its actual diameter.

For builds ...

• ... with elements mounted through boom (Folded Dipole in element plane) use these dimensions


• ... with 8 mm elements mounted on 25 x 25 mm boom use these dimensions

Attention: Refl, DE, D1 shall be mounted on an inserted piece of 20x20 mm boom, D1 is modified.
D1 : Position: 156.5, length 311.5 + 7.5 mm of BC + 1.1 mm of SBC = D1 : 320.1 mm









Downloads

EZNEC file of this Yagi with 4 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               1.89 m
E-plane               1.94 m

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


TANT screenshot of this Yagi with 4 mm elements


Gain vs. isotr. Rad.  25.54 dBi
Gain vs. Dipole       23.39 dBD
-3 dB H-plane, appr.  -.- deg.
-3 dB E-plane, appr.  -.- deg.
F/B                   -.- dB
F/R                   -.- dB
T_ant                 29.3 K*
G/T                  10.87 dB*

TANT screenshot of this Yagi with 8 mm elements


Gain vs. isotr. Rad.  25.59 dBi
Gain vs. Dipole       23.44 dBD
-3 dB H-plane, appr.  10.0 deg.
-3 dB E-plane, appr.  10.0 deg.
F/B                   33.6 dB
F/R                   32.8 dB
T_ant                 26.0 K*
G/T                  11.43 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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