DG7YBN / 432 MHz / GTV 70-11w
  Last Update May 13th 2017




.......



Performance Data and Geometry
Pattern and VSWR
Download as File
This Yagi with bent Folded Dipole
Stacking
Matching


GTV 70-11w Yagi   with bent Driven Element

Wideband OWA style medium size Yagi with focus on EME + SSB band but covering 430-440 MHz


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.

Find the GTV 70-11w listed in the VE7BQH G/T tables

2 x GTV70-11w built by Kazuo, 7L1TIG

Photo: with kind permission of Kazuo, 7L1TIG

(operated with 20 .. 70 W and WSJT such a 2 x 1 m size array will clearly produce some results as QRPP EME station)

Kazou made a whole set of websites about DG7YBN 70 cm Yagis.
A very clear and methodic work. I recommend this to read. Use a free website online translator.

GTV 70-11w with sheet metal dipole
GTV 70-7n with sheet metal dipole


4 x GTV70-11w with folded dipole, built by Bernd, DL7APV

on 20 x 20 mm boom, 4 mm elements through boom and 6 mm dipole, see details below
4 Bay of GTV 70-11 Yagis with Open Feed Lines, sun noise up to 8.8 dB (at an sfi around 80)

Return Loss at 200 => 50 ohms with folded dipole and balun



Current distribution

3D Pattern




Performance Data

Specs: with 8 mm elements @ 432.1 MHz

Gain vs. isotr. Rad.  15.0 dBi
Gain vs. Dipole       12.9 dBD
-3 dB H-plane         34.2 deg.
-3 dB E-plane         37.0 deg.
F/B                  -31.6 dB
F/R                  -27.9 dB
Impedance               50 ohms
Mechan. Length        2012 mm incl. 2 x 30 mm stand off
Electr. Length        2.81 λ

Stacking dist. h-pol.
top-to-bottom         1.09 m or 3.59 ft
side-by-side          1.18 m or 3.87 ft


How many OMs have been looking up this design?

Flag Counter

Here is an add-on by the 'DXzone' web in which you may rate the GTV 70-11w design and its website.

Rate this site
The DXZone.com

(with 10 = top)


Geometry





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

Actual BC for on a 20 x 20 mm Boom with standard insulators is 7.5 mm, SBC is 1.564 mm,
total length to add is ~ 9.06 mm


                  Refl   DE(b)   DE(a)   D1     D2     D3     D4     D5     D6     D7     D8     D9
Pos.                 0    85.8   104.5   150    246    428    651    902    1166   1439   1709   1952
NEC 1/2 ele.	 165.5	(161.7)  (33.5)	 153.5  151.5  146.0  142.5  140.0  138.5  136.5  132.5  129.0
Boom 20x20 mm    340.0  (332.4)  (67.0)  316.0  312.0  301.0  294.0  289.0  286.0  282.0  274.0  267.0

Bent Dipole: DE(a) is the inner straight length and pos. on boom, DE(b) is position of tips and span width when bent



Find a CAD Drawing of this Yagi with 8 mm elements & standard insulators on 20 x 20 mm boom in the download section



Geometry for 4 mm elements     

The SBC is 1.56 mm. (Correction: D1 = 2 x 159 mm / 09.02.2015)
Using a large calliper gauge to control lenghts to the 10th of a millimeter is a must.

                  Refl   DE(b)   DE(a)   D1     D2     D3     D4     D5     D6     D7     D8     D9
Pos.                 0    87.0   104.5   150.5  246    428    651    902    1166   1439   1709   1952
NEC 1/2 ele.	 168.0	(163.2)  (33.5)	 159.0  156.0  151.0  147.75 146.0  144.25 142.5  138.75 135.75
Lengths ex. BC   336     326.4   (67.0)  318.0  312.0  302.0  295.5  292.0  288.5  285.0  277.5  271.5


Table 1: GTV 70-11w, 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!

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: 40 mm
Offset front: 40 mm

Note: This includes a "Segmentation Density Correction" (SBC) of 1.56 mm plus an offset of 0.70 mm per element = 2.26 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



Same with 5/8 inch x 1.6 mm wall boom and 300 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








Radiation Pattern and VSWR Plots

Elevation and Azimuth plot at 432.1 MHz

 


SWR and Return Loss plots - simulated with 4nec2



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










Downloads

EZNEC file of this Yagi with Ø 8 mm ele.  


CSV file for the Yagi Element Configuration Tool with 4 mm elements


CAD Drawing of this Yagi with 8 mm elements on 20 x 20 mm boom     










GTV 70-11w 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 6 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.

Geometry of the Folded Dipole

In the model we use the center of the tube, regardless of its actual diameter.
With this height is 44 mm, span width is 326 mm. Adding the real diameter of 6 mm we end up with

inner height = 38 mm, outer span width = 332 mm, see sketch



Note     Folded Dipole mounting in plastic brackets compensation

Whatever plastic block is used to suspend or mount the dipoles wires will need to be compensated
by adding ~ 0.1 mm per millimeter of wire running in plastic. If you attach a 20 mm plastic block on top
of the boom to lead the dipoles upper wire a length of 2.0 mm / 2 = 1.0 mm needs to be added to the dipoles
span width. Assumed it runs free of contact to plastic on the down side.
We use factor 1/2 in a folded dipole then since it is a full wave loop.

Same applies to any BC if the wires run very close (~ < 3 mm) to the boom.










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               1.18 m
E-plane               1.09 m


A vertical 2 Yagi stack




Elevation plot and data of 2 Yagi bay using DL6WU stacking distances


Gain vs. isotr. Rad.  17.93 dBi
Gain vs. Dipole       15.78 dBD
-3 dB H-plane, appr.  40.8 deg.
-3 dB E-plane, appr.  16.8 deg.
F/B                  -32.1 dB
F/R                  -30.0 dB
T_ant                 --.- K*
G/T                   -.-- dB*
Theoretical numbers - these do not include phasing line losses
nor imperfections caused by H-frames or mast poles etc.
*) T_sky = 20 K, T_earth = 350 K as in VE7BQH G/T table



A 4 Yagi bay




Azimuth Plot (Elev. Plot see 2 x vert stack above)


Gain vs. isotr. Rad.  20.91 dBi
Gain vs. Dipole       18.76 dBD
-3 dB H-plane, appr.  15.4 deg.
-3 dB E-plane, appr.  16.8 deg.
F/B                  -31.5 dB
F/R                  -30.5 dB
T_ant                 32.8 K
G/T                   5.74 dB


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


TANT screenshot











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


Flag Counter