DG7YBN / 432 MHz / GTV 70-7n
  Last Update Jan. 26nd 2016




.......



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


GTV 70-7n Yagi   with bent Driven Element

EME + SSB narrow bandwidth version ... strictly G/T breeding

This little Yagi has a high F/B, which makes it quite useful as a contest stack
The bent DE (K6STI style) transforms from approx. 17 ohms to 50 ohms at feed point.
You might also take a look at the only 40 cm longer GTV 70-9w, which should be less
demanding in absolute dimensioning.

The GTV 70-7n is EME tested in many QSOs


In case you have never build a Yagi with bent DE for 432 MHz before or have little experience
in home brewing Yagis in general ... or simply want to achieve top performance ...

I strongly recommend to build this little 7 ele. as a Test-Yagi to find the exact BC and learn how
to trim the bent DE for best VSWR on this pocket version before moving to a long boomer. It was
my prime intention to give you a practicable narrow band width Test-Yagi at hand when I enclosed
it in the Dubus Article introducing the GTV Long Yagi series.


• GTV 70-7n built by Thomas, M0ABA for use at MX0CNS for demonstrating QRPP 70 cm EME

Tom reports to receive HB9Q peaking -20 dB on first test in WSJT with that single small Yagi
and a Microset Preamp with built in coax relays only:

And first complete EME QSO with Bernd, DL7APV on 2016-01-22 with 80 Watts and the single 7 element Yagi:

Elements are of Ø 4 mm, mounted insulated through a 5/8 inch square tube boom, split DE from Ø 8 mm tube
pushed onto a plastic center piece, which is 'pierced' through the boom. The symmetrising Quarterwave line is
made from Aircom 5 with a ferrite core right at the split point where it connects to the dipole.

Here are photos of the dipole arms mount - a plastic rod that is pushed through the boom. This construction
enables a zero offset between dipole and element plane when using elements through boom.
I have described such a dipole mount with a few sketches here

• Take a look at photos explaining how to build this Yagi on the GTV 70-4m website

The 3/4 λ symmetrising line is made from Aircom 5 coax

All the above photos, building and testing by Thomas, M0ABA - tnx!




• GTV 70-7n modified for the 403-406 MHz Radio Sonde Band built by F4GRT



Philippe, F4GRT reports his first impressions

"Today I could decode the position of a radiosonde at 550 km (the Balearics) from my QRA and another also
at 550km at Saragossa (Spain). I am at Salon de Provence, 50km from Marsille. The emitting power of the
radiosonde was only 100mW. The antenna impedance is 50 + j0 ohms and SWR is of 1.01:1 in the center of the
403-406 MHz band."

Current Distribution & 3D pattern






• A lightweight GTV 70-7n built by Kazuo, 7L1TIG

First image: comparing to K1FO 8 ele. Yagi with good result. Note the stand off insulators held by an acryl glass plate.



In a later version (Jan. 2015) the bent dipole is made from 10 x 2 mm sheet metal, which helped to better Return Loss > - 30 dB



Photos: with kind permission of Kazuo, 7L1TIG

Find a VSWR chart further down on this website.
See his website about Amateur Radio with focus on 430 MHz antennas for portable use (in Japanese)

Kazou made a whole set of websites about small DG7YBN Yagis, all redesigned in MMANA for 430-431 MHz.
A very clear and methodic work. I recommend this to read. Use a free website online translator.

GTV 70-4m with sheet metal dipole
GTV 70-7n with sheet metal dipole
GTV 70-7n with thin rod for dipole
YBN 2-2w scaled to 70 cm




• See the amazing portable version build by 7M2MZO (in Japanese) here





This website has been viewed by how many 70 cm enthusiasts since Jan. 2016?

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Performance Data

Gain vs. isotr. Rad.  12.9 dBi
Gain vs. Dipole       10.8 dBD
-3 dB H-plane         41.4 deg.
-3 dB E-plane         48.4 deg.
F/B                  -29.4 dB
F/R                  -21.9 dB
Impedance               50 ohms
Mechan. Length        1012 mm
Electr. Length        1.46 λ

Stacking Dist. h-pol.
top-to-bottom         0.85 m
side-by-side          0.98 m


Geometry

The 8 mm element geometry data are to fit On-Boom-with-Standard-Insulators style of building.
The 4 mm elements are ment for an 'elements through boom' built.
Segmentation BC and Base BC (see BC page) must be added.

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.

                                                                 


        Pos.    Full Length      1/2 Length    1/2 Length
                                   in NEC
				 
Refl.     0        330.0           163.0          162.0
DE(b)  80/78       296.0        33.5-148.7     33.5-148.3
DE(a)   110         67.0          0-33.5         0-33.5
D1      172        313.0           154.5          152.0
D2      307        308.0           151.0          149.0
D3      523        300.0           147.0          144.5
D4      785.5      292.0           143.0          140.0 
D5     1016        281.0           136.5          133.5
                 ele. 4 mm       ele. 1/4"      ele. 8 mm
The Drivers diameter is 10 mm for all examples. Use EZNEC's Auto-Segmentation at 1050 MHz.

For the SBC the frequency impact is 433.55 MHz - 432.10 MHz = 1.45 MHz
Multiplication with the 70 cm correction factor of 0.92 mm/MHz results in 1.33 mm to add to the common BC.

• "Ready to saw and drill" data for mounting 8.0 mm elements on boom with standard insulators on 20 x 20 mm boom including a 30 mm offset from booms end:



• "Ready to saw and drill" data for mounting 4.0 mm elements insulated through boom with SM5BSZ's BC.exe applied
Note that with an elements insulated through boom built for best results boomlength and positions to first /last element must be kept as given.
Because the position of an element relative to its nearer boom end is a serious parameter in the BC.exe.

This table is only valid for:
Boom shape: square
Boom dim: 5/8 in x 5/8 in (15.9 mm)
Wall thickn.: 1.6 mm
Holes in boom: 6.0 mm
Offset rear: 40 mm
Offset front: 40 mm



•" Same data set for 4 mm elements as above, but with rear boom end offset = 300 mm for formast mounting



Sketch of Bent Dipole









Pattern and VSWR Plots

Elevation and Azimuth plot at 432.1 MHz

 


RL and SWR plot


Simulated and real world VSWR of 7L1TIG's lightweight build (a version remodelled in MMANA)







Downloads

EZNEC file of this Yagi with Ø 1/4" elements  

EZNEC file of this Yagi with Ø 8 mm elements  

EZNEC file of this Yagi with Ø 4 mm elements  


CSV file for the Yagi Element Configuration Tool 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.


4 x GTV 70-7n bay - a very compact array

Gain vs. isotr. Rad.  18.8 dBi
Gain vs. Dipole       16.7 dBD
-3 dB H-plane         13.2 deg.
-3 dB E-plane         10.4 deg.
F/B                  -33.6 dB
F/R                  -26.3 dB
T_ant                 36.2 K*
G/T                   3.25 dB*

Theoretical numbers, no phasing line losses
nor imperfections caused by mast included
*) T_sky = 20 K, T_earth = 350 K as in VE7BQH G/T table

Stacking Dist.    DL6WU Formula
H-plane               0.85 m
E-plane               0.98 m

Elevation plot and data of 4 Yagi stacked vertically using DL6WU stacking distances


Gain vs. isotr. Rad.  18.8 dBi
Gain vs. Dipole       16.7 dBD
-3 dB H-plane         13.2 deg.
-3 dB E-plane         41.8 deg.
F/B                  -33.6 dB
F/R                  -26.3 dB









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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