Performance Data and Geometry
Pattern and VSWR
Download as File
This Yagi with bent Folded Dipole
GTV 70-25m Yagi with bent Driven Element
EME + SSB band version
This Yagi has very low back lobes for its length. It may serve as single antenna for Tropo or even EME.
A 4 Yagi bay will make an excellent 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.
Take a look at the 2 x GTV 70-25m built by Sverker, SM7THS
and what he reports abt. operating EME with these on QRZ.com
Almost ready built GTV 70-25m at PA2CV, Alex
Below, on left: Build completed and ready to hit the moon 2016-10-15, click on image to view in large
And 2016-10-16 on right: First test as EME novice with 100 W out, instantly an almost QSO with PI9CAM due to much drift in trx.
Slideshow: Ingenious bent dipole for the GTV 70-25m by Alex, PA2CV. 8 mm soft copper tube with brass screws in the tips
Gain vs. isotr. Rad. 18.9 dBi (4 mm elements and low segmentation) Gain vs. Dipole 16.8 dBD -3 dB E-plane 22.2 deg. -3 dB H-plane 22.8 deg. F/B -36.9 dB F/R -34.0 dB Impedance 50 ohms Mechan. Length 5820 mm Electr. Length 8.39 λ Stacking Dist. h-pol. top-to-bottom 1.76 m side-by-side 1.80 m
EZNEC wire table for Ø 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: 20 x 20 mm
Wall thickn.: 2.0 mm
Holes in boom: 6.0 mm
Offset rear: 30 mm
Offset front: 30 mm
<= NEC Geometry 4 mm ele. insulated through boom incl. SM5BSZ BC.exe Correction
<= NEC Geometry 8 mm ele. semi insulated on boom incl. DG7YBN BC and an SBC of 1.37 mm
Pattern and VSWR Plots
Elevation and Azimuth plot at 432.1 MHz
SWR and Return Loss plots - simulated with 4nec2
Return Loss plot - PA2CV's build: 430.0 to 435.0 MHz (tnx Alex!)
EZNEC file of this Yagi with 4 mm elements
EZNEC file of this Yagi with 8 mm elements
GTV 70-25m 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 308 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.
SWR and Return Loss plots - simulated with 4nec2
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 top-to-bottom 1.76 m side-by-side 1.80 m
Azimuth plot and data of 4 Yagi bay using DL6WU stacking distances
Gain vs. isotr. Rad. 24.84 dBi Gain vs. Dipole 22.69 dBD T_ant 26.4 K* G/T 10.63 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
Elevation plot and data of 6 Yagi bay using DL6WU stacking distances
Gain vs. isotr. Rad. 26.58 dBi Gain vs. Dipole 24.43 dBD T_ant 26.1 K* G/T 12.42 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