Performance Data and Geometry
Pattern and VSWR
Download as File
GTV 70-23m Yagi with bent Driven Element
EME + SSB band, with some loss usable for FM up to 435 MHz
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.
2015-04-17: Nice photo of a GTV 70-23 m over GTV 2-16w at SP8MRD on qrz.com
GTV 70-23m built on 20 x 20 mm boom by Rickus, ZS4A
Following the building samples given on my web closely he reports a VSWR of 1.2 mid band without any tuning done.
Note the boom to mast mounting plate as described here arranging the pole to be underneath the boom in a symmetrical way
Gain vs. isotr. Rad. 18.7 dBi Gain vs. Dipole 16.5 dBD -3 dB H-plane 23.0 deg. -3 dB E-plane 23.6 deg. F/B -34.9 dB F/R -32.3 dB Impedance 50 ohms Mechan. Length 5240 mm Electr. Length 7.55 λ Stacking Dist. h-pol. top-to-bottom 1.70 m side-by-side 1.76 mGeometry
The 8 mm element geometry data are to fit On-Boom-with-Standard-Insulators style of building.
Segmentation BC and Base BC (see BC page) must be added. "Ready to saw" data will follow shortly.
<= NEC Geometry 8 mm ele. semi-insulated on boom ex. BC
<= NEC Geometry for 4 mm ele. insulated through boom excluding BC
Ø 3/16 inch (4.763 mm) Elements - Through Boom - Dimensions (BC acc. SM5BSZ's BC.exe)
"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.: 1.5 mm
Holes in boom: 7.5 mm
Offset rear: 40 mm
Offset front: 40 mm
Note: This does include a "Segmentation Density Correction" (SBC) of 1.98 mm.
Which does include a correction for the insulators, which is 0.7 mm as a fix offset.
Read abt. the SBC here .
Pattern and VSWR Plots
Elevation and Azimuth plot at 432.1 MHz
SWR and Return Loss plots - simulated with 4nec2
EZNEC file of this Yagi with 4 mm elem.
EZNEC file of this Yagi with 8 mm elem.
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 1.70 m E-plane 1.76 m
Elevation plot and data of 4 Yagi bay using DL6WU stacking distances
Gain vs. isotr. Rad. 24.51 dBi Gain vs. Dipole 22.36dBD -3 dB H-plane, appr. 10.2 deg. -3 dB E-plane, appr. 10.5 deg. F/B -32.6 dB F/R -32.3 dB T_ant 27.8 K* G/T 10.08 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