Performance Data and Geometry
Pattern and VSWR
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GTV 70-17m Yagi with bent Driven Element
EME + SSB to mid of band Longyagi
This Yagi has very low back lobes for its length. It may serve as single antenna for Tropo or make quiet 4 Yagi EME array.
It also makes a quiet contest antenna due to its very high F/B and clean rear pattern. The bent DE (K6STI style) transforms from approx. 17 ohms to 50 ohms at feed point.
Specs: with 8 mm elements @ 432.1 MHz
Gain vs. isotr. Rad. 17.3 dBi Gain vs. Dipole 15.1 dBD -3 dB E-plane 26.6 deg. -3 dB H-plane 27.8 deg. F/B -38.3 dB F/R -31.5 dB Impedance 50 ohms Mechan. Length 3628 mm Electr. Length 5.23 λ Stacking Dist. h-pol. top-to-bottom 1.51 m or 4.95 ft side-by-side 1.44 m or 4.74 ft
Geometry for 8 mm elements
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: 1 x 1 inch
Wall thickn.: 1/8 inch (3.175 mm)
Holes in boom: 6.0 mm
Offset rear: 40 mm
Offset front: 40 mm
Note: This includes a "Segmentation Density Correction" (SBC) of 0.90 mm plus an offset of 0.70 mm per element = 1.60 mm.
for compensation of the insulators shown with the GTV 70-19m website. Note: Other insulators will need slightly 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.
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 elements
EZNEC file of this Yagi with 8 mm elements
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 1.44 m E-plane 1.51 m
Elevation and azimuth plot and data of 4 Yagi bay using DL6WU stacking distances
AGTC_lite screenshot of this Yagi with 8 mm elements
Gain vs. isotr. Rad. 23.20 dBi Gain vs. Dipole 21.05 dBD F/B 33.6 dB F/R 32.8 dB T_ant 28.5 K* G/T 8.65 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