Antenna “Wave channel” 3 elements with a split vibrator for a frequency of
142 MHz

Description: The antenna is made on an aluminum crossarm measuring 25X12X2 mm, 900 mm long, the elements are made of a hollow tube with a diameter of 6 mm
with a wall thickness of 1 mm. The antenna elements are attached to the crossarm using
plastic fasteners. The elements do not electrically touch the crossarm.
The fasteners are made of PETG polymer plastic using additive
technologies (an Ender 3 3D printer was used) with 100% filling.
The RG-58 cable is 5.57 m long (half-wave repeater), with an SMA-m connector. A
ferrite ring is used as a current cutoff along the braid.
Antenna dimensions:
Frequency f: 142 MHz
Wavelength λ: 2 m 111 m

Element diameter d: 6 mm
Boom diameter D: 25 mm
Total number of elements: 3
Boom length: 593 mm
Gain: 7 dBi (approx.)
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Reflector length R: 1 m 37 mm
Reflector position R = 0
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Vibrator length F: 1 m 1 mm
Vibrator position F (R-F): 422 mm
Connection gap g <= 28.1 mm
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Length D1: 950 mm
Director position D1 (R-D1): 581 mm
Distance F-D1:  158 mm
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Active vibrator shape: Split
Boom with square cross-section.
Elements in the center of the metal boom and isolated from it
Calculation is carried out taking into account boom correction.
Real parameters obtained.

Operating frequency range by SWR 2, MHz: ~130 – 150;
Antenna resistance, Ohm: ~50;
Power, max, W: 50;
Reactance, pF: ~300-400
Gain: 7 dBi (approx.)
Note: The method of antenna fastening is left to the consumer. For
fastening the antenna, approximately 300 mm of crossarm are left behind the reflector.
The design of the braid current cutoff can be modernized: take a 1/4 wave cup instead of
ferrite. The screws screwed into the ends of the vibrator and
reflector serve as electrical extensions of the latter, and are also used
to fine-tune the antenna. It is strongly not
recommended to unscrew them or change the screwing depth.  All threaded connections are secured with glue.

The cost of the antenna, taking into account retail prices on the radio market, the construction market of Simferopol, and the Ozone marketplace as of November 2024:

Traverse 25X12X2 mm, length 1000 mm: 264 rubles (Ozone)
Aluminum tubes 1000X6X1 mm, 3 pieces: 215 rubles (Ozone)
Plastic for 3D printing (~75 g): 75 rubles (Ozone)
Bolts 6X45 (4 pcs), 6X55 (2 pcs), nuts, washers M6 (6 pcs): ~60 rubles (construction market)
Terminals for vibrator, 2 pcs.: 20 rubles.  (Radio Market B-12)
RG58 cable 5.57 m: 390 rubles (Radio Market B-12)
SMA-m connector, under common, 1 pc.: 150 rubles (Radio Market B-52)
Ferrite ring, used: 20 rubles (Radio Market Gena)
Insulating tape, glue, heat shrink tube, hot glue, grease for solder, flux,
solder: 70 rubles
Total: 1204 rubles.
Sources:
https://r4uab.ru/antenna-430-440-mhz/
https://3g-aerial.biz/onlajn-raschety/raschety-antenn/raschet-antenny-uda-yagi-dl6wu
http://ra6foo.qrz.ru/stakan.html