НесHow many years ago I made 2 small antennas with a range of 70 centimeters, with a number of elements of 5 and 7. An attempt to establish radio communications over a distance of 35 kilometers showed that an antenna of 7 elements was not enough for reliable communication.

Introduction

The range of 70 centimeters (435 MHz) is customary for radio amateurs to “bypass”, because crane operators, car alarms, security guards and illegal immigrants work in it. Radio amateurs give preference to the 2 meter range (145 MHz), exclusively in horizontal polarization. The reason is that everyone works this way, and a correspondent should be looked for where everyone works. As a rule, ultrashort wave antennas have a length of at least 6-8 meters (9-12 elements in the 2 meter range), and the used transmitter power is 50-100 W.

Practice the 70 centimeter range

I spent several evenings establishing radio communications in the 70 cm range with a long-distance correspondent - an acquaintance of mine. Communication was carried out by agreement, with feedback via messenger. In terms of signal level, it was slightly higher than the noise level - the distance of 35 kilometers and the usual whip omnidirectional antenna on the other side and the power of 5 W had an effect.

A comparison of the 2 meter and 70 centimeter ranges showed two interesting features:

1. In the city, the reception of weak stations in the 144 MHz range is limited by airborne noise - the S-meter deviates to S2 even without a pre-amplifier. The range is 430-440 MHz, very quiet outside the LPD area, noise level S0-S1, the signal level meter shows nothing - 0 points.
2. A 70 cm directional antenna is more efficient (more gain and better lateral rejection) than a 2 meter antenna of the same length. That is, a 7-element antenna with a range of 70 cm can be heard better than a 5-element antenna. range of 2 m. The uda-yagi antenna of 5 elements for the 144 MHz range copes well with local communications (via a repeater), but gives in to long-range ones: there is not enough gain.

Convenience of 70 cm range

When using an antenna from a balcony, the maximum length of the 144 MHz antenna traverse does not exceed 2 meters, which limits the number of elements to 5-6 elements and the gain to 10-11 dbi. There is no way around this fundamental limitation of 144 MHz. At the same time, a 70 cm antenna allows you to place more elements on the boom and makes it lighter, for “aiming” at a correspondent from the hand.

For the 2 meter range I used a 5 element wave channel antenna, and for the 70 centimeter range I used a 7 element antenna. In the absence of passage (strong wind, cold cyclone) in the range of 2 meters I did not receive anything, while at 70 centimeters I heard presence, clicks, tone messages, sometimes turning into a legible signal, especially if a 1750 Hz tone or DTMF was used on that side (reception was in FM modulation).

Thus, in the city and at medium distances, up to 40 kilometers, the 70-centimeter range (430-440 MHz) outperforms the “two”, both in terms of radio communication quality and convenience, when using a directional antenna on at least one side.

Purpose of calculation

The goal of antenna calculations is to obtain antenna sizes of 430-440 MHz with better characteristics than a 7-element antenna.
The dimensions of which, however, would allow it to be used on the balcony.

The original Uda-Yagi antenna has 7 elements in the 435 MHz range. Gain G=12 dbi

Antenna characteristics:

• Traverse length - 98 cm (1.4 WL)
• Gain - 12 dbi
• Protective ratio F/B - 21.5 db
• Bandwidth level SWR<1.2 - 424...446 MHz.

Long uda-yagi 9 elements of the 435 MHz range. Gain G=13.7 dbi

Antenna characteristics:

• Traverse length - 167 cm (2.4 WL)
• Gain - 13.7 dbi
• Protective ratio F/B - 23.5 db
• Bandwidth level SWR<1.2 - 410...445 MHz.

Uda-Yagi antenna 10 elements 435 MHz band. Gain G=14.0 dbi

Antenna characteristics:

• Traverse length - 147 cm (2.16 WL)
• Gain - 14.0 dbi
• Protective ratio F/B - 22.5 db
• Bandwidth level SWR<1.2 - 425...445 MHz.

Narrowband uda-yagi antenna with 10 elements in the 435 MHz range. Gain G=14.8 dbi

Antenna characteristics:

• Traverse length - 188 cm (2.76 WL)
• Gain - 14.8 dbi
• Protective ratio F/B - 20 db
• Bandwidth level SWR<1.2 - 427...442 MHz.

Wideband uda-yagi antenna with 11 elements in the 435 MHz range. Gain G=14.7 dbi.

Antenna characteristics:

• Traverse length - 180 cm (2.64 WL)
• Gain - 14.7 dbi
• Protective ratio F/B - 24 db
• Bandwidth level SWR<1.2 - 425-445 MHz.

Uda-Yagi antenna 12 elements 435 MHz band. Maximum gain 15.2 dbi.

Antenna characteristics:

• Traverse length - 210 cm (3 WL)
• Gain 15.2 dbi
• Protective ratio F/B - 24 db
• Bandwidth level SWR<1.2 - 427...446 MHz.

Notes

All antennas use a split vibrator, as it is the easiest to manufacture.
The diameter of the tubes from which I have to make the antenna is 4 mm, the material is aluminum.
The diameter and material of the vibrator tubes does not matter. The material of the traverse is dielectric (wood or PVC). To fasten the elements to the supporting pipe, you can use plastic pipe holders from a plumbing store.
Antenna input impedance 50 Ohm (cable connection directly).
To suppress common-mode current through the braid (common mode), you need to use a shut-off choke made of coaxial cable (a coil of 3-4 turns with a diameter of 32 mm) near the power point. With precision manufacturing, antenna tuning is not required; coordination with the cable is ensured by calculation. The length of the cable to the radio station is arbitrary, but the shorter the better (for example, 1.3-1.5 meters).

Antenna models:
Yagi_MMANA.zip

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Dimensions of the 5-element Uda-Yagi antenna for the FM range 87.5-108 MHz

Yagi antennas for 144 MHz (Hairpin) and 435 MHz

Antenna for "Fox Hunt" at 144.7 MHz

Simple dual-band antennas for the 144 and 433 MHz amateur radio bands