Antenna

Radiation of radiowave happens via Antenna.

We know many different antennas but we’ll try to explain different types :

  • Random wire
  • EFHW
  • dipole
  • yagi
by direction or shape type:
  • vertical
  • V – shaped
  • inverted V – shaped
  • L – shaped
  • horizontal
  • directional – yagi
  • etc.
Random wire means to use undefined wire length (not related with wave length) mostly used with Antenna Tuner for better balancing. Consist of two wire undefined characteristic. Two wires we call radiation (or hot) and counterpoise (cold, grounding). Radiation wire can be in different position – vertical, horizontal or in between/under angle – sloper. Counterpoise should be laying on the ground in direction of radiation. Here are some hints of length to USE (so no quite random): in meters
x Wave
128,9
124,1
105,8
61,9
45,1
36,3
32,6
25,6
21,6
17,7
12,5
10,8
8,8
in feets:
x Wave
423
407
347
203
148
119
107
84
71
58
41
35,5
29
Here are some hints of length to AVOID (so no quite random) : in meters
Frequency MHz 1/2 Wave 2nd Multiple 3rd Multiple 4th Multiple
1,9 75,0 150,0 224,9 299,9
3,8 37,5 75,0 112,5 150,0
7,2 19,8 39,6 59,4 79,2
10,1 14,0 28,0 42,1 56,1
14,2 10,1 20,1 30,2 40,2
18,1 7,9 15,8 23,8 31,7
21,3 6,7 13,4 20,1 26,8
24,9 5,8 11,6 17,4 23,2
28,5 4,9 9,8 14,6 19,5
in feets
Frequency MHz 1/2 Wave 2nd Multiple 3rd Multiple 4th Multiple
1,9 246 492 738 984
3,8 123 246 369 492
7,2 65 130 195 260
10,1 46 92 138 184
14,2 33 66 99 132
18,1 26 52 78 104
21,3 22 44 66 88
24,9 19 38 57 76
28,5 16 32 48 64
source : http://www.hamuniverse.com/randomwireantennalengths.html
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Popular type of antenna with asymmetrical length of  poles. result of asymmetry is high-impedance (2,000-4,000 ohm) wire antenna that resonates on its fundamental frequency and all harmonics above. This antenna needs to be balanced (to bring the wire’s high impedance feedpoint closer) to the desired 50 ohms with baluns (unun 49:1 or 64:1), which eliminates the need for an antenna tuner in most cases.

A loop antenna is a radio antenna consisting of a loop or coil of wire, tubing, or other electrical conductor usually fed by a balanced source or feeding a balanced load.

‘Magnetic’ because they pick up the magnetic component of an electromagnetic field, unlike the usual antenna forms (dipoles, yagi antennas, vertical antennas), which only respond to the electrical component.

The small loop antenna is known as a magnetic loop since it behaves electrically as a coil (inductor)

Magnetic antennas can be built very compact, good for limited spaces or ‘mobile’ use, e.g. on boats with limited space. Radials or other counterweights are not necessary, the radiation is largely independent of the distance of the antenna to the ground.

At the resonance frequency, magnetic antennas are quite narrow-banded. This has the advantage that on the one hand only few harmonics are radiated, on the other hand the antenna acts as a very narrow-band additional preselector and thus prevents overdriving of the usually quite broadband receivers by signals far away from the receiving frequency.

Nice practical MLA is construction of G4FON. Antenna uses Coax RG-58 or better it’s shield (3,5mm). I changed to RG-59 with shield diameter 4,4mm. Feeding comes on bottom via toroid FT114-43 (40m -5 turns, 30m-3 turns, 20m-2 turns). On top is variable capacitor (or trimmer via switch to precalibrate)

Some more info:

Also

There are many coax cables for different operations (and different characteristics):

  • RG-50 – Standard cable for mobile installations
  • RG-8X – Larger and lower loss than RG-58 but still convenient for shorter cable runs and jumpers.Up to 50 feet in length at 50 MHz or below and up to 25 feet in length at 146 MHz (Rule of Thumb)
  • RG-8U – General purpose coaxial cable, best for long cable runs

source : https://hamradioschool.com/coaxial-cable-use/

Different types of Connectors or better RF connectors :

  • BNC (Bayonet Neill–Concelman) –  small size makes it suitable for smaller, lower-power radios and it can handle RF up to microwave frequencies. The most used in QRP.
  • PL-259 – connect most all modern HF transceivers and VHF/UHF mobile rigs to the antenna
  • N-type – physically similar to the PL-259/SO-239 pair, the N connector can handle high power levels above 300MHz and is commonly found on UHF radios and test equipment
  • SMA (Sub-miniature version A) – connector supports RF up to microwave frequencies but due to its small size it has limited power-handling capability.
We differentiate many different use of wires:
  • antenna wire (random, long, efhw, etc.)
  • magnetic wire or formal Solderable Enamelled Copper Winding Wire (for balun or filter making, etc.)

Balun (BALanced-UNbalanced) and Unun (UNbalanced- UNbalanced) are used to improve transmitter (transceiver) to antenna radio transmission. 

  • Balun 1:1 is using a toroidal core and coaxial cable. It’s simple RF choke works as a balun by preventing signals passing along the outside of the braid. Such a device can be used to cure television interference by acting as a braid-breaker.
  • Balun 1:9 –

Traps are in short frequency switches.

Choke are meant to prevent signals passing along the outside of the braid. It’s simple device can be used to cure television interference by acting as a braid-breaker.