H - Hotel - di-di-di-dit
H.
Half-Duplex Operation.
Communication in both directions, but only one direction at a time (not simultaneously). Typically, once a party begins receiving a signal, it must wait for the transmitter to stop transmitting, before replying.
See also: Duplex Operation, Full Duplex Operation, Simplex Operation.
Half-Wave Dipole.
A basic antenna used by radio amateurs. It consists of a length of wire or tubing, opened and fed at the center. The entire antenna is ½ wavelength long at the desired operating frequency.
Half-Wave Rectifier.
A circuit that allows only half of the applied ac waveform to pass through it.
Ham-Bands-Only Receiver.
A receiver designed to cover only the bands used by amateurs. Usually refers to the bands from 80 to 10 meters, sometimes including 160 meters.
HB9CV.
A very popular two-element beam which can be considered as a log-periodic dipole array with only two elements.
Hamfest.
American for Radio Rally.
Hand-Held.
A portable transceiver small enough to fit in the palm of your hand or clipped to your belt. Sometimes called an H-T, Handie-Talkie or Walkie-Talkie.
Harmful Interference.
Interference that seriously degrades, obstructs or repeatedly interrupts a radio communication service that is operating in accordance with the Radio Regulations.
Harmonics.
Signals from a transmitter or oscillator occurring on whole-number multiples (2×, 3×, 4× etc) of the fundimental or operating frequency.
Helical Antenna.
A helical antenna is an antenna consisting of a conducting wire wound in the form of a spiral, or helix. In most cases, helical antennas are mounted over a ground plane. Helical antennas can operate in one of two principal modes: normal (broadside) mode or axial (or endfire) mode.
In the normal mode, the dimensions of the helix are small compared with the wavelength. The far field radiation pattern is similar to an electrically short dipole or monopole. These antennas tend to be inefficient radiators and are typically used for mobile or Hand-Held communications where reduced size is a critical factor.
In the axial mode, the helix dimensions are at or above the wavelength of operation. The antenna then falls under the class of waveguide antennas, and produces true circular polarization. These antennas are best suited for animal tracking and space communication, where the orientation of the sender and receiver cannot be easily controlled, or where the polarization of the signal may change. Antenna size makes them unwieldy for low frequency operation, so they are commonly employed only at frequencies ranging from VHF up to microwave.
Axial-mode helical antennas can have either a clockwise (right-handed) or counter-clockwise (left-handed) polarization. Helical antennas can receive signals with any type of linear polarization, such as horizontal or vertical polarization, but clockwise polarized antennas suffer a severe gain loss when receiving counter-clockwise signals, and vice versa.
Helical Resonator.
A compact resonant filter circuit to block multiple interfering signals.
Hellschreiber.
A method of sending and receiving text using facsimile technology. This mode has been around along time, it was developed by Germany prior to World War II. The recent use of PC sound cards as DSP units has increased the interest in Hellschreiber and many programs now support this new...well old mode. There is a single-tone version (Feld-Hell). This the method of choice for HF operation. It is an on-off keyed system with 122.5 dots/second, or about a 35 WPM text rate, with a narrow bandwidth (about 75 Hz). Text characters are "painted" on the screen, as apposed to being decoded and printed. Thus, many different fonts can be used for this mode including some basic graphic characters. A new "designer" flavour of this mode called PSK HELL has some advantage for weak signal conditions. As with other "fuzzy modes" it has the advantage of using the "human processor" for error correction; making it the best overall mode for live HF keyboard communications. Feld-Hell also has the advantage of having a low duty cycle meaning your transmitter will run much cooler with this mode.
See also: Digital Modes page.
Henry (H).
The SI unit of inductance. It is named after the American scientist Joseph Henry (short history).
If the rate of change of current in a circuit is one ampere per second and the resulting electromotive force is one volt, then the inductance of the circuit is one henry.
Hertz (Hz).
The name given to the phrase 'cycles per second' named after Heinrich Rudolf Hertz (short history). 1Hz is once a second, 50Hz is 50 times a second etc. The basic unit of frequency.
HF.
HF Digital Modes.
High-Pass Filter.
A filter designed to pass high-frequency signals, while blocking
lower-frequency signals.
High Frequency (HF).
The portion of the radio spectrum from 3 MHz to 30 MHz or 3,000,000 to 30,000,000 cycles per second. Various Amateur bands exist in the HF region of the Radio spectrum:
| ITU Region 1 (Including UK) |
|---|
| Band | Frequency Range |
|---|
| 80 meter | 3.500 - 3.800 MHz |
| 40 meter | 7.000 - 7.200 MHz |
| 30 meter | 10.100 - 10.150 MHz |
| 20 meter | 14.000 - 14.350 MHz |
| 17 meter | 18.068 - 18.168 MHz |
| 15 meter | 21.000 - 21.450 MHz |
| 12 meter | 24.890 - 24.990 MHz |
| 10 meter | 28.000 - 29.700 MHz |
In popular useage HF tends to include the 160 meter MF band.
See also: EHF, LF, MF, SHF, UHF, VHF.
Homebrew.
Home designed and/or constructed equipment.
Horizontal Polarisation.
Where the direction of the radio wave oscillates side to side.
HPF.
Huffman Coding.
A lossless (reversible) coding method for data compression developed by David A Huffman whilst he was a student at MIT. As an example, imagine a block of text to be encoded and compressed. The text is scanned and a frequency table is built up of how often particular words appear. The words that appear most frequently in the text are replaced by symbols, with the table used as a key to what the symbols represent. The symbol table is transmitted with the compressed data for use in the decoding process which simply replaces all the symbols with the original words. Huffman coding is used in fax machines and various digital radio modes such as PACTOR.
See also: Digital Modes page.
Hybrid.
A class of electronics construction that uses both valves (tubes) and transistors, or latterly ICs. More recently applied to broadcast receivers and televisions that can receive both analogue and digital signals.
See also: Solid State.
Hz.