Mobile rig
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This article is about Amateur radio, for commercial equipment, see Mobile radio.
A mobile rig, or automobile rig, is a class of amateur communications system that is midway between a base station (building-mounted) and portable (body mounted). It is mounted to a motor vehicle usually with the microphone and control panel in reach of the driver. In the US, such a device is typically run off of the host vehicle's 12 volt electrical system.
Mobile rigs can be home-made by amateur radio enthusiasts or may be purchased from an amateur radio equipment supplier and immediately used out-of-box. In the US, some amateurs modify commercial two-way radios and use them on amateur frequencies. A typical mobile rig consists of a radio transmitter-receiver, typically housed in a single box, and a microphone with a push-to-talk button. Each installation would also have a vehicle-mounted antenna connected to the transmitter-receiver by a coaxial cable. Some models may have an external, separate speaker which can be positioned and oriented facing the driver to overcome ambient road noise present when driving.
Amateurs were pioneers and experimenters who developed the first mobile radio equipment. Early mobile rigs operated on High Frequency (HF) bands. Some were amplitude modulation phone (voice) and some used continuous wave, (CW) to send Morse code messages when parked. Because of wavelengths in the 15- to 80-meter range, HF antennas were large and the antenna patterns were affected by the host vehicle's steel body. Electrical traits of antennas were modified so they would not have to be a full quarter wavelength. Tube type radios used dynamotors - essentially a twelve volt motor that turned a generator to make high voltage B+. Some early mobile rigs were the size of a suitcase. Later technology evolved to use vibrators and solid-state power supplies in order to make high voltage for the tubes. These circuits included inverters which changed the 12V DC to AC which could be passed through a transformer to make high voltage. The high voltage side of the transformer was rectified to make DC for the vacuum tubes, (called valves in British English). A common trait of tube type mobile rigs was their heavy weight partly caused by every design including iron-core transformers in power supplies. High voltage supplies were inefficient and tube filaments added to current demands, taxing vehicle electrical systems. Amateurs expanded the technology to work on frequency bands into the centimeter wavelengths, UHF.
Solid state equipment arrived in the 1960s, with more efficient circuitry and smaller size. By the mid 1970s, tube-type power amplifiers had been replaced with high-power transistors. Modern equipment is microprocessor controlled, operates on multiple frequency bands, and has built-in options such as cross-band repeat. Amateurs pioneered telephone connectivity and packet radio data communication from cars. Mobile vehicular or ship-based systems exist today including amateur wireless systems in trucks, vans, cars, boats, or motorcycles. A wireless station on a bicycle such as N4RVE's behemoth would also be categorized as Mobile.
