Transverter
| Transverter | |
|---|---|
| Name from | Transmitter plus converter |
| What it does | Converts a radio's transmit signal up to another band, and received signals from that band back down |
| Common IF bands | 28 MHz (10 meters) and 144 MHz (2 meters) |
| Common target bands | 222, 902 and 1296 MHz, 2.3, 5.7 and 10 GHz, and higher |
| Operating | |
| Drive level | From about a milliwatt to a few watts, depending on the design |
| Modes | Whatever the radio supports: SSB, CW, FM, digital |
| Control | PTT line from the radio; often a sequencer |
| Receive-only version | Converter, downconverter or upconverter |
A transverter is a device that lets a radio built for one band operate on another, usually higher, band. The name combines transmitter and converter. On receive, it converts signals from the new band down to a band the radio already covers, called the intermediate frequency or IF. On transmit, it takes the radio's low-power signal on the IF, converts it up to the new band and amplifies it. Paired with an HF transceiver or a 2-meter multimode radio, a transverter is the usual way onto the upper UHF and microwave bands for SSB and CW, where ready-made radios are scarce or do not exist at all.
How it works
A transverter contains a local oscillator (LO), a mixer, filters and amplifiers. The mixer combines the LO with the incoming signal and produces sum and difference frequencies, and a filter keeps the one that is wanted. A 1296 MHz transverter with a 144 MHz IF, for example, uses an LO at 1152 MHz: 1152 + 144 = 1296, so a radio tuned to 144.100 MHz is really operating on 1296.100 MHz. A 10 GHz transverter with the same IF uses an LO at 10,224 MHz to reach 10,368 MHz, the usual narrowband calling area.
The radio supplies the tuning, modes, filters and display, so the transverter itself can be fairly simple. The operator adds the offset mentally, or uses a radio or software that displays the real frequency.
Ten meters is a common IF for the 6-meter, 2-meter and 222 MHz bands, and 2 meters is common for 902 MHz and above. A higher IF makes filtering easier. A mixer also responds to an unwanted image frequency on the other side of the LO, twice the IF away from the wanted signal. With a 28 MHz IF at 1296 MHz the image is only 56 MHz away and hard to filter out; with a 144 MHz IF it is 288 MHz away.
Drive level and connections
Most transverters expect very little drive, from about a milliwatt to a few watts depending on the model. A 100-watt radio connected straight to an input meant for a milliwatt will destroy it. Some radios have a dedicated transverter port with a low-level output, a separate receive input and a keying line. Otherwise, the radio is set to its lowest power and an attenuator brings the level down further.
The transverter also needs a keying line from the radio so it switches to transmit at the right moment. Some can sense the incoming RF instead, but a wired line is more reliable.
Sequencing
A serious station adds a power amplifier, a mast-mounted preamplifier and coaxial relays. They must switch in the right order. When the operator keys up, the preamplifier is switched out and the relays settle before the amplifier is enabled and RF is applied; returning to receive, the steps run in reverse. A sequencer does this with delays of a few tens of milliseconds between steps. Without one, a relay can switch while carrying RF, which pits its contacts and can destroy the preamplifier.
At 10 GHz and above, feed line loss is so high that the transverter is often mounted at the antenna, with only the IF, power and control lines running to the operating position.
Frequency accuracy
Any error in the LO appears directly in the output. An LO only one part per million off at 10 GHz puts the signal about 10 kHz away from where the dial says, and temperature changes make it drift. Microwave stations therefore lock the LO to a precise 10 MHz reference, often a GPS-disciplined oscillator, so two stations can find each other quickly and narrowband digital modes decode properly.
Converters and downconverters
A receive-only version is called a converter. Before transceivers covered VHF, many amateurs reached VHF by placing a converter ahead of an HF receiver. Today, modified satellite-TV low-noise block downconverters (LNBs) are a cheap way to receive 10 GHz signals, and upconverters shift HF signals up into the range of software-defined radio receivers that cannot tune HF directly.