High Performance Radio
I build radios for fun, and to stay sharp in electronics. In 2011 I started a project to build my entire radio station using commercially available components. For those components and modules not available at a reasonable price (or not available at all), I had to make my own. Because it takes about 10-25 man-years to design and produce a modern HF transceiver, I had to rely on commercially made modules as much as possible in order to reduce development time. The end result was a series of innovative uses for existing components which led to a radio of a rather different design concept.... and the performance has proven to be surprisingly good.
The first radio featured a single conversion design with a wide bandwidth IF at 50 MHz. I used readily available 50MHz low noise amplifiers in the IF, with a 100KHz-30MHz low noise amplifier as a front-end RF amplifier. the initial construction took about 4 months, with much of the time spent developing the hardware and firmware for a state-of-the art dds synthesizer that was capable of doing the job. When completed, the radio was found to have superb sensitivity and a remarkable absence of spurious responses (birdies) as are commonly found in present-day dual , and triple conversion radios. The operational frequency range of the radio is 100 KHZ to 30 MHz, continuously tuning, with a measured SNR of 0.05 uV @ 10 dB or better, and frequency stability greater than 0.25 ppm. The DDS boards share a common heat sink allowing thermal tracking of the on-board TCXO, and the single conversion design tends to compensate for TCXO drift , since they are both likely to drift in the same direction, and at similar rates. Two years after an initial calibration against WWV to within 0.5Hz, the receiver remained within 2Hz accuracy. The radio was capable of receiving on HF and on the 50MHz ham band at the same time by using the 50MHz IF as a direct conversion receiver. The radio was controlled via RS-232 using commonly available terminal software, and the DDS boards communicated cooperatively using a controller area network.
A third DDS board was soon added as a transmitter/exciter. A 15W transmit driver was built from a Motorola reference design, with a 180 watt rf power amplifier added later. An RF filter deck for the HF transmitter with coaxial relay switching was constructed to assure that the spectral purity of the transmitter met FCC requirements.
Later, the IF was split, and a fourth DDS board was added to allow the addition of a 1.8 MHz software defined radio. In this configuration, the SDR was a dual conversion radio, with the analog radio remaining as a single conversion design with a double sideband detector. The open source package "QUISK" was used on a PC running Linux to demodulate the I/Q output using a sound card as an analog to digital converter. The SDR and the analog radio were usable at the same time.
Images of this radio
The inside of the bottom chassis of the radio. The software defined radio is in the small box on the left side wall of the chassis.
The DDS board. This is at the very heart of all the radios on this page. This board has made so many things possible.
The radio a year or so later, showing the selector switch for the RF deck, the noise bridge, and the 15 Watt driver amplifier. The 180Watt power amplifier is in the rear of the rack with the RF deck.
A closer view of the front of the rack installation.
The RF deck, with plug-in filters.
The coaxial relays for the RF deck.
The station went through a process of evolution where I developed a concept of how this radio ought to work. I eventually developed a new version of this concept. This new radio featured a 70 MHZ IF, with continuous coverage from 50 KHz through 52 MHz. Receiver SNR is measured at 0.1uV @ 10 dB across the operational range.
A complete radio consists of a receiver/IF board, a DDS synthesized local oscillator, and a DDS synthesized beat frequency oscillator, and an AF board. A third dds board may be connected to the controller area network to use as a transmitter/exciter. A new control head with optical shaft encoders can be added to the radio. Additionally up to 16 radios can be connected to the CAN , with each radio individually controllable from a single control position, either via RS-232 or by means of the control head. This new radio is much smaller, and is comparatively inexpensive as compared to the original. The new AF board has a switch selectable active filter for reception of CW. Using these boards it is possible to build a complete radio that will fit in the palm of your hand and weigh in at less than a pound.
Images of this radio.
An early prototype
The radio with control head.
Inside the radio.
The control head board
The receiver/IF board
Te receiver AF board.
Thus far, all of the radios shown have been limited to continuous wave radiotelegraphy. I wanted something a little more, with a few more features, and the ability to transmit SSB voice signals. I wanted to build a full-featured HF transceiver.
I started by developing a filter type single-conversion SSB exciter/transmitter prototype. Once I had the transmitter working, I began using it on the air with good results, and proceeded to built my latest radio. Using parts cannibalized from my older projects I assembled the radio in about a month, with a couple of weeks to work out the software and assorted bugs and quirks. The end result was a nice HF transceiver capable of reception from 100 KHz through 30 MHz, and transmitting from 1 MHz through 30 MHz. It supports continuous wave radiotelegraphy, single-sideband with and without carrier, and full double sideband with or without carrier.
Images of this radio
The prototype transmitter under construction.
The prototype transmitter with LCD and optical shaft encoder.
The completed transceiver.