W8ZR Multicontroller Overview

Overview

Welcome to the website for my homebrew "HF Receiver Multicontroller," described in the May 2004 issue of QST. Click on the above navigation panel for technical details, answers to FAQs, schematic diagrams, assembly instructions and other information. [NOTE: Circuit boards and enclosures are no longer available for sale.]You can also post a message to the multicontroller discussion group. I hope you find the site useful and that you'll email me your comments and suggestions. Let's all do our part to keep the homebrew art alive! Thanks!
---Jim Garland W8ZR

	WHAT IS IT? The W8ZR Multicontroller is a broadband antenna distribution amplifier for hams and SWLs who have several receivers and need a convenient way to switch among them. It has inputs for both 50 ohm and high-Z antennas, with active outputs for up to 8 receivers. The multicontroller spans 0.1-55 MHz, with an optional filter to screen local AM broadcast band signals. It also can mute any combination of up to seven receivers, so that comparing receiver performance or switching between receivers in a contest is just a matter of flipping a switch.
In addition, the multicontroller has a control input that can be used to mute simultaneously all the connected receivers. Hook up the control jack to your transceiver's external relay line and all the receivers in your station will mute when you transmit. An overload circuit automatically disconnects the receivers if dangerous RF voltage is induced onto your receiving antenna.
Another useful feature is a wideband +12 dB low noise preamplifier to perk up older vacuum tube receivers and help compensate for poor antennas. In addition, the high-Z antenna input can be used to match short wire antennas to 50 ohm receivers. What this all means is that the multicontroller can greatly simplify your station's operation, since you won't have to hook up a snarl of cables when you want to change, evaluate, and compare your receivers.

IS IT HARD TO BUILD? The multicontroller uses readily available off-the-shelf parts. The entire circuitry is contained on four printed circuit boards, with no point-to-point wiring. For those (like me) who don't enjoy filing, drilling, and labeling panels, I've also ordered a limited number of custom metal enclosures, with prepunched and silkscreened panels. You can also obtain complete parts lists from this site and easily order the other parts from on-line distributors. To simplify construction, you can also download detailed assembly instructions and other information.

The Multicontroller's circuitry is housed on four modular printed circuit boards that snap together to eliminate point-to-point wiring. The completed boards then slide into slots in the enclosure, so that no drilling or mounting hardware is required. Once the parts are gathered, it takes 7-10 hours to wire the boards and assemble the completed unit.
	The guts of the multicontroller are on one large double-sided circuit board. Commercial accessaries often use inexpensive "wall warts" to save manufacturing costs, but I don't like them cluttering up my station. The multicontroller runs off 115/230 VAC and has a built-in power supply that supplies +/- 12VDC and +/- 5VDC.
An x-ray view of the main circuit board shows the top copper traces in red and the bottom traces in light blue. Most of the RF circuitry is on the right side, where a large (blue) ground plane enhances shielding and minimizes crosstalk between the multicontroller's 8 channels. The small rectangular red area on the right is a top-side ground plane for the wideband preamplifier. Careful attention to layout and shielding of the preamp circuit ensures unconditional stability over its wide frequency range.
	My original multicontroller took six months to build. It was particularly time-consuming to lay out the printed circuit boards, drill and label the front panel, and debug the circuitry. On the left is the most recent multicontroller, with its custom silk-screened and prepunched panels and the latest revision circuit boards. This one only took me about 6 hours to build! I didn't plaster my callsign on this version, since I figured you'd rather not have "W8ZR" displayed in your station.

HOW MUCH DOES IT COST? If you duplicate mine exactly with all new parts, the multicontroller will set you back about $225-$250. I know this is a lot of money, but the multicontroller isn't a mass-produced product. Furthermore, building one's own gear means there is no need to cut corners, so I've designed the multicontroller to very high, instrument-grade standards. Thus, if you can stand the hit to your wallet, you'll find that this project is not only fun to build, but will also dress up your station.

If you missed me at the 2004 Dayton Hamvention (left) and have questions about the Multicontroller: Click on the FAQs link here or on the banner.

Please let me know if you have any comments or suggestions about the multicontroller or this website. I welcome email. Thanks for looking!