Transmitter Boards Design

[NZ0I]

The 2-Band ARDF Transmitter boards design is far enough along to draw a few conclusions:

The full-featured transmitter will consist of four separate boards: Digital Interface, Transmitter, Antenna Matching, and Power Supply. Only the first two boards are required. You can skip the Antenna Matching board if you plan to handle 80m antenna matching outside the transmitter. Likewise, if you plan to use an external 12V battery or power supply you can leave out the Power Supply board.

In order fit all four boards into the same chassis box, a larger Hammond box is required. The Hammond 1554G2GYCL costs only about $1 more than the originally targeted box, provides about 0.8-inch of additional vertical height, and has an identical PCB footprint. So it appears that the Hammond 1554G2GYCL will do the job, and still this will be a very compact transmitter, and no redesign of the PCBs is required.

The Power Supply board will have a battery holder for an 18650 LiIon battery, so the board will be fully self contained, with no external battery required. It will support charging from a USB +5V source (located on the Digital Interface) or a 5V-6V 1A wall wart power module.

The Antenna Matching board will hold separate SWR sensors for the two bands, and five relays (32 combinations) for selecting the best capacitance value for matching the 80m antenna. Antenna connectors will be Phoenix CombinCon connectors (0.3" pitch). The 2M band antenna connector will have 3 conductors (RF, gnd, sense), and the 80m antenna connector will have 4 conductors (RF, gnd, sense1, sense2) - the different sizes will make it difficult to connect an antenna for the wrong band. The sense lines are grounded to indicate the presence of an antenna, and for 80M the type of antenna (classic, sprint, or fox-O).