10 Position Dip Switch Settings

Here is a programming aid to help determine settings for R301, R304, T301, T304 Units and newer R302 Receivers.  (Note there is a separate page for other units.)  This is information too lengthy to publish in the instruction manuals, and it includes a chart for all possible frequencies.

Setting Channel Frequency.

The channel frequency is determined by frequency synthesizer circuits, which use a dip switch in conjunction with programming in a microcontroller to set the channel. The microcontroller reads the dip switch information and does mathematics, applying serial data to the synthesizer ic whenever power is applied or the dip switch is changed. Following is a discussion of how to set the dip switch to the desired channel frequency.

NOTE: If the frequency is changed more than about 1 MHz, a complete alignment of the receiver should be performed, as described in later text. Optimum operation only occurs if the synthesizer is adjusted to match the frequency switch setting and all the tuned amplifier circuits are peaked for the desired frequency.

To determine what channel frequency to use, the microcontroller adds the frequency information from the dip switch to a "base" frequency stored in eprom used for microcontroller programming. Each model of the Receiver or Exciter has a particular base frequency. For example, the R301-2 has a base frequency of 144.000 MHz, as shown in Table 1 in its instruction manual. Refer to the table in the manual for your unit to determine the base frequency for the unit you have.

Dip switch settings are binary, which means each switch section has a different weighting, twice as great as the next lower section. Sections have weights such as 5 kHz, 10 kHz, etc., all the way up to 2.56 MHz. (See Table 2 or the schematic diagram in the manual for switch values.) For very large increments, there is even a jumper which can be added to the board between E6 and E7 for a 5.12 MHz increment.

The system sounds cumbersome, but it really is fairly simple, and you don’t need to do this frequently. The instruction manual tells you how to program the dip switches using a piece of paper or a small calculator to aid in determining which sections of the switch to turn on. The following chart gives settings for all possible frequency combinations of the dip switches and the jumper.

To use the chart, first determine the base frequency for the band you are using, for example, 144.000 MHz as mentioned above. Subtract that base frequency from the channel frequency you want to use. Then, look up the resulting difference frequency in the chart below.

Next to the frequency you choose in the chart is a stream of data, indicating:

• whether or not a jumper is required from E6 to E7 – "J" = jumper and "N" = no jumper.
• settings for the ten dip switches positions, from 1 to 10, listed in two groups of 5 just to make it more readable. "0" indicates switch position open, and "1" indicates switch position closed.