Application Note #9

Subject: Rainbow Tuner System Configuration

I've had several questions about how to wire up the Rainbow Tuner. Here is some info about how this can be be done.

The Rainbow consists of two main blocks, an SWR bridge and an antenna tuner. The two are not connected together on the pc board so that they can be used separately. The blocks are shown below:

The SWR bridge IN and OUT connections are shown paired for coaxial cable connections. There is actually only one GND pin. It should be wired to the shield of the coax cable. These connections are on the left hand side of the Rainbow PC board.

The tuner connections are located on the right-hand side of the PC board. There are separate GND pins for both sides of the tuner. Actually the "50 OHMS" and "GND" pins shown here on the left and located at the upper right of the pc board are mis-labelled (on the PC board, that is). The one that is marked "50 OHMS" is actually GND and vice versa. The ANT and GND pins are marked correctly.

The GND connections on the PC board are completely separate between the SWR bridge and tuner sections since carrying through the ground on the board would have meant a more sophisticated (expensive) printed circuit board. Since the connection must be done externally, it is recommended that coaxial cable be used to make sure of a good 50 ohm shielded connection.

Switch S1 is used to switch the SWR bridge in-line when the tuner is being adjusted or to bypass it after tuneup. The bridge has a 6 dB loss, so you probably don't want it in-line except while you are checking SWR. The SWR bridge GND pin is connected to the shield of both connectors J1 and J2. As mentioned above, the connection between bridge and tuner should be made with coax cable. The coax cable *can* be hardwired (eliminating connectors J2 and J3) if you *never* want to use either the bridge or the tuner separately.

Strictly speaking, switch S1 is not really necessary. My prototype Rainbow used connectors J1, J2 and J3 without the switch. To put the bridge in-line, I connected the xmtr cable to J1 and ran a jumper coax connector from J2 to J3. After tuneup, I disconnected the coax jumper from J3 and ran the xmtr coax in its place.

Coaxial connectors can be any convenient type. If the Rainbow is mounted in an Altoids tin or other small container, RCA phono jacks are an inexpensive choice. If you have them available, SMA connectors are even smaller. If size is no object, BNC type connectors are a very good way to go. And if no attempt at miniaturization is made and commonality with other ham gear is important, the ubiquitous SO-239 "UHF" connector can be used.

Connections to any of the coax connectors mentioned are generally as in this figure.

Hope this helps!

72/73,

Joe E., N2CX
from Southern New Jersey, y'all
home: n2cx@voicenet.com