Introduction

I bought my RCS-4 at a ham fest. It consisted of the Control Box and the Relay Box, for $15. That was because the Relay Box had burned up, and the original owner did not want to fix it. He had cleaned up the internal PC board and removed the burned parts, but then decided to just sell it. I had to do some cleanup and replace some parts, but it's been working fine since then. And that was over 20 years ago. I guess I'm not sure how you manage to burn up the Control Box.

Description

The Ameritron RCS-4 is intended for remote switching of up to 4 antennas. It consists of two separate boxes, the Control Box and the Relay Box. The Control Box is small and stays in the shack and connects to your transceiver with a short (1' to 3') of coax. Depending on the antennas your working with, there might also be a Antenna Tuner between the transceiver and the Control Box. The Control Box adds a voltage (0V, -V, +V, AC) to the output coax using a technique call the Bias-T. The Bias-T technique adds a control voltage at one end of a section of coax, and then extracts it at the other end. The voltages are isolated at each end using high voltage capacitors.

Note: While it isn't spelled out on the diagrams, the Control Box has two connectors. One says "To Station" and goes to the transceiver. The other says "To Relay Box" and goes to the coax that leads to your antenna. If you include a device to match your antenna (Antenna Tuner), it needs to be on the "To Station" side. Try not to get them mixed up. The RCS-4 will not work properly if connected backwards.

The Relay Box is intended to be mounted remotely, at the feed point for up to 4 antennas. At the input to this box, the added conrol voltage is removed from the coax and is used to control a bank of relays. With the Control Box powered off, the control voltage is "0V", which routes the RF on the input to Antenna 4. When the control voltage is "-V" or "+V", Antenna 3 or Antenna 2, respectively, is selected. When the control voltage is "AC", Antenna 1 is selected. All of the control voltages are decoupled from the switching relays and do not appear at any of the antenna terminals. When there is no power applied to the Relay Box, Antenna 4 is selected.

The RCS-4 in Reverse

It's possible for the RCS-4 to be used in reverse. By that I mean, it can be used in the shack to select one of four possible rig setups, that feed a single antenna. I have done this myself. I had a situation where I had multiple radios at my operating position. I had a IC-735, a SB-101, a HR-1680/HX-1681, and a HW-8 all being fed with a single coax from a multi-band dipole. It was annoying to have to reach behind all the radios and switch to the one I wanted to use. So I employed the RCS-4 in the shack. The diagram on the left shows this setup. I just secured the Relay Box to the side of my shelving and used short jumpers to connect everything up. The coax leading to the antenna can include a tuner.

RCS-4 Relay and Control Box Schematic (older)

Below is a schematic of the RCS-4 Relay Box and Control Box, that I have. It is considered to be the older design with the open-frame type of relays. I have seen some complaints that the route from input to output is slightly different, depending on which antenna is selected. You can see this by tracing the route for the RF, in the drawing below. But I don't recall seeing any figures that indicated that it really matters. To me, its just nit picking a perfectly good unit.

On the right is the schematic for the RCS-4 Control Box. This box is intended to sit near your transceiver, and be between your transceiver and your antenna feed line. Depending on your antennas, there may also be a antenna tuner between the transceiver and the RCS-4 Control Box.

Note: Do not place a tuner after the RCS-4 Control Box. That would disrupt the voltages added to the coax, which are needed to switch the remote RCS-4 Relay Box.

Operation of the RCS-4 Control Box is pretty simple. There are two half-wave power supplies. One for positive voltage (+V) and one for negative voltage (-V). The voltages will be about 14 VDC at the rotary switch. The rotary switch selects one of four voltages (0V, -V, +V, AC). These voltafes are coupled to the coaxial cable center conductor with RFC-2. Capacitors C1, C2, and C3 isolate the transceiver from the added voltage and couple the RF to the coaxial cable. This arrangement is known as a Bias-T. On the other end, at the RCS-4 Relay Box, a identical circuit is used to extract the switching voltages from the coaxial cable, before it is applied to the feed point of the antenna.

RCS-4 Relay Schematic (newer)

On the right is the schematic for the newer version of the RCS-4. It takes the same 4 input voltages that the older version used, but is a bit more streamlined. Schematically, the relays may look similar, but they are not. The older version used three open-framed relays with DPDP switches. Whereas, the new version uses smaller encapsulated relays with SPDT switches.

Operationally, the new version is the same as the old version. With no power applied (0V) from the Control Box, Antenna 4 is selected. Applying -V activates RLY202 and RLY203 selecting Antenna 3. Applying +V activates only activates RLY201 selecting Antenna 2. Lastly, applying AC activates all the relays and select Antenna 1.

I didn't include a schematic for the new Control Box because, for the most part, it is exactly the same as the old Control Box. Although, some where over the years Ameritron removed the power transformer and added a Wall Wart transformer. The Wall Wart transformer simply supplies 12 VAC to the Control Box, which take care of the rest. Personally, I would rather have the transformer in the Control Box. I find that Wall Warts are clumsy and take up too much room.

Note that there are no values on some of the components. Like C202 and C201. That's because, on the schematic I obtained, there were no part values. I don't recall where it came from. However, the intended purpose of C202 and C201 is to provide extra filtering for the DC voltage applied to the relays and are probably around 100 µF. This help to keep the relays from dropping out.