What is a Transfer Relay?

Guest Writer: Bill True, WA9ASD

That’s when you get on a bus and buy a transfer so you can give it to your buddy to use to ride his bus to work for the cost of a transfer. Well, not exactly. If you Google “Transfer Switch” most of what you will find are AC power transfer switches. These are used to switch your AC power from the power company to your backup power source; generator, solar panels or battery backup. If you have a home AC generator your power company will require one and your local building codes people will have to certify it. It could be manual or automatic. We offer a Generator Transfer Switch. 

Is it a switch or a relay? The answer is confusing. My answer is as it pertains to Surplus Sales. A switch is a manually operated device.  Contacts are actuated with a twist or flip of a lever. It must be physically switched. A relay has a coil with a set of contacts operated by an armature. apply a voltage and cause a change in the position of the contacts. Switch: manual; Relay: electric.

Amphenol 300-11002-2 Transfer Relay

Amphenol 300-11002-2 Transfer Relay

An RF Transfer Relay allows you to connect 2 transmitters to 2 loads. One to a dummy load and the other to an antenna. When the relay switches the two transmitters are swapped between the antenna and dummy load. Another way to look at them is to consider a 2 position switch with ports 1, 2, 3 and 4. At rest port 1 is connected to port 3 and port 2 is connected to port 4. When activated the connections reverse. Port 1 is connected to port 4 and port 2 is connected to port 3. Broadcasters use these to connect both their main and backup transmitters to the antenna/dummy load for almost instant changeover to the backup transmitter. It can also be used to control the antenna connection to a transmitter and receiver. In the “at rest” position the receiver is connected to the antenna and the transmitter is connected to a dummy load. By switching on the relay when the transmitter is activated the antenna gets connected to it and the receiver goes to the dummy load, protecting it from the strong RF from the transmitter.

Another kind of reverse (perverse?) usage is to provide automatic grounding of an antenna when not in use. Whenever the transceiver is powered-up the transfer relay is activated connecting the transceiver to the antenna. When the transceiver is turned off the transfer relay de-activates connecting the antenna to ground. The same thing can be accomplished with a knife switch for open wire feed lines.

We have a couple of very high quality “N” Transfer Relays available from some of the most highly regarded manufacturers; Amphenol, DowKey and Transco (now a part of Dow Key Microwave). SMA Transfer Relays by DowKey. C connector Transfer relays.  EIA Transfer Relays for the Broadcasters.  Waveguide style Transfer Relays.

As you can see, transfer relays can be an important and valuable addition to your station. Call us if you have any further questions.