What is an HF Triplexer?

 Sometime back we had discussed about diplexers used for LEO satellite operations and duplexers used for repeaters. Diplexer is meant for two different bands like VHF and UHF while duplexers are meant for two frequencies on the same band. Now what is an HF triplexer used for? HF triplexer is typically used to connect three radios to a single multi-band antenna as during field day operations. Advantage is that multiple radios can be operated by multiple operators without having to put up different antennas for each radio. Outputs of the three radios, operating 20, 15 and 10m bands can be combined into a single output by the HF triplexer and sent to a single triband antenna. The triband antenna should be a well tuned antenna with VSWR of 1.5:1 or lower on all bands. HF triplexer cannot be used on non-resonant antennas which need a tuner to operate. Additional protection for the receivers are needed to prevent overloading from the other transmitters connected to the HF triplexer.

Insertion losses of HF triplexers are usually low, in the range of 0.25-0.35 dB. Isolation by the HF triplexer from the other bands may range from 20 to 40 dB, which is not enough to protect the receivers. Though receivers can take a power of up to 1W without getting damaged, they can work well only if the interfering signal is less than 1mW. That would mean 30dB additional attenuation needed at the input of each radio. This can be achieved by using additional band pass filters at the input of the radios in addition to the HF triplexer. Both the HF triplexer and the bandpass filters should have specifications matching the power output of the radios to be used. Typical HF triplexers are for 200W operations. Harmonic interference can be expected on 10m from the 20m radio output. That can be avoided by not working on the exact harmonic of the frequency being used by the 20m radio.