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Bias tees come in useful for a variety of applications where power and or signalling is needed down a run of coaxial cable. This can be used to power remote devices at the far end of a transceiverís coax. Pre-amplifiers, relays, ATUs and switches can all be controlled this way:combining radio, power and signalling down one common coaxial cable. No longer can you just send RF down a cable and supply components with power or signalling with an additional cable. There is no reason not to combine signals with the right components.


Bias tees fit that nicely if they are designed properly. Here is shown a simple design worthy of inspection as itís performance has proved itself in the home installation. You will need two, one to inject the power and one to recover the power at the far end. The RF paths are AC coupled no DC power should be injected back into the transceiver or to the antenna.



This design of bias tee is fabricated as in previous designs within a small die-cast aluminium box measuring approximately 95 by 30 by 30mm. This size box appears suitable to mount all the components without too much fiddling. RF connections are made with N-type connectors and the DC connection is provided via an SMA socket.


Measured performance.


This specific design has undergone a number of performance tests to establish the suitability for its intended use. Insertion loss, VSWR, RF to DC port isolation and AC and DC power handling characteristics were all primary considerations.


Insertion loss with the prototype shown was measured (1.8 to 30MHz), this was measured as < 0.1dB.† VSWR < 1.03:1. RF/DC port isolation >96dB (120dB loss 1.8 to 18MHz). DC current capacity 1.0 amp max, working current 0.5amps. Maximum DC supply voltage 26v, working voltage 24 maximum. Maximum RF power, this could be the 400w, but as yet to be measured. Below is the plot showing RF/DC port isolation and the circuit diagram.


Extension to a new radio system is currently being developed to provide computer controlled remote HF antenna switching for the new antennas being developed at the home QTH.

HF Bias Tee

For additional information which includes photos, component listing and all the other frequency plots, please use the contact email address given on this website.