# What kind of losses do you get from an LC network matching the antenna's impedance?

If you have a transmitter that is perfectly on your frequency but you have an antenna with some impedance what types of losses, and of what magnitude, will you expect from a tuner in between your transmitter and antenna?

For example lets say your system as a whole with no tuner has an SWR of 3 and your system with a tuner is now 1:1. Are there power losses from an LC network used to match impedances?

What are these losses called? Is it easy to calculate wasted power? Is it frequency dependant? Is there a way to approximate delivered power from a given capacitance and inductance on a line with a specific SWR?

## 1 Answer

An ideal LC network causes no losses whatsoever, because ideal inductors and capacitors do not dissipate power — they have no resistance. The actual loss in your matching network is determined by the actual resistances of the components. It is frequency-dependent because the overall behavior of the network is, and it is also power-dependent due to saturation of inductors' magnetic cores (unless your inductors are air-core).

The other major source of loss in this type of configuration is the loss due to standing waves in the feed line between the antenna and tuner (just as if you were not using a tuner). This is why tuners are best placed near the antenna rather than the transmitter.

• The feedline losses are not always the largest loss. Analyses by W8JI and VK1OD both showed that the T network (the most common tuner topology) can be as poor as 35% efficient when the inductance is near maximum and the impedance mismatch is near the maximum that the tuner can compensate for. Even in more moderate situations, they are often worse than 60% efficient. With 100 feet of ladderline, the tuner could contribute 10 times more loss than the feedline in an extreme case.. – Hamsterdave Mar 12 '17 at 1:10
• @Hamsterdave Thanks for the correction; I have removed that claim. – Kevin Reid AG6YO Mar 12 '17 at 1:20
• @Hamsterdave - I fully agree. However, those are worst-case scenarios for a T-network tuner when not adjusted properly. To minimize losses, the user has to adjust it using as little inductance and as much capacitance as possible to obtain a good match. And one thing that hams overlook is that significant loss in a tuner manifests itself as heat. It often only takes a few watts of loss to make the coil in a 300 watt rated tuner burn your fingers. Ever touch a resistor operating near its maximum rating? Ouch! :-) – Mike Waters Mar 12 '17 at 20:58