In a LC (inductor-capacitor) bandpass filter, there is typically a relationship between bandwidth and filter loss. Bandwidth refers to the range of frequencies that can pass through the filter relatively unattenuated, while filter loss represents the amount of signal power that is attenuated or lost as it passes through the filter.

In an ideal LC bandpass filter, the bandwidth is determined by the quality factor (Q) of the filter, which is a measure of its selectivity. The higher the Q factor, the narrower the bandwidth. However, a higher Q factor also leads to higher filter loss.

In practical LC filters, there are various factors that contribute to losses, such as the resistance of the inductor and capacitor components, parasitic resistances, and the presence of non-ideal elements. These losses can affect the filter’s overall performance, including its bandwidth and filter loss.

Generally, as the bandwidth of a LC bandpass filter increases, the filter loss also tends to decrease.

It’s important to note that the actual relationship between bandwidth and filter loss can depend on the specific design and implementation of the LC bandpass filter, as well as the desired performance requirements. Different design techniques and components can be used to optimize the trade-off between bandwidth and filter loss, balancing the desired selectivity with acceptable levels of attenuation.

Standard RF Filter

The standard filter has a loss of approx. 4-5dBm and a approx. 100KHz bandwidth.

Frequency response of the standard filter.

Low loss RF Filter

An alternative low loss RF Filter is shown below. It has lower loss approx. -2dBm and a flatter passband that covers the whole of the 40M band but has slower roll-off.

Changes

C2 and C4 change to 150pF ( NPO or COG Type Capacitors )

The turns ratio for the two coils change from 2:31 to 6:19.

Frequency response of the low loss filter.