Theory of Operation
9
Frequency Response
Bird Plug-In Elements have a flat frequency response over their specified
operating range. A sample set of curves is shown in
Figure
5
. Notice that for the
low power element, the rolloff outside its frequency band is more pronounced
than for the high power elements. For example, at 40 MHz the 10C element will
have a loss of 4 dB, giving a reading of about 40% of the true value For the 100C,
the loss will only be about 1 dB, for a reading at 80% of the true value, and the
500C should be within the normal 5% of full scale tolerance.
Figure
5
Representative Frequency Response
These curves are typical for all element types (H, A, B, C, D, ...) at their
respective frequencies. Since C elements have a frequency range of 100 - 250
MHz, response curves for other element types can be approximated by
replacing the 100 and 250 MHz points on the chart with the extremes of the
element’s frequency range, and recalculating the other frequency points
accordingly. For example, for a B element (range 50 - 125 MHz) simply divide all
frequencies by two. For an E element (range 400 - 1000 MHz) multiply all
frequencies by four.
Harmonics or subharmonics that lie outside of the frequency range of the
element may exist in the circuit under test. A rough approximation of the
element’s response to harmonics can be made with these curves. Using an
element for measurements outside of its frequency range is not recommended.
The response curves presented are only typical, and not guaranteed.
