What is the sensitivity?
On our first direction finders, the receiver’s squelch was used to determine whether a signal was present or not. It was necessary with these models to adjust the squelch so that the receiver remained squelched under no signal conditions. The sensitivity was then equal to the squelch threshold of the receiver which was approximately the same whether the receiver were connected to the direction finder summer/antenna or to a single antenna element of the same type used in the direction finder. (For mobile operation this would correspond to a single magnetic mounted whip). On current models, the direction finder may be operated with the receiver’s squelch opened, and the sensitivity is greater.
We measure sensitivity by driving the inputs to the RF summer through a signal splitting device that simulates the antenna. The input signal level is adjusted until the standard deviation of the bearing is approximately 5 degrees. This input level, after compensating for the loss in the signal splitter, then corresponds to the published sensitivity. The measured values will depend on the receiver used, and in our case, we use an Icom R8500 in the NBFM mode (15 KHz bandwidth). Typical values measured in the 150 MHz range are:
|*Summer with overload protection|