1101242-5
(rev.
6-98)
MENTOR
RADIO
CO.
The three indicator lights at the upper right on the front panel are all of the high brightness
light-emitting diode (LED) type. They operate only when transmitting. From left-to-right
the indicator functions and colors are: transmitter carrier (yellow), modulation (green) and
antenna (red).
The transmitter carrier indicator circuit samples the transmitter radio frequency power out-
put at the Model MB antenna connector. Thus the circuit is more than just a “stuck micro-
phone” indicator. If the lamp is on, the transmitter is producing a radio frequency carrier
signal. If the microphone p-t-t switch is pressed, and the lamp does not turn on, the trans-
mitter is not working properly.
The modulation lamp should light only when the operator speaks into the microphone.
Due to the nature of voice modulation, this lamp will “flicker” as you talk. Failure to light
indicates a problem in the microphone, the microphone connector or the modulation cir-
cuits. Note that the lamp will not light if the microphone is held too far from the speaker’s
mouth.
The red antenna lamp warns of a bad antenna system. It lights when transmitting if there is
more than 10% reflected antenna power. This is equivalent to an SWR (standing wave ra-
tio) exceeding 2:1. Most good antenna installations have an SWR less than 1.6, with re-
flected power less than 5%. If the ANT lamp lights, a person skilled in antenna installa-
tions should inspect the coaxial cables, connectors and the antenna itself, and correct any
problems found. Note that some antennas must be cut to a certain length to match the fre-
quency in use. If the Model MB has two or more widely spaced channels, a “broadband”
antenna may be necessary to achieve low reflected power on all channels.
Note: The Model MB is designed to withstand high SWR. It
is not necessary to cease transmissions if the ANT lamp
comes on. However, the system should be inspected as soon
as possible, since performance is impaired. In particular,
make sure the antenna connector on the rear of the MB has
not been inadvertently removed or loosened.
Thoughtfully used, the three transmitter indicator lights can suggest the causes and solu-
tions to many communications problems.
