working right, you can’t tell the voter is there. We usually have the output selector connected to our repeater
controller (all CAT-300s and 500s) to change the tail beep to different tones for identification of different
site selections because we can’t tell which site is selected by audio alone.
Since the audio actually only passes through one op amp and one analog gate, there is very little
distortion compared to the original signal (much less than 1db). Cross talk between channels is typically less
than -60 db. The passband is 30 to 20,000 Hertz. All subaudiable tone are passed.
Once the audio characteristics are matched properly, you can use the noise adjustments (R41-48) to
tailor your particular installation. In a system with a receiver at the repeater site, you may want to increase
the noise for that site slightly to force selection of the remote sites.
Trouble Shooting:
In case of trouble, start with the basics. Look at the solder connections and check for bridges. Be sure
all the parts are in the proper place and polarity is correct. Use the voltage test points to check for specific
voltages.
There are a few things that can go wrong with building the kit, but the kits are very reproducible. Our
first ten assemblies of the V2.0 PC boards yielded ten voters that worked first time and provided identical
performance.
If your unit is not working at all, but you have good voltage and amps checks, look at the crystal clock
on the 68HC11 with a scope coupled through a 10 pf capacitor. If you don’t have a scope, tune an HF radio to
8.0 MHz and listen for the clock. If there is no clock, this may also indicates that the code is not executing. Look
around the sockets and connections between U1 and U2 for problems.
If there is still no LCD data, look at the data lines going to the module. You should be able to see data
being sent with and O-scope. Check the Contrast voltage, it should be near 0.1 volts.
For audio problems, diagram 1 shows typical audio voltage and signal readings taken with a signal
generator and oscilloscope a various stages of the voter for channel 1. These readings are meant to be used for
trouble shooting and initial calibration. Once set up in your system, the actual readings may vary somewhat
depending on how customized the installation is.
Most voting problems result from mismatched audio levels or characteristics. To check for those types
of problems, move a misbehaving channel to another input. If the problem follows, it’s probably the audio
from the receiver. Also, be sure there is no distortion before connecting to the Voter.
If your receiver is expecting to see a low impedance load (8 to 600 ohms), you may have to place a
loading resistor across the output of your receiver for proper impedance matching. Since the input to the voter
is high impedance, it will not load down your receiver.
For COR problems, be sure to check the Disable and Disable States menus and the Disable hardware
inputs (J3). If any of these have been set in a position that you do not expect, the result may seem like a COR
malfunction.
If something should occur that would prevent one channel from having less than 3.5 volts DC on its
noise test point, readjust all channels to read 3.0 volts DC. You can go as low as 2.5 volts for all channels for
the noise test point voltage and still maintain good performance from the voter.
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