Net/Rom Node Information for the Sysop - Part Three
by Andy Nemec, KB9ALN
This is part 3 of a series designed to help node Sysops learn more about
the popular TheNET X-1J series of nodes. We'll skip over the more common
user commands and devote our discussion to commands used by the Sysop.
In this installment, we look at ADC.
What is ADC?
ADC is both a user command, and a Sysop command that can take four
forms. A user typing "ADC" can retrieve data that is gathered by an Analog-to-Digital
Converter channel wired to the TNC. There are four such channels, and they
can be used to set up an S-meter, a Deviation meter, a thermometer or a
voltmeter, among other things.
Actually, all ADC channels are really voltage meters, they are just
calibrated and set up to dispense a particular type of meter reading. The
sysop ADC commands are longer, and work in conjunction with the METER
command. Giving you a complete run-down on how to construct, calibrate,
and adjust an S-meter is beyond the scope of this article. We'll only touch
on this for those who may be entertaining the thought of adding something
interesting to their node stack. The complete instructions can be found
in the NETX1JR4 package available at the TAPR
software
library (www.tapr.org).
Basic Setup
The Analog-to-Digital converter inputs accept a voltage range of 0 to 3
volts maximum. In the example of an S-Meter, one finds a suitable voltage
from the reciever, or constructs circuitry that produces it. The documentation
in the X1JR4 package has some very helpful ideas on how to do this.
Once a suitable voltage has been found or created, you determine how
the voltage relates to the signal strength, and what voltages correspond
to minimum and maximum signal strengths. This is done with a signal generator
and a step attenuator. A graph of these values is made.
Once this is known, a decibel multiplier factor is calculated. After
this is obtained, and the zero-signal (noise floor) reading is known and
graphed, a "multiplier figure" is found on a trial-and-error basis. After
this, the Analog-to-Digital Converter is wired into the TNC (again, detailed
instructions are contained in the X1JR4 package).
The approprite wiring is put into place, a particuilar ADC channel is
selected, and the configuration process can begin.
Sysop Commands
In addition to the user ADC command, there are 4 ADC commands for the Sysop.
They are ADC1, ADC2, ADC3, and ADC4. These commands are used to enter a
text string that follows the ADC channel output. This text string is limited
to a maximum of 8 characters. These have to be entered into the node after
a cold start and are not "burned into" the node's EPROM.
To enter the text for the ADC1 channel, first this command is issued
to clear the text that may already be in the buffer:
ADC1 *
Then we enter the text that tells us what we are measuring. If we want
this to be an S-Meter, we would enter this:
ADC1 S-Units
The most complex command associated with setting up the ADC metering systems
is the METER command itself. Basically, the METER command dictates
what the ADC voltage will be displayed as, how to make this voltage conform
to a particular scale, and how to multiply the ADC channel reading so that
the meter reaeds correctly.
The METER commands configure:
- The Mode of the meter; whether it will be an S-Meter, a Voltmeter,
or whatever.
- Scaling factor for deviation.
- The S-Meter or dbm meter multiplier factor and noise floor values.
- The voltmeter multiplier value.
- The voltmeter offset values on a per-channel basis
Conclusion
We probably won't talk more about the METER command later in this series.
Showing you examples of how to set up one of these meters is complex and
cannot cover every application. For that, I can only refer you to the X1JR4
package - it has extensive documentation not only on the commands themselves,
but also has circuitry examples. That's all for this part. We'll continue
next time in our series by discussing the ALIAS and ARP commands.
Proceed
with Part 4
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to Part 2
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