Buck Rogers K4ABT Handbook page 50

; Packet Radio "The Basics"
Section 1
THE DEVIATION METER SCALING FACTOR
This is the parameter previously described in section 3.31 of the overview guide. It scales the deviation
meter display. One change however from X-1J. Setting it to zero does not disable the deviation meter -
bit 0 of the meter mode word as described above controls whether it is enabled.
When set to a value in the range 1 - 255, the meter is enabled and the value is used as a scaling factor.
The ADC is an 8 bit device, so it will give a response in the range 0 - 255, corresponding to an ADC input
voltage in the range 0 - 3 volts DC. If optimally configured, this corresponds to the maximum audio level
possible for the given receiver discriminator.
The ADC reading ( 0 - 255 ) is multiplied by the meter parameter value ( 1 - 255 ) to give an answer in
the range 0 to 65 KHz ( approx. ). This is the value displayed in the MHeard list.
Hence, if, for example, a DC voltage of 2 volts at the input to the ADC corresponds to 3.4 KHz deviation,
the ADC reading will be 171 ( +- a few ) and the Meter parameter will need setting to 20 ( i.e. to 3400 /
171 ).
If the ADC reading is 254 or higher, then in order to indicate an overrange, the symbol '>' will precede
the corresponding deviation entry in the heard list.
The signal strength meter noise floor value
This parameter sets the 'no signal' offset applied to input readings from the signal strength meter. It is
subtracted from the count read from the ADC to give a reading based on a no signal value of zero. If the
no signal ( noise ) reading is, for example 0.65V, corresponding to an ADC count of 256 * 0.65 / 3 or 54,
then 54 is subtracted from each ADC signal strength reading to give an integer from 0 to 201 for an input
reading between 54 and 255.
The S meter display format multiplier
This parameter operates in a similar manner to the dBm multiplier ( section 3.31.5 ) but having divided
the intermediate result by 256, that value is displayed as an integer in the range 0 to 9 preceded by the
letter 'S'. If the value exceeds 9, it is displayed as 'S9+'. If the dBm multiplier has been set up correctly,
then set this parameter to the dBm multiplier divided by the number of dB per S point.
The dBm meter display format multiplier
This parameter is used to convert an ADC reading for the signal strength meter into a dB count. The
ADC reading is converted into a count from 0 to n, according to the description contained in section
3.31.3. It is then multiplied by this parameter and divided by 256. When added to the dBm noise floor
value ( section 3.31.6 ), this gives the displayed dBm value in the heard list.
ILLUSTRATION SECTION Charts & Node Drawings TheNET
"2 N 1" Handbook
The Packet Radio
Section 2
Buck Rogers K4ABT
by
; The X1J4 System Node Operator's (SNO) Handbook
X1J4 System Node Operators Handbook __ Page 50