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freq_spec.txt
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# Freq Spec
The frequency specification, or freq spec, is a data extension to encode
a VHF/UHF frequency and optionally include other information about a
channel including squelch settings and offsets for repeaters.
Freq specs are often used for object packets advertising repeaters,
but may also be used to encode the currently used channel in
a comment field, a status, or message.
The first part of a freq spec is the encoding of a frequency in MHz,
followed by an optional alternate receive frequency and an optional list of
unordered five-byte modifiers.
All of these modifiers have a leading space to separate them from the
previous field.
The freq spec is terminated by any text which does not match one of
the freq spec modifier formats.
VHF/UHF frequencies are encoded
as a 10 byte string such as ``146.520MHz", so implementations may limit
their support to this three decimal three digit format.
*** Note: Need to specify to use ASCII 0x2E decimal point for international users.
HF and microwave frequencies are encoded as shorter or longer numbers
before the decimal point, and HF frequencies should not be padded to 10 bytes.
For example the 40m QRP calling frequency is written as ``7.030MHz"
and the 23cm SSB calling frequency is written as ``1296.100MHz".
The 3x3 format should be used whenever possible,
but stations requiring more than three significant figured after the
decimal point may include them.
This is particularly important for narrowband channels which are 500Hz off of a round 1kHz. For example, FRS channel 1 may be written as ``462.5625MHz".
*** Note: This isn't quite right. Current radios presume the fourth digit on narrowband channels
If a freq spec requires encoding an arbitrary separate input frequency instead
of a repeater offset,
this optional field may follow the main frequency
and is simply written using ``rx" instead of ``MHz".
I.e. ``␣446.000rx"
The modifiers include:
* ``␣Tnnn" - Encode the subaudible tone which starts with "nnn".
I.e. T100 indicates 100.0Hz, where T127 indicates 127.3Hz
* ``␣Cnnn" - Encode and decode the subaudible tone starting with "nnn"
* ``␣Dnnn" - Encode and decode DCS code "nnn"
* ``␣Toff" - Use carrier squelch
* ``␣1750" - 1750Hz tone burst access
* ``␣+nnn" | ``␣-nnn" - Repeater offset in 10kHz
* ``␣Rnnm" | ``␣Rnnk" - Range of the station in miles or kilometers
# Freq Spec Examples
"146.520MHz +000 Toff" - Simplex channel with carrier squelch
"146.760MHz -060 T091" - Repeater with negative 600kHz offset and tone of 91.5Hz
"442.300MHz C127 +500" - Repeater with PL encode and decode of 127.3Hz and +5MHz offset
"440.150MHz D255 +500" - Repeater with DCS code 255 and +5MHz offset
"146.460MHz 446.500rx T107 R35m" - Crossband repeater with input on 446.500MHz using a tone of 107.2Hz, an output on 146.460MHz using carrier squelch, and a usable range of 35 miles
"162.525MHz R50m" - A station with a range of 50 miles
"147.190MHz 1750 R40k" - Tone burst access with a range of 40km