Q: Why will subtone be installed on this repeater ?  Is it a user restriction ?

A: A subtone squelch is a lot more sensitive than an ordinary noise or signal squelch.  It will prevent very weak portable stations from breaking up.  A classical squelch is also temperature sensitive and may require operator adjustment interventions when room temperature changes a lot .  This is  not very practical when  the control operator lives at a large distance from the repeater site.  Subtone squelch systems don't open in error on intermodulation signals as often present at elevated sites.


Q: I have a very old radio that has no subtone.  Will I be left out in the cold ?

A: Several little circuits are available on the web to add subaudio to the microphone signal, and are so small they can be incorporated in the microphone.  They are low cost and based on PIC processors.  Dedicated CTCSS encoder chips are also available such as the CML FX315.


Q: why is 131,8 Hz selected as a tone for ON0TB ? (NOT used today)

A: because practice showed us that the lowest tone frequencies have slower opening times and are prone to false triggering as already found out in the early seventies, we decided to use the same tone as already in use in Brussels and the province of Antwerp and Limburg, simplifying user programming.


Q: what is the standard deviation setting for current FM radios ?

A: IARU recommends 3 kHz peak deviation for a 12,5 kHz channel separation.  CTCSS deviation is normally set at 10%.  Unfortunately most German repeaters still are set for the old 1980 frequency raster of 25 kHz and operate at a far too high 5 till 7 kHz deviation, causing severe splatter on the neighbour 12,5 kHz channels.  Deviation has nothing to do with power settings ! 



Q: how can I make my radio compliant with this 3 kHz setting ?

A: most Yaesu radios have a menu setting "NARROW".  This selects a better narrower IF strip and reduces the deviation to 3 kHz.  There are also engineering settings available that allow exact alignment.  With the popular radios like FT817 FT857 FT897 it helps also to turn down the default "FM MIC" 50 setting to 20.
Kenwood radios have the menu option "half deviation".  Icom also has a "narrow" menu item.
Please use the narrow setting on your radio while operating on ON0TB.