Info from Frank H. Bauer and Miles Mann.
A1 - B1 - B6 ? How many channels ?
Frank:"The Ericsson MP-A radios have a bank of 64 discrete frequency channels.
Four zones (A-D) with 16 frequencies in each zone".

Yes, Channel B1 is the public voice channel for Europe, Central Asia and Africa (region 1).

As Miles describes, Channel A1 is the Region 2 & 3 (Americas, Asia, Australia) frequency and Channel B6 is the world-wide packet frequency.

I hope this helps.

73, Frank Bauer, KA3HDO
ARISS-International Chairman

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Miles says:...There are three published public channels for ISS.

Channel A1 = Public Voice Regions 2 & 3 145.800 / 144.490

Channel B1 = Public Voice Region 1 145.800 / 145.200

Channel B6 = Public Packet word wide all Regions 1, 2 & 3 145.800 / 145.990

All other channels are reserved for special operations and school schedules.

Lets assume ISS is West of Iceland running Voice with the USA.
They will be on channel A1.
Then, If they figure out they have passed to the East of Iceland, they may say "switching to channel B1" for voice over europe, etc.

Miles WF1F
www.marex-na.org