Thanks, that helps. I've seen that page but didn't glean that reasoning.
I dug up an older ARISS posting which hopefully adds a bit more to the good explanation by Dan just a minute ago:
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The "new" radio is actually a Kenwood D710 which is located in the Russian Service module. The Service Module is where the ARISS team performed most of its contacts in the past as it was near the table where all the crew had dinner. Since the first contacts with ARISS in 2000, the ISS has significantly expanded, both in size and in crew size. ARISS has expanded too, with an additional station location in the Columbus module, which is on the other end of ISS (about football field in length). This is where the US, Europe, Japan and Canada conducts most of its experiments and where they spend most of their time. Right now we are using a lower power radio, an Ericsson handheld, in the Columbus module, as it was already on-board ISS (launched in 2000). Our near term plans is to upgrade the Columbus station to a higher power radio (mobile radio class). Keep an eye out for these plans to mature.
Note that we are unable to move radios from the Russian segment (Service Module) to the US segment (where the Columbus module is located) as the power systems are different (28V vs 120 V) and certification for the Kenwood radios was only performed for the Russian segment. At the last ARISS International meeting, the delegates agreed with a plan to make sure all future equipment is interoperable and certified across the ISS. This will cost more money and take more time, but should provide more equipment flexibility for ARISS.
For now, APRS is using the lower power radio in the Columbus module.
I hope this helps explain things.
73, Frank Bauer, KA3HDO ARISS International Chair & AMSAT-NA V.P. for Human Spaceflight Programs
-- 73 de JoAnne K9JKM k9jkm@amsat.org AMSAT VP User Services