Hello Osmocom CNI folks,
I am getting ready to set up my own GSM network using nanoBTS hardware
(currently going through the incredible pain of satisfying all
dependencies to get Osmocom CNI software running on Slackware - because
no one makes binary packages for Slackware to my knowledge, I have to
compile from source), and I found this note in this wiki page:
https://osmocom.org/projects/osmobsc/wiki/NanoBTS_Getting_Started
"Do not power up the device without a TX antenna"
Can someone please educate me (and possibly other wondering souls)
*why* one must not power up a nanoBTS with no Tx antenna connected?
I understand how it can be a bad idea to actually turn on Tx output
with an open antenna connector, as the lack of 50 ohm termination
would case Tx energy to reflect back to the PA or whatever internal
components this unit has, but it is also my understanding that these
units turn on their Tx only after they establish a good link with a
BSC, with the BSC then telling the nanoBTS what ARFCN it should
transmit on, and at what power level. Therefore, if I am powering up
a nanoBTS for the purpose of getting its DHCP to work and doing
abisip-find and ipaccess-config steps on it, then during this phase
prior to osmo-bsc configuration, the unit's Tx output should be fully
off - so what would be the problem with having no Tx antenna?
For context, once I get past initial DHCP etc configuration, before I
deploy my nanoBTS on live air, I intend to check its Tx output first:
instead of an antenna, connect an RF measuring instrument (I'll use my
CMU200 in the non-GSM-specific "generic RF analyzer" mode) to the Tx
output port, verify that the frequency it transmits on matches the
ARFCN I configure in osmo-bsc, and verify that Tx power control is
working - and only then put the real antenna on. But it would be
cumbersome to bring the unit into the lab with the CMU200 while I am
sorting out DHCP etc, hence I wonder if it would be OK to have nothing
at all connected to the Tx port while I work on those preliminary
steps.
M~