Newbie + questions: C123 and Racal 6103

Steve Markgraf steve at
Sat May 15 01:05:02 UTC 2010

Hi Joerg,

Joerg Albert wrote:

> I've recently got pointed to this project. Haven't dealt with any GSM
> software since the mid-90ies, so I thought it may be some fun to look 
> at the software and participate if I find enough time. I've got access
> to a Racal 6103 and a C123 to start with.

Your help is very appreciated!

> 1) Do I need attenuators if I wire the C123 to the Racal? Guess not,
> but I don't want to fry the input of the Racal.

No, but you have to connect it to the "Main RF" N-connector, which also 
has some large attenuator in its RF path. And, regarding to the manual, 
you have to terminate the "AUX RF" with a 50 Ohms resistor in this case.

If you only want to play with the higher layers and don't want to do any
accurate power measurements, you just can put some wire in the AUX RF
connector and turn the TX power to -40dBm, in my case this works almost 
  throughout the whole basement.

> Does the MS-147 jack on the C123 switch off the internal antenna if 
> anything is plugged in?

Yes, this is the right connector, and it does switch off the antenna. 
But I have no idea about the required length of the middle pin, my 
MS-147 cable is still on the way.

> 3) Does the PA of the C123 survive without any antenna connected (i.e.
> if it gets most of the HF reflected back) e.g. in continuous transmit mode?

Well, it may "survive" somehow, but I heard from the USRP that the PA 
may wear out if no load is connected, and this is rather a slow process 
instead of an instant failure. I wouldn't try it though, especially when 
continously transmitting.

> 4) A C123 without battery doesn't start the vendor firmware, display is
> blank, LED are on, flicker from time to time.
> Is this a hardware problem or just the vendor firmware missing the battery,
> i.e. any problem to download osmocom software without any battery?

The current supplied by the charger is not enough, and since the Calypso 
itself controls charging, this won't work, neither with the original 
firmware, nor with osmocom. The flickering of the charging-LED stops 
immediately if a battery is inserted.

as well.


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