Originally Posted by
le Pingouin
For TCU the "b" isn't displayed at all.
In ADS-B only coverage we see a four bladed "propeller" symbol and the "b" disappears. For TCU they still see a circle symbol regardless of whether it's SSR or ADS-B.
Most TCU do not receive adsb. They need an extra processor to convert the adsb returns into a fake radar return. This is available in sydney, melbourne and hobart.