What is the minimum RSSI Value being logged?

[mpjf01]

During a recent flight with one of my gliders I kept getting RSSI alarms and telemetry lost messages. On looking at the log I see several instances during one flight where the RSSI was reported as zero for a number of log cycles, after which it returned to a more reasonable level. I'm wondering if it really was zero and if so, is zero really where one would expect it to be (a number less than 1) or are values, say, <40, being shown as zero. I'm struggling to explain to myself what could cause the readings for this flight. I have attached the log, flight in question starts at about 14.30.

[Kilrah]

What is logged is whatever is received... Zero would mean that no telemetry is being received.

[dinamich]

You had three flight without problems, but the last flight shows RSSI drops to zero. Which means that telemetry was lost for that time. What changed between flight 3 and 4 to cause this?

[mpjf01]

In the last flight I flew into a really strong thermal that took the glider up to 425m. The telemetry lost messages from the Tx made me try to get out of it as quickly as I could. With full crow and a nearly vertical dive it still was going up so I went to speed mode and flew out of it.

In this case it would seem (as I understand it) that the RF link to the plane was still functioning at a level to enable me to keep control but the RF link from the plane was out of range. Is the difference a result of the antenna types that are used, being (visually at least) different between Tx and Rx? I have read somewhere (DIY Drones I think) the Frsky telemetry is only ever transmitted from one of the two receiver antenna. If this is true could it just be that the transmitting antenna was temporarily occluded?