SECTION 2. ASSEMBLING THE RADIOTELEMETRY NETWORK
2-5
second quality record would apply to how well the
repeater received from the remote, and the third
record would apply to how well the base received
from the repeater.
A "Quality Record" is made up of five values as
follows:
First Value
test packet size;
Second Value
front of 2T envelop;
Third Value
back of 2T envelop;
Fourth Value
front of 1T envelop;
Fifth Value
back of 1T envelop.
The "test packet size" is usually around 238, but
varies a little depending on network layout. This
value will be half or less of the expected 238 if
packets are being lost for one reason or
another. For example, if packets are being
walked on by outside RF activity, the test packet
will not make it though and will be retransmitted
at a smaller size. Over RF, data is transferred
as a stream of bits encoded into short and long
periods of time between transitions. We call the
short time a "1T" period and the longer a "2T"
period. Each transition is expected to fall within
a certain window of tolerance to be valid. If
there is too much error in the signal and the
transition falls outside its allotted window, the
packet will be in error and be retried. As a
packet is received the RF95T keeps track of the
transition that occurred closest to the front of
the allowable window and closest to the back.
These values are kept for both the 2T and 1T
windows and are the last four values of the
"Quality Record". Both windows are 204 ticks
long, so if the transmission was perfect, the
data envelope front and back would both be
close to 102. The closer the front value gets to
0 and the closer the back value gets to 204, the
worse the quality.
