M7/M7L/M7LT Modular Satellite Modem
Maintenance
M7/M7L/M7LT - Rev. 0.05
4-5
4.3.2.
Built-in BERT
The modem contains a complete transmit and receive Bit Error Rate Test (BERT) function. Each
direction is independent and can be used for either loop-back testing or uni-directional testing with
another modem on the other end of the link. Since the internal test patterns are based on industry
standard test patterns it is possible to use the built in BERT with an external BERT or any brand of
modem at the other link end as long as the interoperability of the test patterns has been verified. The
IF Loop-back state and the BERT state are both stored in non-volatile memory, therefore if the unit is
powered off during IF loop-back and/or BERT test it will return to this state when powered up again.
CAUTION!: Enabling the BER Test set will result in disruption of any traffic currently through the
M7 in the direction that is enabled. BER Tests should not be performed on a live
traffic unit.
The modem BERT can be “pointed” in two possible directions. The normal mode involves the BER
transmitting in the direction of the satellite and receiving from the satellite direction. Added in the M7
is an alternate mode which allows the BERT to transmit and receive toward the terrestrial data
interface side. The direction is controlled via the Interface
<Intf: Test
– BER I/O>
parameter and can
be selected for either “Satellite” or “Terrestrial”. The Satellite direction looks to the modem as if a DTE
is sending and receiving data. The Terrestrial direction appears to the line as if a DCE device is
sending and receiving data.
The Modulator (Transmit) BERT is enabled at
<Intf: Test
– Send BER>
, and the Demodulator
(Receive) BERT is enabled at
<Intf: Test
– Rcv BER >
. With either transmit or receive being enabled
by choosing either the 2047 or 2^23-1 test pattern options. Both BERT setting should be the same to
operate properly.
When the Demodulator receive BER Test is enabled, there are seven (7) test status items shown in
the Interface Test column. These seven (7) items are:
1. BER
– The ratio of errored bits to un-errored bits since the test began or was last reset.
Expressed in bits per bit as x.yyy E-power where the mantissa (x.yyy) is always between 0
and 10 and power is the power of 10. For example 1.200 E-6 is 1.2 errored bits in 10^6 bits,
or 1.2 errors per million bits. No errors are expressed as 0.000E-power. Since Errored bits
do not accumulate during a sync loss, it is possible to lose sync for several seconds and not
have the BER affected.
2. BER Sync Loss
– The total number of sync losses that have occurred since the test began
or was last reset.
3. BER Errors
– The total number of bit errors that have occurred since the test began or was
last reset. Errored bits do not accumulate during a sync loss.
4. BER Bits
– The total number of bits that have been received since the test began or was last
reset.
5. BER EFS
– Error Free Seconds. The percentage of the total number of seconds with no
errors occurring during that particular second. Compiled since the test began or was last
reset. No errors are shown as “100.00%”. Errored seconds accumulate during a sync loss.
6. BER Erred Sec
– The total number of seconds with errors occurring during that particular
second, since the test began or was last reset. Errored seconds accumulate during a synch
loss
7. BER Total Sec
– The total number of seconds since the test began or was last reset.
The test is reset or started over by viewing any of the 7 status items listed above and pressing the
“Edit” or “0” key, then responding to the prompt “Enter to Restart” by pressing “Enter”. A restart on
any items resets all items and values.
A single error may be inserted when the BER test is active to verify proper operation by using the
<Intf: Test
– Send BER>
parameter and pressing “3” and “Enter”. This could be useful since it is
sometimes difficult to see errors with the Turbo Product Codes FEC.
