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P300H P300 Series Modem Installation and Operating Handbook Page 122
Test: 1:Loopbacks [Off] 2:RF & FEC [Off]
3: PSU/Temp 4:Int BERT [ESC]
Test Menu
Loop (now Intfc): 1 Off, 2 Interface (L+R),
3 FEC (L), 4 I.F. (L) (
More)
Test, Loopbacks Menu
6.16 TEST MENU
The test menu is as shown below, and leads on to the menu’s described in the following few paragraphs.
When either a loopback or test mode are active, the TEST LED on the front of the equipment illuminates.
Each of these options is now discussed in turn:
6.16.1 Test, LOOPBACKS Menu
This screen show the most common loopbacks, but by pressing the down arrow further options are
provided. The loopback options are:
OFF Normal operation is selected.
INTERFACE (L+R) An interface loop (Local and Remote) is selected, providing both a terrestrial loop
and a loop to the data from the remote end of the satellite link. The exact
implementation of the loop is interface dependent. On G.703 cards it is a `copper
loop`, on other cards the loopback is provided by a multiplexer at TTL levels. If
an INTERFACE LOOP doesn’t make the sync light on the firebird come on, your
looking in the wrong place, its not the modem, try the cables !
For the remote loopback to function when this loopback is selected the clocking
must be configured in a mode where it would work if the loop were made in the
cables. Rx clocking must be set to something other than Tx Clock (switch to
Satellite if this is the normal setting) and the Tx clocking must the set to Tx Clock
In.
FEC (L) The data is looped back after the FEC just before it enters the modulator
providing a local loop only. The Tx data continues to be transmitted, and the Rx
data from the satellite is ignored. ESC & Aux channel data (which is present in the
data stream at the FEC) is also looped.
I.F. (L) The Tx IF signal is looped back within the modem a IF. Tx data is transmitted as
normal, and the Rx RF signal is ignored. The Rx IF Frequency is automatically
adjusted to match the Tx IF Frequency (so the loop will function). ESC & Aux
channel data (which is present in the data stream at the IF port) is also looped.
When the loopback is switched off the RX IF Frequency is restored.
NOTE: The Tx IF Level needs to be set to above -10dBm for the loopback to
function reliably. Do NOT change the Tx IF Level for a loopback if the
modem is still on satellite !
Cont’d....