TV Modulator: Terra MT-27P (B/G, D/K: ch. 1-69 & S9-S17, with AC/DC adapter)
...and the view after removing the flap
Top view. The push-buttons "+" and "-" are used for setting output channel. The left side pot underneath sets proper deviation of sound subcarrier, and the right lower corner pot - RF output level.
Termination load and mounting screws included
Output level adjustment allows to match the signal to other signals within the installation, also concerning other modulators connected in cascade.
50 kHz is the standard deviation for input audio signal of 0.775 V RMS. The adjustment of deviation ensures similar deviation for a little different audio levels. The standard deviation can be obtained within the range of 0.150-0.775 V . Correct adjustment is essential for equal volume levels on individual TV channels.
Switching on the power with pressed one/two of the keys on the modulator will allow to set some other parameters:
| || |
During switching on the key
"-" is being pressed
During switching on the key
"+" is being pressed
|During switching on both keys "-" and "+" are being pressed|
| || || |
|Possibility of setting sound subcarrier 6.5/5.5 MHz||Possibility of setting video modulation factor +/- 6% with 2% step||Possibility of setting output frequency +/- 2.5 MHz with|
250 kHz step
The standard depth of video modulation is 75%, however sometimes it can be useful to change it a little, e.g. when the source generates alphanumeric characters a bit exceeding proper limit. The possibility of setting video modulation factor within +/-6% enables correction in such cases, optimizing the signal quality. In practice it is seen as little change of brightness and contrast of the picture, e.g. of that characters. Generally, when the original and converted (by the modulator) picture has regular quality (no overmodulation), and sound is clear as well - no correction is needed.
Changing a little output frequency one may attempt to eliminate interferences coming from neighboring channels, when they are fixed in the system. Making offset of the output modulator's frequency there is a chance to solve that problem. The possible range is +/-2.5 MHz at 250 kHz intervals. Generally, when the signals within installation are of good quality, that feature is not used.
- two standards (B/G & D/K),
- PLL synthesis,
- protection against tampering,
- RF loop,
- F-type connectors (output, input) and RCA sockets (audio & video inputs).
To sum up - the TV standard and channel are set in "soft" way using keys and the display. Sound deviation and output signal levels are set with pots. Additionally, there can be done some signal corrections, described above (see the pictures).
1-69 & S9-S17
|Video carrier offset|| MHz|
+/-2.25 with 0.25 step
| Sound subcarrier|| MHz|
6.5 (D/K) / 5.5 (B/G)
230V/ 50 Hz / 3VA
-10 to +50