MMSSTV does not start receiving automatically
MMSSTV normally detects the VIS signal and starts receiving automatically. It can also analyse synchronization-pulse timing.
If automatic start fails, the original documentation recommends manually selecting the expected SSTV mode below the Auto button.
The squelch setting also affects automatic triggering. A high squelch threshold requires a stronger signal before reception begins.
The picture is slanted
A slanted picture normally indicates a sampling-clock difference. MMSSTV provides three correction methods:
- High-accuracy slant adjustment.
- Automatic slant adjustment.
- Manual slant adjustment from the Sync window.
If the corrected value should be retained for future pictures, press Mem.
Synchronization is lost during reception
MMSSTV can use automatic stop, restart and re-synchronization functions. Auto Resync attempts to recover the image when synchronization is lost.
The original manual notes that QRM, multipath and weak signals can reduce the effectiveness of automatic synchronization and slant analysis.
Audio or timing is being lost
The original documentation recommends increasing the RX FIFO when timing is lost during receive, and increasing the TX FIFO when timing is lost during transmit.
Raising the low-level sound-processing priority can also help if audio samples are being lost.
The computer pauses during reception
The RX buffer contains a large amount of audio data. On computers with limited memory, RAM buffering could cause paging and intermittent pauses.
The original manual recommends selecting FILE buffering, or turning the RX buffer off when automatic slant adjustment is not needed.
CPU usage is too high
The Basic Operations documentation suggests several ways to reduce CPU load:
- Increase the sound-card FIFO size.
- Disable RxBPF.
- Use FILE or NONE for the RX buffer.
- Turn the TX BPF off.
- Keep Loopback off when simultaneous TX/RX processing is unnecessary.
Another program blocks MMSSTV
If another radio program is using the COM port or sound card, MMSSTV may be unable to restore normal operation. Close the competing application and restore MMSSTV again.
TX picture is slanted but RX is correct
Some sound cards use different effective sampling clocks for playback and recording. MMSSTV therefore provides a separate TX clock offset.
The original calibration procedure uses an external line-out to line-in loopback and a Martin 1 transmission to determine the TX offset.
Wrong sound card selected
MMSSTV can select the audio device by DeviceID. With a single sound card,
the original documentation says that -1 selects the default
device, while numbered IDs select specific sound cards.