Slow Scan Photos

Return to Recap of EOSS-72

If you listen to the audio from the cross band repeater at approximately 22 minutes and 20 seconds into the recording you will hear the first slow scan picture being transmitted.

Most of the interference present results from two problems. On this first attempt the audio level for the transmitter was set much too low. All the lines present in the upper half of the picture are do to this low audio level being interfered with by the xband repeater's on board audio (the constantly transmitting CW ID). Towards the bottom of the picture that interference seems to go away leaving just a very noisy picture (expected with low audio levels). This is because the repeater pauses the ID prior to sending an APRS packet and the controller sensing someone on the input will HOLD that packet until the frequency drops or a critical time limit is reached in which case the system will superimpose the packet.

33 minutes 13 seconds into the recording the second SSTV pictures was transmitted. In this second attempt (above) the audio level for the SSTV transmission was boosted to near perfect levels. Had I been using a better antenna, this would probably have been received close to perfect except for the problems with the CW ID.

If you look at the upper third of the picture you can see some interference. This is the CW ID. Note that this disappears and for the middle portion of the picture there is practically no interference with the exception of that one line (which is the APRS packet deciding it had just waited long enough).

Towards the bottom of the picture it becomes total hash. At that point in the transmission, the repeater's automated robot voice was triggered (by a timing loop). When the robot goes off it mutes the background input audio and replaces it with its own "voice". Just what the herringbone effect is (left side of the picture), I have no idea