80-Bus News

than a legit callsign, followed by the message ‘DE G6MFR’, then any station in the ‘earwigging’ mode will see:

G6MFR: CQCQ DE G6MFR

The receiving station, say G2XXX, can then open a communications channel to you simply by programming the destination callsign as the callsign just received. So his channel becomes G2XXK –> G6MFR. G2XXX can then send a message (or even no message), say KN DE G2XXX, where upon you will see:

G2XXX: KE DE G2XXX

What’s the problem? Well, as you were sending to a mythical station called CQCQ you can’t go back to G2XXX until the packet program gives up trying to contact the station CQCQ (16 tries over the space of a couple of minutes), or without first having escaped from the program and then reRUNning it. This takes time and clears the screen so if you’ve got a bad memory like me, then you’ve forgotten who was calling in the first place.

The program needs to know when no-one else is transmitting to allow the anti-collision logic to work. This is done by manually opening the squelch and the consequent white noise is detected by the tape I/O (probably as random numbers) indicating that the program is free to transmit. When a strong blank carrier is up, or data is being received, the program inhibits transmit and goes to sleep for a random period before trying again. Now this has snags. A noisy incoming signal which doesn’t quite trigger the tape I/O could be ignored or interpreted as a free channel allowing transmit (this sort of error occurs on signals worse than about 4 by 5). Secondly, white noise must be present to indicate the channel is free. This precludes any phase lock signal shaping circuits which could be used to reconstitute a noisy signal, thereby much improving the sensitivity of the system. Now the rig squelch circuit is much better at differentiating between signal and no signal than the computer, so a logical development would be to return the squelch line to the computer to detect a channel free condition. For sideband use, a phase lock shaper could be used and the out-of-lock line from this may be used to indicate a free channel.

… and BBC BASIC

It was to investigate my niggles and with a mind to convert the program to my machine that I started to poke around inside the program. Now I haven’t paid much attention to the BEEB machine in the past, prefering my machine which I consider superior and, at least, I understand. Some people tell me the BEEB is the most fantastic machine since the invention of the rocket propelled roller skate, whilst others tell me that all BEEBs should be collected, along with their owners, put in a large box and dumped at the bottom of the Marianas Trench as an insidious danger to mankind. I know of one gentleman who made a considerable loss by trading in an almost new Gemini MultiBoard machine for a BEEB, whilst I know of another who can’t wait to trade his BEEB for a Galaxy when he can rake up the necessary. So overall, on a statistical sample of two, 50% of BEEB owners are loonies whilst the other 50% have seen the light and should be helped as much as possible. Certainly the BEEB seems to me to be overpriced and has gained a sort of cult acceptance which it does not deserve, but then the same could be said for some of the other machines around, so… there you go!!