4 June 1994
Norman McLeod
Thanks to Brian Lister of Stockton- on Tees for getting nine out of ten on the Teccy Quiz last week, the best result at the time of writing. Here are the answers and comments I promised last week.
Q1: (c) Six services have to broadcast at a time with DAB, otherwise known as Dead on Arrival Broadcasting: the most expensive technical flop in radio history.
People have likened DAB to the Betamax videotape system, but personally I think that's a bit unfair on Betamax. The Beta system shifted millions of VCR's, not so much in the UK but certainly in the US, and was responsible for bringing video recording to the home for the first time on a significant scale. I don't think DAB will be anything like as successful;
Q2: (b) is the correct answer. See the discussion on stereo in Issue 92;
Q3: (c) is about the limit. I counted over forty stations in a hotel room in Paris last time I was there seven years ago, and there wasn't a lot going on above 105 MHz then. I don't know how many of the stations I could hear were legal, but they were all clear reception on a my reasonable but hardly opulent travelling radio;
Q4: (d) 1593 kHz is the one to watch;
Q5: (c) 20m has been permitted to FM RSL's in most places on an experimental basis since January, and my latest chat with Prem Mangat at the DTI reveals that in future stations will all be able to apply for this height, though with no guarantee that they will get as much power as they would have got at 10m;
Q6: (c) The Virgin relay at Lydd in Kent uses the unusual frequency of 1224 kHz, adjacent to the big network channel of 1215 kHz;
Q7: (c) The pre-emphasis required by FM transmissions amounts to a boost of 10.32 dB at 10 kHz relative to 315 Hz, if you want to be precise about it. This is otherwise known as fifty microseconds;
Q8: (a) Yes, the first-ever RSL, then known as Special Event Radio, took place at the Greenbelt Festival in Northamptonshire in August 1984 with a power so low that anywhere else it could have been written off as a spurious emission from a high-power transmitter.
We actually thought they had slipped a decimal point when we saw it. For all that, 50mW produces a surprising 2mV/m at a 1km radius, just enough for daytime reception with a following wind within a small camp. And it's cheap;
Q9: (b) The bandwidth of legal AM transmissions in the UK is never more than 6.5 kHz, and in some cases less. Other broadcasters, particularly in Southern Europe, Africa and the USA broadcast 10 kHz of audio, sometimes more. This results in US AM quality being half-way between our AM and FM in quality terms, making it a more serious contender in a competitive market.
Widening the bandwidth will allow better AM audio quality at the expense of adjacent-channel interference. I am not convinced that current arrangements in the UK are optimal - daytime services in many areas could run more bandwidth without causing any grief;
Q10: (b) The bandwidth on FM is limited by the Zenith stereo system to about 15 kHz, allowing elbow room for the pilot tone at 19 kHz.
Any readers wishing to comment on what I have said are welcome to call me on 01 273 684 172 or send e-mail to normac@fastnet.co.uk
Copyright NJ McLeod 1995