02-03-2014, 11:47 PM
I too can confirm that tiny MW transmitters are not on Ofcom's radar. While setting up a medium wave RSL recently, a senior member of Ofcom was there to check my installation. (That's not something they normally bother with, not an actual visit, but he knew the station operator, it was on his way to work and he did some measurements out of interest, which saved me doing the calculations for the official submission. So, Ofcom don't usually even bother with a 1 watt AM RSL with a range of a few miles unless there is a reported technical or programming problem.)
I informally asked him about their position on small 'pantry' transmitters, and he more or less said they don't want to know: "There are more important things to worry about". But yes, he agreed they are technically illegal. And we then discussed the legality of using a signal generator modulated with tone or music to transmit a few yards across a workshop. We just laughed; you see, it starts to get silly when you consider what will radiate.
The ones I make run off a PP3 with a total current of about 7mA, so that's about 60mW DC input, probably about 20 mW RF output. Take into account the grossly inefficient antenna of only about 1 metre of wire and no earth, and you're radiating a few tens of micro watts. Presumably this "100mW limit" that's been mentioned is ERP isn't it? On MW that would need at least a couple of watts RF output and/or a pretty good antenna.
If only all those SMPS radiated so little! They cause MUCH more grief.
UK commercial stations on AM can malfunction for weeks before anyone notices and reports it. Even then Ofcom don't drop everything to deal with the matter unless it's causing interference to some other service.
In the medium to long term, MW (and probably LW) will just go fallow and are likely to be nominated as officially unmonitored.
Ian
I informally asked him about their position on small 'pantry' transmitters, and he more or less said they don't want to know: "There are more important things to worry about". But yes, he agreed they are technically illegal. And we then discussed the legality of using a signal generator modulated with tone or music to transmit a few yards across a workshop. We just laughed; you see, it starts to get silly when you consider what will radiate.
The ones I make run off a PP3 with a total current of about 7mA, so that's about 60mW DC input, probably about 20 mW RF output. Take into account the grossly inefficient antenna of only about 1 metre of wire and no earth, and you're radiating a few tens of micro watts. Presumably this "100mW limit" that's been mentioned is ERP isn't it? On MW that would need at least a couple of watts RF output and/or a pretty good antenna.
If only all those SMPS radiated so little! They cause MUCH more grief.
UK commercial stations on AM can malfunction for weeks before anyone notices and reports it. Even then Ofcom don't drop everything to deal with the matter unless it's causing interference to some other service.
In the medium to long term, MW (and probably LW) will just go fallow and are likely to be nominated as officially unmonitored.
Ian
