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About Wireless Microphones by Ross Tester and Digital TV W ireless (aka cordless) microphones are used in their countless thousands around the country. Pretty much every hall, church, theatre, gym, sporting body . . . you name it – they use, or have used, one or more wireless microphones. VHF Wireless Microphones Until the last few years, most wireless microphones were on the VHF bands. Some very low power (10µW) “toys” were on the FM radio bands but these had the unfortunate habit of being swamped by FM radio stations – especially given the proliferation of those in recent times. Most of the rest used “unoccupied” upper-VHF TV frequencies but once digital TV started, most of those unoccupied frequencies became occupied, especially in capital cities! Scratch the vast majority of VHF wireless mics. There was (and we believe remains) a very tiny portion of VHF spectrum, just a couple of MHz, which according to ACMA, the government body which controls these things, may still available for VHF wireless mics. But we’d be most reluctant to recommend anyone purchase a VHF wireless mic even in that tiny band (just above 200MHz) – it could be changed at any time. Wireless microphones are legal in this country under what is known as a “LIPD” class licence – that stands for low interference potential device. Part of the LIPD licence requirement is that users not only must NOT cause interference to other licenced users on that frequency but even more importantly have no recourse whatsoever if they are caused interference by other licenced users. And given the fact that most wireless microphones have around 3-10mW output power and those other licensed users might range up to a million watts or more (eg, some analog TV stations), guess who wins! STOP ! ss, ESnS PR t t o pre eue we t iss sta As this t out a media the u ACMA p further clarify sue. ment to icrophone is t sm wireles can view this a / u You ov.a cma.g www.a ANDARD/pc T WEB/S _600208 =PC 40  Silicon Chip If the picture shows a telescopic whip antenna (like this one) you can almost certainly assume it is a VHF model. Don’t buy it! UHF Wireless Microphones Which brings us to another sticking point. UHF Wireless Mics have become the “norm” in recent years, for the most part occupying the UHF spectrum from 520MHz through to 820MHz (and some “pro” models higher; – 915-928MHz). That hasn’t been a problem – until now! Digital TV, once again, has become the nemesis. As you would know, in most areas of Australia – and in all areas by December 10 this year – analog TV will cease. Either you will have bought a new digital TV or a digital set-top-box to feed your old analog TV . . . or you’ll be puzzling at the snowy non-picture on your set. That’s the good news, believe it or not. The bad news is that even the digital TV stations currently transmitting in the “high” UHF band (band V), from 694 to 820MHz, have moved/are moving/will be moved down to the “low” UHF band (band IV) from 520 to 694MHz (TV channels 28-35). “Fantastic”, you say. “No more interference to wireless microphones above 694MHz.” You’re right – there won’t be (from digital TV, anyway). But that’s not good news either. The Government auctioned off the newly-vacant high UHF spectrum during April/May 2013 for mobile phone/data services. They’ve called it the “Digital Dividend”. And you can bet that if you’ve just paid millions of dollars for spectrum space, you won’t look too kindly on a gym instructor, preacher or sports announcer interfering with your customers’ reception. In fact, ACMA have already stated that high-band UHF wireless microphones will not be permitted (the class licence will be withdrawn) once the Digital Dividend is sold. So where does that leave users? Unfortunately, to a large degree, out in the cold – definitely if you have a band V UHF wireless microphone and possibly even if you have a low-band model. Quite simply, wireless mics on frequencies above 694MHz are destined for the bin. The vast majority cannot be modified to be operated in a legal way; even if they could, the cost could well be prohibitive. If you have a band IV UHF model which coincides with a digital TV station in your area, the same comments apply. What you need to do between now and next year is check to see if your frequency/ies are or are not on a digital TV station around your area. If not, you may be in the clear. The digital TV bandplan (and much more information besides!) is available on the ACMA website (www.acma. gov.au). If you’re in a country area, you’re arguably better off because of the lower number of digital TV transmitters/ translators in the country versus the capital cities. But even then, if you suffer interference, bad luck! (You might be able to flog your gear off to someone away from your area with a different digital TV setup). Some five years ago (December 2008 to be precise), Free siliconchip.com.au The rules are changing – don’t be caught out by rogue traders! TV Australia published an amazingly detailed document which showed – down to the postcode – the areas where wireless microphones were allowed and where they were not, dependent on their operating frequency(ies). The beauty of this guide, which came under the moniker of “Operational Practice OP-27 – Operation of Wireless Microphones in the television broadcast channels”, was that it listed all areas in Australia with the TV channels being used and which frequency wireless mics could and could not be used in those areas. As we said, this was back in 2008, long before the Digital Dividend and TV channel re-stacking, so it’s almost certain that the information is out of date. And we haven’t been able to find a more recent document. But it is a good place to start – and gives you some idea of the complexity of this whole subject! If you’re interested, you can download the 85-page OP-27 PDF from: www.freetv.com.au/media/Engineering/ OP_27_-%20_Issue_3_-_Operation_of_Wireless_Microphones_in_the_Television_Broadcasting_Channels_-_December_2008.pdf (It may be easier to log onto the FreeTV website, click on Operational Practices and scroll down to OP27). It’s worthwhile pointing out one comment made in that OP: ACMA have licenced a large number of “self-help” very-low-power TV translators for “black spot” coverage – and these are not covered in the listings. Under the LIPD class licence, you cannot cause interference to these translators either and must suffer any interference they cause. Because analog TV sound is transmitted as FM, any wireless mic receiver on (or even near) the same frequency will pick up the audio from the TV transmitter. Indeed, because of “capture effect” of FM, the receiver will automatically grab the strongest signal – and if that’s the TV translator, so be it! OK, so why are soon-to-be-useless wireless mics still available? A very good question. Unfortunately, the answer is not so good! Most suppliers are well aware of the impending changes and many are desperate to unload what will be useless stock as soon as they can to “mug punters” . Changes are also happening in the US and many European countries so a lot of overseas stock is being offered in Australia at apparently bargain prices. It’s the old story. A little (or no!) knowledge is a dangerous thing. If you don’t know what to ask, they won’t volunteer the information. And why would the secretary or treasurer of a local church or sporting group, asked to buy a new wireless microphone, have any idea that he/ she was being sold a pup? For example, take a look at “wireless microphones” on ebay. At the time of writing, there were 1796 wireless microphones being offered – the vast majority from overseas. siliconchip.com.au For more detailed information: see www.acma.gov.au/WEB/STANDARD/ pc=PC–312475 and www.acma.gov.au/webwr/–assets/main/ lib100059/geninfo.pdf Searching through these, probably half were VHF (some actually being advertised as “professional VHF”). Others you had to look closely at to tell because the advertiser conveniently left that part out. If there’s a picture and it shows a telescopic (whip) antenna, it’s almost certainly a VHF model. Of the rest, all but five (yes five!) were in the soon-to-be withdrawn high-band UHF. Beware of claims such as “Australian Standard” (what does that mean?). Or “New FCC Approved Frequencies” (we don’t happen to have an FCC in Australia!). Or “Legal anywhere in EU” – we aren’t exactly part of the EU. There are plenty of other puff words which should make you wary. By the way, congratulations to the ebay seller who stated that the used wireless mic he was selling was a VHF model and might not be usable in metropolitan areas. At least one honest trader! Our tip: if you’re in the market for a wireless microphone, be very careful about buying on line – ebay or any other source. If you do, check it out thoroughly – if the advertiser doesn’t list the frequency of operation, don’t buy it. You could do your dough! As an exercise, we sent a message to several advertisers asking what the frequency/ies of operation were. Some didn’t respond, some were very vague and some even quoted the audio frequency range. Helpful – not! So what to do? If you are buying locally/retail, ask the supplier to guarantee in writing that the model you are buying will be suitable for use in your area after 2014. Fair-dinkum suppliers should be able to do so. We wouldn’t be buying from an online supplier (particularly from overseas). But realistically, until there is some definitive guide on what will and what won’t be usable in your area, if possible we’d defer buying any new wireless microphone SC equipment. You will be much safer that way! Conversely, one or two short “rubber duck” antennas (which may or may not be removable) mean it’s highly likely to be UHF. However, you still have to be very careful about what frequency it operates on, especially now with digital TV. Two antennas usually means it’s a “diversity” receiver. June 2013  41