Radio microphone licences and you

I was providing the Pa and Plasma screens for the speeches and the best mans presentation at a wedding last weekend. This involved the usual small compact speakers on stands, a hand held radio mike for the father of the bride and groom’s speeches from the top table and a lapel radio microphone for the best man, so he was free to hold his speech in one hand and the computer clicker in the other. The equipment was set up the night before and all was well. The radio microphone was tuned to one of the JFMG suggested channel 38 frequencies, which I have a licence for. No interference fine. The next day when I arrived back on site in plenty of time, so I thought, for the speeches, I found out that there was a Videoographer. In fact there were two of, them  both with a nice camera each .One camera had two Sennheiser camera mounted  radio microphone systems on it and the other had one . So in all between us we were using Five systems. Before I got back to site the Videoographers had already looked at my equipment and made sure that there systems were not on the same frequencies as mine. However they did not know any thing about licencing and had now idea that  you could not just willy nilly (randomly) use any frequency even though they had checked that all the microphones had been set to different frequencies.

So here we are with five radio microphone systems and no time to check whether the frequencies that they were set to would cause any inter modulation interference problems. My maths isn’t that fast . As fare as the licencing was concerned, the frequencies their systems were tuned to did not lie in the uhf dereg band 863 MHz to 865 MHz, so they definitely weren’t  legal and could have been fined for using them. Currently the use of unlicensed equipment is a fine of up to £5,000 and/or six months’ imprisonment on summary conviction or on conviction on indictment an unlimited fine and two years’ imprisonment and forfeiture of equipment.

As time was now short before the speeches were due to start, the only thing for it was to re tune their systems to 3 more of the recommended frequencies in channel 38 and I would  use them under my name and licence for the event .

The only problem now was, I don’t remember all the preferred channel 38 licence frequencies!  Thank goodness for the internet and mobile phones with internet access. On the JFMG web  site there is a table of the frequencies we needed. so just in time all the systems were set up to the correct frequencies and the speeches went without a hitch.

When you need to hire correctly licensed and set up radio microphone systems talk to me don’t risk the crackles, bangs and hisses

Here is a copy of the info on the site. If you are using radio microphones. Get a licence and use the frequency plan so you don’t end up with a fine and interference when you least need it

UK Wireless Microphone Licence:

UHF – (1 year or 2 year Licence)

Specifications:
RF bandwidth is limited to 200 kHz. Transmitter power is limited to 10mW if handheld, 50mW if body-worn.

There has recently been an addition to the PMSE shared user frequencies in addition to the channel 38 band there is a new band of frequencies between  823 and 832 MHz which are now under the same licence as the channel 38 “PMSE shared user licence” . So if you have a “PMSE shared user licence” you may well be able to licence the equipment that used to be used on the derg frequency , channel 70, so long as it can be tuned to this new band. here is the link to the relevant info on the JFM website http://spectruminfo.ofcom.org.uk/spectrumInfo/ukpfa?service=all&freqStart=823&freqStop=832&unit=MHz&submit=View+results+below

Channel 38 is available on shared non protected basis from�606.500 – 613.500 MHz. Licensees may use any frequencies within this range.

Radio microphone shared frequency bar , channel 38

Guard bands have been included at each end of channel 38 to avoid interference with future services in channel 37 and channel 39 and facilitate free-roaming use throughout the UK.

shared2

10 Channel plan:

The UK Wireless Microphone Licence does not specify spot frequencies in channel 38 but the 10 channel plan below will ensure that all frequencies can operate in the same location without harmful interaction. This plan is a suggestion only. Users and manufacturers can devise their own plans that could involve any number of frequencies within the range.

Channel 38 – 10 channel set ratings
2Tx IM(3) and 3Tx IM(3)
25k050k0100k0Risk Index
606.600022✔ 1.50
607.500035✔ 2.75
608.150042✔ 2.50
609.150034✔ 2.50
609.950036✔ 3.00
610.550044✔ 3.00
611.250024✔ 2.00
612.300043✔ 2.75
613.150031✔ 1.75
613.500002✔ 0.50
Score total22.25
Average✔ 2.225

In developing the plan we ensured that each frequency is safely spaced apart. However interaction can sometimes occur between frequencies even when appropriate spacing is applied. This unwanted interference can occur when equipment is operated close together in the same vicinity. It is known as intermodulation or “mixing”.

In the real world these unwanted signals appear on or close to the frequencies being used. To help make sense of this we have devised a figure of merit that we have called the “Risk Index”. This is calculated according to the quantity of unwanted signals and their spacing from the frequencies we are trying to use. Closer spacings have a higher risk of causing interference so are given a higher weighting in the sum.

About John Maggs

AvatarI have been in the industry and supported many events for many years. I pride myself in providing a personalised service and deliver a first class service.