DIY directional antenna for 2.4Ghz radio mics
At our church we’ve had a lot of problems with radio mics. We had a nice UHF Shure system which has been working well for a few years, but started dropping out quite regularly. After swapping around transmitters, receivers and frequencies we still couldn’t get a dropout-free setup, so instead bought a Line 6 XD-V55 digital system.
I’ve been a fan of Line 6 radio products since I bought their digital wireless system for my guitar about 4 years ago. I learnt then that analogue wireless systems use compression to keep the signal level high, otherwise you would hear noise (hiss) from the underlying radio signal. Digital systems don’t do this, so you can get a signal that is essentially identical to what is coming in to the transmitter. Modern digital systems operate in the 2.4GHz range which is shared with WiFi and things like digital baby monitors and security cameras.
So… we put the digital system in, walk-tested the room and made sure it was all working perfectly. Then during the church celebration, it started dropping out again. We moved the antennas around, changed the position of the receiver, turned off our WiFi, tried different frequencies and nothing would fix it. It also seemed to be quite time-dependent: the first part of the morning from 10-10.45 was usually fine, then around 11am it would start dropping out. As we’re on the edge of the town centre, we decided it might be all the shops opening up around 10-10.30am and starting to make use of their WiFi.
The answer is a directional antenna (the ones supplied with most radio systems are omnidirectional) so that the receiver’s reception is concentrated on the area at the front of the room rather than from all around. Line 6 do sell these, but they’re £160 a pair which is a lot of money if they turn out not to be the right solution. They’re also 180 degrees, which is actually quite wide, and they’re amplified which sounds good but when the issue is interference rather than distance an amplifier can just amplify the interference.
So it turns out that, because these radio mics operate in the same frequency as standard WiFi, they’re compatible with a wide range of antennas designed for WiFi. I found a flat panel antenna on eBay for 12 quid which has 14 dBi gain and about 60-90 degree width.
Setting it up on a mic stand so that the antenna is well above everyone’s heads and angled down a bit works well, and so far we have had three mornings with no drop out at all.