Wireless range

[BillESC]

I've told this story before but was at the church today and took a picture. I'm standing next to the United Unitarians Church taking a picture of the Mount Vernon Baptist Church. I installed the sound systems in both churches with the Baptist church first by several years.

When I finished the installation the the Unitarian church I received a frantic call from the Baptists the following Sunday....The Unitarians wireless mic was broadcasting through the Baptists sound system...

I had installed Audio Technica's ATW 2120 handheld wireless mic systems in both churches. A simple change of frequency of the Unitarians system fixed the problem, but hey . . . it looks to be more that the posted 300' of normal range not to mention walls, etc.

 

[techieman33]

Looks a little close for my comfort. RF can do some strange things if the weather is right.

 

[chausman]

Looks a little close for my comfort. RF can do some strange things if the weather is right.

That's still some impressive distance.

 

[BillESC]

That's still some impressive distance.

Agreed, it never dawned on me that one system would affect the other. That's why I didn't change the factory default frequency setting.

 

[BillESC]

And this was the Audio Technica 2000 series which has a fixed output of 10mW whereas if I had gone with the 3000 series or greater the selectable output gives the user 10mW or 30mW transmission output.

 

[avkid]

Not bad for 1/4 wave antennas.

 

[FMEng]

30 mW versus 10 mW: A whole 4.8 dB more signal. That mostly just looks better on the spec sheet.

 

[Chris15]

30 mW versus 10 mW: A whole 4.8 dB more signal. That mostly just looks better on the spec sheet.

... But will consume 3 times more battery to sustain

 

[mbenonis]

This doesn't surprise me in the least bit. Let's make a few assumptions here. I'm going to ballpark the distance at around 1000' ft (300m or so) and say the frequency is at 600 MHz. 0 dB gain antennas all the way around. Even with these specs, the path loss in free space is 77 dB. Given a 50 mW bodypack, that is +17dBm - 77dB = -60 dBm. That is a LOT of power still! Say each wall is worth 10 dB, you're still at -80 dBm. Assuming the channel bandwidth is a nice round 200 kHz, your noise floor is at -100 dBm or so. That leaves you with 20 dB SNR, which is plenty for good demod.

 

[chausman]

Given a 50 mW bodypack, that is +17dBm - 77dB = -60 dBm. That is a LOT of power still! Say each wall is worth 10 dB, you're still at -80 dBm. Assuming the channel bandwidth is a nice round 200 kHz, your noise floor is at -100 dBm or so. That leaves you with 20 dB SNR, which is plenty for good demod.

But the transmitter is 10 mW, not 50 mW.

And this was the Audio Technica 2000 series which has a fixed output of 10mW...

Or does that not change anything significant?

 

[Chris15]

So deduct 7dB for 10mW rather than 50mW...

 

[FACTplayers]

We have some Shure SM58's? I think. Old old mics. Our AD would always make the football announcements using this mic, but he would never leave the high school. The signal would travel across a parking lot and to the field, roughly 3/10 of a mile. Crazy range.

 

[techieman33]

We have some Shure SM58's? I think. Old old mics. Our AD would always make the football announcements using this mic, but he would never leave the high school. The signal would travel across a parking lot and to the field, roughly 3/10 of a mile. Crazy range.

SM58 is just the handheld, it's the same mic as the corded version with various wireless parts to work with many of shure's wireless lines.