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Saltwater Kills!

May 12th, 2016

Saltwater kills.  These are two words that should never be in the same sentence when you are trying to get your wireless microphones to work.  What do Saltwater and Radio Frequencies (RF) have in common?  Answer: Nothing, really.

But, I have a scenario for you that may help you make a connection.  Imagine you are setting up AV in a 16,000 square foot convention hall. You walk into the room with a wireless microphone and it works perfectly. Then, you fill the room with 100 police officers who are carrying radios and cell phones. Why would the microphone cut out?

What do you think the answer is?

  1. The radios interfere
  2. The police officers
  3. The cell phones
  4. All of the above

The answer is the police officers.  Their bodies are 50-70% water, combined with salt.  This means that human bodies are insulators also known as, “a substance that does not readily allow the passage of (fill in the blank).”  In this case, more policemen in the room mean more insulators.  Each police officer is limiting the passage of the RF signal which the wireless transmitter needs to reach the receiver.  Sometimes this is in the form of “cutting-out” all together (loss of signal) or a distorted “robotic voice” comes through the speakers.

 

Volume

This volume control figure is a good example of what happens when you introduce an insulator into a flow of RF signal.   If you lower the volume, the salt water increases, which decreases the flow of RF. But as the volume control goes up to a higher number, the RF flows more freely.

The question now is, “How do you overcome this?”  The most common response to this example is to add external antennas around the room, but there is more to consider here.  I will layout the steps for you next.

But first, a quick Myth Buster – The primary goal of getting better RF reception is to get as much 12v power to a group of active antennas as possible. If you can light up the powered antenna light then you are good to go and you’ll have all the coverage you’ll need to compensate for a room full of people. This visually would look right but it’s just not true.

 

 

Instead, here are the steps to install a Diversity Wireless Microphone Set-up in a meeting room, when external antennas are required.

  1. Run the right wire. There are two methods.
    1. RG8 Coax can safely go 150′ with acceptable loss.
    2. Fiber Optic can go thousands of feet.
  2. Use Passive Antennas and place them where they look aesthetically pleasing. But try to keep the Antenna A at least five feet from Antenna B. The garbage in/out rule applies here.  If you don’t put in the right wire, adding active antennas only picks up more garbage down the line, which in most cases makes a problem worse.
  3. Add an In-line Amplifier. If you get yourself in a position to retrofit an existing system, install these as close to the antenna location as possible.

MW_0315_RFessentials_F1

Remember: The plan is to pick up the strongest, cleanest signal via the Antennas so keep them in the room and visible.

For more information about wireless microphone distribution, check out this informative blog my friends at RF Venue have put together.

Helping you keep your signal clean,

Tony, the AV Guy

Tony, the AV Guy


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