Welcome to Viviana´s quick start guide for your new RF engineer´s starter kit!
Here, we want to guide you through 5 important wireless basics which may give you more confidence in your daily work as a sound or RF engineer on stage or on set.
Additionally, you can find “How To” videos at the bottom of the site which will show you how to correctly use your new Viviana wireless accessories.
It´s easy, that´s it! 😀
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Education
RF basics - about reflection, absorption and free space path loss:
An antenna is a device that transforms electrical signals into electromagnetic waves and vice versa (reciprocity). An electromagnetic signal emitted by the antenna is heavily affected by its surroundings.
The RF signal will be reflected multiple times across the walls of a room or some obstacles. This is why all wireless systems work with diversity reception with two receive antennas – in case one antenna receives two signals that cancel each other out (out of phase) at one point in time the other one will most likely be able to pick up a better signal (in phase). Mounting the receive antennas at a good height of at least 3 meters to retain “line of sight” between transmitter and receiver is important to consider to avoid the RF signal to be reflected or absorbed by obstacles or a human crowd.
Materials which are electrically conductive absorb most of the RF energy. Hence, a transmitter with its whip antenna under a costume with metal components will be obstructive to the RF signal. A human body is made up of water to its most parts and water is electrically conductive. This is why mounting a transmitter on a human body can be problematic when expecting the best range. Additionally, human sweat (salt water) covering the whip antenna is highly problematic as well and will take away some of the expected emitted radiated power.
Lastly, due to free space path loss (FSPL), the RF signal strength will lose around 6 dB per distance doubling and per doubling the frequency. This is shown in the formula for free space path loss:
d… distance in meters
f… frequency
c… speed of light at 300 000 km/s
RF levels and useful terms
Wireless transmitters deliver an output power between 1 mW and 250 mW (depending on where on the globe you are and which devices can be used on a regulatory basis). A wireless receiver´s sensitivity is in the range of around -90 dBm and -20 dBm. Any value over or below it will be either too strong (RF overload) or too low (audio mute) for the receiver to demodulate the audio signal from the RF frequency. To show you some values in mW and dBm you may study the table below or use it for later reference.
Table 1:
| mW | dBm |
| 0.01 mW | -20 dBm |
| 0.1 mW | -10 dBm |
| 1 mW | 0 dBm |
| 2 mW | 3.0103 dBm |
| 3 mW | 4.7712 dBm |
| 4 mW | 6.0206 dBm |
| 5 mW | 6.9897 dBm |
| 6 mW | 7.7815 dBm |
| 7 mW | 8.4510 dBm |
| 8 mW | 9.0309 dBm |
| 9 mW | 9.5424 dBm |
| 10 mW | 10 dBm |
| 100 mW | 20 dBm |
This picture will explain some additional important terms. It shows the screen of the RF Venue RF Explorer Pro spectrum analyzer and as a transmitter, we used a digital Shure ADX1 bodypack transmitter.
Whip antennas - strengths and weaknesses
A whip antenna is a piece of wire converting the electrical energy coming from the transmitter´s SMA connector into electromagnetic energy.
The length of the antenna is dependent on the frequency range of the wireless system. Nowadays, UHF systems are the most common ones and use frequencies between 470 MHz and 694 MHz, depending on where on the globe you are.
A UHF whip antenna typically is a quarter of a wavelength long which results in a length between 10 to 15 cm.
This formula shows that the higher the frequency the smaller the antenna and the lower the frequency the longer the antenna. The ok-ish antenna size is one of the reasons why the UHF spectrum has become so popular for a professional wireless system. The RF propagation is the other one – UHF frequencies propagate easier around obstacles and travel further as higher frequencies in the 5.8 GHz spectrum using the same RF output power.
A whip antenna is mounted on a human body which will affect the antenna´s performance heavily. A human body absorbs most of the power radiating from the antenna. The loss is generally around 10 dB as shown in the previous paragraph. Watch the video below to see how the Viviana Pebble body wave antenna helps overcome the weaknesses of a traditional whip antenna.
Secondly, when the antenna touches the human body, we speak of antenna detuning. This term is also used in RF design – the antenna behaves differently in free field as opposed to when integrated into a housing for example. Objects in the near-field environment of an antenna change its resonant frequency, causing an impedance mismatch. See the results of the Viviana RF Saver preventing the antenna from detuning. The VNA (vector network analyzer) shows that the RF signal loss (dBm) of the antenna with the RF Saver is reduced to a minimum because it does not touch the skin and is fully surrounded with air:
Importance of using high quality materials and pouch protection
How many times have you seen a belt pack dropping on the floor because of faulty mounting techniques? And have you had the chance to send a body pack transmitter or receiver to service because of sweat ingression?
As a professional person, you would like to protect the talent on stage or on set and also reduce service costs by using the wireless devices responsibly. This is why Viviana´s products use high quality materials which offer sweat protection and are skin friendly. The pouches offer a soft protector to protect both the device and the talent. The strong velcro holds the devices firmly inside for many shows and the grip technology will keep the whole strap or pouch firmly in place throughout the show. Also, consider correct cable management to make sure that no loose loops are hanging or standing off.
Focus on the performance
An artist, musician, actor or any talent on stage or on set can be subjected to many overwhelming tasks. Make them feel safe so that they do not even have to think about having to carry around a body pack on stage. They will be able to focus on the performance as you will be able to focus on your task – which is using Viviana Sound Solutions´s accessories now! 😁
