Audio Ltd. systems have been designed to offer the highest
quality of performance to the most critical user while at the same time
offering simple “Plug in and go” simplicity. The huge dynamic range
means that one mic gain setting will handle almost anything. Nevertheless
even if you drive into more than 20dB overload, the system will handle
it, and without distortion.
Although a switch is fitted too, all Audio receivers and transmitters have an on off link in the cable plug. So you know if you pull the cable out, the unit is off.
High quality gold plated microwave SMA connectors are used for antennae, allowing cables to remote antennae, mast head and distribution amplifiers.
Complex high performance design inside, robust and simple to use outside. So when you are under pressure to perform, you don’t have to worry about fiddly setting up of your wireless systems.
Radio Waves are electromagnetic radiation, the same as Light Waves. Just as with light, areas can fall into shadow, particularly where there are metal objects which can reflect and absorb RF energy. But more importantly and in common with the other wave propagated medium we are all familiar with, Sound, radio waves suffer from constructive and destructive interference, or phase cancellation. This can mean that even in a location of relatively high signal strength, loss of signal can still occur. Where the transmitter or receiver or other RF reflecting objects are moving then phase cancellations can come and go very quickly causing the all too familiar burst of noise or dropout.
There are actually two basic types of diversity applied to radio reception: Frequency diversity and Spacial diversity. In both cases the aim is to provide different numbers of whole wavelengths from the transmitter to the receiver antenna, or even physically different paths.
Frequency diversity which was used on HF transmissions achieved this by transmitting the same signal on two or more different frequencies. Any reflections from the ionosphere causing phase cancellation on one frequency would have different phase on the other frequency and therefore not cancel. Widely different frequencies will also take a different path completely and suffer from a quite different set of losses and reflections.
Spacial diversity traditionally used two antennae and two receivers at the receiving end. Providing the antennae were far enough apart to ensure that a different combination of phases of signals were present on each, then phase cancellation occurring at the receiving end could be eliminated. This however was of less use against cancellations which had occurred far away in the ionospheric disturbances of the signals. It is clear that this system can only work if the antennae are a good proportion of a wavelength apart.
The situation is quite different for VHF and UHF radio mics. Here we are not concerned with strange distortions of the signals by the upper atmosphere. The main problem is simple reflection. RF energy bounces around the rooms and streets where a recordist needs to work. This can mean that phase cancellation is a major problem in any built up environment. However, when electromagnetic signals reflect they change their polarisation. This is why polarising sunglasses reduce reflected glare. It also means that the mix of signals appearing at the receiver antenna are not simply polarised in the same plane as the transmitting antenna. Audio Ltd. recognised that this means that the traditional received wisdom that antennae must be at least a wavelength apart for diversity to work is no longer valid for radio mics. In fact polarisation diversity works exceptionally well with Audio’s Dx2020 and Dx2000 receivers.
Diversity is not however an excuse for making insensitive receivers. There are also shortcut ways of achieving some of the benefits of diversity reception. For example simply having two antennae and switching to the other one as soon as the signal gets weak or drops sharply on one, hoping that the signal will be better on the other, is a system which has been practiced by some exponents. There are a number of problems, one in particular, with this scheme which we won’t detail here. Audio took the approach of taking the same full receiver design with full sensitivity and selectivity, and then duplicating it. Careful monitoring of RF level over a huge dynamic range which is individually tracked on each unit means that the receiver can never switch to a worse signal. A noiseless switching circuit was developed to take full advantage of the accurate level detection and allow switching as often as needed without noise or clicks.
The combination of these techniques has resulted in a full true dual diversity system which has changed the way many recordists work.
Read users comments on Audio’s diversity systems.
One of the difficutlties of manufacturing for the world
market is the need to supply on almost any frequency. Europe has
very tough type approval and EMC requirements too. Audio designs
all its kit to meet all of these demanding requirements and this means
that we can supply any frequency range you need from 150 to 1000MHz to
suit local regulations.
Whatever band you work in, intemodulation can always be a problem. Good receiver design helps to reduce this. In the case of wireless mics intermodulation can also occur in the transmitters, if they are operated in close proximity.
No matter how good the design, it is essential to take account of the intermodulation properties of the frequencies in use. For example any 3 equally spaced frequencies in the same band will be useless. Audio has a small program we and our distributors use in house to check out frequencies. It can also auto-generate good frequencies if you are not tied by legislation to given ones. You can download this program for your own use.
What is Intermodulation?
Intermodulation
is the "Multiplication" of one frequency by other frequencies.
This occurs due to non-linearities in the input stages of receivers prior
to the main I.F. filtering. A trigonemetrical identity shows that when
one Sine or Cosine function is multiplied by another then the resulting
function contains new frequencies consisting of the sum and difference
of the frequencies of the two original functions. This process is
used in all superheterodyne receivers to convert the input frequency to
the I.F. frequency in a misnamed stage known as a Mixer. Mixing
is commonly thought of as "Addition" whereas it is "Multiplication"
which is happening here.
This effect can happen in any stage which shows non-linearity, and will
always happen to some extent in the "Mixer". Good design
attempts to minimise this effect, however for Wireless Microphones it
is best to always avoid frequencies with 3rd order hits within the receiver
pass band and essential to avoid 3rd order hits below 25 kHz. Direct
hits result in "Birdies", whistling sounds as the direct hits
"Beat" together. Although in theory a direct hit is on exactly
the same frequency, in practice there will always be some difference and
this difference will be in the low audio range resulting in audible whistles.
Hits outside the audible band may affect any audio processing (e.g. companding)
which is being used as, although the human ear cannot hear them, the audio
processing circuitry may do. In the case of Wireless Microphones,
intermodulation can also occur in the output stages of transmitters, since
they are often operated in close proximity.
Winmod is a simple piece of software we and our distributors use to evaluate and generate frequencies free of intermodulation.
Every Audio
Ltd system is tested to work at -20°C. After all, they have
to work wherever you work, even if it's Everest
