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(12) It is always advisable to “walk” the coverage area to ensure that there are no areas
of poor coverage. Signal “dropouts” (little or no signal in small areas) are indicated by
the “TX” LED going out or by a brief “fizzing” sound in the audio (which may or may
not be followed by a silent period due to squelched audio). The audio may be
conveniently monitored with a set of headphones plugged into the stereo phone jack on
the receiver. If a “dropout” area occurs, the antenna can usually be repositioned to
eliminate the problem. Frequently, a change of just a few inches in location will solve
the problem completely.

Antennas

The receiver antenna may be the most important single component in a wireless-
microphone system. However, this is the item most often overlooked in setting up a
system, and is frequently the cause of quite unnecessary problems. Proper selection and
placement of the receiving antenna is vitally important in any wireless-microphone
system.

Antennas are a particular issue with miniaturized wireless-microphone equipment such
as the R-27 receiver, in that antenna size tends to seem disproportionately large in
comparison to the equipment itself. This is easy to understand, in that the length of the
antenna is several times the maximum dimension of the receiver. However, while
electronic circuitry can be miniaturized without significant performance compromises,
the same is not true of antennas. That is, while components can be made almost
arbitrarily smaller, physical constants (such as wavelength) cannot. The net effect is
that, while antennas whose dimensions are far less than a wavelength do exist, they are
seriously less efficient than larger antennas. About the smallest antenna with reasonable
efficiency is the 1/4-wavelength design, which must be about 16.5 inches (42 cm) long
at 180 MHz.

Of course, electrically small antennas (such as the “rubber duckie”) are widely
available. These units are normally 7 to 14 inches (19 to 35 cm) long, much shorter
than 1/4 wavelength. However, such designs merely make the best of a bad situation by
providing a good impedance match at the tuned frequency. This at least avoids adding
matching loss to an already low efficiency. In general, even the best such designs are 3
to 6 dB less efficient than a simple 1/4-wave whip. In practical terms, the working
range of a system using this type of antenna will be only 50 to 70% of that of the same
system using a good-quality 1/4-wave whip (available as an option from your Vega
dealer).

The antenna should not be positioned near metallic objects, and especially not parallel
to them. The best arrangement is orienting the antenna vertically and at right angles
with nearby metallic objects. A location relatively high with respect to the person using
the transmitter is also desirable; about 8 or 9 feet (2.5 m) above the floor is usually
best.

A coaxial adapter is provided to convert the “rubber duckie” for right-angle use if this
is necessary. The “rubber duckie” is often used for body-worn applications (with the
receiver slung over the shoulder or on a belt, for example). In this case, efficiency will
be even lower due to absorption of the RF energy by the body. An additional loss of 5
to 10 dB is likely, reducing range by another factor of two or three. If range is a
problem (as evidenced by severe dropouts), using the supplied rubberized whip antenna,
or an optional 1/4-wave whip antenna (Vega Model 121BNC standard or Model 221
two-piece, which screws together), or a limp-wire antenna (Vega Model 224) may be
necessary.

6

R-27 Portable

Summary of Contents for R-27

Page 1: ...099 0050A Model R 27 Wireless Microphone Receiver Instruction Manual...

Page 2: ...y both the dealer and the freight carrier if damages or losses are found so that claims may be expedited Unpack the unit or units carefully We recommend saving the shipping cartons they are very usefu...

Page 3: ...n both units to the factory or authorized service location when changing frequencies to ensure the best results Because of the very high performance of these units and the specialized test equipment r...

Page 4: ...s control has approximately 46 dB of operating range and has an audio taper Connectors Antenna ANT Front panel BNC connector for use with the antenna supplied XLR Audio Output Rear panel mounted full...

Page 5: ...ansmitter MIC switch is on The audio levels should now be set for the system With the microphone correctly positioned speak loudly into it If necessary turn the audio gain on the transmitter up or dow...

Page 6: ...antennas About the smallest antenna with reasonable efficiency is the 1 4 wavelength design which must be about 16 5 inches 42 cm long at 180 MHz Of course electrically small antennas such as the rubb...

Page 7: ...minimized This reduces the likelihood of short circuits and improves the ability of the clamp to grip the cable firmly Just enough heat should be used to obtain a free flow of solder but to allow lea...

Page 8: ...fail to work or may damage the contacts when inserted Damage to the contacts usually requires a return to the factory or authorized service center Exhausted batteries will cause numerous problems inc...

Page 9: ...ts the source has become a wideband transmitter and nothing can be done to the wireless equipment to correct the problem that will not seriously degrade performance Fortunately this type of problem is...

Page 10: ...amages Some states do not allow the exclusion or limitation of incidental or consequential damages so the above limitation may not apply to you This warranty gives the customer specific legal rights a...

Page 11: ...rols Headphone monitor mic level adjustment power switch ON OFF Connectors XLR 3 pin male audio program output BNC coaxial antenna jack miniature stereo phone jack 3 5 mm Indicators 4 LED TX on 30 dBm...

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