Bird Technologies 429-83H-01 Series-Manual - Manual (Page 24)

TX RX Systems Inc. Manual 7-9439-6 09/03/09 Page 16
matic mode for distribution attenuation adjust-
ments.
The factory default setting for TTA Net Gain is 3.0
dB of attenuation and the factory default setting for
receiver multicoupler Distribution is 1.0 dB of atten-
uation. These are the initial settings that are pro-
grammed into your system when you first turn it on.
You will need to adjust these values to optimize
your system. This is done through software inter-
face via the menu select keys. Your settings will be
stored in system memory until you change them
again even if the equipment is powered down.
Setting the TTA NET GAIN Attenuation
The total amount of TTA Net Gain attenuation for
your system is composed of two parts, the main
line cable loss (which is fixed, based on cable type
and length) as well as the TTA Net Gain attenua-
tion setting (which is variable, depending on soft-
ware selection). This is illustrated in the formula
below.
Main Line Loss + Software Setting = Total
It has been found in practice that different levels of
total TTA Net Gain attenuation are required for dif-
ferent types of modulated signals to obtain the best
performance. Table 5 lists the optimum total TTA
Net Gain attenuation value for various signal types.
It should be kept in mind that these values are not
extremely critical. Systems that depart from these
values can still give reasonably good performance,
but may degrade somewhat when extremely strong
and very weak signals are present, as compared
with an optimized system.
The TTA Net Gain attenuation is programmable
and needs to be adjusted to optimum levels for the
type of signals being processed. The default fac-
tory setting is 3 dB. Further reduction may only be
necessary when the main transmission line loss is
low; that is, when line loss does not reduce the
TTA gain enough to obtain the desired total TTA
Net Gain attenuation level.
DETERMINING NEEDED ATTENUATION
To calculate how much attenuation is needed to
optimize the TTA Net Gain of your system use the
following formula;
TTA Net Gain(dB) = Gain TTA(dB) - Line loss(dB)
For example, if the TTA gain is 24 dB and the main
transmission line loss is 3 dB:
TTA Net Gain = 24 dB - 3 dB = 21 dB
If your system uses FM Voice, you would like a
TTA Net Gain as close to 13 dB as possible. The
amount of TTA Net Gain attenuation required is
calculated with the following formula;
Attenuation(dB) = Actual(dB) - Desired(dB)
Attenuation = 21 - 13 = 8 dB
So in this example the TTA Net Gain attenuation
setting should be 8 dB. If the sign of the calculated
attenuation had been negative it would indicate
that we could actually use more gain! No attenua-
tion would be required.
The programmable attenuation for optimizing your
TTA Net Gain attenuation is adjustable from 0 to
15.5 dB in 0.5 dB increments. To adjust the value
perform the following steps.
1) Press the DOWN ARROW button on the front
panel to scroll through the menu choices until
you reach the ATTENUATORS menu.
2) With the ATTENUATORS menu displayed
press the ENTER button to step down to the
TTA Net Gain sub-menu.
3) Press the ENTER button again to advance to
the TTA Net Gain adjustment screen. The cur-
rent TTA Net Gain setting will now be displayed.
Use the UP and DOWN ARROW buttons to set
the TTA Net Gain to the desired value. The
attenuation setting works in a forward loop fash-
ion, starting at 0 and increasing to 15.5, a but-
ton press after 15.5 returns the setting back to
0.
Type of Signal The optimum total
amount of TTA NET GAIN
FM Voice 13 dB
Digital 10 dB
Table 5: Optimum total TTA NET GAIN.