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Input drive and power output:
The amplifier should give full output with approximately 7W input. Excessive input
power should be avoided and the amplifier should always be operated in a responsible
manner.
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The KL405 features an input attenuator
that may be used to reduce the output of the
amplifier if the drive radio does not have the facility to reduce its output power.
The input attenuator should NOT however be used to reduce the input power level of the
drive radio if it is greater than 10W! Otherwise the attenuator may be damaged from
overheating. There are 5 levels of input attenuation and position 6 is direct input, with no
attenuation. So setting to position 1 will provide the lowest output power from the ampli-
fier, and position 6 the maximum output.
Maximum output power considerations:
All amplifiers have a maximum output and this occurs shortly after gain compression
where by Pin no longer produces a proportionate increase in power output . The amplifier
should always be operated at a point below its saturated output. Trying to extract every
last watt by overdriving the amplifier will not actually help your signal to be stronger,
you will in fact cause higher levels of distortion which will make your signal less intelli-
gible at the distant receiver station.
Running the amplifier a little under max output will also allow the amplifier to run cooler
and make it more reliable for many years of use.
As an example consider the following situation.
1 'S' point on a receiver is usually approximately calibrated at 6dB so for example the
difference between S5 and S7 2 'S' points is 12dB.
The difference between 7W and 180W is about 14dB a healthy increase to your signal
strength, more than 2 'S' points, with the same antenna. Now lets say for example you
run the amplifier at a moderate 125W output by slightly reducing the input power, the
difference between 180W and 125W is 1.6dB which when you compare this to 6 dB per
S point is actually very little and as the amplifier is not running at its absolute maximum
will give a cleaner output with less distortion that will actually make a difference at the
distant receiver for the better!!
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