7
Input drive and power output:
The amplifier should give full output with approximately 25W input. Excessive input power
should be avoided and the amplifier should always be operated in a responsible manner.
The KL503 HD features an input attenuator
a
that may be used to reduce the output of the am-
plifier 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 25W! 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 amplifier, 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 overdriv-
ing 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 intelligible 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 differ-
ence between S5 and S7 2 ‘S’ points is 12dB.
The difference between 25W and 300W is about 11dB a healthy increase to your signal
strength, almost 2 ‘S’ points, with the same antenna. Now lets say for example you run the am-
plifier at a moderate 250W output by slightly reducing the input power, the difference between
250W and 300W is less than 1dB 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 out-
put with less distortion that will actually make a difference at the distant receiver for the bet-
ter!!
8
0
2
4
6
8
10
12
25,000
26,000
27,000
28,000
29,000
30,000
G
a
in
(dB
)
Frequency (MHz)
Typical Gain vs Frequency
0
50
100
150
200
250
300
350
0
5
10
15
20
25
30
35
40
O
ut
pu
t P
ow
er
(W
)
Input Power (W)
Typical Output Power KL503 28.000 MHz