5
Operation:
Before using the amplifier the user must be familiar with all of the controls and be sure that it
has been connected correctly. Refer to Page 3 of this instruction manual.
Important!!
Before the amplifier is switched on, switch
[
,
the power output of the drive radio should be
adjusted correctly if it is capable of outputting a power greater than 25W. This may be done
with the amplifier connected but switched off. 35W is the maximum permissible input power to
the amplifier, but approximately 25W input should be sufficient to realise full output, and an
input power of 2-25W is OK as it is not necessary to run the amplifier at full output if not re-
quired.
When the amplifier is switched on LED
`
is illuminated.
The amplifier does not have protection against excessive input power and as such the responsi-
bility will be with the user not to overdrive it. Maximum input should not exceed 35W. The
best performance of the amplifier will be obtained if the amplifier is operated at just less than
full output which should be achieved with about 25W input.
If the drive radio cannot be reduced below 35W then the input attenuator should not be used to
lower the input to the amplifier. The input attenuator can and should only be used to reduce the
output of the amplifier if required. There are 5 levels of attenuation position 6 is direct input.
Damage will occur if the amplifier is operated above 35W input power.
When the amplifier is in transmission LED
^
is illuminated. When it is OFF the amplifier is in
receive state.
The installation location must also provide a suitable ground system both for RF and the AC
power supply, (if used). This is very important safety requirement for any radio transmission
equipment but as power increases becomes increasingly important. A good RF ground will also
help to prevent any returned RF from causing problems with the equipment. Usually erratic
operation of equipment when in transmission may be attributed to RF being present or poor RF
grounding. Installations where a good RF ground is not possible like operation above the
ground floor may require alternative solutions such as artificial earths or the connection of 1/4
wave counterpoises to the operating equipment. Correct RF earthing techniques are however
beyond the scope of this manual.
Mobile use should ensure that the ground connections are well bonded to the vehicle chassis
ground for best operation.
6
Antenna Considerations:
The amplifier is designed to work into a 50 ohms resistive load and any antenna outside of this
requirement must use an antenna tuning unit between the output of the amplifier and antenna.
It is recommended to check that the antenna to be used is sufficiently rated for at least 500W
power handling before connecting this product. It is also recommended to check that the VSWR
does not change considerably with increased power as this would indicate that the antenna was
not suitable for high power use.
Cable losses particularly increase with increasing frequency. Always use a good quality 50
Ohm feeder and keep the length as short as possible. Not only will this allow more power to
reach the antenna but will also increase the signal strength at the receiver.
This amplifier should not be operated into mismatched loads, (high VSWR) An acceptable level
should be less than 1.5:1. Less than 2.0:1 is acceptable but some reduction in power may be
seen and the amplifier will work less efficiently and generate more heat. There is no protection
for excessive VSWR so it is advised that the antenna is tuned correctly for the frequency it is to
used on to avoid damage to the amplifier.
Mode:
The KL503 HD may be used for all of the common narrow band transmission modes such as
SSB, CW,AM,FM, SSTV and data modes etc.
RX Preamplifier:
The KL503 HD is fitted with an RX preamp, that when activated can help to increase the re-
ceived signal level. This can be used when the signal level is low to help improve intelligibility
of the received signal. The RX preamp can be used independently of the amplifier however
when the amplifier and preamp are both activated the preamp is automatically switched out of
line when the amplifier is in transmission. Switch
\
is used to switch the preamp on and off.
LED
_
is illuminated when the preamp is switched on.
Warning: Transmit Time.
Hi Duty cycle modes such as FM and Data modes etc. operate the amplifier at full power all of
the time unlike modes like SSB and CW that are either intermittent or only reach peak output
for very short times, these high duty cycle modes will run the amplifier much harder and gener-
ate more heat in the same amount of time. It should be noted that the amplifier although capa-
ble of being used with these modes should not be operated continuously. A transmission time of
more than a few minutes should be avoided to avoid excessive transistor junction temperature.
The exact time for transmission in these modes will depend on numerous factors such as, how
good the ventilation around the amplifier is if there is sufficient space for freely flowing air to
circulate, etc. If the ambient temperature is high this will reduce the total time in transmission.
Common sense should be exercised if the heat sink is becoming too hot then sufficient time
should be allowed to let it cool down before reuse.
