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 3,4 of this instruction manual.
Important!!
Before the amplifier is switched on, the output power of the drive radio should be adjusted cor-
rectly if it is capable of outputting a power greater than 5W. This may be done with the ampli-
fier connected but switched off. 10W is the maximum permissible input power to the amplifier,
but approximately 5W input should be sufficient to realise full output, and an input power of
0.5-5W is OK as it is not necessary to run the amplifier at full output if not required.
Switch on the amplifier by pressing and holding switch
[
for 2 seconds. There will be a single
audible tone followed by a short self test after which the amplifier will be ready to use. The
currently active band filter will be shown by the position of the Illuminated LED
a
above it.
The band filter may be chosen manually by the user or automatically by the amplifier during the
first transmission. To change the current band use the right
_
and left
`
’BAND’ buttons. If
the wrong band filter is selected by the user the amplifier will automatically change it on the
first transmission without error.
When the amplifier is in transmission LED
^
is illuminated. When it is OFF the amplifier is in
receive state.
To switch off the amplifier press the ON / OFF button
[
for about 3 seconds. The amplifier
will beep 3 times and then switch off.
The amplifier is protected against excessive input power, antenna VSWR, and temperature.
Maximum input should not exceed 10W. The best performance of the amplifier will be ob-
tained if the amplifier is operated at just less than full output which should be achieved with
about 5W input.
For a mobile installation the leads should not exceed a length of 3m and they should be con-
nected directly to the auto battery. An additional fuse at the battery is recommended to provide
protection in case of cable short circuit to chassis ground from the amplifier to the battery.
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 results.
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, (ATU / AMU), between the output of the ampli-
fier and antenna.
It is recommended to check that the antenna to be used is sufficiently rated for at least 200W
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. VSWR up to 2.0:1 is also possible but some reduction in power may
be seen and the amplifier will work less efficiently and generate more heat. At about 2.5:1 the
amplifier will signal an error
]
and will no longer transmit. The antenna should be tuned cor-
rectly and the amplifier maybe used again. The amplifier will automatically return from this
error after a signalling the error tone followed by flashing the Prot. LED to signal the current
error. (See error table pg. 9).
Mode:
The MLA100 may be used for all of the common narrow band transmission modes such as
SSB, CW,AM,FM, SSTV and data modes etc. QSK operation is also possible up to about 30
wpm.
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. The MLA100 is thermally protected and
will signal an error
]
when the transistor case temperature reaches a certain point in order to
protect the transistors. (See error table pg. 9).
