Operation:
Before using the amplifier the user must be familiar with all of the controls and be sure that it
has been connected correctly.
Important!!
Before the amplifier is switched on the power output of the drive radio should be adjusted cor-
rectly if it is capable of outputting a power greater than 10W. This may be done with the ampli-
fier connected but switched off. 10W is the maximum permissible input power to the amplifier,
but approximately 8W input should be sufficient to realise full output, and an input power of 1-
10W is OK as it is not necessary to run the amplifier at full output if not required.
The amplifier features protection against excessive input power and will switch in a 3dB at-
tenuator when the input power reaches approximately 12 to 15W, if the input power is more
than about 15-20W the amplifier will disable the input relay and put the amplifier into a protec-
tion mode. The input power should be reduced to an acceptable level and then to restore opera-
tion the amplifier must be reset by cycling the on / off switch. The 3dB attenuator can also be
selected manually to reduce the output power of the amplifier if the input power is not adjust-
able say for instance a fixed 10W output. It should not however be used to reduce the input
power to the amplifier from a radio that has say 20Watt output. The maximum input to the am-
plifier should always be adjusted on the radio.
The cross sectional area of the cables used to connect the amplifier to the PSU should not be
less than 6mm
²
or 10 AWG
.
They should also be kept as short as practicably possible to avoid
voltage drop due to ohmic losses. This is less of a problem in a fixed installation where the
power supply may be placed close to the amplifier.
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 may also be connected inline 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
line supply. 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 equip-
ment when in transmission may be attributed to RF being present or poor RF grounding. Instal-
lations where a good RF ground is not possible like operation above the ground floor may re-
quire alternative solutions such as artificial earths or the connection of 1/4 wave counterpoises
to the operating equipment. for the bands being used . Correct RF earthing techniques are how-
ever beyond the scope of this manual.
The protection circuit for excessive input power should not be regarded as a 100% protection
for all levels of input power. Up to about 50W the circuit will work very effectively and will
save the amplifier from damage, above 50W for example accidental 100W or more applied to
the input the protection circuit can not be expected to provide complete protection. In most
cases the protection will act sufficiently quickly to protect the transistors from damage but this
condition is not guaranteed!!! For this reason when using the amplifier with a 100W capable
radio, caution should be used as not to accidentally switch on the amplifier before the power has
been reduced to 10W or less.
Switch on the power supply to the amplifier followed by the amplifier on off switch on the front
panel. After switch on there is a short delay of approximately 10 seconds whilst the amplifier
carries out a quick self test procedure. During this time the LED display of the output power
and output filter will flash on and off one at a time from top to bottom. When the test is finished
the current filter selected will be indicated by the relevant LED and also for the 3dB attenuator
if set to ON. SSB delay has no LED associated with it so the switch position must be checked
if required on or off.
Filter selection maybe be made manually but for most operation, if changing bands frequently,
the filter selection can be left in the AUTO position. Every time the amplifier switches to TX
when there is RF present the frequency is calculated and the correct filter latched in circuit. The
filter will remain selected until either another frequency (band) is used outside of the filters
range or the amplifier is switched off. The default filter in Auto mode after switch on is the 10-
12m filter.
Warning:
Filter Selection
If using the manual filter selection care must be taken to make sure that the correct filter is se-
lected for the band in use. This is only of concern if the frequency of use is higher than that of
the cut off frequency of the selected filter. (For example transmission on 14.275 MHz (20m)
with the 80m filter selected. As the cut off frequency of the 80m filter is 4Mhz it will not pass
RF at 14.175 MHz and the transistors will see a very high SWR and could be damaged. The
amplifier is protected for these conditions but this should obviously be avoided especially at full
power.
Selecting the wrong filter but having a transmission frequency lower than the filter cut-off fre-
quency does not cause an error or harm to the amplifier but any harmonics of the transmission
frequency will be transmitted if they fall under the cut-off frequency of the filter causing unnec-
essary QRM on other bands. (e.g. transmission on 1.845 MHz with the 15-17m filter selected
would allow also all of the harmonics to be transmitted without attenuation, on 3.69, 5.535,
7,38........ All the way up to the 11th harmonic with the 12th lying outside of the 12-17m filter
this is almost the worst example but as can be seen it’s quite important.
Warning:
ATU / Non resonant Antennas
Non resonant Antennas and ATU’s (Antenna Tuning Unit). Before transmission you must make
sure that there is a suitable load connected to the antenna output of the amplifier. Transistor
amplifiers should not be operated into mismatched loads, (high VSWR) An acceptable level
