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. At about 2.5:1 the am-
plifier will signal an alarm and enter protection. A power reset should be performed and the
amplifier should not be used again until the VSWR has been reduced.
The antenna should be tuned so that the load is as close to 1.1:1 as possible, see above. This
should also be carried out with the amplifier switched off and the drive radio at low power,
10W should be sufficient for most tuners to carry out the matching process. If an Automatic
ATU is used it should, once it has found a suitable match, be disabled such that it may not carry
out another tuning cycle until instructed to do so.
Depending on the type of antenna and ATU being used it may be possible to generate very
high and low impedance loads that can look to the amplifier almost like open or short circuits,
operating the amplifier at full output whilst trying to tune a non resonant antenna with a tuner
either manual or automatic can be catastrophic for the transistors due to the load mismatch. The
protection circuit will in most instances cut in at a VSWR of 2.5:1 but if the amplifier is being
used at full power whilst tuning the antenna it is possible that the transistors may sustain dam-
age due to the load mismatch. You have been warned!!
Now that the input power has been adjusted correctly, the antenna tuned, (If required), opera-
tion can continue. Input power can be adjusted to give the required output power or the ampli-
fier may be run at it’s full output.
If using a resonant antenna and having the amplifier set to AUTO (Filter selection), band
changes can be as fast as the time it takes to change the band on the drive radio. However
changing band on a non resonant antenna always requires the amplifier to be switched off
whilst the antenna is retuned to an acceptable VSWR.
MODE:
The HLA300 may be used for all of the common narrow band transmission modes such as
SSB, CW,AM,FM, SSTV and data modes etc.
Warning:
Transmit Time.
Hi Duty cycle modes such as FM, Data modes and AM 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
generate more heat in the same amount of time. It should be noted that the amplifier although
capable of being used with these modes should not be operated continuously. A transmission
time of more than a minute or two should be avoided to avoid excessive transistor junction tem-
perature. The exact time for transmission in these modes will depend on numerous factors such
as is the amplifier fitted with the cooling fans, How good is the ventilation around the amplifier
is there 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 to touch then sufficient time should be allowed to let it cool down be-
fore reuse. The amplifier has a thermostat that will block the operation of the amplifier if too
high a temperature is reached and automatically returning back operation when the temperature
has reduced.
Protection:
Excessive Heat sink temperature:
Three short beeps LED 4 OFF
Excessive Input Power:
Three long beeps LED 4 Flashing
Excessive SWR or LP Filter Error:
Three long beeps LED 4 Flashing
Input drive and power output:
The amplifier should give almost full output with approximately 8W input. This should be the
nominal input power. You may find that less power is required on the lower bands and slightly
more is required on 10m to obtain full output.
Maximum output power considerations:
All amplifiers have a maximum output and this occurs shortly after gain compression where by
Pin no longer produces an 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 ampli-
fier will not actually help your signal to be stronger, you will in fact cause higher levels of dis-
tortion 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 10W and 150W is nearly 12dB a healthy increase to your signal
strength, 2 ‘S’ points, difficult to achieve with an antenna alone for most ham operators, espe-
cially if space is limited. Now lets say for example you run the amplifier at a moderate 120W
output by slightly reducing the input power, the difference between 150W and 120W is less
than 1dB which when you compare this to 6 dB per S point is actually very little and as the
amplifier is running not 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!!
Warranty:
This product is covered by a 24 month warranty commencing from the date of purchase. The
original purchase receipt will be required for any claim. This warranty does not cover aesthetic
damage or damage to the RF power transistors from incorrect use.
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