HSP BLA703 User manual

BLA703
HF 25—30 MHz Linear Amplifier
Specifications:
Operation Frequency:
Modulation Types:
Transistor:
Max I/P Current:
Power Supply:
Input Fuse (Internal):
Input RF Power:
Output RF Power:
25—30 MHz (10 m Amateur HF Band)
SSB,CW,AM, FM, data etc (All narrowband modes)
16x RM 3 MOSFET
8A / 120V. 4A 230/240Vac
110-120V or 230-240V Model specific
8A or 4A (5x20 mm Fast)
1-30 W max (All modes)
550 W max
Maximum bypass power (Amplifier off): 50W max
Input VSWR: 1.1—1.5:1
Output VSWR Maximum:
Harmonic Output:
Dimensions:
Weight:
2.5:1
>-50dBc 25-30MHz
410 mm x 175 mm x 305 mm
13 kg
WARNING: Before using this product please read
carefully all of the information in this manual or at least the quick
start guide!!! This is extremely important to avoid damage or
incorrect operation !!!
Ver 1.0 Dic. 2023
2
Quick Start Guide:
A more complete installation guide is featured later
1.
Connect the RTX input connector to the transceiver
with a 50 Ohm patch cable.
2.
Connect the ANT Output of the Amplifier to VSWR
Bridge / Wattmeter (If required), then the ATU (If
required) and then the Antenna (50 Ohm load
Impedance).
3. Make sure that the amplifier AC switch is switched
off.
4.
Connect the Amplifier AC power cable to the AC Net-
work. Pay attention that you have the correct BLA703
model for the AC voltage of your country.
5.
Adjust the RF output power of the transceiver to
10 W (30W max) if it is capable of more than 30W
output
6.
Switch on the Amplifier. After a short boot period
press the STB /OPR button until the LED turns green,
indicating ‘Operate mode’.
7. Try a brief transmission to check that the antenna
VSWR is acceptable with the amplifier in use. Any
large increase in VSWR indicates that the Antenna is
not suitable for the power being used. Operation
should be halted immediately to avoid damage to the
Amplifier / Radio / ATU etc.
8. If everything is OK you can increase the input drive
and / or change the output power level to suit your
output power requirements.

3
Front / Rear Panel Description
Front Panel
1. Standby / Operate Switch and TX indicator
2. SSB Delay ON / OFF Switch and LED
3. Input Attenuator (LOW / MID / HIGH), (For output power adjustment).
4. RX Preamplifier ON / OFF Switch and LED
5. Alarm LED
6. Main AC Amplifier ON / OFF Switch
7. Output Power Indicator
8. VSWR Indicator
9. Cooling fans air intake
Rear Panel
1. Antenna SO239 RF Output connector
2. AC Input power connector. (AC Line voltage model specific)
3. RTX SO239 RF Input
4. Phono PTT input connector
4
Installation:
Unpack the amplifier from its shipping carton and inspect for any signs of damage.
The amplifier should be installed in a place that allows good ventilation and
provides a suitable base to support it. Failure to allow for reasonable ventilation
will cause the amplifier to overheat and shutdown prematurely. A short 50 Ohm
patch lead should be used to connect the amplifier's RTX SO239 input [3]
connector to the output, (Antenna Socket) of the drive Radio. The length of this
cable is not critical but should be of good quality and be kept as short as
practically possible. The ANT output connector [1] of the amplifier should then
be connected to the antenna being used.
If an external VSWR/Power meter is to be used the amplifier should be connected
to the input and then the antenna to the output. This order of connection is very
important. Check also that the Antenna is suitably rated for the power output
level. (Antenna VSWR should not change much from low to high power). The
antenna should be tuned before connecting the power amplifier or with the
amplifier switched OFF! .
In SSB mode it is recommended that the PTT input be utilised if the drive radio has
a suitable PTT output control. If there is no PTT input available the front panel
button  should be set to SSB. (LED Illuminated). This adds a short delay to the
release time of the RTX relays so that pauses in speech do not cause the RTX relay
to drop out. In AM or FM mode the SSB delay switch should be set to OFF.

The amplifier must be connected via the AC input connector  ,on the rear panel,
to a suitable AC power outlet of the correct voltage. The amplifier is supplied in
either 115/120V or 230/240V versions.
The installation location must also provide a suitable ground system both for RF
and the AC power supply, (if used). This is a very important safety requirement for
any radio transmission equipment, but as power increases it 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.
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 30W.
This may be done with the amplifier connected but switched off. At 35W input the
amplifier will sound and alarm and enter into protection, approximately 25-30W
input should be sufficient to realise full output, and an input power of 5-30W is OK
as it is not necessary to run the amplifier at full output if not required. (See ‘Input
Drive and Output Power on page 7).

5
It is recommended to start with the amplifier set with the input attenuator set to
the LOW position for the first transmission and the input power adjusted between
5 and 10W. (Low is the default setting at switch on).
Switch on the Amplifier AC switch (). Then switch the amplifier from ‘Standby’ to
‘Operate’ by pressing button (). The microphone PTT can then be pressed, and
if in AM or FM mode the amplifier will switch to TX (TX LED Illuminated) and
amplify the input signal. In SSB mode there will need to be modulation
otherwise with no modulation there will be no RF output from the drive radio.
The output power meter  shows the relative output power of the amplifier. The
last line of the scale relates to 550W output. If the output is driven beyond this
then the amplifier will sound an alarm, (6 beeps and the alarm led will flash 6
times) and transmission will be blocked.
If the drive radio cannot be reduced below 35W then it may not be used with the
amplifier, as the input attenuator CANNOT 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 3 levels of attenuation: LOW, MID and HIGH.
Pressing button  repeatedly will cycle through the 3 levels. LOW is the
default position when the amplifier is switched on.
NOTE: Damage will occur if the amplifier is repeatedly operated
above 35W input power.
The VSWR indicator  displays the output VSWR as measured at the antenna
connector of the BLA703. VSWR protection protects the BLA703 against excessive
antenna mismatch. When the load VSWR as measured at the ANT output
connector increases above 2.5:1, (the last red line of the VSWR indicator), the
amplifier will sound indicating an error (Two beeps and the Alarm LED will flash
twice), and transmission will be blocked. To reset the error it will be necessary to
retune the antenna to reduce the VSWR and then return to ‘Standby’ and back to
‘Operate’.
The BLA703 is protected against out of band transmissions. The export model will
sound an alarm, (Four beeps / Four flashes), if the transmission frequency is
below 25MHz or above 30MHz. The FCC version will sound an alarm (Three beeps
and three flashes if the frequency is below 28.000MHz and above 29.700MHz. To
reset the error it will be necessary to change the input frequency to that suited by
the BLA703 and then return to ‘Standby’ and back to ‘Operate’.
The BLA703 is protected against excessive output power. As the gain of the
BLA703 varies slightly over its range of frequency operation it is possible to
overdrive the amplifier on the lower frequencies when the input attenuator is set
to HIGH. The output power of the amplifier is limited to 550W. Exceeding this will
cause the amplifier to sound an Alarm (6 beeps and the Alarm LED will flash 6
times). To reset the error it will be necessary to reduce the input power and then
return to ‘Standby’ and back to ‘Operate’.
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 1000W power handling before connecting this amplifier. It is also
recommended to check that the VSWR does not change considerably with
increased power as this would indicate that the antenna is 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 2.5:1 is still possible but
some reduction in power may be seen and the amplifier will work less efficiently
and generate more heat. Beyond 2.5:1 VSWR the amplifier will enter protection
mode.
OPERATING MODE:
The BLA703 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 BLA703 is fitted with an RX preamplifier, that when activated can help to
increase the received 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.
Button  is used to switch the preamp on and off. The PRE LED is illuminated
when the preamp is switched on.
Warning: Transmit Time.
Heavy 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 heavy 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 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 allowable total transmission time.
Common sense should be exercised. The BLA703 is fitted with two large cooling
fans which offer a very efficient way of cooling the heatsink. At switch on they will
run for a few seconds and then switch off. When the heatsink temperature reaches
40°C they will switch on and remain on until the heatsink returns below this
temperature. As the heatsink temperature increases so will the speed of the fans,
in 3 levels. If the heatsink temperature becomes excessively high,(65°C), the
amplifier will block further transmission, sound an audible alarm and the amplifier
will automatically reset this condition only when the heatsink temperature returns
to 55°C.

7
Input Drive and Power Output:
The amplifier should give full output with approximately 25-30W input depending on
the trans-mission frequency. Excessive input power should be avoided and the
amplifier should always be operated in a responsible manner. If the input power
exceeds 35W the amplifier will sound an audible alarm, (1 beep and the Alarm LED
will flash once) and transmission will be blocked. In order to reset this condition it is
necessary to reduce the input power, and switch the amplifier from ‘Operate’ to
‘Standby’, then back to ‘Operate’.
The BLA703 features an input attenuator  that may be used to reduce the output
of the amplifier 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 35W! Otherwise the attenuator may be
damaged from overheating. There are 2 levels of input attenuation: LOW and MID.
Position HIGH is a direct input, with no attenuation. So setting to position LOW will
provide the lowest output power from the amplifier, and position HIGH the
maximum output.
When using SSB mode it is recommended to use the PTT input connector to switch
the amplifier from RX to TX. If there is no PTT input available the front panel switch
 should be set to SSB. This adds a short delay to the release time of the RTX
relays so that pauses in speech do not cause the RTX relay to drop out. In AM or
FM mode the SSB delay switch should be set to Off.
Maximum Output Power Considerations:
All amplifiers have a maximum output, and this occurs shortly after gain
compression, whereby Power input 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 overdriving 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 difference between S5 and S7 (2 ‘S’ points) is 12dB.
The difference between 25W and 500W is about 12dB, a healthy increase to your
signal strength, 2 ‘S’ points, with the same antenna. Now let's say for example
that you run the amplifier at a moderate 400W output by slightly reducing the
input power. The difference between 500W and 400W is less than 1dB which,
when you compare this to 6 dB per S point, is actually very little. As the amplifier
is not running at its absolute maximum, it will deliver a cleaner output with less
distortion, and that will actually make a difference for the better at the distant
receiver!
8

9
Typical Harmonic Output
Error List:
When the amplifier enters into protection mode an audible tone is emitted
and the Alarm LED will be flashing. Depending on the number of flashes/
beeps the error can be decoded from the following table.
1. Excessive input power >35W
2. Excessive Antenna VSWR >2.5:1 (BLA703 O/P antenna connector)
3. Error Frequency FCC (25.000MHz-27.995MHz and 29.705MHz –30.000 MHz)
4. Error frequency <25MHz and >30MHz
5. Error excessive temperature. Heatsink >65°C
6. Error excessive output power >550W
To reset the amplifier from one of the above alarm conditions it is
necessary to: first fix the error, be it reduce the antenna VSWR, or
reduce the input power. Then switch the amplifier from ‘Operate’ to
‘Standby’ and back to ‘Operate’.
If the error is from excessive temperature the amplifier will reset itself
when the heatsink temperature has returned to an acceptable level: 55°
C.
10
123456 7 8910 11 12 13 15 16 17 18
14
Output Power Meter
The output power LED display shows the
approx-imate output power into a 50 Ohm
non reactive load. It is calibrated so that
LED 20, (the last column), is set to
approximately 550W. Above this level the
BLA703 will enter into excessive power
protection.
12345678910
VSWR Meter
The VSWR Meter LED display shows
the current level of reflected RF from
the antenna at the ANT port of the
amplifier. It is calibrated so that LED
10 is illuminated with a VSWR of 2.5:1
and at this point the amplifier will
enter into excessive antenna VSWR
protection.
1: <1,6:1
2: 1.7:1
3: 1.8:1
4: 1.9:1
5: 2.0:1
6: 2.1:1
7: 2.2:1
8: 2.3:1
9: 2.4:1
10: 2.5:1
1: <25W
2: 25W
3: 100W
4: 130W
5: 135W
6: 155W
7: 225W
8: 265W
9: 290W
10: 320W
11: 335W
12: 365W
13: 415W
14: 420W
15: 450W
16: 480W
17: 505W
18: 550W

11
Notes:
12
Attention:
The use of Linear Amplifiers are controlled by specific laws
within the country of use. These laws must be known to the
user and are entirely the responsibility of the user. The
manufacturer declines any responsibility from unlawful use.
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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