Friday, 2 October 2015

PA70H – 50 watt RF amplifier for 70Mhz.

© design Piotr Bryl SP2DMB ver. 1.1 14.01.2014

This documentation concerns the construction of a power amplifier for the 4m
band. The main part of the device is Mosfet Mitsubishi RD70HVF1 . Although it is
dedicated to the higher band, but it is stable at 70MHz.
The ranges of output power from 45 to 55W, with input power about 3-5W. The
system is powered by a standard voltage 13,8 V and consumes approx 7- 8A.
The amplifier consist of: power transistor and additional elements, that allow for quick
configuration of any device . Therefore, the board includes all the necessary blocks for
a complete amplifier. PCB is one-sided, plated with solder mask . Dimensions:
84x146mm .
The amplifier have a simple security circuits : over current, exceeded SWR and
temperature control. These additional circuits will allow for the safe use of the amp
and let a smaller heat sink assembly . The size at which the heat sink is not required
for the fan is: 124x150x35mm
Kits will be available in two versions: PA70HLI and PA70H . The first version will
require input signal abt. 100mW ( LI - Low Input ) and requires an additional driver
amplifier - PA70. Second version approx max. 3 -5W (H - high) .
The amplifier can to be control to transmission mode – PTT:
- By giving GND (standard) : -P
- By giving +13.8 V: +P
- RF VOX - automatically turns on when a signal RF (with adjustable delay)
Amplifier box has dimensions of 160 x 80 x 190mm . The heat sink has additional
place for driver PA70 .
On the following pages is a description of the amplifier PA70H .
Below is a block diagram:

1.RF VOX - allows you to work without additional cable for PTT . To use it you
must set a time constant DELAY by potentiometer . The PCB includes two space
for electrolytic capacitors (if need).
2. PTT PLUS - amplifier can be started by entering the +13.8 V input .
3. PTT GND – entering mass – GND, amplifier is switching for transmitting .
4. FAN TEMP CONTROL - this is a temperature sensor based on the LM35 . This
sensor is located close to the power transistor and is connected through the
thermal grease to the heat sink. When temperature increase signal from the
sensor increase also. This signal come in to amplifier LM358, After amplification
drives the transistor BD139 and the fan start. Potentiometer P1 you can adjust the
threshold of the fun. Fan speed is directly proportional to the temperature.
5. ATMEGA8 PA CONTROL - optional add-on to the amplifier. This is the RF
Multimeter that the display shows : supply voltage U , current I, DC power P,
graphic display of the RF output power , heat sink temperature t and SWR.
6. INP / OUT – relay, switching rf input signal.
7. PA RD70HVF1 - 50W amplifier.
8. SWR BRIDGE - measuring bridge:FWD and REF . RF – bridge signals may
control: MULTIMETER , microampere , LED line . If the signal is too small , it can
be amplified in the second - free operational amplifier . The outputs of the bridge
can be adjusted using potentiometers .
9. L PF- 70MHz low pass filter.
10. FINGER – antenna relay.
11. SWR ERROR - protection against excessive SWR . Exceeding the
predetermined level execute reduction of the gate voltage to zero. Power drops
from 50W to 30W, and the current of 7A to 4A. The block is equipped with a
second exit for any driver , for example - PA70 with RD16HHF1.
12. BIAS PROTECT - executive transistor, which reduce voltage to zero when
then SWR is over 2. It has an additional output .
13. DRIVER POWER CONTROLLER - this is a regulated power supply. Allows for
smooth power control driver with driver RD16HHF1. By varying the drain voltage
(5 to 11V ) - the output power is change continuously.
Circuit diagram:


Installation and commissioning
I used heat sink: width 124mm,height 35mm. It may be smaller, but you will need to
apply the fan (the control is on the board). The length of the heat sink is 146mm, as
much as the PCB. Fasten the plate to the heat sink and drill the holes. Then rifling on
the M3. If there is a PA with + driver, do the holes for the PA70.
PCB PA70H must be extremely placed, so that RD70HVF1 fell in the middle of the
heatsink (better heat removal).

After this we remove the chips remaining after treatment:
After screwing the pcb, we must do soldering diodes 1N4148:
Capacitors, inductors and other elements:
Before installing the power transistor RD70HVF1, check the operation all circuits: RF
VOX, PTT by GND (-P), PTT by +13,8V (+P), threshold of the fan if need.
Potentiometer 4.7k for BIAS of transistor (RD70) set to GND.
Connection diagram
Some pictures for explain:
Relay INP/OUT. Coaxial cable left - INP/OUT 70MHz. Right bypass for RX.
From left side: black POT 50k - setting DELAY when switching from transmit to
receive, at the top (visible part) - 4,7 k - adjustable output voltage LM317 power
supply, at the bottom of the 4.7 k - setting the gate voltage RD70HVF1.
On the right fallows: polymer fuse 6A (yellow), at the bottom of the fuse there is
place for LM35 temperature sensor.
Top left: potentiometer (black) - gain control of the second operational amplifier, on the
right ( also black) – adjusting threshold fan (system works with LM35 thermometer).
Two blue potentiometers: top - REF reflected voltage regulation, bottom - FWD
forward voltage regulation. Signals comes from SWR bridge – a photo below:
In the same shield box is the relay antenna (FINDER) and LPF:
Power amplifier stage with RD70HVF1. Use additional connectors (wire CuAg) to
solid connect source to the GND. Please remember to coat thermal grease the
bottom of transistor !!!
Power amplifier in box:
Connect voltage to the PA and switching it to transmitting (without RF input
signal). Potentiometer 4.7k set the voltage approximately 1.9 -2.0 V at the gate of the
Connect input rf signal and adjust to the highest power output (VR capacitors).

Parts list
= 1 x Finder
Ant1 = 1 x Antenne
C2 = 1 x 68p/100V
C3 = 1 x 100p/100V
C4 = 1 x 68p100V
C20 = 1 x 40p
C32 = 1 x 12p
C34 = 1 x 22p
C36 = 1 x 2,2p
C37 = 1 x 47μ
C38 = 1 x 22μ
C45 = 1 x 25p
C50 = 1 x 1μ
C57 = 1 x 47μ*
C1,C63 = 2 x 47p/500V
C12,C49 = 2 x 10μ
C21,C22 = 2 x 56p
C33,C46 = 2 x 65p
C58,C62 = 12 x 4,7n
C61 = 26 x 100n
C9,C13,C52 = 3 x 100μ
D3 = 1 x 2,7V
D11,D12 = 11 x 1N4148
F1 = 1 x 12A
F polimer1 = 1 x 6A
Jp1,Jp2 = 2 x Jumper
L1 = 1 x 2t/6,5mm/CuAg 1mm
L2 = 1 x 10t/6,5mm/1,2mm
L4 = 1 x FB
L5 = 1 x 5t/6,5mm/diam 1mm CuE
L6 = 1 x 15uH
L14 = 4 x 33μH
L3,L10 = 2 x VK200
L7,L8,L9 = 3 x
LED1,LED2 = 2 x
M = 1 x Motor
P,P,P,P,P3 = 5 x 4,7k PR
P1,P2 = 2 x 22k PR
Q1 = 1 x RD70HVF1
Q2 = 1 x BD139
Q3 = 1 x BDP953
Q6 = 1 x BC 547
Q4,Q5 = 2 x BCP52
R1 = 1 x 120
R5 = 1 x 820
R15 = 1 x 8,2k
R23 = 1 x 240
R16,R19,R21 = 3 x 2,2k
R20,R22 = 6 x 1k
R3,R4 = 2 x 220
R24 = 5 x 4,7k
R7,R13 = 2 x 100k
R8,R11 = 2 x 1,8k
Rel1 = 1 x 2 x Um
SW1 = 1 x 1×ON
U1 = 1 x LM358
VR1 = 1 x LM35DZ

VR2 = 1 x LM317

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