HF PACKER
AMP
V4R6
Page 48
Note: The TEST jumper is transition sensitive since you are
waking the processor when applying the jumper. Multiple
transitions will cause the U2 chip not to respond. If this occurs,
try again. You may have to cycle power and try again to get
the LED to light.
FAN Option J6
An external fan is controlled by an output on pin 7 of U2
connected to transistor, Q3. The fan is plugged into J6. The
fan has red/black leads signifying the polarity of the leads. The
plus lead is red. It must be connected to pin 1 of J6 with the
black wire to pin 2 of J6. The fan is operated by the controller,
U2. If carrier is detected or PTT is activated, you will have the
fan activated. The fan is triggered on when carrier or PTT is
present and goes off when the hold time has expired.
5V Regulator
While we are on the CONTROL HFPA 10 schematic, let us
look at the voltage circuit, U1. This is a part which regulates
the 12V input down to 5V for the controller, U2. (Vcc = 5V).
The part requires bypass capacitors C10 and C11 as stated on
the data sheet for the part to prevent instability.
Panel LED
The front panel houses the TX LED. This LED is powered by
the transmit voltage (29.5V) and is a direct indication that you
have this voltage. It will be LIT during actual transmit or during
TEST when the H3 jumper is in place. Current is limited by the
R18, the 3K 1/4w resistor. A common building problem is the
connections from the panel to J5 on the wrong pins.
MOSFET AMP HFPA 10 Schematic
Follow along the descriptions as you view this schematic.
RF_IN
signal is shown on the extreme left side. This is the
transmit output from the transceiver at this point. The signal
reaches this point if
TX
is activated. The impedance of the
transceiver is 50 ohms and the transceiver is happiest when it
sees a 50 ohm impedance load.
Pi-resistive Network
That is where R3, R7 and R8 comes into play. This
combination of resistors is actually a pi-resistive network that
has two functions. First is the impedance termination and
second is an attenuator for the amplifier input. The AMP is set
up for a max RF input of 0.63W at the gates of the MOSFETs.
Overdriving the amp will cause audio distortion at the least and
failure of the MOSFETs at the most. We must transition
between the max RF output from the transceiver to the 0.63W
level with the pi-resistive network. The standard default
network is set up for 9dB attenuation. This is equivalent to an
8:1 power ratio. Looking at the choice, 5W/8 = 0.625W at the
gates of Q1 and Q2. The table in the upper left quadrant of the
schematic shows values of the pi-resistive network for other
max transceiver output levels. It is not physically possible due
to size constraints to have each network on board and choose
between them. This is a build option that the user must decide.
What is the best network to match their transceiver? The
FT817 has both a 2.5W and 5W output either the 6 or 9 dB
network could be used but there is always a danger if using
the 6 dB network that the user may accidently operate with
5W. The overdrive will distort and blow the MOSFETs. So, for
safety reasons, the 9 dB attenuator is the best choice.
L2 and T3
The signal out of the pi-resistive network next passes through
L2 , an impedance matching, to reach T3. The function of T3,
1:1 BALUN is to provide two outputs with 180 degrees phase
Summary of Contents for PackerAmp V4
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