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Construction Notes for the 30W 1296MHz Amplifier
Overview:
E-Mail link for this Amplifier: The instructions included with this kit were carefully checked for accuracy, however, it
is possible that an error has been overlooked and caught by a fellow kit builder. In an effort to communicate
corrections, additions, or perhaps suggestions, an E-Mail account has been established. If you are interested in
participating in this communications link send a ‘test’ message to: 1296Amp@Cox.Net The 1296Amp e-mail account
will be checked each day for activity. All information sent to this address will be forwarded to those who have asked
to participate. E-mail addresses sent to: 1296Amp@Cox.Net will not be commercially shared. Upon request, a
WORD.DOC of these instructions, including color figures, will be sent.
Amplifier design, parts, and inventory: The amplifier is designed around an Infineon PTF 10021, LDMOS FET. The
device is rated: VDD = 28VDC, IDQ = 360mA, POUT = 30W, Efficiency = 50%, GaindB = 13dB. The final design and board
layout closely follows the ‘Test Circuit’ that was suggested by the chip’s manufacturer.
All the parts required to assemble the amplifier are included with the exception of the input and output connections
[SMA, N-Type, etc], the heat sink, and enclosure. These parts were not included to allow the builder to customize the
amplifier to fit his specific needs.
It is assumed the builder has experience in assembling SMT parts, including intimate knowledge of Murphy’s 11 th Law of
Electronics i.e.: The speed a SMT component disappears across the workbench is directly proportional to its
replacement co$t. To assist you in eliminating ‘escaping’ parts, the components have been affixed to an inventory
sheet. It is suggested that you remove a part from the sheet only when ready to solder it to the PCB.
------- Please do not open the FET anti-static bag until instructed to do so ------Suggested Construction Procedure:
1.
PCB preparation- Using a diagonal cutter; trim away the area where the FET will be positioned. Use a flat file to
remove the PCB material until the pads for the small vias are totally removed; see Figure 1 and 2. Use a VOM to
determine there is no continuity between the upper two large FET pads (GATE/DRAIN) and the lower clad ground
surface.
2.
Heat-sink preparations- The heat sink must dissipate approximately 55W of heat during operation. The heat
sink, Figure 3, used for the photograph is classified as: aluminum, flatback, 5X8”, 0.375” base plate, 24 X 1” fins.
Consult the Internet1 and/or E-Bay to obtain proper sink material. Insufficient sinking will allow an elevated operating
temperature, resulting in thermal damage to the FET. 2 If you happen to find a piece of 0.250 aluminum plate the size
of the PCB in your junk box, leave it in the junk box- it won’t dissipate sufficient heat to protect the FET. The area
of your junk box 0.250” ‘sink’ is 9.5 Sq/In, the area of the sink in Figure 3 is 136 Sq/In. Forced air cooling (12V
computer muffin fan) can be used allowing a smaller area of the sink to be used, however there is a risk, fan failure
may result in FET failure.
Using the layout dimensions contained on the engineering drawing, Illustration 2, establish the layout of your heat sink.
Drill and tap 10 #4-40 PCB mounting holes, 8 for the PCB board, and 2 for to secure the FET. You may also desire to
include taped holes for the 28V/Gnd standoffs, and other special needs for your application.
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2
Also see: http://www.communication-concepts.com/heat_sink.htm
www.electronics-cooling.com/Resources/EC_Articles/JUN95/jun95_01.htm
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There are a number of different ways to mount the PCB/FET/Sink combination. Due to the physical dimensions of the
FET, and the thickness of the PCB, the SOURCE and the GATE tabs do not physically contact their respective pads on
the PCB. Figure 7, 8, and 9 address this problem.
3.
Mounting the parts- Prior to soldering any components on your PCB, it is recommended that you use rubbing
alcohol and a Q-tip to remove any surface oil that may be present. The component silkscreen on the board will assist
you in locating the parts. The soldering pads for C8 are very small, use a blade to scrape away some of the solder mask
if needed. Due to their size, C6 and C10’s position is not included in the silkscreen, however, their position can be seen
in Figure 4, 5, and 6. In addition, C6 and C10 are polarized so proper indexing is critical. It is recommended these two
components be installed last. When all the components are mounted, except the FET, take a few minutes to double
check all connections for cold joints, solder splashes, correct parts in locations, polarity reversal, etc.
4.
Adjusting the Bias Level- Using a VOM, check the resistance between the board’s Vcc and GND pad, it should be
greater than 20K. Assuming no shorts were found, the Bias pot can be preset at this time. With the PCB oriented so
that the RF IN terminal is on the left, adjust the R1 pot fully CW (clockwise). Now apply a low current (100 mA?)
variable voltage supply to the Vcc and GND terminals. Slowly bring up the Vcc voltage to 6 V while monitoring the
current. When the input voltage reaches 6V you should note the following:


The voltage at the output of IC-1 (junction IC1-R1-C11), 7805, to GND. should be 5V?
The voltage at the GATE of the FET should be 3.6 +/- 0.1V
----- Leave the pot in its fully CW direction until instructed to re-adjust it ----Assembly of the PCB-FET-Heat sink: Use alcohol and Q-tips to remove any oil film or flux residue from the top
surface of the heat sink. Place the PCB on the sink and temporarily secure it with four mounting screws. Attach a
properly grounded anti-static wrist strap to your wrist. Open the bag containing the FET, place the FET in its PCB
opening making sure the DRAIN (which has a notch) is toward C4 and the PCB’s output terminal. Temporarily mount the
FET in place using two mounting screws. Align the PCB, FET, and other items. Solder the FET to the PCB. Install the
remaining screws and tighten all screws until snug without stripping the holes.
Initial Tune-Up- If this was a perfect world, you could connect the amplifier to 28 V and squeeze the PTT . . . . and
the wattmeter would pin out at 30W. However, to avoid the embarrassment of seeing the ‘smoke escape’ it is
suggested that the Tune-Up be made in two steps: (1) at 12V which will allow you time to familiarize yourself with the
device, and then if all operates as expected (2) at 24V and full power out.
(1) Preliminary Tune-Up- Prior to connecting any voltage, double check the position of the pot, is it in the CW
position? Connect a suitable 50 ohm load to the amplifier’s output. To avoid an impedance error being reflected back
into the DRAIN, the load should ideally be a 50 ohm resistive rated at 30+ watts. Connect a signal generator, or 50
ohm impedance to the input. Apply 12V to the Vcc and GND terminal. The I DQ (Current, Drain, Quiescent) should be
approximately 20 mA +/-. SLOWLY turn the bias pot CCW monitoring the IDQ and VG . You should be able to ramp IDQ
upward stopping at 200 mA. Apply 10 dBm of drive at 1296 MHz, the IDQ should increase as the drive is applied, RF
output should be noted.
(2) Final Tune-Up- Assuming an output signal was obtained in the above preliminary tune-up, turn off the RF
drive and 12V to the amplifier. *****
Return the Bias pot to the fully CW position-----
Apply 28V to the Vcc and GND. With no RF drive, SLOWLY advance the bias pot until the I DQ is 300 – 360 mA is
obtained. The FET is rated at IDQ = 360mA Max. While monitoring the POUT, increase the RF input drive to a maximum
of 33 dBm., the output should be approximately 25-32W, 44-45dB. The current should be about 2A at 28 VDC.
Wrap Up: Mount the amp in an enclosure of your choice and start microwaving the ether. 
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Parts ProvidedC1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C12
C13
ATC 100B 33 pF*
ATC 100B 1.2 pF*
ATC 100B 0.5 pF*
ATC 100B 33 pF*
ATC 100B 33 pF*
10 uF
0.1 uF
ATC 100B 33 pF*
0.1 uF
10 uF
0.1 uF
0.1 uF
L1
L2
IC1
R1
R2
R3
Q1
10 nH
10 uH 3.8A
7805
10K Adjustable
2.2
24.9K
PTF10021 FET
PC board
*C1-C5, C8 are specifically designed by American Technical Ceramics Corp. for use at microwave frequencies. If one of
these gets ‘misplaced’ be advised a junkbox replacement will typically not work.
Suggested tools and hardware neededDrill, drill bits and taps
Flat file
Small side cutters
Small insulated screwdriver or tuning tool
Anti-static wrist strap
Grounded soldering iron and rosin core solder
Tweezers, Q-tips and rubbing alcohol (Jack Daniels not recommended)
Signal source with output up-to 4W at 1296 MHz
50 Ohm load (50W recommended)
Power meter with attenuator rated to 50W
Adjustable power supply with current limiting (0-28VDC, 0-3A)
18 AWG hookup wire (for connecting amp to power supply)
Screwdrivers for the pc board and RF connectors mounting screws
4-40 Pan head screws (10 required)
RF connectors (2 required) and mounting screws (Users choice)
*****
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Illustration 1 Schematic goes on this page
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Illustration 2 engineering drawing of layout goes here
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Figure 1- The unmodified PCB.
The mounting location of the FET will be in the
center of the PCB under the component identifier
‘Q1’. To create the opening or footprint for the
FET, first remove the enter portion of the 8 large
holes using a pair of diagonal cutters.
Figure 2- PCB with FET footprint removed
After removing the 8 large holes, use a small
square file to square up the opening. Use the 30
small vias as your guide or border of your opening.
All portions of the vias must be removed or there
will be a short circuit between the top and the
bottom-clad surfaces.
Figure 3- The Heat sink
The heat sink selected was 5” X 8” X 1”. Some of
the black anodizing was removed to enhance its
photographic contrast. Using the dimensions given
on the engineering drawing of the board (see Figure
10) mark, center punch, and drill the tap holes for
the # 4-40 hardware. Eight holes are required for
the PCB, and 2 are needed for the FET. The eight
larger holes in the sink are for mounting the
assembly to an enclosure. The two large boreholes
are to facilitate the SMA connectors.
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Figure 4- Parts mounted
This photograph shows all the mounted parts with
the exception of the SMA, FET, and a few
capacitors.
Figure 5- Mounting C6 and C10
The (-) terminal of the electrolytic capacitors, C6
and C10, are soldered to the large ground pad. A
larger wattage iron may be required when soldering
to the PCB’s ground surface due in part to the heat
sinking of the large copper surface. This close-up
shows the (+) terminal of C10 soldered to the right
of the capacitor.
Figure 6- Mounting C6
The area where the (+) terminal of C6 is connected
is congested. You will find sufficient space just to
the right of C7.
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Figure 7- Connecting the FET to the PCB
Due to the height of the SOURCE and GATE
terminals of the FET (0.100”) and the thickness of
the PCB (0.064”), soldering the FET becomes a
problem. There are 3 solutions: 1) bend the
terminals down so they touch the PCB, 2) end mill a
0.036 depression in the surface of the sink so the
FET will mount lower, or 3) elevate the PCB using
some form of standoffs.
Figure 8- Elevating the PCB
The photograph shows a 0.035 washer placed under
one of the 8 PCB mounting screws. If this solution
is adopted, all 8 mounting screws must be fitted
with washers.
Figure 9- FET DRAIN terminal
Once the PCB has been elevated, the DRAIN
terminal of the FET and the surface of the PCB
will be in contact.