Build a 1500 Watt LDMOS Solid State Amplifier, the Easy Way John Eisenberg K6YP 3-16-2017

Why consider such a thing? ✔Solid state amplifiers are broadband and require no tuning. ✔I hate the 180 second warm up time associated with “modern” ceramic tubes. The pileup can grow from 1 or 2 guys to hundreds in 3 minutes. ✔What a great learning experience for me as I have never worked with LDMOS.

Goals ✔Pout 1500W min 1.8-50 MHz ✔50V dc operation ✔Better than -30 dBc IMD ✔-50dBc Harmonics (FCC requires -43dBc) ✔Compact rack mount unit < 4 RU ✔Complete protection (Temp, VSWR, Current, Overdrive) ✔Easy to build

Result

Easy to build much mo’ better. ✔Make use of available printed circuit boards, kits and pre-built modules ✔Stay away from having to install large numbers of SMT parts. Thru hole is much mo’ better. ✔Commercial panel and chassis ✔Standard parts, nothing exotic ✔No difficult machining

W6PQL, the best kept secret in amps W6PQL, Jim Klitzing is a retired HP engineer He is an avid VHF, UHF and microwave operator He has introduced a series of LDMOS amplifier modules and a complete family of 1kW amplifiers covering 160m through 23cm Located in Fremont His pricing is fair and reasonable Many of my illustrations are from his web site.

My Amp Uses W6PQL Modules 2 1kw 1.8-54 MHz PA modules 1 power splitter and 1 power combiner W6PQL controller board One 10dB 100W attenuator board 2 high current switches 1 low pass filter board 1 input and one output RF SPDT relay PCB 2 directional couplers / VSWR sensors 2 bar graph indicators 1 ALC board

And some other stuff as well ✔1 Unified Microsystems BCD 14 band decoder board ✔A Chinese fan speed controller from EBAY ✔Several simple hand wired vector board assemblies ✔3 Surplus 50V, 25A power supply units ✔1 Surplus power supply rack

Parts is parts ✔The power supplies were very cheap but only 2 out of 6 worked, 2 still don’t ✔I let W6PQL solder down the LDMOS transistors. Voids are not your friend! ✔Watch out for fan noise. Think through your thermal design carefully.

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Under the hood at about 80% complete

BLF188XR LDMOS MOSFET BLF188XR LDMOS Device XR means extremely rugged. You can draw a continuous arc on the open output connector of a BLT188XR amplifier without failure! The BLF188XR device soldered down to a W6PQL machined copper heat spreader

W6PQL 1 kW LDMOS 1.8-54 MHz Amplifier Module

Ampl Module Current and Pout

20 meter Linearity Pout vs. Pin

Harmonics must be filtered Amp harmonics measured without LPF at 7.2 MHz Amp harmonics with LPF in place meet FCC -43 dBc spec with margin.

Switched Low Pass Filter

Switched Low Pass Filter Board

In Phase Power Combiner and Power Splitter V V

Power splitter and combiner High power combiner board 100 Ohm 500 Watt Resistor Input power splitter board

Amplifier Bypass Relays Input SPDT RF Relay Output SPDT RF Relay Pout =1500W, Zload =50ohms V =273.9Vrms or 387.3Vpeak I =5.47Arms or 7.75Apeak Yes these low cost relays can handle 2kW with low VSWR to >100MHz External VSWR can induce large currents and voltages which the relay must handle

Input Pi Attenuator The combined amplifier modules produce 1.5kW with only 2.5W of input power. Thus an attenuator is needed to reduce the drive power by a factor of 10 or 10dB. Caddock thin film power resistors work well in such an application to above 54 MHz. 10 dB, 100 W Attenuator

ALC Detector The ALC detector produces a negative voltage proportional to amplifier input power. This voltage is fed back to the ALC input on the transceiver to maintain constant output power from the amplifier. Here is an SMT assembly job even I can handle ALC detector

Dual Directional Detector Dual Directional Detector Assembly Coupling = -20LogN-10dB Coupling = -26dB -10dB Coupling = -36dB

W6QPL Amp control board ✔Sequences antenna relay, amp bias, power supply voltage and RF drive hold off ✔High temp and high VSWR protection ✔Turns on fans at a set temperature ✔Shuts down amp if wrong LPF band selected ✔It is ANALOG!!

W6PQL Control Board I bought this board assembled!

High current switch and bar graph display ✔Two high current switches are used to activate or kill PA +50V on start up or in the case of a fault. One for each PA module. ✔The bar graph displays read out forward power in ~200W increments to 1800W and reflected power in 25W increments to 250W. It is driven by a directional detector.

High current switch and bar graph display High Current Switch (40A) It takes two of these, one for each amplifier pallet Bar Graph Display One for forward and one for reflected power

Band Decoder ✔The United Microsystems BCD14 band decoder takes input from the accessory output on my K3, and selects the appropriate LPF band. If the K3 is not connected the LPF bands are selected using the front panel band switch.

Band Decoder This came assembled as well United Microsystems BCD14 Band Decoder board

Fan Speed Controller ✔The 48V dual fan speed controller was found on EBAY and came with two thermistors for sensing temperature. ✔It worked great once I was finally able to decipher the Google translated instructions the vendor supplied. ✔It contains the only uP in the amplifier

Fan Speed Controller 48V Fan Speed Controller (Less than $10 on EBAY) The fan speed controller monitors and reads out the heat sink temperature and controls fan speed to maintain a constant heat sink temperature

50V, 75A power supply Assembly ✔The modules and rack were obtained on EBAY for peanuts. ✔The units are server power supplies and are power factor corrected and are designed to be hot swapped and easily paralleled ✔The units sound like a Boeing 747 on takeoff and will soon be replaced with commercial Meanwell telecom supplies

Power Supply Assembly Under Test Power Supply with 4 five ohm resistors in parallel. 50V/1.25ohms = 40A or 2000 watts.

Amplifier test data Measured with a Bird 30 dB, 4kW attenuator and a dual channel HP438A power meter. Dual channel capability allows the HP438A to also provide gain information. Gain=Pout/Pin The accuracy of diode type power meters like the Bird 43 and nearly all “ham radio” power meters is severely degraded by harmonics IMD at 14.2 MHz with 2 375W tones (1500W PEP), spaced 20 kHz is -32dBc

K6YP Amplifier Test Frequency 1.9 MHz Pin dBm Pin Offset Pout dBm Pout Offset Pout (W) Gain Left PA Right PA Total PA Pdc Efficiency Measured dB Actual Current A W % -7.9 38.93 31.03 4.44 49.57 54.01 251.8 22.98 9.7 10.5 20.2 1010 24.9 -5.3 33.63 7.25 56.82 480.8 23.19 13.0 14.0 27 1350 35.6 -3.3 35.63 9.43 59 794.3 23.37 17.0 18.0 35 1750 45.4 -1.8 37.13 10.86 60.43 1104.1 23.3 20.5 21.5 42 2100 52.6 -0.9 38.03 11.36 60.93 1238.8 22.9 22.0 23.0 45 2250 55.1 1.5 40.43 12.21 61.78 1506.6 21.35 25.0 26.0 51 2550 59.1 4.5 43.43 12.89 62.46 1762.0 19.03 28.0 29.0 57 2850 61.8 3.7 -6.5 38.95 32.45 4.50 49.56 54.06 254.7 21.61 10.0 11.0 21 1050 24.3 -3.0 35.95 7.92 57.48 559.8 21.53 15.0 16.0 31 1550 36.1 -1.3 37.65 9.56 59.12 816.6 21.47 18.5 19.8 38.3 1915 42.6 0.0 10.66 60.22 1052.0 21.27 43 2150 48.9 1.4 40.35 11.45 61.01 1261.8 20.66 24.0 48 2400 3.8 42.75 61.77 1503.1 19.02 27.2 53.2 2660 56.5 8.0 46.95 12.63 62.19 1655.8 15.24 30.0 2950 56.1 7.2 -5.0 39.00 34 4.11 49.55 53.66 232.3 19.66 22.1 37.2 7.64 57.19 523.6 19.99 15.7 31.7 1585 33.0 -0.3 38.7 9.13 58.68 737.9 19.98 37 1850 39.9 1.3 40.3 10.48 60.03 1006.9 19.73 21.8 43.6 2180 46.2 3.0 42.0 11.41 60.96 1247.4 18.96 52.0 5.0 44.0 61.76 1499.7 17.76 26.2 52.2 2610 57.5 7.4 46.4 62.44 1753.9 16.04 28.2 56.2 2810 62.4 14.2 -2.6 38.98 36.38 4.61 49.66 54.27 267.3 17.89 12.0 24 1200 22.3 -0.2 38.78 7.34 57.00 501.2 18.22 32 1600 31.3 1.7 40.68 9.08 58.74 748.2 18.06 19.0 38 1900 39.4 3.4 42.38 10.44 60.10 1023.3 17.72 23.5 45.5 2275 45.0 4.8 43.78 11.33 60.99 1256.0 17.21 50 2500 50.2 6.5 45.48 12.14 1513.6 16.32 27.0 55 2750 55.0 46.38 12.77 62.43 1749.8 16.05 31.0 60 3000 58.3

Frequency 21.2 MHz Pin dBm Pin Offset Pout dBm Pout Offset Pout (W) Gain Left PA Right PA Total PA Pdc Efficiency Measured dB Actual Current A W % -1.8 39.05 37.25 4.24 49.73 53.97 249.5 16.72 11.5 23 1150 21.7 1 40.05 7.3 57.03 504.7 16.98 16.0 32 1600 31.5 2.4 41.45 9.09 58.82 762.1 17.37 19.0 18.0 37 1850 41.2 3.7 42.75 10.26 59.99 997.7 17.24 22.0 20.0 42 2100 47.5 5 44.05 11.22 60.95 1244.5 16.9 24.0 48 2400 51.9 7.1 46.15 12.21 61.94 1563.1 15.79 27.5 27.0 54.5 2725 57.4 8.2 47.25 12.77 62.5 1778.3 15.25 30.0 29.0 59 2950 60.3 28.2 -1.4 39.10 37.7 4.22 49.87 54.09 256.4 16.39 10.2 9.8 20 1000 25.6 1.6 40.7 7.17 57.04 505.8 16.34 14.0 13.5 1375 36.8 3.3 42.4 8.89 58.76 751.6 16.36 17.5 33.5 1675 44.9 4.8 43.9 10.21 60.08 1018.6 16.18 21.0 40 2000 50.9 6.5 45.6 11.11 60.98 1253.1 15.38 46 2300 8.0 47.1 11.91 61.78 1506.6 14.68 51.5 2575 58.5 48.9 12.56 62.43 1749.8 13.53 26.5 56.5 2825 61.9 50.2 0.2 39.40 39.6 4.01 50.04 54.05 254.1 14.45 12.0 13.0 25 1250 20.3 3.2 42.6 6.97 57.01 502.3 14.41 17.0 35 1750 28.7 5.0 44.4 8.77 58.81 760.3 22.5 44.5 2225 34.2 6.9 46.3 9.97 60.01 1002.3 13.71 27.2 53.7 2685 37.3 9.5 10.9 60.97 1250.3 12.07 32.5 33.0 65.5 3275 38.2 50.3 11.2 61.24 1330.5 10.94 34.0 68 3400 39.1 SAT Freq Offset dB Pout W 1.9 49.57 53.98 250 38.93 49.56 56.99 500 38.95 7.2 49.55 58.75 750 39.00 14.2 49.66 60.00 38.98 61.76 1500 Output Attenuator 63.01 Input Coupler & 10dB Pad P(dBm) from P(Watts)

Conclusion ✔The result of this work is a solid, reliable 1500W LDMOS solid state amplifier that looks OK and is a pleasure to use. ✔LDMOS MOSFETs are capable of more than 1kW from a single device and offer excellent IMD performance and efficiency ✔The cost was half what others charge for a 1500W SSA in today’s market.

Conclusion continued ✔Most importantly the amplifier was a fun learning experience ✔The amplifier can be further linearized using Pure Signal pre-distortion running on an Anan 100D or Flex 6X00 transceiver ✔Finally the design and building process kept me entertained and out of trouble for several months worth of evenings.