Build a 1500 Watt LDMOS Solid State Amplifier

Build a 1500 Watt LDMOS Solid State Amplifier, the Easy Way John Eisenberg K 6 YP 3 -16 -2017

Why consider such a thing? ✔Solid state amplifiers are broadband 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 1500 W min 1. 8 -50 MHz ✔ 50 V dc operation ✔Better than -30 d. Bc IMD ✔-50 d. Bc Harmonics (FCC requires -43 d. Bc) ✔Compact rack mount unit < 4 RU ✔Complete protection (Temp, VSWR, Current, Overdrive) ✔Easy to build

Result

Easy to build ✔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

W 6 PQL, the best kept secret in amps ✓ W 6 PQL, 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 1 k. W amplifiers covering 160 m through 23 cm ✓ Located in Fremont ✓ His pricing is fair and reasonable ✓ Many of my illustrations are from his web site.

My Amp Uses W 6 PQL Modules ✓ 2 1 kw 1. 8 -54 MHz PA modules ✓ 1 power splitter and 1 power combiner ✓ W 6 PQL controller board ✓ One 10 d. B 100 W 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 50 V, 25 A 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 W 6 PQL 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

BLF 188 XR LDMOS MOSFET BLF 188 XR LDMOS Device XR means extremely rugged. You can draw a continuous arc on the open output connector of a BLT 188 XR amplifier without failure! The BLF 188 XR device soldered down to a W 6 PQL machined copper heat spreader

W 6 PQL 1 k. W 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 d. Bc 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 =1500 W, Zload =50 ohms V =273. 9 Vrms or 387. 3 Vpeak I =5. 47 Arms or 7. 75 Apeak Yes these low cost relays can handle 2 k. W with low VSWR to >100 MHz External VSWR can induce large currents and voltages which the relay must handle

Input Pi Attenuator The combined amplifier modules produce 1. 5 k. W with only 2. 5 W of input power. Thus an attenuator is needed to reduce the drive power by a factor of 10 or 10 d. B. 10 d. B, 100 W Attenuator Caddock thin film power resistors work well in such an application to above 54 MHz.

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. ALC detector Here is an SMT assembly job even I can handle

Dual Directional Detector Assembly Coupling = -20 Log. N-10 d. B Coupling = -26 d. B -10 d. B Coupling = -36 d. B

W 6 QPL 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!!

W 6 PQL 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 +50 V on start up or in the case of a fault. One for each PA module. ✔The bar graph displays read out forward power in ~200 W increments to 1800 W and reflected power in 25 W increments to 250 W. It is driven by a directional detector.

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

Band Decoder ✔The United Microsystems BCD 14 band decoder takes input from the accessory output on my K 3, and selects the appropriate LPF band. If the K 3 is not connected the LPF bands are selected using the front panel band switch.

Band Decoder This came assembled as well United Microsystems BCD 14 Band Decoder board

Fan Speed Controller ✔The 48 V 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 u. P in the amplifier

Fan Speed Controller 48 V 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

50 V, 75 A 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. 50 V/1. 25 ohms = 40 A or 2000 watts.

Amplifier test data ✓ Measured with a Bird 30 d. B, 4 k. W attenuator and a dual channel HP 438 A power meter. ✓ Dual channel capability allows the HP 438 A 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 2 375 W tones (1500 W PEP), spaced 20 k. Hz is -32 d. Bc

K 6 YP Amplifier Test Frequency Pin d. Bm Pin Offset Measured d. B -7. 9 38. 93 -5. 3 38. 93 -3. 3 38. 93 -1. 8 38. 93 -0. 9 38. 93 1. 5 38. 93 4. 5 38. 93 Frequency Pin d. Bm Pin Offset Measured d. B -6. 5 38. 95 -3. 0 38. 95 -1. 3 38. 95 0. 0 38. 95 1. 4 38. 95 3. 8 38. 95 8. 0 38. 95 Frequency Pin d. Bm Pin Offset Measured d. B -5. 0 39. 00 -1. 8 39. 00 -0. 3 39. 00 1. 3 39. 00 3. 0 39. 00 5. 0 39. 00 7. 4 39. 00 Frequency Pin d. Bm Pin Offset Measured d. B -2. 6 38. 98 -0. 2 38. 98 1. 7 38. 98 3. 4 38. 98 4. 8 38. 98 6. 5 38. 98 7. 4 38. 98 1. 9 MHz Pin d. Bm Pout Offset Pout d. Bm Pout (W) Actual Measured d. B Actual 31. 03 4. 44 49. 57 54. 01 251. 8 33. 63 7. 25 49. 57 56. 82 480. 8 35. 63 9. 43 49. 57 59 794. 3 37. 13 10. 86 49. 57 60. 43 1104. 1 38. 03 11. 36 49. 57 60. 93 1238. 8 40. 43 12. 21 49. 57 61. 78 1506. 6 43. 43 12. 89 49. 57 62. 46 1762. 0 3. 7 Pdc W 1010 1350 1750 2100 2250 2550 2850 Efficiency % 24. 9 35. 6 45. 4 52. 6 55. 1 59. 1 61. 8 Gain d. B 21. 61 21. 53 21. 47 21. 27 20. 66 19. 02 15. 24 Left PA Right PA Total PA Current A 10. 0 11. 0 21 15. 0 16. 0 31 18. 5 19. 8 38. 3 21. 5 43 24. 0 48 27. 2 26. 0 53. 2 29. 0 30. 0 59 Pdc W 1050 1550 1915 2150 2400 2660 2950 Efficiency % 24. 3 36. 1 42. 6 48. 9 52. 6 56. 5 56. 1 Gain d. B 19. 66 19. 99 19. 98 19. 73 18. 96 17. 76 16. 04 Left PA Right PA Total PA Current A 10. 5 21 15. 7 16. 0 31. 7 18. 5 37 21. 8 43. 6 24. 0 48 26. 2 26. 0 52. 2 28. 0 56. 2 Pdc W 1050 1585 1850 2180 2400 2610 2810 Efficiency % 22. 1 33. 0 39. 9 46. 2 52. 0 57. 5 62. 4 Gain d. B 17. 89 18. 22 18. 06 17. 72 17. 21 16. 32 16. 05 Left PA Right PA Total PA Current A 12. 0 24 16. 0 32 19. 0 38 23. 5 22. 0 45. 5 26. 0 24. 0 50 28. 0 27. 0 55 31. 0 29. 0 60 Pdc W 1200 1600 1900 2275 2500 2750 3000 Efficiency % 22. 3 31. 3 39. 4 45. 0 50. 2 55. 0 58. 3 MHz Pin d. Bm Pout Offset Pout d. Bm Pout (W) Actual Measured d. B Actual 34 4. 11 49. 55 53. 66 232. 3 37. 2 7. 64 49. 55 57. 19 523. 6 38. 7 9. 13 49. 55 58. 68 737. 9 40. 3 10. 48 49. 55 60. 03 1006. 9 42. 0 11. 41 49. 55 60. 96 1247. 4 44. 0 12. 21 49. 55 61. 76 1499. 7 46. 4 12. 89 49. 55 62. 44 1753. 9 14. 2 Left PA Right PA Total PA Current A 9. 7 10. 5 20. 2 13. 0 14. 0 27 17. 0 18. 0 35 20. 5 21. 5 42 22. 0 23. 0 45 25. 0 26. 0 51 28. 0 29. 0 57 MHz Pin d. Bm Pout Offset Pout d. Bm Pout (W) Actual Measured d. B Actual 32. 45 4. 50 49. 56 54. 06 254. 7 35. 95 7. 92 49. 56 57. 48 559. 8 37. 65 9. 56 49. 56 59. 12 816. 6 38. 95 10. 66 49. 56 60. 22 1052. 0 40. 35 11. 45 49. 56 61. 01 1261. 8 42. 75 12. 21 49. 56 61. 77 1503. 1 46. 95 12. 63 49. 56 62. 19 1655. 8 7. 2 Gain d. B 22. 98 23. 19 23. 37 23. 3 22. 9 21. 35 19. 03 MHz Pin d. Bm Pout Offset Pout d. Bm Pout (W) Actual Measured d. B Actual 36. 38 4. 61 49. 66 54. 27 267. 3 38. 78 7. 34 49. 66 57. 00 501. 2 40. 68 9. 08 49. 66 58. 74 748. 2 42. 38 10. 44 49. 66 60. 10 1023. 3 43. 78 11. 33 49. 66 60. 99 1256. 0 45. 48 12. 14 49. 66 61. 8 1513. 6 46. 38 12. 77 49. 66 62. 43 1749. 8

Frequency Pin d. Bm Measured -1. 8 1 2. 4 3. 7 5 7. 1 8. 2 21. 2 Pin Offset d. B 39. 05 39. 05 Frequency Pin d. Bm Measured -1. 4 1. 6 3. 3 4. 8 6. 5 8. 0 9. 8 Frequency Pin d. Bm Measured 0. 2 3. 2 5. 0 6. 9 9. 5 10. 9 SAT Pin d. Bm Pout Offset Pout d. Bm Pout (W) Actual Measured d. B Actual 37. 25 4. 24 49. 73 53. 97 249. 5 40. 05 7. 3 49. 73 57. 03 504. 7 41. 45 9. 09 49. 73 58. 82 762. 1 42. 75 10. 26 49. 73 59. 99 997. 7 44. 05 11. 22 49. 73 60. 95 1244. 5 46. 15 12. 21 49. 73 61. 94 1563. 1 47. 25 12. 77 49. 73 62. 5 1778. 3 28. 2 Pin Offset d. B 39. 10 39. 10 Gain d. B 16. 72 16. 98 17. 37 17. 24 16. 9 15. 79 15. 25 Left PA Right PA Total PA Current A 11. 5 23 16. 0 32 19. 0 18. 0 37 22. 0 20. 0 42 24. 0 48 27. 5 27. 0 54. 5 30. 0 29. 0 59 Pdc W 1150 1600 1850 2100 2400 2725 2950 Efficiency % 21. 7 31. 5 41. 2 47. 5 51. 9 57. 4 60. 3 Gain d. B 16. 39 16. 34 16. 36 16. 18 15. 38 14. 68 13. 53 Left PA Right PA Total PA Current A 10. 2 9. 8 20 14. 0 13. 5 27. 5 16. 0 33. 5 21. 0 19. 0 40 24. 0 22. 0 46 27. 5 24. 0 51. 5 30. 0 26. 5 56. 5 Pdc W 1000 1375 1675 2000 2300 2575 2825 Efficiency % 25. 6 36. 8 44. 9 50. 9 54. 5 58. 5 61. 9 Gain d. B 14. 45 14. 41 13. 71 12. 07 10. 94 Left PA Right PA Total PA Current A 12. 0 13. 0 25 17. 0 18. 0 35 22. 0 22. 5 44. 5 26. 5 27. 2 53. 7 32. 5 33. 0 65. 5 34. 0 68 Pdc W 1250 1750 2225 2685 3275 3400 Efficiency % 20. 3 28. 7 34. 2 37. 3 38. 2 39. 1 MHz Pin d. Bm Pout Offset Pout d. Bm Pout (W) Actual Measured d. B Actual 37. 7 4. 22 49. 87 54. 09 256. 4 40. 7 7. 17 49. 87 57. 04 505. 8 42. 4 8. 89 49. 87 58. 76 751. 6 43. 9 10. 21 49. 87 60. 08 1018. 6 45. 6 11. 11 49. 87 60. 98 1253. 1 47. 1 11. 91 49. 87 61. 78 1506. 6 48. 9 12. 56 49. 87 62. 43 1749. 8 50. 2 Pin Offset d. B 39. 40 MHz Pin d. Bm Pout Offset Pout d. Bm Pout (W) Actual Measured d. B Actual 39. 6 4. 01 50. 04 54. 05 254. 1 42. 6 6. 97 50. 04 57. 01 502. 3 44. 4 8. 77 50. 04 58. 81 760. 3 46. 3 9. 97 50. 04 60. 01 1002. 3 48. 9 10. 9 50. 04 60. 97 1250. 3 11. 2 50. 04 61. 24 1330. 5 Freq Offset d. B 1. 9 49. 57 3. 7 49. 56 7. 2 49. 55 14. 2 49. 66 21. 2 49. 73 28. 2 49. 87 50. 2 50. 04 Output Attenuator Pout d. Bm Pout W 53. 98 250 56. 99 500 58. 75 750 60. 00 1000 60. 97 1250 61. 76 1500 62. 43 1750 63. 01 2000 P(d. Bm) from P(Watts) Freq Offset d. B 1. 9 38. 93 3. 7 38. 95 7. 2 39. 00 14. 2 38. 98 21. 2 39. 05 28. 2 39. 10 50. 2 39. 40 Input Coupler & 10 d. B Pad

Conclusion ✔The result of this work is a solid, reliable 1500 W LDMOS solid state amplifier that looks OK and is a pleasure to use. ✔LDMOS MOSFETs are capable of more than 1 k. W from a single device and offer excellent IMD performance and efficiency ✔The cost was half what others charge for a 1500 W 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 100 D or Flex 6 X 00 transceiver ✔Finally the design and building process kept me entertained and out of trouble for several months worth of evenings.