ECE 445 Senior Design Project Fall ’06

1. ECE 445 Senior Design Project Fall ’06 Ben Niemoeller Larry Dietrick Albert Rhee

2. Introduction • New age of wireless weaponry • Defense mechanism against remote triggers for explosives • Jamming enemy communication lines

3. Radio Jammer • Reasons for choosing this project • Professor Bernhard • Military uses • RF interests

4. Objectives • Signal-to-Jamming ratio • Victim-to-Jamming • Victim-to-Control

5. Preliminary testing Reverse - 50 ms Forward – 35 ms Left – 55 ms Right – 40 ms

6. Preliminary jamming setup

7. Jammed control waveform • Produced by summing a 49.86 MHz carrier wave with the victim controller output • Car does not respond to this waveform - ‘1’ and ‘0’ are indistinguishable

8. Original Controller’s Transmitter Circuitry

9. Features • RF amplification to create a stronger signal and range • Comply with all FCC regulations by not distorting other important frequencies • Transmitting high powered signals at 49MHz • Transmitting a high enough level of noise at 49 MHz to distort signals from the original transmitter

10. Basic Functionality/Features • Noise Signal • Oscillator • Amplifier • Antagonist Control Signal • Control Logic • Oscillator • Amplifier

11. Power Amplification Logic ‘NOR’ Gate Hardware Overview

12. Final Product • Overview of Main Components tagged

13. 49.86 MHz oscillator • Used to modulate control signals • Transistor amplifies initial thermal excitation (no input required!); crystal confines output to an extremely narrow frequency range (49.86 MHz)

14. Completed Oscillator Circuit

15. Oscillator Design • 2N5179 transistor provides gain • Resistors used for DC biasing of transistor

16. Blocking Oscillations at the Fundamental Frequency • Crystal is inductive at about 16.62 MHz and all odd multiples thereof (i.e., 49.86 MHz, 83.10 MHz, etc.) • Circuit oscillates at the lowest of these frequencies that features a capacitance in shunt with crystal. → Present a shunt inductance at 16.62 MHz, and a shunt capacitance at 49.86 MHz (manufacturer specification: 20 pF)

17. Blocking Oscillations at the Fundamental Frequency Reactance at 16.62 MHz = +j*(139) Reactance at 49.86 MHz = -j*(141) (corresponds to 22.6 pF)

18. Challenges in Oscillator Implementation • Finding the appropriate shunt network • Inductive/capacitive requirements • Needed overall shunt capacitance near 20 pF at 49.86 MHz • Printed component values do not equal real component values • Even when they did, values weren’t always practical for this type of circuit Required help from Prof. Steve Franke (ECE 453)

19. Active Buffer for Impedance Transformation • Impedance buffer consists of 2N3013 and biasing resistors – has low small-signal output resistance • Allows us to drive 50-ohm Gain Block in next stage of circuit

20. Voltage regulators • Parts of our circuit require +5 and +9 V supplies • The voltage regulators serve to step down the +12 VDC supply voltage to +5 and +9 volts • This allows our circuit to be powered by a single +12 VDC supply, a voltage commonly found in motor vehicles

21. +5V Regulator • Vout = 1.25[1 + (R5 + R6)/R4] + 10-4(R5 + R6)

22. +9V Regulator • Vout = 1.25[1 + (R2 + R3)/R1] + 10-4(R2 + R3)

23. Heat sinking • Heat sinks for the LM317 regulators are integrated onto the circuit board

24. Heat sinking • These vias provide a solid ground and thermal connection for the amplifier IC

25. Active buffer switch • The active buffer transistor is turned on and off via a discrete CMOS switch • The switch modulates the bias voltage of the base of the transistor • This switched active buffer modulates the on-off-key signal with the 49.86 MHz carrier wave

26. Active buffer switch • L3 blocks the RF from the oscillator • Switch is an inverter – control logic needed to ‘correct’ the inversion

27. Functions of Control Logic • To tell the oscillator when to jam and when to spoof • To interface the TX2C encoding chip to the CMOS active buffer switch

28. Functions of Control Logic • Open-collector buffers used to match voltages and drive currents to various parts of the circuit • Logic implemented with 1 7400 NAND IC and 1 7407 hex buffer IC

29. Gain Block • Intermediate amplifier – provides 15dB of gain • WJ AG402-86 gain block chip tuned to operate at around 50 MHz • Two-terminal device – DC power is supplied through the RF output pin

30. Gain Block • R10 sets bias current, L1 prevents RF from being shorted to ground through C8

31. Power amp • Provides 13 more dB of gain • Power output as used in our circuit is +24 dBm (251 mW) • WJ AH101 driver amplifier IC • Two-terminal device – DC power is supplied through the RF output pin

32. Power amp • Antenna length of 7 feet gave best performance (best match) – this is slightly longer than a ¼ wavelength

33. Transmitting Antenna • Final amp. output impedance is 50 ohms • Tried to match electrically short monopole antenna that came with one of the remote-controlled cars. • Impedance measurement on VNA: 1400 + j*300 ohms • But from E&M theory: radiation resistance of an electrically short monopole is less than 50 ohms, with a capacitive reactance.

34. Matching to the Antenna • Using antenna parameters in theoretical equations: expected impedance is 1.4 – j*579 ohms. • Tried to resonate capacitive reactance and match resistance to 50 ohms using a lossless L-network. • Circuit performance became worse.

35. Use of original antenna Antenna orientation Antenna Progression

36. The Solution • Used long piece of wire connected to output. • Trial and error on the antenna size: device had best range with wire length of 7 feet

37. Final Antenna

38. Tests Performed on Final Device • On 12 V DC, max. current draw is 340 mA (4.08 W max power consumption) • Smooth operation of car up to 80 feet (compared to 35 feet for original controller) • Sporadic operation of car up to 115 feet (compared to 45 feet for original controller)

39. Tests Performed on Final Device • With jammer/spoofer 40 feet from car: • Victim controller must be 8 feet away to “jam the jammer” • Victim controller must be 5 feet away to regain control

40. Tests Performed on Final Device • Oscillator (with buffer) output: -4.8 dBm at 49.8596 MHz • Output power after amplifier gain block: 11.0 dBm (approx.) • Output power after final amplifier stage: 24.0 dBm (approx.)

41. Device Output in Freq. & Time Domain (Demodulated) Zero span – key pressed (control signal is being sent) 1 MHz span – highest output level

42. Successes/Solutions • Isolate 49.86 MHz • Modify oscillator circuit • Capacitors and Inductors • Faster switching transistor • Extra Power Amplification • Antenna • Deciding on simple antenna due to time constraints

43. Recommendations • Antenna • Matched network for more reliable signal transmission • More efficient antenna (orientation and type) • More than one antenna in spaced out areas • Power • Battery pack • Mobile

44. More Recommendations • Minimize space • Put all RF onto one integrated board • Encasement

45. Credits • Professor J. Bernhard • Professor S. Franke • Northrop Grumman • Jim Jensen • Dan Blase