Welcome to B.A.R.K.’s TECHNICIAN CLASS

1. Welcome to B.A.R.K.’sTECHNICIAN CLASS Multi – Mode Radio # 13

2. Multi-Mode Radio A multi-mode transceiver is a radio that can send and receive several different types of emissions. AM/SSB, FM, CW, and AFSK are good examples of different modes. For UHF band weak signal work, use a multi-mode transceiver.

3. Multi-Mode Radio Why is bandwidth an important issue for hams? Example: 2 meter band = 144-48 MHz, or 4 MHz bandwidth FM repeaters require both an input & output frequency. Each signal is FM and occupies 15 KHz of space for a total of 30KHz/repeater. You can fit 12 repeaters in the 4 MHz bandwidth allotted to ham radio.

4. Multi-Mode Radio Each mode requires a utilizes amount of bandwidth. The narrowest bandwidth mode is CW at 150 Hz. For the best CW reception use a filter of 500 Hz. The advantage of a receiver with multiple filters is that it permits noise or interference reduction by selecting a filter bandwidth matching the mode.

5. Multi-Mode Radio Amplitude Modulation Bandwidths AM with both sidebands- 6 KHz The sidebands are “mirror images” of each other, they contain the same information. AM Carrier- 250 Hz The carrier is un-modulated. It is the basic signal to which information is added (modulation).

6. Multi-Mode Radio Single Sideband A single sideband signal is an AM signal with the carrier and one sideband suppressed. A good filter to use for a SSB signal would be 2.4 KHz. Single sideband- 2.5 KHz BW Amateurs use a convention as to which sideband is used for each band. The 40 , 60, 80 and 160 meter bands use the lower sideband (LSB). For 20 meters and above use the the upper sideband (USB).

7. Synopsis The frequency changes in an FM signal. An FM signal has a of bandwidth from 5 – 15 KHz. The amount of FM deviation is determined by the amplitude of the modulating signal. Frequency Modulation- 5 -15KHz Increased deviation of an FM signal results in more bandwidth.

8. Multi-Mode Radio AM & FM Modulation

9. Multi-Mode Radio A simple CW transmitter Figure T4 Oscillator Driver Amplifier Antenna Oscillator- Electronic circuit that develops the RF signal at a specific frequency (usually the carrier frequency). Driver- amplifies the oscillator signal to a level sufficient to drive the final amplifier stage. Keyer- Turns the driver and amplifier on and off. Amplifier- Amplifies the signal and provides a set output impedance for the antenna.

10. Multi-Mode Radio Heterodyning Made Easy In radio signal processing, heterodyning is the generation of new frequencies by mixing two oscillating waveforms. Mixing two frequencies creates a total of four frequencies, the sum, difference and two original frequencies. Example: Heterodyning 20 Hz & 30 Hz would create these frequencies: 20 Hz, 30 Hz, (two original frequencies) 50 Hz (the sum of the original frequencies) 10 Hz (the difference of the original frequencies) Only one of the heterodyne frequencies is desired and the rest are filtered out. In a transmitter the remaining signal is usually the RF carrier frequency.

11. Multi-Mode Radio A circuit that combines a speech signal and an RF carrier is a modulator. The function of a mixer in a superheterodyne receiver is to shift the incoming signal to an intermediate frequency. Station Signal Signal C at 455 kHz MIXER (In AM Broadcast Receiver) Signal A at 800 kHz (or at 1200 kHz) Intermediate Frequency Local Oscillator Signal B at 1255 kHz (or at 1655 kHz) Block Diagram of an AM Broadcast Receiver Mixer

12. Multi-Mode Radio Single-Conversion Super Heterodyne Receiver A single conversion receiver is easily identified by having a single intermediate frequency amplifier. A dual conversion receiver would have two intermediate amplifiers. The super heterodyne mixer shifts the incoming signal to an intermediate frequency. Dual conversion receivers have somewhat improved selectivity and interference rejection.

13. Multi-Mode Radio RF Preamplifier In the block diagram the first stage is the RF amplifier. Received RF signals are often measured in micro-volts. So the first stage of a receiver amplifies them to a usable level. Amateurs will sometimes use RF pre-amps placed between the antenna and the receiver. The pre-amplifier is used to compensate for cable loss. The higher the received frequency, the higher the cable loss. Pre-amps are usually used for UHF and microwave reception.

14. Multi-Mode Radio AM/SSB & CW Receiver A product detector is a type of demodulator used in AM, SSB and CW receivers. A product detector detects CW or SSB signals.

15. Multi-Mode Radio The BFO is used to receive CW signals. CW signals are not modulated with an audio component, so we must provide one. The RF amplifier, mixer, local oscillator, and IF amplifier is the same for both CW and SSB; but the CW signal reaches the detector as a single frequency signal with no sideband components. To produce an AF output you must mix the CW signal with an RF signal of the proper frequency. This separate signal is obtained from an oscillator known as a beat-frequency oscillator.

16. Multi-Mode Radio Block 1 is a discriminator. FM receivers use discriminators as opposed to product detectors in CW/SSB receivers. The limiter is used to eliminate over driving the discriminator (block #1).

17. Multi-Mode Radio Fundamental Overload- Interference caused by very strong signals. Selectivity- The ability of a a receiver to discriminate between multiple signals. RIT- Receiver Incremental Tuning (clarifier)- Used to tune the receiver without shifting the transmit frequency. RIT is often used to correct voice pitch of an SSB signal. RIT Adjustment

18. Let’s Review !

19. T7A09 Which of the following devices is most useful for VHF weak-signal communication?A. A quarter-wave vertical antennaB. A multi-mode VHF transceiverC. An omni-directional antennaD. A mobile VHF FM transceiver

20. T7A09 (B)Which of the following devices is most useful for VHF weak-signal communication?A. A quarter-wave vertical antennaB. A multi-mode VHF transceiverC. An omni-directional antennaD. A mobile VHF FM transceiver

21. T8A05 Which of the following types of emission has the narrowest bandwidth?A. FM voiceB. SSB voiceC. CWD. Slow-scan TV

22. T8A05 (C)Which of the following types of emission has the narrowest bandwidth?A. FM voice B. SSB voiceC. CWD. Slow-scan TV

23. T8A11 What is the approximate maximum bandwidth required to transmit a CW signal?A.2.4 kHzB. 150 HzC.1000 HzD.15 kHz

24. T8A11 (B)What is the approximate maximum bandwidth required to transmit a CW signal?A. 2.4 kHzB. 150 HzC. 1000 Hz D. 15 kHz

25. T7A05 What is the function of block 1 if figure T4 is a simple CW transmitter?A. Reactance modulatorB. Product detectorC. Low-pass filterD. Oscillator

26. Synopsis

27. Let’s Review !

28. T7A05 (D)What is the function of block 1 if figure T4 is a simple CW transmitter?A. Reactance modulator B. Product detector C. Low-pass filterD. Oscillator

29. T4B10 Which of the following is an appropriate receive filter to select in order to minimize noise and interference for CW reception?A. 500 HzB. 1000 HzC. 2400 HzD. 5000 Hz

30. T4B10 (A)Which of the following is an appropriate receive filter to select in order to minimize noise and interference for CW reception?A. 500 HzB. 1000 Hz C. 2400 Hz D. 5000 Hz

31. T7A02 What type of receiver is shown in Figure T6?A. Direct conversionB. Super-regenerativeC. Single-conversion superheterodyneD. Dual-conversion superheterodyne

32. T7A02 (C)What type of receiver is shown in Figure T6?A. Direct conversion B. Super-regenerativeC. Single-conversion superheterodyneD. Dual-conversion superheterodyne

33. T7A01 What is the function of a product detector?A. Detect phase modulated signalsB. Demodulate FM signalsC. Detect CW and SSB signalsD. Combine speech and RF signals

34. T7A01 (C)What is the function of a product detector?A. Detect phase modulated signalsB. Demodulate FM signalsC. Detect CW and SSB signalsD. Combine speech and RF signals

35. T8A01 Which of the following is a form of amplitude modulation?A. Spread-spectrumB. Packet radioC. Single sidebandD. Phase shift keying

36. T8A01 (C)Which of the following is a form of amplitude modulation?A. Spread-spectrum B. Packet radioC. Single sidebandD. Phase shift keying

37. T8A08 What is the approximate bandwidth of a single sideband voice signal?A. 1 kHzB. 3 kHzC. 6 kHzD. 15 kHz

38. T8A08 (B)What is the approximate bandwidth of a single sideband voice signal?A. 1 kHzB. 3 kHzC. 6 kHz D. 15 kHz

39. T7A08 Which of the following circuits combines a speech signal and an RF carrier?A. Beat frequency oscillatorB. DiscriminatorC. ModulatorD. Noise blanker

40. T7A08 (C)Which of the following circuits combines a speech signal and an RF carrier?A. Beat frequency oscillatorB. DiscriminatorC. ModulatorD. Noise blanker

41. T7A03 What is the function of a mixer in a superheterodyne receiver?A. To reject signals outside of the desired passbandB. To combine signals from several stations togetherC. To shift the incoming signal to an intermediate frequencyD. To connect the receiver with an auxiliary device, such as a TNC

42. T7A03 (C)What is the function of a mixer in a superheterodyne receiver?A. To reject signals outside of the desired passbandB. To combine signals from several stations togetherC. To shift the incoming signal to an intermediate frequencyD. To connect the receiver with an auxiliary device, such as a TNC

43. T4B08 What is the advantage of having multiple receive bandwidth choices on a multimode transceiver?A. Permits monitoring several modes at onceB. Permits noise or interference reduction by selecting a bandwidth matching the modeC. Increases the number of frequencies that can be stored in memoryD. Increases the amount of offset between receive and transmit frequencies

44. T4B08 (B)What is the advantage of having multiple receive bandwidth choices on a multimode transceiver?A. Permits monitoring several modes at onceB. Permits noise or interference reduction by selecting a bandwidth matching the modeC. Increases the number of frequencies that can be stored in memoryD. Increases the amount of offset between receive and transmit frequencies

45. T4B09 Which of the following is an appropriate receive filter to select in order to minimize noise and interference for SSB reception?A. 500 HzB. 1000 HzC. 2400 HzD. 5000 Hz

46. T4B09 (C)Which of the following is an appropriate receive filter to select in order to minimize noise and interference for SSB reception?A. 500 HzB. 1000 HzC. 2400 HzD. 5000 Hz

47. T4B06 Which of the following controls could be used if the voice pitch of a single-sideband signal seems too high or low?A. The AGC or limiterB. The bandwidth selectionC. The tone squelchD. The receiver RIT or clarifier

48. T4B06 (D)Which of the following controls could be used if the voice pitch of a single-sideband signal seems too high or low?A. The AGC or limiterB. The bandwidth selectionC. The tone squelchD. The receiver RIT or clarifier

49. T4B07 What does the term "RIT" mean?A. Receiver Input ToneB. Receiver Incremental TuningC. Rectifier Inverter TestD. Remote Input Transmitter

50. T4B07 (B)What does the term "RIT" mean?A. Receiver Input ToneB. Receiver Incremental TuningC. Rectifier Inverter TestD. Remote Input Transmitter