CRAC Bilingual Manual: Radio Direction Finding (ARDF) | 无线电测向 (17 questions)

Which of the following activities is suitable for amateur radio operators to organize as competitions or to use for locating QRM (interference)?

1. Aamateur radio direction finding (ARDF)
2. Bswept-frequency Doppler sounding
3. Cecho location
4. Dmonostatic/multistatic PSD analysis

Which of the following items, combined with a receiver, can be used for ARDF activities?

1. Aa directional antenna
2. Ban RF bridge
3. Ca noise bridge
4. Dan SWR bridge

The hidden transmitters used in amateur radio direction-finding activities belong to which category of equipment:

1. Athey are amateur radio station equipment; their establishment and use must be applied for to the radio management authority and approved
2. Bthey are special license-exempt transmitting devices that may be set up and used arbitrarily without any administrative permission
3. Cthey are not subject to radio management; they may be set up and used with mere default approval from the sports authority or a sports civil organization
4. Dthey are sports or game equipment whose performance need not be tested and approved by a radio-inspection department

The IARU (International Amateur Radio Union) rules for amateur radio direction-finding championships require the 144 MHz direction-finding transmitter to use A2A modulation with 70%–80% amplitude modulation, sending the station identifier in audio Morse code at 8–15 WPM. The occupied bandwidth of such emission must not exceed:

1. A6 kHz
2. B12.5 kHz
3. C25 kHz
4. D100 Hz

The receiving antenna of an 80 m-band amateur direction-finder is mostly a combination of a loop antenna and a whip antenna, obtaining a unidirectional cardioid pattern by separately receiving the magnetic-field and electric-field components of the signal. However, as the finder gets closer to the transmitting station, the directivity tuned at a distance degrades, forcing us to re-adjust the whip length. This is because:

1. Ain the far-field region the wave impedance is almost constant, but approaching the near field the wave impedance varies more and more
2. Bwhen approaching the transmitting station, the stronger signal causes overload of the receiver’s front-end semiconductor devices
3. Cwhen approaching the transmitting station, the stronger signal drives the whip antenna into a nonlinear operating region
4. Dwhen approaching the transmitting station, the stronger signal heats and deforms the loop antenna, forcing parameter changes

Sometimes, the shielded loop antenna used in 160/80 m-band amateur direction-finders is replaced by a ferrite-rod antenna similar to that of a medium-wave radio. This is because: (Choose all that apply.)

1. Aif the coil on the ferrite rod is center-placed, the antenna’s receiving characteristic is similar to a loop antenna; moreover, the equipment becomes more compact
2. Bwhen close to the transmitter, the capacitive pickup of the unshielded ferrite antenna affects the directivity, and the operator must handle this skillfully
3. Cwhen close to the transmitter, the stronger signal saturates the ferrite rod, which is equivalent to an automatic gain control (AGC) function
4. Dwhen close to the transmitter, the stronger signal saturates the ferrite rod, which is equivalent to adding an attenuator, aiding bearing taking

Sometimes a 2 m-band ARDF receiver is optionally fitted with a Yagi antenna having only two elements (a driven element and a reflector). This is because: (Choose all that apply.)

1. Aa two-element antenna still has some directivity and is lighter; for a skilled finder it remains practical
2. Bin the near-field region close to the transmitter, the operator normally uses the antenna’s null for positioning, where the number of elements is not critical
3. Cin the near-field region close to the transmitter, the operator can temporarily add a director to the antenna to obtain sharp directivity
4. Din the near-field region close to the transmitter, a three-element Yagi’s directivity actually worsens, affecting correct bearing determination

Sometimes amateur operators build a 2 m-band ARDF receiver using an HB9CV antenna. Which of the following statements about the HB9CV antenna is correct? (Choose all that apply.)

1. Ait is a dual-driven-element Yagi; the director and reflector are fed with a 225° phase shift via phasing jumpers
2. Bthe HB9CV antenna has a fairly wide bandwidth, good unidirectional characteristics in both horizontal and vertical orientations, and is easy for the operator to carry around
3. Chowever, this antenna needs capacitive coupling to cancel the inductive reactance of the phasing jumpers, which keeps the SWR high
4. Dthe HB9CV is a light and efficient ARDF antenna, but unfortunately cannot be used for contacts because it is directional

In the data-communication segment of HF amateur bands, we sometimes hear on SSB a signal consisting of two tones that alternate at a certain rate. The communication mode using such a signal may be:

1. ARTTY
2. BPSK31
3. CFT4
4. DSSTV or FAX

In the data-communication segment of HF amateur bands, we sometimes hear on SSB a signal whose tone stays constant yet seems to keep “wobbling.” The communication mode using such a signal may be: (Choose all that apply.)

1. ABPSK31
2. BQPSK31
3. CFT4
4. DSSTV or FAX

In HF amateur bands, we sometimes hear on SSB a signal whose tone varies periodically, and within each period we can hear “tok-tok” or “clack-clack” sounds. Different stations send this signal with different tone-variation periods, ranging from several times per second to once every one or two seconds. The communication mode using such a signal may be:

1. ASSTV or FAX
2. BPSK31
3. CRTTY
4. DFT4

The spectrum of a CW signal appears as:

1. Aa flickering vertical line
2. Ba fixed straight line
3. Ctwo horizontal straight lines
4. Da sine-wave curve

The spectrum of an RTTY signal appears as:

1. Atwo flickering vertical lines
2. Bone vertical line
3. Cone sine-wave curve
4. Done complex periodic curve

The spectrum of an SSB voice signal appears as:

1. Aa group of asymmetric vertical lines that appear and vary with the speech
2. Ba single line that flickers with the speech
3. Ca fixed straight line
4. Da complex periodic curve

The spectrum of an AM voice signal appears as:

1. Aone fixed vertical line, symmetrically flanked by a group of vertical lines that appear and vary with the speech
2. Ba single line that flickers with the speech
3. Cseveral fixed straight lines
4. Da complex periodic curve

The spectrum of an FM voice signal appears as:

1. Aa vertical line whose height varies with the speech, symmetrically flanked by a group of vertical lines that appear and vary with the speech
2. Ba single line that flickers with the speech
3. Cseveral fixed straight lines
4. Da complex periodic curve

The spectrum of a PSK31 signal appears as:

1. Aa single very narrow peak
2. Ba fixed straight line flanked symmetrically by a group of speech-varying lines
3. Cseveral fixed straight lines
4. Da complex periodic curve