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effective 7/01/2015 thru 6/30/2019

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2015-G9A: Antenna feed lines: characteristic impedance, and attenuation; SWR calculation, measurement and effects; matching networks

2015-G9A01: Which of the following factors determine the characteristic impedance of a parallel conductor antenna feed line?

The distance between the centers of the conductors and the radius of the conductors

The distance between the centers of the conductors and the length of the line

The radius of the conductors and the frequency of the signal

The frequency of the signal and the length of the line



2015-G9A02: What are the typical characteristic impedances of coaxial cables used for antenna feed lines at amateur stations?

50 and 75 ohms

25 and 30 ohms

80 and 100 ohms

500 and 750 ohms



2015-G9A03: What is the characteristic impedance of flat ribbon TV type twinlead?

300 ohms

50 ohms

75 ohms

100 ohms



2015-G9A04: What might cause reflected power at the point where a feed line connects to an antenna?

A difference between feed line impedance and antenna feed point impedance

Operating an antenna at its resonant frequency

Using more transmitter power than the antenna can handle

Feeding the antenna with unbalanced feed line



2015-G9A05: How does the attenuation of coaxial cable change as the frequency of the signal it is carrying increases?

Attenuation increases

Attenuation is independent of frequency

Attenuation decreases

Attenuation reaches a maximum at approximately 18 MHz



2015-G9A06: In what units is RF feed line loss usually expressed?

Decibels per 100 feet

Ohms per 1000 feet

Decibels per 1000 feet

Ohms per 100 feet



2015-G9A07: What must be done to prevent standing waves on an antenna feed line?

The antenna feed point impedance must be matched to the characteristic impedance of the feed line

The antenna feed point must be at DC ground potential

The feed line must be cut to a length equal to an odd number of electrical quarter wavelengths

The feed line must be cut to a length equal to an even number of physical half wavelengths



2015-G9A08: If the SWR on an antenna feed line is 5 to 1, and a matching network at the transmitter end of the feed line is adjusted to 1 to 1 SWR, what is the resulting SWR on the feed line?

5 to 1

1 to 1

Between 1 to 1 and 5 to 1 depending on the characteristic impedance of the line

Between 1 to 1 and 5 to 1 depending on the reflected power at the transmitter



2015-G9A09: What standing wave ratio will result when connecting a 50 ohm feed line to a non-reactive load having 200 ohm impedance?

4:1

1:4

2:1

1:2



2015-G9A10: What standing wave ratio will result when connecting a 50 ohm feed line to a non-reactive load having 10 ohm impedance?

5:1

2:1

50:1

1:5



2015-G9A11: What standing wave ratio will result when connecting a 50 ohm feed line to a non-reactive load having 50 ohm impedance?

1:1

2:1

50:50

0:0



2015-G9A12: What standing wave ratio will result when connecting a 50 ohm feed line to a non-reactive load having 25 ohm impedance?

2:1

2.5:1

1.25:1

You cannot determine SWR from impedance values



2015-G9A13: What standing wave ratio will result when connecting a 50 ohm feed line to an antenna that has a purely resistive 300 ohm feed point impedance?

6:1

1.5:1

3:1

You cannot determine SWR from impedance values



2015-G9A14: What is the interaction between high standing wave ratio (SWR) and transmission line loss?

If a transmission line is lossy, high SWR will increase the loss

There is no interaction between transmission line loss and SWR

High SWR makes it difficult to measure transmission line loss

High SWR reduces the relative effect of transmission line loss



2015-G9A15: What is the effect of transmission line loss on SWR measured at the input to the line?

The higher the transmission line loss, the more the SWR will read artificially low

The higher the transmission line loss, the more the SWR will read artificially high

The higher the transmission line loss, the more accurate the SWR measurement will be

Transmission line loss does not affect the SWR measurement





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