Wednesday, March 25, 2009

General Class Exam Grab Bag, Bob, No. 44

Tonight I will be going over some questions from the General Exam Question Pool. The first set deal with S-meters so it will be a practical test of the information provided in Lee's talk of March 4, 2009.

G4D04 (C)
What does an S-meter measure?
A. Conductance
B. Impedance
C. Received signal strength
D. Transmitter power output
If you have trouble remembering this just think S for strength.

G4D05 (D)
How does an S-meter reading of 20 db over S-9 compare to an S-9 signal, assuming a
properly calibrated S meter?
A. It is 10 times weaker
B. It is 20 times weaker
C. It is 20 times stronger
D. It is 100 times stronger
One Bel which equals 10 Decibels is 10 times the power. So two Bels, 20 Decibels, is 10 times 10 which equals 100 times the power.

G4D06 (A)
Where is an S-meter generally found?
A. In a receiver
B. In a SWR bridge
C. In a transmitter
D. In a conductance bridge
We are measuring received signal strength so the logical place to find it is in the receiver circuitry.

This next set of questions deal with connectors.

G4D07 (A)
Which of the following describes a Type-N connector?
A. A moisture resistant RF connector useful to 10 GHz
B. A small bayonet connector used for data circuits
C. A threaded connector used for hydraulic systems
D. An audio connector used in surround sound installations
N connectors are screw on connectors that are not only moisture resistant but have excellent SWR properties at UHF frequencies. Ironically, the UHF connector (also known as PL-259 for the male connector and S0-239 for the female connector) is not as good at UHF as the N connector. The specifications I found for the UHF connector indicate DC - 300MHz but it is commonly used for 440MHz FM communication and works pretty well.

G4D08 (D)
Which of the following connectors would be a good choice for a serial data port?
A. PL-259
B. Type N
C. Type SMA
D. DB-9
The first three connectors are all coax connectors intended for radio waves. The DB-9 is a 9 pin connector roughly in the shape of a D. On a side note, even though the computer world is leaving DB-9 connectors behind, Amateur Radio is slow to change and you will still find the DB-9 in use.

G4D09 (C)
Which of these connector types is commonly used for RF service at frequencies up to
150 MHz?
A. Octal
B. RJ-11
D. DB-25
Based on the explanation for G4D07, you should immediately say UHF. As for the other connectors, I have no idea what an Octal connector is, an RJ-11 connector is the typical telephone connector, and a DB-25 connector is an older version of the DB-9 with 25 pins instead of 9.

G4D10 (C)
Which of these connector types is commonly used for audio signals in amateur radio
A. PL-259
C. RCA Phono
D. Type N
As with the question above on serial data, PL-259 (UHF), BNC and Type N are all used for radio frequency transmission. The RCA Phono connector is the one commonly used for audio. This is the one where the plug has a center pin and a thin circular shield with no threads or bayonet mount. It just pushes on.

G4D11 (B)
What is the main reason to use keyed connectors over non-keyed types?
A. Prevention of use by unauthorized persons
B. Reduced chance of damage due to incorrect mating
C. Higher current carrying capacity
D. All of these choices are correct
Keyed connectors ideally will only make a connection when they are correctly aligned. Therefore they reduce the chance of damage due to incorrect mating. Note it says reduce, not eliminate. Depending on how the key is implemented, it may be possible to force connectors together in a way they were not meant to go. If you ask me how I know this I will not admit to it being firsthand knowledge.

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