April 25, 2014

FCC Technician Exam Question Of The Day (T7C09)

Q) Which of the following is the most common cause for failure of coaxial cables?

A) Moisture contamination

NJ2X Notes:
Moisture contamination is a common cause of failure in coaxial cables. However, what causes moisture contamination? In our own case, we have had it caused by chewing!  No, we do not have a penchant for dining on coaxial cable. However, it seems that squirels and dogs do. On one occasion, a squirel attacked and chewed the sheath of the coaxial cable that ran up the side of a large maple tree.  On another occasion, our dog was bored and decided to dig and chew on about 3 feet of Bury Flex coaxial cable.  Fortunately, neither animals were hurt. 

Expensive lessons on both occasions since the cables were useless once the jacket was penetrated.  The next time around we buried conduit to provide an underground run from the entrance to the point just below the antenna.  The cable is now safe from the elements, dogs, and lawn mowers.

April 24, 2014

FCC Technician Exam Question Of The Day (T8C04)

Q) Which of the following is good procedure when contacting another station in a radio contest?

A) Send only the minimum information needed for proper identification and the contest exchange

NJ2X Notes:
Efficiency counts in radio contests.  The more stations you can contact in a given period of time the higher your score.  You gain an edge over the competition when your contact rate exceeds theirs.  One way to improve your rate is to make sure you understand the specific requirements for contest you are participating in regarding the exchange.  This allows you to both deliver, receive, and log the required information.  Including extra unnecessary information only slows your rate (and that of your contact).

April 23, 2014

FCC Technician Exam Question Of The Day (T8B04)

Q) Which amateur stations may make contact with an amateur station on the International Space Station using 2 meter and 70 cm band amateur radio frequencies?

A) Any amateur holding a Technician or higher class license

NJ2X Notes:
International Space Station Size & Mass
  • Module Length: 167.3 feet (51 meters)
  • Truss Length: 357.5 feet (109 meters)
  • Solar Array Length: 239.4 feet (73 meters)
  • Mass: 924,739 pounds (419,455 kilograms)
  • Habitable Volume: 13,696 cubic feet (388 cubic meters)
  • Pressurized Volume: 32,333 cubic feet (916 cubic meters)
  • Power Generation: 8 solar arrays = 84 kilowatts
  • Lines of Computer Code: approximately 2.3 million

April 22, 2014

FCC Technician Exam Question Of The Day (T7C03)

Q) What, in general terms, is standing wave ratio (SWR)?

A) A measure of how well a load is matched to a transmission line

NJ2X Notes:
Standing wave ratio (SWR) is the ratio of the amplitude of a partial standing wave at an antinode (maximum) to the amplitude at an adjacent node (minimum), in an electrical transmission line.

SWR is used as a measure of efficiency for radio transmission lines.  SWR is important since it provides an indication of the radio waves reflected back toward the transmitter.  Under ideal conditions, a radio transmission cable would have an SWR of 1:1 (1 to 1) indicating that all power is being delivered to the antenna and none being reflected back to the transmitter.  An infinite SWR indicates all power is being reflected back to the transmitter (with none being delivered to the antenna).  High SWR ratios are to be avoided and can indicate RF is being radiated in the shack, RF is being wasted as heat, and equipment failure may result.

April 21, 2014

FCC Technician Exam Question Of The Day (T7B07)

Q) Which of the following may be useful in correcting a radio frequency interference problem?

A. Snap-on ferrite chokes
B. Low-pass and high-pass filters
C. Band-reject and band-pass filters
D. All of these choices are correct

NJ2X Notes:
We use ferrite chokes for both bringing down the general received interference level and preventing RFI on our consumer grade electronics.  We have installed ferrites throughout our house on our phone lines, power cables, and cable TV coaxial cables.  Look for type for  type 31 and 43 ferrites at hamfests.

We also have low-pass filters installed between the antenna and our shortwave receiver.

April 20, 2014

FCC Technician Exam Question Of The Day (T7D11)

Q) Which of the following precautions should be taken when measuring circuit resistance with an ohmmeter?

A) Ensure that the circuit is not powered

NJ2X Notes:
  • Ensure that the circuit is not powered.
  • Be certain the circuit is deenergized and discharged before connecting an ohmmeter. 
  • Do not apply power to a circuit while measuring resistance.

April 19, 2014

FCC Technician Exam Question Of The Day (T8C01)

Q) Which of the following methods is used to locate sources of noise interference or jamming?

A) Radio direction finding

 NJ2X Notes:
Radio direction finding involves using antennas and receivers to determine the location of an RF source.  The are many different techniques:
  • Directional antennas - Using highly directional antennas such as yagi's, loops, etc. you can determine the direction of the signal.
  • Pseudo-doppler  - antennas are arranged in a circular array and then sequentially sampled to simulate the effect of a rotating antenna.  This modulates the received signal and the phase of this modulation can be used to determine the direction of the signal.
  • Phase interferometer - the phase difference between two spacially separated antennas is used to determine the direction of the signal.
Using triangulation in conjunction with the above techniques can help pinpoint a transmitter's location.