March 31, 2014

FCC Technician Exam Question Of The Day (T6C01)

Q) What is the name for standardized representations of components in an electrical wiring diagram?

A) Schematic symbols

NJ2X Notes:
Schematics are extremely useful means of documenting and communicating the components and interconnections of an electronic circuit.  Each type of electrical component has a schematic symbol associated with it for easy identification (see our article on NJ2X.COM: What is the schematic symbol for a ferrite bead?).

March 30, 2014

FCC Technician Exam Question Of The Day (T6C11)


Q) What is component 4 in figure T3?

A) Antenna

NJ2X Notes:
Check out NJ2X.COM for other FCC Technician Exam questions related to the schematic symbol.

Below is a picture of the internals of the MFJ-989D ANTENNA TUNER, 1.8-30 MHZ which you hook up between your HF transceiver and antenna. Notice the large variable roller inductor pictured at the bottom. The knob for changing the inductuctance is just visable on the left.  The two large devices in the middle and top left are variable capacitors.

MFJ-989D Antenna Tuner Internal View

March 29, 2014

FCC Technician Exam Question Of The Day (T6C13) D

Q) Which of the following is accurately represented in electrical circuit schematic diagrams?

A) The way components are interconnected

NJ2X Notes:
Electrical schematic diagrams accurately depict the type of components (e.g. capacitor, resistor, transistor, vacuum tube, transformer, etc.) and how the components are interconnected.  Schematics are invaluable for communicating circuit design and construction.

March 28, 2014

...the pathway to a dark age

“The method of science is tried and true. It is not perfect, it's just the best we have. And to abandon it, with its skeptical protocols, is the pathway to a dark age.” ― Carl Sagan


FCC Technician Exam Question Of The Day (T6C10)

Q) What is component 3 in figure T3?

A) Variable inductor


NJ2X Notes:
Check out NJ2X.COM for other FCC Technician Exam questions related to the schematic symbol.

Below is a picture of the internals of the MFJ-989D ANTENNA TUNER, 1.8-30 MHZ, LEGAL POWER.  Notice the large variable roller inductor pictured at the bottom.  The knob for changing the inductuctance is just visable on the left.
MFJ-989D Antenna Tuner Internal View

March 27, 2014

FCC Technician Exam Question Of The Day (T6D02)

A) What best describes a relay?

Q) A switch controlled by an electromagnet

NJ2X Notes:
Relays are very useful devices that allow switches to be controlled electrically.  An electromagnet is activated to control the mechanical switching action.

March 26, 2014

FCC Technician Exam Question Of The Day (T6D01 )

Q) Which of the following devices or circuits changes an alternating current into a varying direct current signal?

A) Rectifier

NJ2X Notes:
This is the basic rectifier circuit.  AC enters the circuit on the left passes through the bridge recitifier (4 diodes) and is changed into DC.  The capacitor bleeds off AC artifacts thereby providing filtering to the DC voltage.

March 24, 2014

FCC Technician Exam Question Of The Day (T7D08)

Q) Which of the following types of solder is best for radio and electronic use?

A) Rosin-core solder

NJ2X Notes:
Don't use plummer's or acid core solder for electronics or electrical applications.  Rosin-core solder will work very well and will not damage your circuit.  The Rosin Flux Core cleans the oxide off the foil and components being soldered which aids in wetting and creating a good electrical and mechanical joint.

March 23, 2014

FCC Technician Exam Question Of The Day (T7B03)

Q) Which of the following may be a cause of radio frequency interference?

A. Fundamental overload
B. Harmonics
C. Spurious emissions
D. All of these choices are correct


NJ2X Notes:
Fundamental overload - fundamental overload of a reciever is interference caused by very strong signals from a nearby source.


Harmonics - Powerful station transmitters may produce a small amount of output at twice their operating frequency (the "second harmonic"), and this can be a source of interference for stations operating at the same frequency as the second harmonic.

Spurious emissions - An emission, on frequencies outside the necessary bandwidth of a transmission, the level of which may be reduced without affecting the information being transmitted.

Harmful interference - Interference which endangers the functioning of a radionavigation service or of other safety services or seriously degrades, obstructs or repeatedly interrupts a radiocommunication service operating in accordance with the Radio Regulations.

March 22, 2014

FCC Technician Exam Question Of The Day (T7B01)

Q) What can you do if you are told your FM handheld or mobile transceiver is over deviating?

A) Talk farther away from the microphone


NJ2X Notes:
The sound of an overdriven signal is unpleasant to listen to.  The microphone gain control is often overused and abused.  Improve your antenna and station before cranking up the gain.

March 21, 2014

Consensus Science...


“I would remind you to notice where the claim of consensus is invoked.  Consensus is invoked only in situations where the science is not solid enough.  Nobody says the consensus of scientists agrees that E=mc2.  Nobody says the consensus is that the sun is 93 million miles away.  It would never occur to anyone to speak that way.” ― Michael Crichton



FCC Technician Exam Question Of The Day (T7B06)

Q) What should you do first if someone tells you that your station's transmissions are interfering with their radio or TV reception?

A) Make sure that your station is functioning properly and that it does not cause interference to your own television

NJ2X Notes:
It is important to rule out a malfunctioning station first.  If your station is not functioning properly, you definately want to know and resolve the issue immediately.  Often the problem is not with the station but the poor quality of filtering and shielding in consumer grade electronics.

The common-mode filter or choke can be very effective when it comes to RFI.  The common-mode filter or choke surpresses common-mode RF energy travelling on wires and coaxial cables connected to the TV.

March 20, 2014

FCC Technician Exam Question Of The Day (T7D03)

Q) How is an ammeter usually connected to a circuit?

A) In series with the circuit

NJ2X Notes:
An ammeter is an test instrument used to measure the current flowing through a circuit.  An ammeter is always placed in series when measuring the current.  An ammeter has a low impedance (resistance) so that there is a negligible voltage across it.  Thus the ammeter does not disturb or materially become part of the circuit.

March 19, 2014

FCC Technician Exam Question Of The Day (T7D06)

Q) Which of the following might damage a multimeter?

A) Attempting to measure voltage when using the resistance setting


NJ2X Notes:
To avoid accidental damage, confirm the multimeter settings before connecting to the circuit.



March 18, 2014

FCC Technician Exam Question Of The Day (T7B02)

Q) What is meant by fundamental overload in reference to a receiver?

A) Interference caused by very strong signals


NJ2X Notes:
High-pass, low-pass, or band-pass filters between the antenna and receiver can be useful in blocking interference from powerful broadcast stations causing fundamental overload on a receiver.

March 17, 2014

FCC Technician Exam Question Of The Day (T7C01)

Q) What is the primary purpose of a dummy load?

A) To prevent the radiation of signals when making tests

NJ2X Notes:
A "dummy load" is essentially a large resister that has several important attributes:

1) It "looks like" an antenna to the transmitter by presenting a 50-ohm impedence.
2) It has sufficient sufficient power handling capacity (e.g. 1W, 10w, 100W, 500W, 1500W).
3) The dummy load turns all power transmitted into it, into heat (i.e. no RF energy radiated).


Heathkit Cantenna Dummy Load

March 16, 2014

FCC Technician Exam Question Of The Day (T7B09)

Q) What could be happening if another operator reports a variable high-pitched whine on the audio from your mobile transmitter?

A) Noise on the vehicle's electrical system is being transmitted along with your speech audio

NJ2X Notes:
The ignition system on any vehicle is often the source of RFI.  Ignition and injection systems both include an inductor which produces a high-voltage pulse for firing the spark plug.  The spark plug creates a considerable amount of RFI which is radiated throughout the car's wiring system.  This can cause a great deal of noise on a mobile ham radio.  Fortunately, there are several effective techniques which can be used to reduce or eliminate RFI generated by a vehicle including: filtering the power and replacing worn ignition wires and plugs.

March 15, 2014

FCC Technician Exam Question Of The Day (T7B04)

Q) What is the most likely cause of interference to a non-cordless telephone from a nearby transmitter?

A) The telephone is inadvertently acting as a radio receiver

NJ2X Notes:
The FCC published an interesting bulletin (FO-10) in 1986 regarding telephone interference.  Technology has come a long way since then.  However, the article is still interesting and relevant.  The installed base of simple hard wired telephones is still very large.


INFORMATION BULLETIN
Federal Communications Commission
Field Operations Bureau
_________________________________________________________________
Telephone Interference
----------------------

This  document has been prepared to assist you  in  understanding why  interference  to your telephone system  occurs.  Recommended solutions   for  you  and  your  authorized   telephone   service technician are also provided.

                                        Bulletin FO-10
                                        September 1986


                WHY TELEPHONE INTERFERENCE OCCURS

Telephone   technology  today  uses  circuitry  which,   if  left unprotected,  will  respond to the radio frequency  (rf)  signals from nearby radio transmitters such as Amateur, Citizens Band and
AM/FM  broadcast stations.  When the telephone circuitry responds to the rf signal you hear the interference on your telephone. The rf  signal can be entering at the telephone instrument or on  the
inside or outside wiring.

Cordless telephones are also susceptible to rf signals.  Cordless phones  are low-power transmitters using  radio  frequencies.  As with  any radio transmitter,  they can receive interference  from other  nearby transmitters.  Interference can also occur if  your neighbor's  cordless  phone is using the same radio frequency  as yours.  Since  the FCC does not offer interference protection  to cordless   telephones,   you  should  contact  your   dealer   or manufacturer for assistance when interference occurs.

                      RECOMMENDED SOLUTIONS

The  installation  of  a modular filter is suggested as  a  first step.  Modular filters are available from most telephone  stores. It can be easily installed by you if your telephone has a modular jack.  You may wish to verify if the filter can be returned for a refund if it does not eliminate the interference.

The  effectiveness of filtering may vary according to the type of telephone  you  are  using.  Also,  modifying  certain  types  of telephones,  as suggested below, may be impractical or expensive.
When  it  is,  consider changing to another brand or  model  with better interference protection.

If you have taken the above steps,  and the interference is still present, the telephone instrument or wiring will probably have to be  filtered.  YOU  SHOULD NOT INTERNALLY MODIFY  THE  INSTRUMENT YOURSELF  NOR  ATTEMPT  FILTERING  OUTSIDE  PHONE   LINES.   ONLY AUTHORIZED  SERVICE  TECHNICIANS MAY INTERNALLY MODIFY TELEPHONE INSTRUMENTS.  ONLY TELEPHONE COMPANY PERSONNEL MAY FILTER OUTSIDE TELEPHONE  LINES.  This  rule is designed to ensure  that  phones continue to comply with FCC registration standards.

Interference  picked up by the inside wiring can be corrected  by installing  SHIELDED  inside wiring.  If you have  subscribed  to inside line maintenance,  the local telephone company can install
shielded  inside wiring for you.  If you have NOT  subscribed  to inside line maintenance,  they can still perform this service for a fee.


                   SERVICE TECHNICIAN SECTION

If  your customer has tried the modular filter and shielded their inside wiring and the interference is still present, we recommend you filter the inside of the telephone instrument.  Interference   in  older  rotary  dial  phones  (without  special features)  can  usually  be  resolved  by  bypassing  the  carbon
microphone.  Install  a 0.001 mfd ceramic disc capacitor  in  the back of the mouthpiece in the handset. Where possible, solder the capacitor  directly  to the microphone contact fingers  with  the
shortest possible leads.

Phone instruments with special features such as memory, automatic redial,  speakers, push-button dialling, and sound amplification, contain  components which are sensitive to rf signals.  Shielding
and  bypassing of these components are necessary to  isolate  the affected  circuit(s).  Refer to the design  specifications.  Bell System  technicians may refer to the Bell Systems Practices Plant
Series Manual Section 500-150-100 for necessary modifications.

Another  possible  solution would be to  install  ferrite  cores. These  are donut-shaped devices through which the phone cord  can be wound.  Ferrite cores are available in various sizes.  Use one
with a hole large enough to permit passing the phone cord through it two or three times.

To  install  a  ferrite core,  first disconnect  the  phone  cord between  handset and telephone base.  Loop the phone cord through the core two or three times.  Tape or fasten the core as close as possible to the handset.  Reconnect the phone cord.  Two  ferrite cores  on the handset might be necessary.  If so,  place one near the handset and another near the telephone instrument.

If  the interference continues after filtering the phones  and/or installing inside shielded wiring,  the interference is  probably entering  the  system  through  the  outside  wiring.  The  local telephone  company  service  department should be  contacted  for assistance.  Only telephone company personnel may filter  outside telephone  lines.  Two devices which may be used for  eliminating outside interference are:

-a  40 BA capacitor installed at the service entrance  protector,
and
-a 1542A inductor installed at the connector block.

Your  next  step  would  be  to  have  the  telephone  instrument filtered.   If  you  own  your  phone,   contact  the  dealer  or manufacturer for assistance. If you lease your phone, contact the local phone company's service department.  You may wish to  share the  Service Technician Information section of this document with the technician assigned to assist you.

Even  though you may be experiencing interference to  other  home electronic entertainment equipment, such as televisions, stereos, or  VCRs,  the telephone should be filtered.  If the RF signal is entering  the  telephone system,  the interference  can  only  be eliminated  at the point of entry.  Filtering or shielding of the phone instrument also offers future protection to your  equipment from other rf signals.

You  may  provide  to  the FCC the name  and/or  address  of  the owner/operator   of  the  radio  equipment  involved  when  other equipment  is receiving interference.  The FCC  will  communicate
with  that  person  to  determine  if  they  can  assist  you  in eliminating the interference.  FCC office addresses are listed at the end of this document.

CAUTION:   Only    authorized   service   technicians    may internally  modify  telephone  instruments.  Only telephone  company  personnel may filter  outside telephone lines.

END

March 14, 2014

Science is a way of thinking...

Science is a way of thinking much more than it is a body of knowledge. -- Carl Sagan

FCC Technician Exam Question Of The Day (T7B05)

Q) What is a logical first step when attempting to cure a radio frequency interference problem in a nearby telephone?

A) Install an RF filter at the telephone

NJ2X Notes:
Example of a telephone line RF filter.


March 13, 2014

FCC Technician Exam Question Of The Day (T7A01)

Q) What is the function of a product detector?

A) Detect CW and SSB signals

NJ2X Notes:
CW - Continuous Wave

SSB - Single Sideband

Product Detector - converts an incoming signal from RF frequencies to audio frequencies.


March 12, 2014

FCC Technician Exam Question Of The Day (T7B08)

Q) What should you do if a "Part 15" device in your neighbor's home is causing harmful interference to your amateur station?

A. Work with your neighbor to identify the offending device
B. Politely inform your neighbor about the rules that require him to stop using the device if it causes interference
C. Check your station and make sure it meets the standards of good amateur practice
D. All of these choices are correct

NJ2X Notes:
United States Code of Federal Regulations, Title 47, Part 15 (47 CFR 15) are Federal Communications Commission (FCC) rules and regulations regarding unlicensed transmissions regulating everything from spurious emissions to unlicensed low-power broadcasting.  Electronic devices radiating unintentional emissions must be reviewed to comply with Part 15 before they can be advertised or sold in the US market.

March 11, 2014

FCC Technician Exam Question Of The Day (T7D07)

Q) Which of the following measurements are commonly made using a multimeter?

A) Voltage and resistance

NJ2X Notes:
A multimeter is an extremely useful piece of equipment for any ham or budding electronics enthusiast.



March 10, 2014

FCC Technician Exam Question Of The Day (T7D05)

Q) What instrument is used to measure resistance?

A) An ohmmeter

NJ2X Notes:
An ohmmeter is a test instrument that measures electrical resistance (unit of measure ohms).  Every amateur radio workbench needs to have an ohmmeter.

Ohmmeter

March 9, 2014

March 8, 2014

FCC Technician Exam Question Of The Day (T6D11)

Q) Which of the following is a common use of coaxial cable?

A) Carry RF signals between a radio and antenna

NJ2X Notes:
Coaxial cable is often referred to simply as, "coax".  There are many different types of coaxial cable; however, they all have a center conductor surrounded by a dielectric which is wrapped by a shield and then covered by an outer insulator.  We happen to use the Davis RF Bury-FLEX ™ cable and have had good results with it.

Davis RF Bury-FLEX 50-ohm Coaxial Cable



The NJ2X.com Kindle Edition is now available.


March 7, 2014

Astound ourselves....

If we did all the things we are capable of doing,
we would literally astound ourselves. -- Thomas Edison


FCC Technician Exam Question Of The Day (T6B05)

Q) Which of the following electronic components can amplify signals?

A) Transistor

Transistors



NJ2X Notes:
A signal can be amplified by using a device which allows a small current or voltage to control the flow of a much larger current from a dc power source.  Vacuum tubes and transistors are the basic devices capable of providing control of this kind. 

There are many varieties of transistors.  Two general types are the bipolar junction and field-effect transistor.  With bipolar transistors, a small input current controls a large current flow through the device.  With field-effect transistors, an small input voltage controls a large current flow through the device.

March 6, 2014

FCC Technician Exam Question Of The Day (T6B07)

Q) What does the abbreviation "LED" stand for?

A) Light Emitting Diode

NJ2X Notes:
LED's are semiconductor devices that convert electrical energy to light.  This is the electrical schematic symbol for an LED:
LED

March 5, 2014

March 4, 2014

FCC Technician Exam Question Of The Day (T7A13)

Q) Where is an RF preamplifier installed?

A) Between the antenna and receiver

NJ2X Notes:
The RF preamplifier is used to boost the received signals.  This is useful to overcome significant signal loss due to long coaxial cable runs from the antenna to the receiver.  Signal loss on coaxial cable can be a problem on UHF and VHF frequencies.

Antennta --> RF Preamplifier --> Receiver

For an example, check out the Hamtronics receiver preamp for VHF and UHF ham applications.

March 3, 2014

FCC Technician Exam Question Of The Day (T6C02)

Q) What is component 1 in figure T1?


A) Resistor



NJ2X Notes:
resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. Resistors act to reduce current flow, and, at the same time, act to lower voltage levels within circuits.

Resistor color code chart


Checkout the other resistor related exam questions on NJ2X.COM.

March 2, 2014

FCC Technician Exam Question Of The Day (T7A12)

Q) Which term describes the ability of a receiver to discriminate between multiple signals?

A) Selectivity

NJ2X Notes:
Selectivity is a performance measure of a radio receiver's ability to respond only to the radio signal it is tuned to and reject other signals nearby in frequency.  Selectivity performance is accomplished and enhanced through the use of filters.

March 1, 2014

FCC Technician Exam Question Of The Day (T6B12)

Q) What is the term that describes a transistor's ability to amplify a signal?

A) Gain

NJ2X Notes:
The transistor's key feature is its ability to use a small signal applied to control a much larger signal (gain).  A transistor can amplify a signal by controlling its output proportionaly to the input signal.

Schematic symbol for the PNP transistor