Technician Class Series – Run Some Interference Protection


Hello everybody and welcome back to Everything Hamradio! Today we are going to continue our series on the Technician Class License Question Pool! Today we will be talking about Interference Protection.

As always, the correct answers will be in bold. I also recommend that you only read the correct answers when studying for your test. If you do this, when you take your test and you see a question, there will be a better chance that the correct answer will jump out at you easier. Some say that this approach is kind of like cheating, but the way that I see it, you will always be learning something in this hobby and you don’t have to know everything there is to know about the hobby to get your license.

If you would like to purchase a copy of the Technician Class study book, written by Gordon West, WB6NOA with Eric P. Nichols, KL7AJ, that this series is loosely based around, below is a link to it.

Let’s move on to the good stuff, shall we?

T7B10 What might be the problem if you receive a report that your audio signal through the repeater is distorted or unintelligible?

  1. Your transmitter may be slightly off frequency
  2. Your batteries may be running low
  3. You could be in a bad location
  4. All of these choices are correct

There are many things that could contribute to a poor signal report on a FM repeater. Your radio could be slightly off frequency. Even though you are not exactly on frequency, because of the bandwidth that you use when you transmit, you can hear someone talking up to almost 2.5 MHz away from where they are talking. If you are using a hand-held transceiver and you are running off of a battery, your battery could be getting low. The lower your battery, the less output wattage you are transmitting, so when you first start talking you may be just fine, but the more you talk, the lower the battery and the less wattage you put out. The lower wattage might not be able to reach the repeater as well. You also could just be in a bad location. Many things around you can affect your transmission; the buildings around you, hills, even trees on some UHF frequencies. So, the answer to this question is D. All of these choices are correct

T4B01 What may happen if a transmitter is operated with the microphone gain set too high?

  1. The output power might be too high
  2. The output signal might become distorted
  3. The frequency might vary
  4. The SWR might increase

The microphone gain is much liked screaming. It will increase the volume of it and if it is set to high, it can distort it. I’m sure that you have talked on the phone to someone who was super loud or that you had a hard time understanding, but when you asked them to speak quitter

T7B01 What can you do if you are told your FM handheld or mobile transceiver is over-deviating?

  1. Talk louder into the microphone
  2. Let the transceiver cool off
  3. Change to a higher power level
  4. Talk farther away from the microphone

Since most FM handheld or mobile transceivers do not have a microphone gain, if someone says that you are over-diviating, you have two options, talk softer or back off of the microphone a little bit. The best way to do it is to back off the microphone some, because you talk the way you talk all the time, so you are pretty much set if your way of that, but being new, or not, it is easier to train your muscle memory to hold the microphone away from your mouth a little bit.

T2B07 What could cause your FM signal to interfere with stations on nearby frequencies?

  1. Microphone gain too high, causing over-deviation
  2. SWR too high
  3. Incorrect CTCSS Tone
  4. All of these choices are correct

If you radio does have a microphone gain built into it, if it is set to high, it will over-deviate your transmissions causing you to use more bandwidth. When this happens, someone talking on a frequency close by will be able to hear you and is called harmful interference and you could get in trouble for that.

T4B05 Which of the following would reduce ignition interference to a receiver?

  1. Change frequency slightly
  2. Decrease the squelch setting
  3. Turn on the noise blanker
  4. Use the RIT control

On higher end radios, like HF radios or SSB radios, it could have a noise blanker option. If it does, this could reduce any ignition interference that you are hearing.

T4A10 What is the source of a high-pitched whine that varies with engine speed in a mobile transceiver’s receive audio?

  1. The ignition system
  2. The alternator
  3. The electric fuel pump
  4. Anti-lock braking system controllers

This will commonly be referred to as Alternator Noise.

T4A12 What could be happening if another operator reports a variable high-pitched whine on the audio from your mobile transmitter?

  1. Your microphone is picking up noise from an open window
  2. You have the volume on your receiver set too high
  3. You need to adjust your squelch control
  4. Noise on the vehicle’s electrical system is being transmitted along with your speech audio

This is a common problem when you get your power from the fuse box or from the 12 volt cigarette lighter plug. Some vehicles don’t have any filters on the alternator leads, therefore the sound from the electrical current for your alternator can piggy back into and through your radio transmissions. Some DC plugs have built-in chokes to “fix” this problem. This is why it is always best to get power directly from your battery.

T4A09 Which of the following could you use to cure distorted audio caused by RF current flowing on the shield of a microphone cable?

  1. Band-pass filter
  2. Low-pass filter
  3. Preamplifier
  4. Ferrite choke

RF Current flowing on the outside of microphone cables is generally on the common mode sort, which is normally most effectively cured by the use of ferrite beads or cores surrounding the conductor. Ferrite Chokes are clam shell iron devices that clamp around the outside of the cable and will minimize the current flowing along the outside of a wire.

T7B12 What might be the first step to resolve cable TV interference from your ham radio transmission?

  1. Add a low pass filter to the TV antenna input
  2. Add a high pass filter to the TV antenna input
  3. Add a preamplifier to the TV antenna input
  4. Be sure all TV coaxial connectors are installed properly

First thing you should do is check to make sure that all your TV coax connections are installed correctly. Anytime that you have any kind of interference or short, the first place you should always look is at the connectors because these are your weak links in your wiring setups.

T4A04 Where must a filter be installed to reduce harmonic emissions from your station?

  1. Between the transmitter and the antenna
  2. Between the receiver and the transmitter
  3. At the station power supply
  4. At the microphone

If harmonic emissions are coming from your station, you will need to install them between your transmitter and the antenna.

T7B03 Which of the following may be a cause of radio frequency interference?

  1. Fundamental overload
  2. Harmonics
  3. Spurious emissions
  4. All of these choices are correct

T7B11 What is a symptom of RF feedback in a transmitter or transceiver?

  1. Excessive SWR at the antenna connection
  2. The transmitter will not stay on the desired frequency
  3. Reports of garbled, distorted, or unintelligible transmissions
  4. Frequent blowing of power supply fuses

If your antenna is fairly close to where you are using your radio at and you get reports of garbled, distorted or unintelligible transmissions, you may have a RF Feedback issue. Try increasing the distance between your radio and your antenna and chances are your transmission will clear up.

T6D12 Which of the following is a common reason to use shielded wire?

  1. To decrease the resistance of DC power connections
  2. To increase the current carrying capability of the wire
  3. To prevent coupling of unwanted signals to or from the wire
  4. To couple the wire to other signals

Shielded wire helps Shield your wires from unwanted signals encroaching into your system. Pun definitely intended…:)

T7B06 Which of the following actions should you take if a neighbor tells you that your station’s transmissions are interfering with their radio or TV reception?

  1. Make sure that your station is functioning properly and that it does not cause interference to your own radio or television when it is tuned to the same channel
  2. Immediately turn off your transmitter and contact the nearest FCC office for assistance
  3. Tell them that your license gives you the right to transmit and nothing can be done to reduce the interference
  4. Install a harmonic doubler on the output of your transmitter and tune it until the interference is eliminated

The first thing that you need to do is make sure that your station is operating properly and check you TV to see if you are getting the same interference on the channel that your neighbor is receiving it on. If you are not and your system is operating correctly, it’s not on your end, but bad shielding on your neighbors end. If you like your neighbor and you want to keep up good relationship with them, it is best to go and attempt to correct the problem for them instead of just saying, “Sorry, all my equipment is working correctly, so it on your side” and leave it at that.

T7B02 What would cause a broadcast AM or FM radio to receive an amateur radio transmission unintentionally?

  1. The receiver is unable to reject strong signals outside the AM or FM band
  2. The microphone gain of the transmitter is turned up too high
  3. The audio amplifier of the transmitter is overloaded
  4. The deviation of an FM transmitter is set too low

Generally this occurs on a poorly made consumer grade product that doesn’t have proper shields. If the receiver is unable to reject strong signals, then you can get bleed over from amateur radio.

T7B04 Which of the following is a way to reduce or eliminate interference by an amateur transmitter to a nearby telephone?

  1. Put a filter on the amateur transmitter
  2. Reduce the microphone gain
  3. Reduce the SWR on the transmitter transmission line
  4. Put a RF filter on the telephone

Much like TV, if you are receiving signals that do not belong on the frequency that you are listening on, you need to put a RF filter on it; whether it is a TV or telephone.

T7B07 Which of the following may be useful in correcting a radio frequency interference problem?

  1. Snap-on ferrite chokes
  2. Low-pass and high-pass filters
  3. Band-reject and band-pass filters
  4. All of these choices are correct

Filters and Chokes are two of the ways that you can correct interference. Whether those filters are pass or reject filters, it doesn’t matter as long as they are used as intended.

T7B05 How can overload of a non-amateur radio or TV receiver by an amateur signal be reduced or eliminated?

  1. Block the amateur signal with a filter at the antenna input of the affected receiver
  2. Block the interfering signal with a filter on the amateur transmitter
  3. Switch the transmitter from FM to SSB
  4. Switch the transmitter to a narrow-band mode

Here you can use a band pass or a band reject filter on the antenna input. If you use a band pass, the filter needs to pass the frequencies of televisions channels, if it is a reject, you should reject the amateur bands that it is receiving interference on.

T7B09 What is a Part 15 device?

  1. An unlicensed device that may emit low powered radio signals on frequencies used by a licensed service
  2. A type of amateur radio that can legally be used in the citizen’s band
  3. A device for long distance communications using special codes sanctioned by the International Amateur Radio Union
  4. A type of test set used to determine whether a transmitter is in compliance with FCC regulation 91.15

A part 15 device is an unlicensed device that may emit a low powered radio signal on frequencies used by a licensed service. A FRS radio and a wireless routers are two such devices.

T7B08 What should you do if something in a neighbor’s home is causing harmful interference to your amateur station?

  1. Work with your neighbor to identify the offending device
  2. Politely inform your neighbor about the rules that prohibit the use of devices which cause interference
  3. Check your station and make sure it meets the standards of good amateur practice
  4. All of these choices are correct
 Be a good neighbor and amateur radio operator and help them to fix the problem.

So that brings us to the end of this section. Next week we will be talking about Emergencies! Please share my blog with your friends and if you have not done so already, please subscribe to my email list to get the latest and quickest notifications of any new post that I publish. Please Like me on Facebook, and follow me on Twitter, Google+, LinkedIn. Links to all of these can be found under social on the menu.

Thanks for stopping by. If you have any questions or comments about today’s post, please leave them in the comments below or shoot me an email a

Until next time…

73 de Curtis, K5CLM

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