The louder the voice signal in an FM transmitter the greater the frequency deviation of the modulator. If we are over deviating the frequency then we need to reduce the amplitude of our voice. Therefore the correct answer is to talk farther away from the microphone or not talk so loudly.

Last edited by davsel. Register to edit

Tags: frequency modulation best practices arrl chapter 5 arrl module 11

Microphone gain might cause distortion, splatter or over deviation, but it wouldn't cause the signal to jump into a broadcast AM or FM band - they're too far away from the amateur bands.

Similarly, if the audio amplifier of the transmitter were overloaded, it might distort, but wouldn't shift the frequency or cause harmonics to be radiated.

If the deviation of an FM transmitter were set too low, the signal would sound very quiet, the opposite of loud or even loud enough.

The only remaining choice is the right one, that the receiver is unable to reject the strong signals outside of the broadcast band.

Another explanation: Your amateur radio station may interfere with a nearby radio receiver if your signal is so strong that the receiver cannot reject the signal even though your signal is not on the frequency to which the receiver is tuned. This is called overload.

Last edited by ki5hav. Register to edit

Tags: arrl chapter 9 arrl module 23

There are many things that can cause interference with radio signals. All three of those listed here can cause interference, therefore the correct answer is "All of these choices are correct".

Fundamental overload - This is a case when the transmitted signal is so strong that it overloads the receiver which prevents proper reception of the desired signal.

Harmonics - When a sine wave is distorted (not pure) it creates harmonics that are integer multiples of the fundamental frequency; these harmonics end up getting into receivers at these harmonic frequencies interfering with operation on those frequencies. See this reference: 5.0 Transmitter Harmonic Emissions.

Spurious emissions - There are a number of undesirable emissions that can interfere with normal signal reception. Most of these can be termed Spurious emissions. From ITU, 1.145 "Spurious emissions include harmonic emissions, parasitic emissions, intermodulation products and frequency conversion products but exclude out-of-band emissions."

Last edited by rjstone. Register to edit

Tags: noise and interference arrl chapter 9 arrl module 23

A Ferrite Choke can be placed on a cable to reduce current flow conducted on the shield of audio (and power) cables.

The grey tubes or clamp on ferrite devices add inductance to the cable to block the common mode RF energy that may leak from the radio onto the cables attached to the radio.

Bandpass and low pass filters are too complex to design, test and implement compared to the simplicity of placing a ferrite choke on the cable.

Last edited by jamesmcbride. Register to edit

Tags: radio waves filters troubleshooting noise and interference arrl chapter 9 arrl module 23

The problem here is that the non-amateur radio is receiving signals in the amateur radio band, so a filter on the amateur transmitter won't help - the signal in the amateur band will still be radiated.

Changing the transmitter from FM to SSB will only change the mode of the interference, and it's likely that it will still be received by the TV receiver.

The bandwidth of the transmitted signal isn't the problem - the problem is that the TV is receiving signals in the amateur radio bands. So the only way to reduce or eliminate the signal is to block the amateur radio signal before it gets into the TV, using a filter at the antenna input of the affected receiver.

Last edited by k6yxh. Register to edit

Tags: arrl chapter 9 arrl module 23

If you can't keep your signal out of your own TV, it's unlikely that you can keep it out of your neighbor's. It's much easier to experiment with your own TV.

Once you're sure that your TV is okay and not receiving your signals, you can look for differences in your neighbor's TV set up. It could be that they don't have a good antenna, or that your signal is getting into their cable TV feed line.

Tuning to the same channel lets you know that it isn't harmonic radiation from your station, or at least that the harmonic radiation could be reduced using a filter.

Last edited by raaghavt. Register to edit

Tags: arrl chapter 9 arrl module 23

The best way to eliminate the interference is to not let it in your radio. Just like if you have a noisy roommate, best way to get rid of the noise is not letting them in the room in the first place!

A band reject filter knocks out the frequency range from the FM broadcast station before it ever gets to your radio and has a chance to cause interference.

Silly Hint: FM station plays music; "Band" reject filter

Last edited by johnglasco. Register to edit

Tags: arrl chapter 9 arrl module 23

Cooperation with others is the best way to start solving an interference problem. Many devices, especially digital computers and peripherals, generate RF interference. Turning off devices one at a time is a good way to locate an offending device. For more information see: RF interference

Last edited by str8schuter. Register to edit

Tags: troubleshooting noise and interference best practices arrl chapter 9 arrl module 23

Once it is known that the TV interference is originating from your ham radio transmission, and that your own equipment is functioning within acceptable parameters, your first step is to determine how best to solve or reduce the effects of the interference at the TV.

While it's possible to reduce the effects of the interference by installing a preamplifier at the TV antenna input, you will only be masking the problem rather than solving it. Also, as well-intentioned as they might be, installing filters might not prove very useful because their effective frequency ranges might be so close to those of the TV that the TV signals themselves could just as easily get filtered out with the interference.

Usually the problem will be that something connected to the TV antenna input is acting as an antenna, picking up your transmissions. This is especially true for loose connectors, mismatched connectors, frayed cables, and other damaged or corroded connections. Therefore, checking to be sure that all TV coaxial connectors are installed properly is a good way to satisfy that first step.

Last edited by nojiratz. Register to edit

Tags: arrl chapter 9 arrl module 23

How do each of these cause your signal to be distorted or unintelligible?

"Your transmitter may be slightly off frequency" - If your transmitter is slightly off frequency the receiver will not be able to demodulate the signal and it may sound garbled, distorted and low in volume.

"Your batteries may be running low" - When your batteries are low the audio amplifier cannot generate the proper amplitude signals; the signal is limited by the lower than normal voltage which clips the signal causing it to be distorted.

Also, "You could be in a bad location" - As in real estate, location, location and location are vital. Multipath signals can cause an interference pattern that can make the received audio sound bad.

Last edited by jmv146. Register to edit

Tags: noise and interference batteries troubleshooting radio operation arrl chapter 6 arrl module 14

Your own transmitter output can be picked up by the sensitive circuits inside your microphone. This is called RF feedback. The symptom is that the transmission may be distorted, garbled or unitelligible.

Last edited by tenzin. Register to edit

Tags: noise and interference radio waves troubleshooting arrl chapter 9 arrl module 23