# Tag Info

10

All modulated signals, not just FM, have a bandwidth. The antenna has a bandwidth, which must be wider than the modulation of the signal you are using. Note that receive bandwidth and transmit bandwidth may be different, but generally it is actually difficult to make an antenna with a bandwidth so narrow (for either) that it would be a problem with FM.

7

Or does this antenna have a frequency tolerance? This is closest, but the antenna, itself, does not actually have a “frequency tolerance” (more usually called a bandwidth). Rather, the antenna's properties, including impedance/SWR, radiation pattern, and losses, vary with frequency, and the range of frequencies over which you can transmit are mainly ...

6

Most VHF+ antennas are not that narrow banded. They usually have a low enough Q. Thus, there is usually no need for a tunable antenna. Also, antennas are generally not any different regardless of the modulation type.

5

The number of cars is not an issue. Driving in a city with thousands of cars in your vicinity still allows FM reception. Engines are running, which is probably not the case when watching a film in a drive-in cinema. For good stereo reception (26 dB audio signal to noise) you need a field strength of 100 µV/m or more. In a Rayleigh path with reflections you ...

4

Consider an unmodulated carrier. It has a phase that increases with time at some constant rate. The rate that phase increases is what we call the frequency. What if the frequency isn't constant, but a function of time $\omega(t)$? If the frequency goes higher, phase increases faster. A lower frequency is a slower frequency increase. The phase at any given ...

3

I have seen wire antennas for the FM band before. Such an antenna usually has two wires that are connected to twin-lead feed line, which then connects to a device called a matching transformer or a balun that looks like this: So you could connect two wires to a device like that, and plug that into your receiver. The best way to arrange the wires is in a ...

3

Solved! It was the wireless charging pad integrated into the top surface of the device, which thankfully they provided a means to disable.

2

FM and PM are almost identical; the answer is yes. PM is limited in phase deviation, FM is not. The audio frequency response is different: PM received on a(n) FM receiver lacks lower audio frequencies due to the (apparent) differentiation of the frequency modulation. In a formula: FM audio equals the actual deviation of the frequency; PM audio equals the ...

2

The answer... Various sources can cause this. One common source of interference are battery chargers; either at your house or a neighbor's.

2

Perhaps you are thinking of a switched capacitor filter? Unfortunately, most switched capacitor IC components are (were) designed for audio frequencies, not VHF. Another possibility is to use an LC tuned circuit containing a voltage controlled varicap diode capacitor, controlled by a (digital input) DAC. As per the earlier answer, you can use a use a ...

2

You may like checking out svxlink. I've had success setting it up on a Raspberry Pi, interfaced with a baofeng (pls don't judge) to accomplish VM (as well as successfully interfacing with EchoLink) in a simplex configuration, but only as a prototype... I haven't experience running it for an extended period. Obviously, you can interface the RPi with the radio(...

2

Antennas dont actively compensate for FM deviation. Antenna Q is designed for the antenna application. The bandwidth or Q of communications antennas is fixed by the design to accomodate the range of frequencies expected. Of course tradeoffs are made between cost, and efficiency of the antenna. Besides, the width of the 2 meter band (144 to 148 mhz) is ...

2

For reception, a random piece of wire will be a usable antenna, although an antenna tuned to the desired frequency will be more efficient. I am using Amateur 2 meter band (144 - 148 MHz) antennas to receive marine VHF signals in the 156 - 158 MHz range with no problems. For transmission, properly tuned antennas are much more important, but most antennas ...

1

Welcome to the site and welcome to radio! A 150kHz channel that is "Centered at 96.5 MHz" means that channel will have 150kHz / 2 = 75kHz below 96.5 AND 75kHz above 96.5 MHz. 50kHz guard band between means that there will be at least 50kHz of space between the top-end of one channel and the bottom-end of the next channel so that they don't ...

1

I can imagine a device that listens on a ham frequency to record voice messages and decode commands, and then retransmits recorded voice messages on the same frequency on command. Such a device would be relatively easy to design and build. But there are legal issues, at least in the US. Legally speaking, I presume that you're talking about an automated ...

1

A "simulated inductor" might work in your application: You could adjust the simulated inductance by using an analog multiplexer IC and resistive ladder array IC to change the values of RL and R1.

1

Frequency setting and control can be achieved with a phase locked loop (PLL). The frequency of the oscillator is compared to a known and stable reference frequency. Look for further explanation with search terms: radio PLL, RF synthesizer and frequency stabilisation. Digital control of frequency: fractional PLL and All Digital PLL. See picture. Copyright? I ...

1

In my experience, RF noise from vehicles comes from engine ignition systems (distributors, ignition coils, spark plugs, and spark plug cables) of gasoline-fueled vehicles, but ignition systems in cars made over the last 30 years or so are much better shielded than older cars' ignition systems. Diesel-fueled vehicles don't have ignition systems at all. The ...

1

FYI C4FM is not allowed below 29 Mhz. This is because it is a wide band modulation and uses more than the allowable bandwidth for HF band transmission. Straight FM is not allowed below 29 Mhz for the same reason.

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