Questions tagged [am]

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16
votes
3answers
4k views

Why do we not use AM and FM at the same time to transmit more information?

Amplitude modulation uses the modulation of the amplitude of a carrier wave to transmit data while leaving the carrier frequency constant, and in the case of FM it's just the other way round. Why is ...
10
votes
1answer
1k views

Is FM modulation still more resistant to noise when given the same bandwidth as an AM signal?

FM modulated radio is much more resistant to noise and can deliver better sound quality than AM radio. But FM signals also use more bandwidth than AM signals. In general a wider bandwidth signal is ...
9
votes
1answer
432 views

Why does AM have sidebands?

Why does AM have sidebands? Isn't the whole point of AM to broadcast on ONE frequency and ONLY change the amplitude? In the picture there is only ONE frequency and the amplitude changes, so why ...
6
votes
2answers
185 views

What happens when I and Q are switched?

In https://ham.stackexchange.com/a/1068/9 it's shown that one can use $$ r = \sqrt{I^2+Q^2} $$ to decode AM signals from a direct conversion receiver. It appears that, in this particular case, I ...
5
votes
5answers
2k views

Simple DIY AM receiver for 25/28 MHz

I'd like to build a simple AM receiver for 25 and/or 28 MHz to receive DCF77-formatted time code. It doesn't have to be extremely sensitive or selective - the local clock oscillator will keep time ...
4
votes
1answer
71 views

AM Radio Envelope Dectector

How do you choose the values of the capacitor and the resistor in an envelope detector circuit? In my case, the frequency range is from 20 Hz to 20,000 Hz. Also, am I correct in understanding that ...
4
votes
1answer
1k views

Building a crystal radio with my brother. How does this circuit work?

I'll be visiting home soon after school lets out, and I want to build an AM crystal radio with my little brother. This is the design we'll use: http://crystalradio.net/beginners/ I'll be doing my ...
4
votes
0answers
83 views

Why the value of IF of AM is 455 kHz? [duplicate]

Why the value of intermediate frequency (IF) of amplitude modulation (AM) is 455 kHz? Why not another value?
3
votes
6answers
2k views

Would it be feasible to set up a SSB or AM 2 meter repeater?

Would it be feasible to set up a SSB or AM 2 meter repeater? I want to set up an AllStar full duplex node and like the idea of AM because stations can double without issues. SSB works for weaker ...
3
votes
1answer
2k views

Why are FM radio waves less susceptible to interference than AM?

When studying modulation of radio waves (or of most electromagnetic waves for that matter) I came across this question: Why are FM waves less susceptible to interference than AM waves? I know that ...
3
votes
3answers
318 views

78.5MHz AM receiver self-oscillation

Circuit appears to be working but very easily breaks into oscillation - sometimes just getting up from my desk triggers it, or while tuning, and sometimes after a few seconds with no disturbance that ...
3
votes
1answer
816 views

Why does the output power of some AM transmitters increase when modulated and of others decrease?

I didn't fully understand all the finer details of AM, so I'd like an explanation for the following behavior: I have 3 radios. In AM mode, one of the radios, when modulated, increases output power ...
3
votes
1answer
168 views

I/Q demodulation of DSBSC-AM signals

I was looking at some Stereo FM demodulators on the Internet, and I can't understand the use of the complex to real block for demodulation of the L-R signal (DSBSC-AM) which can be seen in different ...
3
votes
2answers
93 views

Mobile 2m / 70cm dual band with aviation frequency TX capability

Forgive what may be a basic inquiry from a new enthusiast. I am new to amateur radio, just barely passed Technician and General tests. I am also a pilot and have an RR class licence. I believe that I ...
2
votes
2answers
341 views

Broadcast signal deviating with time

I've been just scanning through the HF band at night seeing what all I can pick up, and I'm trying to figure out a particular signal. I'm using a VHF discone, which isn't ideal, but it works well ...
2
votes
3answers
304 views

Improve AM reception on an old Walkman that has no external antenna

I have an old Philips walkman that has AM/FM radio. I tried AM radio. Really I can get clearly 2 country radios. I catched very poorly 4 foreign radios or different countries, but they do lots of ...
2
votes
2answers
69 views

Daisy Chaining AM filters to help with IMD

I live near an AM transmitter, and the input of my RTL-SDR becomes overloaded. I've added an AM filter and it's really helped, however I still get a very strong AM signal with some IMD all over ...
2
votes
2answers
875 views

Why does a Class-C non-linear power amp distort SSB but does not distort AM?

Can someone tell me why exactly a transistor non-linear power amplifier will amplify an AM signal without noticeable distortion, but will distort an SSB signal, giving the familiar scratchy sound ...
2
votes
1answer
104 views

MW AM reception improvements?

Most AM receivers use Envelope detection. Historically this was simple. PLL-based systems are slightly better at low carrier-to-noise levels. Would there be any SNR advantage if each sideband was ...
2
votes
1answer
175 views

How does this circuit work? Why is the antenna connected to the output of the amplification stage?

What is the function of the configuration of R1, C3,C10 and R3? How does the LC tank in this circuit work?
2
votes
1answer
43 views

Poor reception on single AM channel

My car stereo has terrible reception on a single AM station. Other cars get the signal fine and other channels on radio are received fine. I have contemplated some sort of booster for the antenna or ...
2
votes
1answer
143 views

Simple AM Radio Troubleshooting

I just got all the parts to make a simple AM transmitter from Scitoys. I followed the instructions from different websites and they still don't work. I don't know why it's not working. On my ...
2
votes
1answer
79 views

How much field strength to blow out a receiver?

I was wondering what calculations would need to be performed to find out if a receiver will blow out in the given conditions. Portable AM receiver with ferrite rod antenna 200 ft away from MW antenna ...
2
votes
1answer
115 views

feasibility of wireless passive crystal earphones

I just learnt about such a thing as a crystal radio receiver and the following idea came to my mind. I have no background knowledge on electronics nor anything related. What if battery-less earbuds ...
1
vote
3answers
87 views

Radio Waves propagation (Intuitive Understanding of Wave propagation)

I have few similar questions regarding Radio waves communication particularly FM and AM type of Radio wave communication. Please bear with the naivety of the questions. Questions: Radio waves in FM ...
1
vote
1answer
132 views

Is there any way in which elevation *does* affect medium frequency (AM radio) transmissions?

This is a followup to this question of mine. From reading the wiki article, I get that: Radio waves at MF wavelengths propagate via ground waves and reflection from the ionosphere ( called skywaves)...
1
vote
1answer
165 views

Reception for FM stations is offset, but AM stations aren't

I have a Realistic STA-78 AM/FM Stereo receiver I recently rescued from my grandmother's attic. It hadn't been played in a while, but it appears everything is in working order except the FM dial. It's ...
1
vote
1answer
97 views

BFO locked synchronous AM detection

I am fixing up an old classic Yaesu FRG7 general coverage AM/SSB/CW HF receiver. The BFO section is a rudimentry 455 kHz IFT configured as a carrier reinsertion oscillator that that is made to run USB ...
1
vote
1answer
65 views

Why AM modulation side bands have higher frequencies than the carrier?

I cannot understand while the AM modulations have sidebands which are of a frequency higher than the carrier. If for example we are modulating a 4kHz signal to a carrier of 1MHz how we end up with a ...
0
votes
2answers
197 views

Peak envelope power should be 2:1 or 4:1 on meter?

I've always been reading my AM modulated signal on a Bird wattmeter and trying to set the carrier to 1/4 of the peak envelope power (PEP). Recently, I was told by a CBer that you only can see it that ...
0
votes
3answers
142 views

How to make simple AM detector using an LED?

I'm new to amateur radio, and as a beginner project, I wanted to use some of the basic components I have to create an AM receiver. Anyway, what I'm trying to do is create a simple AM receiver that ...
0
votes
4answers
157 views

Building an AM Radio receiver

I am making an AM radio with the specifications of: Part 1. Design a circuit with an antenna for tuning your receiver to a signal of a specific carrier radio frequency so that you can select a certain ...
-1
votes
3answers
72 views

Recommended Books For AM/FM (especially AM) Radio Design

I am trying to gain a better grasp of how to build an AM radio receiver. Can you direct me to some books (or other information) that will help?
-3
votes
4answers
124 views

Transmitting as SW AM station, not ham [closed]

What if I wanted to run a radio broadcast station on a commercial SW band? Say, I am on a boat in international waters. Or say I am in a free country. I monitor the frequency for months and I check ...