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17 votes
3 answers
7k 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 ...
DK2AX's user avatar
  • 624
11 votes
1 answer
2k 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 ...
JanKanis's user avatar
  • 405
11 votes
1 answer
914 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 ...
Axel H.'s user avatar
  • 135
6 votes
2 answers
697 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 ...
Adam Davis's user avatar
  • 12.1k
6 votes
0 answers
3k views

Simple AM receiver with gnuradio / RTL-SDR

EDIT: I have succeeded in getting the AM receiver to work, by replacing the AM Demod block with a Complex To Mag, and a Band Pass filter (this is noted as an alternative in the AM Demod docs). ...
Toby Eggitt's user avatar
5 votes
5 answers
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 ...
oh7lzb's user avatar
  • 2,391
5 votes
2 answers
166 views

How can AM radio work differently when approaching the true frequency from different directions?

I bought a very cheap world band receiver, Nedis RDWR1000GY. It has MW, SW and FM reception. MW is useless where I live (no MW stations nearby and signals don't propagate far), but I was primarily ...
juhist's user avatar
  • 153
4 votes
1 answer
112 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 ...
JackLalane1's user avatar
4 votes
6 answers
134 views

Do changing sidebands have their own sidebands?

An amplitude changing carrier wave causes sidebands to appear next to it when viewed in the frequency domain. But if those sidebands themselves also change with time (because the modulating signal is ...
JanKanis's user avatar
  • 405
4 votes
1 answer
3k 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 ...
BitPusher16's user avatar
4 votes
1 answer
59 views

Effect of using wrong injected frequency when tuning IF cans in an AM radio?

I viewed an interesting video of a restoration of an old AM portable radio. When the alignment steps were being done, the author commented he would inject a 455kHz signal into the radio (the IF of the ...
rasher's user avatar
  • 143
4 votes
0 answers
96 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?
Wei-Cheng Liu's user avatar
3 votes
6 answers
3k 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 ...
Skyler 440's user avatar
  • 7,600
3 votes
3 answers
1k 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 caught very poorly 4 foreign radios or different countries, but they have lots of ...
Lorthas's user avatar
  • 141
3 votes
1 answer
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 ...
MystMan's user avatar
  • 133
3 votes
3 answers
389 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 ...
user avatar
3 votes
1 answer
2k 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 ...
AndrejaKo's user avatar
  • 2,893
3 votes
1 answer
419 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 ...
Ardavast Dayleryan's user avatar
3 votes
1 answer
138 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 ...
user2464424's user avatar
3 votes
2 answers
194 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 ...
Rod's user avatar
  • 31
2 votes
2 answers
479 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 ...
directedition's user avatar
2 votes
1 answer
164 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 ...
Autistic's user avatar
  • 469
2 votes
2 answers
100 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 ...
user14615's user avatar
  • 157
2 votes
2 answers
2k 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 ...
Andrew's user avatar
  • 3,683
2 votes
1 answer
280 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?
Delmer Lopez's user avatar
2 votes
2 answers
160 views

Type of Ground Wire for an AM Crystal Radio - I'm using a longwire antenna

I have way too many choices for ground wire. I am using a crystal radio so I need the BEST not just what will 'get by'. I've seen solid copper 10gauge, aluminum wire etc. I've also seen wide ...
randy k's user avatar
  • 21
2 votes
1 answer
189 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 ...
Derpy's user avatar
  • 95
2 votes
1 answer
51 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 ...
J Greene's user avatar
  • 121
2 votes
1 answer
108 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 ...
Synaps3's user avatar
  • 425
2 votes
0 answers
78 views

trying to get a passive AM bar antenna to work

I pulled a nice big external AM ferrite bar antenna off a working stereo. 5.5" long. it has 4 wires coming off of it. red must be the main wire, because checking that with an LCR meter connected ...
Fyodor's user avatar
  • 31
1 vote
4 answers
1k 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 ...
JackLalane1's user avatar
1 vote
3 answers
612 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 ...
F16Falcon's user avatar
  • 111
1 vote
4 answers
295 views

How can an RF coil emit at 3 different frequencies at the same time during Amplitude Modulation?

This image shows how an AM wave is generated and emitted: This comment explains how 3 separate waves are sent at once to represent an AM wave: the transmitter does not transmit one pure sine wave at ...
Dan's user avatar
  • 311
1 vote
1 answer
431 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)...
Michael A's user avatar
  • 185
1 vote
1 answer
236 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 ...
cnd4747's user avatar
  • 13
1 vote
1 answer
481 views

Need some help to design a DIY MW Radio receiver

AM Medium Wave Radio Receiver Design. First of all, I am a hobbyist and stuff related to electronics are not very strange to me but the chapter of Radio and RF frequency , intermediate frequencies , ...
CoderBittu's user avatar
1 vote
1 answer
228 views

AM radio cross-talk / hearing strong station everywhere

I've built the M0AYF active loop antenna for my RTL-SDR, using BC847C for the amplifier transistors. There are a couple very strong AM stations here, usually playing music. What I'm noticing is that ...
MightyPork's user avatar
1 vote
1 answer
183 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 ...
Autistic's user avatar
  • 469
1 vote
1 answer
65 views

Why does a channel get transmitted for a wide frequency range at night in Amplitude Modulation?

So I bought a radio and for some days I have been noticing that a channel with static frequency at somewhere around 880 KHz Is tuning properly during day time but at night, the channel can be heard ...
Subha Jeet Sikdar's user avatar
1 vote
1 answer
99 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 ...
user7075815's user avatar
0 votes
3 answers
207 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 ...
Newbie's user avatar
  • 171
0 votes
2 answers
511 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 ...
Synaps3's user avatar
  • 425
0 votes
3 answers
674 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?
JackLalane1's user avatar
0 votes
1 answer
44 views

Natural dipole / monopole filtering

Word has it these antennas are broadband, however my calculations show one may not need FM / AM BCB wave traps if not operating around those frequencies. I have run the script here for: ...
kellogs's user avatar
  • 205
0 votes
1 answer
93 views

Can I operate in AM mode using an Alpha 78 amplifier?

I don't have any experience with amplifiers. I bought my first one last year, a used Alpha 78. I cannot find anywhere where it explicitly states that you can use the Alpha 78 in AM mode. I suspect it'...
Sternkobold's user avatar
-2 votes
4 answers
166 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 ...
Gunther Schadow's user avatar