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Questions tagged [am]

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2
votes
2answers
154 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 ...
3
votes
2answers
66 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 ...
15
votes
3answers
3k 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 ...
1
vote
1answer
59 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)...
2
votes
2answers
245 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 ...
1
vote
1answer
39 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 ...
0
votes
2answers
75 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 ...
2
votes
1answer
37 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 ...
1
vote
1answer
60 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 ...
3
votes
1answer
148 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 ...
8
votes
1answer
846 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 ...
3
votes
1answer
647 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 ...
2
votes
1answer
101 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
92 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 ...
2
votes
1answer
963 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 ...
1
vote
1answer
145 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 ...
7
votes
1answer
268 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 ...
3
votes
6answers
1k 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 ...
4
votes
0answers
76 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?
5
votes
1answer
135 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 ...