29 votes
Accepted

Why does the audio on my FM transceiver cut out every 5.5 seconds?

It's a feature not a bug. When turned on, the weather alert function checks the local NOAA station for its alert tone every 5 seconds for half a second... doing so takes over the receiver. I'd turned ...
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  • 2,842
24 votes
Accepted

How can I avoid accidentally transmitting with a Baofeng UV-5R?

It'll be easier just to buy a programming cable and use the free Chirp software to turn off transmit permanently. I did this, and used my Baofeng as a receiver only before getting my licence. EDIT - ...
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  • 256
17 votes
Accepted

How would a time-difference-of-arrival receiver with two antennas know which side the signal is from?

When the tone is present, it is because the antennas are out of phase. One antenna's signal will be leading the other; which one is leading depends on which one is closer to the transmitter (provided ...
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  • 22.7k
15 votes
Accepted

Why would you need a signal generator to receive early satellite transmissions?

The earliest Soviet satellites, like Sputnik 1, transmitted what amounted to a CW stream -- just pulsed RF at pretty low power (later Sputniks transmitted data by pulse width modulation, still ...
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  • 3,871
14 votes
Accepted

How Could Superheterodyne Receiver Ever Work?

The answer is simple: filtering. For example, let's say the desired signal is at 800 MHz, and the intermediate frequency (IF) is chosen to be 100 MHz. Mixing the 800 MHz signal with a 900 MHz local ...
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12 votes
Accepted

Why do I only hear broadcasts from 150 kHz to 29.999 MHz?

It doesn't sound like you're doing anything wrong. Most likely, you are simply only hearing strong stations; broadcasters put much more power into their transmissions than amateurs are legally allowed ...
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  • 22.7k
12 votes
Accepted

Understanding WFM modulation

Your “B” is the stereo difference signal of broadcast FM stereo. It is placed at twice the pilot frequency so that it can be recovered by having the receiver lock onto the pilot signal and frequency-...
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  • 22.7k
11 votes

How can I avoid accidentally transmitting with a Baofeng UV-5R?

If you haven't seen them, the RTL-SDR dongles are really hard to beat for scanning. They let you see a waterfall display so that you can see visually which frequencies are active. It's wonderful!
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  • 753
10 votes

How To Join Packet Radio BBS

A summary of requirements: Licensing: Technician - very minimal requirements Equipment: Transceiver, Terminal Node Controller and terminal Transceiver - traditionally a VHF/UHF FM radio Terminal ...
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  • 580
10 votes
Accepted

Why aren't "ghosts" and intersymbol interference due to unmatched impedance (high SWR) a concern for HF receivers?

Intersymbol Interference (ISI) — or analog equivalents, like ghosting — are relevant only when the difference in time of arrival between the primary and reflected signal are significant compared to ...
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9 votes
Accepted

How to receive a signal from multiple sources simultaneously (helical antenna)

I'm working on a system (theoretical at the moment) whereby I wish to receive data from multiple sources all transmitting at the same time. I've read that a helical antenna is capable of this. I'm ...
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  • 22.7k
9 votes
Accepted

Connect two receiving antennas to the same radio

Yes, you can do this. There are two issues: connecting it to the radio, and the effect on reception. The latter might be problematic enough that using two receivers is actually a better option. ...
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  • 22.7k
9 votes
Accepted

How to calculate power transmitted by monopoles?

10⁻⁴ which I think is too low power. Why? Gut feeling says that is actually pretty good a transmission for such a distance. Notice how your free space path loss is $$\left(\frac{\lambda}{R}\...
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9 votes
Accepted

Phased array (rx only) with separate complete receivers

In short: yes, it's possible, but it's a bit harder than that. You want to drive all of the receivers from a shared clock, and sample them in phase with one another, to form a "coherent receiver&...
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  • 8,730
8 votes
Accepted

What is the difference between a scanner and a receiver?

A scanner is a specialized receiver with features for effectively monitoring many frequencies, classically by tuning to each in rapid succession (scanning) and stopping when a signal is found, then ...
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  • 22.7k
8 votes
Accepted

Share antenna between receiver and transceiver?

Back in the olden days, before transceivers took over, the transmitter and receiver were separate units, and the receiver had to be protected from the transmitter. The solution then, as now, is an ...
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  • 940
8 votes
Accepted

How is the FM-signal demodulated in my receiver?

Essentially, it is an FM to AM converter, followed by an AM detector, followed by an audio amplifier. The heart of this circuit is C1 and L. Together, these make a parallel LC circuit. At resonance, ...
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8 votes
Accepted

Can an antenna be too powerful for certain receivers?

Would the portable ~$40 Tecsun get damaged somehow by a 100-foot antenna because it's designed to work with shorter, portable antennas?  Unless you are within a kilometer or two of a very high power ...
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  • 18.1k
8 votes

Efficiency of short dipole receiving antenna

The efficiency of any antenna has a direct impact on the gain of the antenna. The gain of the antenna equally effects transmit and receive - a characteristic known as reciprocity. The highest gain ...
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  • 18.1k
8 votes

Can a FM tuner (receiver) be detected and triangulated?

The story is about Eric LeMarque who got lost after snowboarding out of bounds in the Sierra Nevada mountains. Radio receivers usually contain some kind of oscillator. Detecting the unintentional ...
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8 votes

What is a "roofing filter"?

The roofing filter is the filter through which the first IF must pass. The roofing filter is an IF filter, specifically the first one. AB4OJ provides a block diagram: As for why it's called a "...
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7 votes
Accepted

Can I improve reception with a more sensitive antenna / preamplifier / better feedline?

These things will significantly help under one condition: the RF noise floor is below the receiver's noise floor. This is almost never the case on HF, where low-noise amplifiers are easy and ...
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7 votes

In SSB how do receivers calculate the frequency offset without a carrier?

No, the receiver does not try to determine a carrier frequency, you do. When receiving SSB, you must adjust the VFO (main frequency control), not just until you hear a signal, but also to adjust to ...
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  • 22.7k
7 votes
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Detecting the listeners

No, that's not possible. There is no practical way to determine whether the transmitted power is usefully received by an antenna, or just absorbed by the ground. It is possible to detect that a ...
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  • 8,922
7 votes

What's the use case behind long AGC constants?

CW is one reason. CW is on-off keying, so if the AGC reacts at a timescale similar to or shorter than the transitions of the signal, it will partially cancel the signal, making it "muddy" and more ...
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  • 8,730
7 votes
Accepted

Unknown kit from DK0TV

This kit is a FM receiver built in 1977 by DK0TV. The receiver works on a single fixed frequency 30.000 MHz FM and has a very good sensitivity. It is used with a 10 GHz Gunnplexer to listen to the 3 ...
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  • 86
7 votes
Accepted

Looking for a book that contained a circuit for receiving (literally) underground amateur radio transmissions

Yes, this most certainly was a thing, and people actually did it. This type of communication has been done at ELF frequencies in the 3-30 kHz range. Their linear amplifiers were ordinary Hi-Fi audio ...
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  • 7,485
6 votes

Is there a way to find out the location where a radio signal is intercepted?

It is possible in principle to detect a receiver. Almost all designs of receivers have a local oscillator (LO), which oscillates at the same frequency as the carrier frequency of the signal it is ...
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  • 22.7k
6 votes
Accepted

Idea for better reception in crowded city

You have a tough problem, because you are surrounded by many noise sources. First, you should make sure that you have eliminated your own apartment's noise, because it is likely to interfere no ...
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  • 22.7k
6 votes

How can I avoid accidentally transmitting with a Baofeng UV-5R?

Chirp can only disable Transmitting on pre-programmed memory frequencies, if you select the vfo it will still transmit. Searching Google for 'uv5r transmit inhibit' yielded this on the fifth hit ...
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  • 61

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