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15 votes
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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 ...
Zeiss Ikon's user avatar
  • 4,107
14 votes
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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 ...
Phil Frost - W8II's user avatar
12 votes
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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-...
Kevin Reid AG6YO's user avatar
  • 24.7k
12 votes

Can larger antennas damage an HT radio?

A larger antenna shouldn't damage a handheld radio. In a quiet area, it will make its receiver more sensitive, and it will radiate more power when transmitting. Try to keep a receiving antenna away ...
tomnexus's user avatar
  • 11.4k
11 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 ...
JSH's user avatar
  • 590
11 votes
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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 ...
Phil Frost - W8II's user avatar
11 votes

Can larger antennas damage an HT radio?

A larger antenna can mechanically damage an HT if it is physically supported by the HT (it can stress the connector on some designs), but if it's on a feed line instead it shouldn't matter. Besides ...
user10489's user avatar
  • 6,485
9 votes
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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&...
hobbs - KC2G's user avatar
  • 12.5k
9 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 "...
Phil Frost - W8II's user avatar
8 votes
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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 ...
Glenn W9IQ's user avatar
  • 18.6k
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 ...
Glenn W9IQ's user avatar
  • 18.6k
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 ...
Phil Frost - W8II's user avatar
8 votes
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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}\...
Marcus Müller's user avatar
8 votes

Why do Baofeng radios have such poor reception reliability?

You get what you pay for. The Baofeng radios take a number of shortcuts in their design to make them cheaper, including leaving out front end filters. The result is that the radio is marginal on ...
user10489's user avatar
  • 6,485
8 votes

Can larger antennas damage an HT radio?

No, it will likely improve reception because the HT antenna is severely compromised and done all the time in mobile applications to use an external antenna.
Dereck's user avatar
  • 565
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 ...
rclocher3's user avatar
  • 9,242
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 ...
hobbs - KC2G's user avatar
  • 12.5k
7 votes
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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 ...
BERNARD's user avatar
  • 86
7 votes
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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 ...
Mike Waters's user avatar
  • 8,071
7 votes

Does the output of a BFO for a short wave receiver have to be exactly a sine wave?

So, the job of a BFO is essentially "faking" the carrier oscillation of the AM transmission that was suppressed, together with the other sideband, so that the rest of the receiver can ...
Marcus Müller's user avatar
6 votes
Accepted

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

Yes. Detecting a receiver is VERY VERY VERY hard to do. Since it is only an absorber rather than transmitter of RF energy, it requires a signal strength meter to detect a dip in RF energy. It requires ...
Katrina Petkovic's user avatar
6 votes

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

While in Chirp go to Duplex and set it to "OFF" If the duplex is set to off then transmission on this channel will be disabled (if the radio supports this capability). Thomas
Thomas's user avatar
  • 61
6 votes

what are the alternatives to LM387 and SA602AN?

LM387 is just a really old, ordinary op-amp as far as I can tell. It has a funny pin configuration, so if you have a PCB already made you need to make modifications. I suggest cutting the traces, ...
Phil Frost - W8II's user avatar
6 votes

Repairing a Tecsun PL-660

I signed up here just to reply to this great (the only one I could find on the internet) question/experience that helped me with an identical problem. I was so close to giving up when I read this ...
vincenzo's user avatar
6 votes

IQ imbalance after quadrature mixing

A quadrature mixer contains two signal paths, I and Q. For a sinusoidal input into the mixer, the outputs will be in quadrature. It's this property that allows a quadrature mixer to distinguish ...
Phil Frost - W8II's user avatar
6 votes

What equipment and software do I need to read raw civilian GPS signals on my Mac?

I will answer this question from a "technology of radio" perspective, because half of the question is very much related to the technology of radio. The other half is related to the decoding of a data ...
Scott Earle's user avatar
  • 4,619
6 votes

Substitute for 455 kHz Ceramic filters in new designs

Since this platform considers questions asking for products as off-topic, I'll interpret your question as: I have an IF receiver, but there's no good filters for the rather low IF it uses (455 kHz)....
Marcus Müller's user avatar
6 votes
Accepted

Why do receiver sensitivities vary so much with frequency?

Detecting a signal is not a question of amplifying the signal: the problem is distinguishing the signal from the noise. Noise by nature is random: individual observations are unpredictable, but as ...
Phil Frost - W8II's user avatar
6 votes
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Locate a ball 1000 times a second

I want to locate a small ball in the air 1000 times a second. The ball is thrown from the ground and then flies in the air for 0.5 seconds until it lands. Distance from the location instrument is 1 ...
Marcus Müller's user avatar
6 votes
Accepted

Using UV5R HTs. Will i lose receiving range by attaching coaxial cable to put my antenna remotely as well as higher?

The answer is that it depends, although in my experience increasing height will always improve range. Height matters a lot in most VHF propagation. For your UV5R HT, antenna height will generally ...
Deepstop's user avatar
  • 246

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