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 ...
- 4,145
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 ...
- 52.4k
13
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 ...
- 12.2k
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-...
- 25k
12
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 ...
- 6,960
11
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 ...
- 52.4k
10
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 "...
- 52.4k
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&...
- 13.2k
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 ...
- 18.6k
8
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 ...
- 13.2k
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 ...
- 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 ...
- 52.4k
8
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}\...
- 17.3k
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 ...
- 6,960
8
votes
Is that a loading coil antenna
This is a variant of an inverted-F antenna.
"Loading coil" is a term usually used with dipole antennas (and slight variations thereof). The idea is that you "load" the antenna to ...
- 17.3k
7
votes
Accepted
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 ...
- 9,320
7
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 ...
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 ...
- 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 ...
- 8,175
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 ...
- 17.3k
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, ...
- 52.4k
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
- 61
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 ...
- 61
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 ...
- 52.4k
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 ...
- 4,669
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)....
- 17.3k
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 ...
- 52.4k
6
votes
Accepted
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 ...
- 17.3k
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 ...
- 246
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