19

My two favorite locations for listening online are: http://websdr.org/ WebSDR was first conceived as a means to make the 25 m radio telescope at Dwingeloo available to many radio amateurs for EME reception. In order to test a preliminary version of the software without using the 25m dish, a shortwave WebSDR was set up on Christmas Eve 2007 at the radio ...


19

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 - When I mean permanently, I mean the radio will not respond to the transmit key being pressed. If you get your license in future, you can reenable this feature ...


15

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 essentially CW). In order to hear it, you needed a Beat Frequency Oscillator -- a BFO -- and with a common radio receiver, the signal generator was standing in for ...


14

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 oscillator (LO) would get the signal into the desired 100 MHz IF, because 900 - 800 = 100. But also the image frequency of 1000 MHz would end up at the IF, ...


12

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 that the antennas are less than 1/2 wavelength apart, so that the phase difference will always be less than 180°). When we switch from the lagging signal to ...


12

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 to, so you can hear them over a much wider range. Advice on the practice of listening: For finding signals, first of all, always use SSB. Even if it's the ...


12

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-double it to obtain the subcarrier signal marking the position of the difference signal. The receiver uses this subcarrier to shift it in frequency down to the ...


9

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!


8

"Pole" comes from the Laplace transform, or it's discrete (for digital filters) equivalent, the Z-transform. Without delving into the mathematics of it, these transforms enable a filter designer to express the response of a filter in terms of some number of poles and zeros on the complex plane. Using these transforms simplifies many tasks of the filter ...


8

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 continuing when the signal ends. The scan function can of course be disabled to use it as a receiver for a single channel. Scanners as commonly discussed are ...


8

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 electronic T/R switch. One approach is an RF sensor that triggers a relay; the MFJ-1708 is one example. A more sophisticated approach uses an active element to ...


8

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, this looks like a very high (for ideal components, infinite) impedance. Away from resonance, the impedance decreases and becomes more inductive or capacitive. ...


8

A summary of requirements: Licensing: Technician - very minimal requirements Equipment: Transceiver, Terminal Node Controller and terminal Transceiver - traditionally a VHF/UHF FM radio Terminal Node Controller - Partly a modem, partly an AX.25 layer manager Terminal - Any serial terminal will do, but most likely you will use a personal computer A ...


8

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 superheterodyne receiver with a known intermediate frequency is powered on and tuned to a particular frequency, because the receiver's local oscillator radiates a ...


8

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 radiation from the oscillator or the mixing products in the receiver is technically possible, but in modern receivers the power is so weak this power is so weak it ...


7

WWV and WWVH broadcast time and frequency reference information continuously, using AM on 2.5, 5, 10, 15 and 20 MHz, so you should be able to pick up all of them using your receiver, given an adequate antenna. At my location (San Francisco Bay Area) with lousy equipment, these signals are only slightly stronger than shortwave broadcast stations, but more ...


7

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 atmospheric noise is high. On VHF and UHF the natural noise floor is lower, and low-noise receivers are more expensive, so it is possible but not guaranteed. It will ...


7

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 afraid you're misinformed. No single antenna, no matter what the design, can be better than another at receiving multiple signals at once. A receiving antenna ...


7

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. Connecting two antennas to the radio If you simply connect two antennas in parallel, the math is just like connecting two resistors in parallel: the impedance is ...


6

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 matter what antenna you use. Try shutting off all electronic equipment (including e.g. fluorescent or LED lights, and power adapters plugged into the wall) in your ...


6

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 http://www.bytebang.at/Blog/Locking+down+a+Baofeng+UV5R%2B+to+disable+unintentional+TX "Within the Uv5R there is a thin rubber pad that pushes against the TX ...


6

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 match the suppressed carrier frequency by ear. Slightly-off SSB signals have a distinct sound, which is not just being too low or high in pitch, because the ...


6

Almost every SDR receiver is capable of receiving the FM broadcast band. The ones which can't are typically SDR transceivers designed for specific HF bands. The harder part of your requirements is the waterfall of “the band … or a significant portion of that range”. The FM broadcast band is 20 MHz wide, and to display all of it straightforwardly requires ...


6

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 transmitter, there is no chance of your antenna collecting enough power damage your receiver. You are more likely to cause damage to your receiver from static ...


6

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 between frequencies above and below the LO. Discarding one of the I or Q components still works as a mixer, but input frequencies above and below the LO become ...


6

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 difficult to copy. 15wpm morse has a dit length of 0.08 seconds, making a dah or an inter-letter space around 0.24 seconds, so a fast 0.1s AGC will do it quite a ...


6

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 stream from multiple GPS satellites, and that is beyond the scope of this site. In order to receive the data from the GPS satellites, your best bet would be to ...


6

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 more observations are made the average tends towards zero. By averaging more observations, the noise can be made arbitrarily close to zero. Signals are not ...


6

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 meter That probably means you're not satisfied with a range resolution of a couple meters – you need a much finer measurement. That means your system must have ...


6

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 the symbol duration. For example, PSK 31 has a symbol rate of 31.25 baud, meaning each symbol is 32 ms long. If the difference in arrival time is significantly ...


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