and could actually work out wavelengths by the size of the antenna on one if they saw a picture.
While not diminishing their accomplishments, divining operating frequency from a picture of an antenna is not difficult to do for one who has studied antenna design even informally. World War Two publicity pictures of warships often had mast sections blocked out to prevent giving away the operating frequencies of the various radios and radars.
One advantage of using TDMA is that noise from the transmitter can be ignored in the receiver design since they are not both operating at the same time. True full duplex single band radios use high Q RF filters on the front end of both the transmitter and the receiver to separate the transmit and receive frequencies which is an added complication that TDMA receivers do not require. It is not enough to have the transmitter on a separate frequency from the receiver unless they are in completely different bands as is sometimes done. Broadband noise from the transmitter on the receiver's frequency can easily raise the background noise to unacceptable levels.
Spread spectrum should help somewhat in a full duplex single band design but it should still take a significant sensitivity hit. It is a subject I have been looking into on and off so to speak.:)
CDMA based systems don't cause this problem because the transmit power is spread out over that entire frequency range, rather than the 200 KHz (or so) that GSM systems use per channel.
The problem is not related to the frequency range that the RF is spread over. If GSM used a spread spectrum like CDMA does but still used TDMA, interference caused by AM rectification of the none constant RF envelope would still take place.
The interference won't be powerful enough to interfere with the speaker cable (unless maybe it's a REALLY small speaker). It's the un-amplified analog lines that feed the amp that pick it up. Use shielded interconnects, or even optical SPDIF, and the problem should go away. Probably won't help your clock radio, though:)
While audio line level signals are often shielded because of the low signal level and higher impedance making them resistant to RF interference, the wires between the audio amplifier and the speaker seldom are. Audio amplifier output stages can rectify AM RF that is picked up by the speaker wires so the problem is not the RF interfering with the speaker cable or the speaker itself but the output stages of the audio amplifier instead.
As for interference within a speaker itself (that is, not arriving by way of the speakerwire used to hook it up) there's not much you can do other than putting a Faraday cage around the speaker, or just moving the source of noise farther away from the speaker.
The problem here is not the speaker itself but instead is the audio amplifier driving it or the signal source. Almost any transmitter using time division multiple access which includes GSM can cause this type of interference in electronics that are not designed and built to be resistant to it which includes shielding and filtering. The problem is the same AM rectification one associated with CB radios, HAM AM transmitters, and occasionally AM broadcast transmitters. In the case of the TDMA noise coming from a speaker, even if the amplifier is shielded the RF can get to it via either the input leads going to the audio source or more likely the output leads going to the speaker which are usually unshielded. AM rectification in any non-linear components (usually diodes or bipolar transistors but field effect transistors can do it also) cause bias changes which can be annoyingly audible at the speaker. In extreme cases, the bias voltage change and rectification can cause oscillation and catastrophic destruction in an audio output stage but this is normally associated with marginally stable power FET designs and their tube predecessors. Sometimes the steps taken in a design to make it more rugged like adding protection diodes makes the AM rectification problem worse.
While consumer electronics has to meet specifications for emitting harmful RF interference, this does not usually include susceptibility. It is common for the FCC nameplate to state, "(1) This device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation." The later usually means you have no legal recourse against the manufacturer or operator of the transmitter associated with the problem unless they are operating unlawfully in some way.
I have occasionally worked in areas where TDMA and AM transmitters were forbidden while constant envelope transmitters (FM, PSK, most QAM) were permitted. While it would be nice to make all electronic designs immune to AM RF rectification, it is not always feasible.
Pinback: All right, Hubble. Prepare to receive new orders. Hubble: You are false data. Pinback: Hmmm? Hubble: Therefore I shall ignore you. Pinback: Hello... Hubble? Hubble: False data can act only as a distraction. Therefore, I shall refuse to perceive. Pinback: Hey, Hubble? Hubble: The only thing that exists is myself. Pinback: Snap out of it, Hubble.
In the last two Ringworld books, the design of the UN ships reveals that they are powered by antimatter and as I recall, The Hindmost tells his allies that the UN has possession of an antimatter system which presumably is the same one Shaeffer and Elephant visited. The Kzinti's source of antimatter remains a mystery. The most recent Man-Kzin Wars book might discuss it.
Shaeffer must have been good about keeping secrets since his son Louis apparently does not know about any of his father's exploits. Oddly enough, he does not even figure them out at the very end of the fourth book when presumably he could.
Did you mean nonvolatile instead of static? Static RAM can be significantly faster then dynamic RAM. I expect that NOR Flash could be as fast as dynamic RAM but the demand just is not there when in speed critical applications you can just copy from slow Flash into faster DRAM and lower the system cost.
Droogs will get you through times of no money much better than money will get you through times of no droogs.
I really hope Fallen Angels wasn't prophetic:
Pyle sighed. "Yes, sir---" He fished in his uniform pocket and pulled out a second warrant and unfolded it carefully, then held it out for Tremont to read. "All right, then. Suspicion of harboring dangerous fugitives." "Fugitives. May I ask who these fugitives are?" "Read it." Tremont adjusted his glasses. He took hold of the warrant in one hand but the policeman refused to relinquish it. Tremont raised an eyebrow, Spock-fashion. "Sorry, Mr. Fielding," Pyle muttered. "I've got to show it to you, but I can't let you have it." "I see." Tremont took his time reading the warrant. The longer he stalled, the better for everyone. "There's nothing about who the fugitives are." "Classified." "Oh. And the space for the judge's signature is blank," he observed. "Just an X." "The judge's name is classified, too." Zaftig looked triumphant. "The mark on the warrant is witnessed," the Green sergeant said, "and the signature is on file at the courthouse." "I knew we had literacy problems---" Pyle looked uncomfortable. "There's precedent," he explained. Tremont nodded. "The Steve Jackson affair. Yes, I understand." Jackson's game company had been seized by the Secret Service under just such an unsigned warrant. His computers, modems, files. Even his printers. Suspicion of hacking. And private ownership of unregistered modems had been legal back then.
Unless you are doing something weird, the Johnson noise will be proportional to the Thevenin resistance no matter what series-parallel combination you use. Four 10 ohm resistors in series-parallel have the same Johnson noise as a single 10 ohm resistor.
Gpu process' and CPU process' are completly different
How are they completely different? They both have large amounts of logic, cache, and clocking with separate core and I/O power supplies while lacking process specific features like EEPROM and DRAM. IC processes are specific enough to preclude easy transfer of a design from any one to another without compromises but what would preclude AMD doing an optimized Opteron based design for TSMC's 55nm process? Is it a limitation of the tool set and process characterization from TSMC?
Alternators have a higher power per weight and volume and are also less mechanically complicated since they have slip rings instead of a commutator which also makes them more reliable.
They did not become practical in cars until the advent of high power silicon rectifier diodes.
It is not uncommon to require a set of magic numbers to be written before writing to protected memory. The magic numbers and/or access pattern is designed so that no simple or likely hardware failure will allow unprotected access. Small discrete or integrated EEPROMs often have this functionality built in.
Even if the solar panel voltage depended on the surface area instead of the series and parallel topology, the necessary charge controller could easily handle any required voltage step up which is arguably the best configuration anyway.
The one that is the basis of the promised mobile WiMAX networks is OFDMA. The point being it has super sexy multiple access in the uplink where the multiple users transmit at the same time, on the same frequency with the orthogonal subcarriers from the same OFDM symbol magically interleaving.
I have been investigating digital radio design and have a couple questions about this. My specific interest is in digital radio design for use in hostile RF environments.
Are the radios full duplex allowing continuous carrier frequency feedback and adjustment? I guess even if they were half duplex then doppler shift adjustment would be possible. I have wondered however if this is related to any problems with high speed mobile usage.
Do the receivers suffer from in band dynamic range limitations or does having a continuously adjustable transmitter output power prevent that type of problem?
Do the proposed white space devices actually use the unused spaces within an active channel? If so, that strikes me as poorly thought out since any transmitted signal would be right in the middle of a television receiver's passband and while the television channel may not be using that particular spot of spectrum the television receiver will still have to contend with a significantly higher dynamic range requirement. The requirements for that type of operation are so high that digital receivers without equal IF selectivity still can not match the performance of superheterodyne receivers when rejecting in band signals.
The only safe bet for a white space using device is to completely reject TV channels which are in use and leave significant guard bands around even those. I would never have expected one to bother attempting to detect and identify a narrow band white space device within an operating TV channel.
I am inclined white list and then require a Proof of Work to bring any message not on the white list to my attention without error prone automated spam checking. When possible, reject at the smtp level of course to avoid relying on the easily forged headers and provide immediate feedback.
Unfortunately, no Proof of Work authentication systems are available yet.
The same principle is used for audio recording as well. Delta sigma AtoD and DtoA converters both take advantage of oversampling and significantly reduce the demands on the anti-aliasing filter. Internally, they both do decimation and digital filtering such that they appear to use a lower sampling rate than is actually used on the analog side. The disadvantage is a higher latency and often the loss of the ability to be used as a sampling converter.
I am not sure if I would call it a jammer but with some work you can build an IR emitting CO2 laser with a power level in the hundreds of watts. Is destruction of the camera a jamming condition?
I have been studying digital receiver design recently for a very similar application. Currently I am looking into how much processing power is really required for real time low latency digital demodulation with a sampled IF and relatively tame (or at least flat group delay) IF filtering.
That doesn't preclude switching in a narrow analog filter (a SAW or other IF filter) when you want the narrow band performance.
This is just what high performance receivers do. In some cases, there are selectable IF filters at more then one intermediate frequency although most designs just use a maximum width IF up until the last filter which is selectable. Further, if the local oscillator frequencies are finely adjustable, then each IF filter can be shifted in a different direction yielding a narrower then normal IF passband with one IF filter providing the lower cutoff and the other IF filter providing the upper cutoff.
Receivers intended to operate in the presence of jamming, usually military receivers, often include tunable notch filters as early as possible in the signal chain. Some older amateur receivers did this as well although DSP notch filtering which automagically removes multiple adjacent low level carrier tones is more common now but it cannot mitigate overload since it happens too late in the receiver signal chain.
If the filter has sufficient rejection, you could even use subsampling.
Absolutely. There are a number of sampling and delta-sigma analog to digital converters which are intended for exactly this type of application and are specified for sampling significantly above their baseband nyquist frequency. Narrow band sampling of IF frequencies above 10.7 MHz is currently feasible. You could also of course use a separate fast sampling circuit in front of a normal AtoD converter.
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While not diminishing their accomplishments, divining operating frequency from a picture of an antenna is not difficult to do for one who has studied antenna design even informally. World War Two publicity pictures of warships often had mast sections blocked out to prevent giving away the operating frequencies of the various radios and radars.
One advantage of using TDMA is that noise from the transmitter can be ignored in the receiver design since they are not both operating at the same time. True full duplex single band radios use high Q RF filters on the front end of both the transmitter and the receiver to separate the transmit and receive frequencies which is an added complication that TDMA receivers do not require. It is not enough to have the transmitter on a separate frequency from the receiver unless they are in completely different bands as is sometimes done. Broadband noise from the transmitter on the receiver's frequency can easily raise the background noise to unacceptable levels.
Spread spectrum should help somewhat in a full duplex single band design but it should still take a significant sensitivity hit. It is a subject I have been looking into on and off so to speak. :)
The problem is not related to the frequency range that the RF is spread over. If GSM used a spread spectrum like CDMA does but still used TDMA, interference caused by AM rectification of the none constant RF envelope would still take place.
While audio line level signals are often shielded because of the low signal level and higher impedance making them resistant to RF interference, the wires between the audio amplifier and the speaker seldom are. Audio amplifier output stages can rectify AM RF that is picked up by the speaker wires so the problem is not the RF interfering with the speaker cable or the speaker itself but the output stages of the audio amplifier instead.
The problem here is not the speaker itself but instead is the audio amplifier driving it or the signal source. Almost any transmitter using time division multiple access which includes GSM can cause this type of interference in electronics that are not designed and built to be resistant to it which includes shielding and filtering. The problem is the same AM rectification one associated with CB radios, HAM AM transmitters, and occasionally AM broadcast transmitters. In the case of the TDMA noise coming from a speaker, even if the amplifier is shielded the RF can get to it via either the input leads going to the audio source or more likely the output leads going to the speaker which are usually unshielded. AM rectification in any non-linear components (usually diodes or bipolar transistors but field effect transistors can do it also) cause bias changes which can be annoyingly audible at the speaker. In extreme cases, the bias voltage change and rectification can cause oscillation and catastrophic destruction in an audio output stage but this is normally associated with marginally stable power FET designs and their tube predecessors. Sometimes the steps taken in a design to make it more rugged like adding protection diodes makes the AM rectification problem worse.
While consumer electronics has to meet specifications for emitting harmful RF interference, this does not usually include susceptibility. It is common for the FCC nameplate to state, "(1) This device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation." The later usually means you have no legal recourse against the manufacturer or operator of the transmitter associated with the problem unless they are operating unlawfully in some way.
I have occasionally worked in areas where TDMA and AM transmitters were forbidden while constant envelope transmitters (FM, PSK, most QAM) were permitted. While it would be nice to make all electronic designs immune to AM RF rectification, it is not always feasible.
Pinback: All right, Hubble. Prepare to receive new orders.
Hubble: You are false data.
Pinback: Hmmm?
Hubble: Therefore I shall ignore you.
Pinback: Hello... Hubble?
Hubble: False data can act only as a distraction. Therefore, I shall refuse to perceive.
Pinback: Hey, Hubble?
Hubble: The only thing that exists is myself.
Pinback: Snap out of it, Hubble.
In the last two Ringworld books, the design of the UN ships reveals that they are powered by antimatter and as I recall, The Hindmost tells his allies that the UN has possession of an antimatter system which presumably is the same one Shaeffer and Elephant visited. The Kzinti's source of antimatter remains a mystery. The most recent Man-Kzin Wars book might discuss it.
Shaeffer must have been good about keeping secrets since his son Louis apparently does not know about any of his father's exploits. Oddly enough, he does not even figure them out at the very end of the fourth book when presumably he could.
Did you mean nonvolatile instead of static? Static RAM can be significantly faster then dynamic RAM. I expect that NOR Flash could be as fast as dynamic RAM but the demand just is not there when in speed critical applications you can just copy from slow Flash into faster DRAM and lower the system cost.
Droogs will get you through times of no money much better than money will get you through times of no droogs.
I really hope Fallen Angels wasn't prophetic:
I have definitely encountered this but reputable resistor manufacturers do not engage in such shenanigans.
Unless you are doing something weird, the Johnson noise will be proportional to the Thevenin resistance no matter what series-parallel combination you use. Four 10 ohm resistors in series-parallel have the same Johnson noise as a single 10 ohm resistor.
He might exit the station without landing or even worse, use the skull.
Gpu process' and CPU process' are completly different
How are they completely different? They both have large amounts of logic, cache, and clocking with separate core and I/O power supplies while lacking process specific features like EEPROM and DRAM. IC processes are specific enough to preclude easy transfer of a design from any one to another without compromises but what would preclude AMD doing an optimized Opteron based design for TSMC's 55nm process? Is it a limitation of the tool set and process characterization from TSMC?
Basically, I'm wondering if it's possible that a pea-sized meteorite could go flying through my head like a bullet.
Only if you try to change the past.
Luckily for me my gun jammed instead. Twice.
Alternators have a higher power per weight and volume and are also less mechanically complicated since they have slip rings instead of a commutator which also makes them more reliable.
They did not become practical in cars until the advent of high power silicon rectifier diodes.
It is not uncommon to require a set of magic numbers to be written before writing to protected memory. The magic numbers and/or access pattern is designed so that no simple or likely hardware failure will allow unprotected access. Small discrete or integrated EEPROMs often have this functionality built in.
Even if the solar panel voltage depended on the surface area instead of the series and parallel topology, the necessary charge controller could easily handle any required voltage step up which is arguably the best configuration anyway.
The one that is the basis of the promised mobile WiMAX networks is OFDMA. The point being it has super sexy multiple access in the uplink where the multiple users transmit at the same time, on the same frequency with the orthogonal subcarriers from the same OFDM symbol magically interleaving.
I have been investigating digital radio design and have a couple questions about this. My specific interest is in digital radio design for use in hostile RF environments.
Are the radios full duplex allowing continuous carrier frequency feedback and adjustment? I guess even if they were half duplex then doppler shift adjustment would be possible. I have wondered however if this is related to any problems with high speed mobile usage.
Do the receivers suffer from in band dynamic range limitations or does having a continuously adjustable transmitter output power prevent that type of problem?
Paper tape? Eee, tha' were lucky. In my day we had to toggle the loader in on front panel switches.
That is what we had to do to load the paper tape.
The first programming language I learned was 8080 machine code programmed using a ProLog PROM programmer. My assembler was a pad of paper and pencil.
Do the proposed white space devices actually use the unused spaces within an active channel? If so, that strikes me as poorly thought out since any transmitted signal would be right in the middle of a television receiver's passband and while the television channel may not be using that particular spot of spectrum the television receiver will still have to contend with a significantly higher dynamic range requirement. The requirements for that type of operation are so high that digital receivers without equal IF selectivity still can not match the performance of superheterodyne receivers when rejecting in band signals.
The only safe bet for a white space using device is to completely reject TV channels which are in use and leave significant guard bands around even those. I would never have expected one to bother attempting to detect and identify a narrow band white space device within an operating TV channel.
It will take fifteen years to get new, offshore IP4 addresses online and they will only supply 3% of the IP4 addresses we need.
- Shamelessly stolen from dkaa.
I am inclined white list and then require a Proof of Work to bring any message not on the white list to my attention without error prone automated spam checking. When possible, reject at the smtp level of course to avoid relying on the easily forged headers and provide immediate feedback.
Unfortunately, no Proof of Work authentication systems are available yet.
The same principle is used for audio recording as well. Delta sigma AtoD and DtoA converters both take advantage of oversampling and significantly reduce the demands on the anti-aliasing filter. Internally, they both do decimation and digital filtering such that they appear to use a lower sampling rate than is actually used on the analog side. The disadvantage is a higher latency and often the loss of the ability to be used as a sampling converter.
I am not sure if I would call it a jammer but with some work you can build an IR emitting CO2 laser with a power level in the hundreds of watts. Is destruction of the camera a jamming condition?
Very well put.
I have been studying digital receiver design recently for a very similar application. Currently I am looking into how much processing power is really required for real time low latency digital demodulation with a sampled IF and relatively tame (or at least flat group delay) IF filtering.
That doesn't preclude switching in a narrow analog filter (a SAW or other IF filter) when you want the narrow band performance.
This is just what high performance receivers do. In some cases, there are selectable IF filters at more then one intermediate frequency although most designs just use a maximum width IF up until the last filter which is selectable. Further, if the local oscillator frequencies are finely adjustable, then each IF filter can be shifted in a different direction yielding a narrower then normal IF passband with one IF filter providing the lower cutoff and the other IF filter providing the upper cutoff.
Receivers intended to operate in the presence of jamming, usually military receivers, often include tunable notch filters as early as possible in the signal chain. Some older amateur receivers did this as well although DSP notch filtering which automagically removes multiple adjacent low level carrier tones is more common now but it cannot mitigate overload since it happens too late in the receiver signal chain.
If the filter has sufficient rejection, you could even use subsampling.
Absolutely. There are a number of sampling and delta-sigma analog to digital converters which are intended for exactly this type of application and are specified for sampling significantly above their baseband nyquist frequency. Narrow band sampling of IF frequencies above 10.7 MHz is currently feasible. You could also of course use a separate fast sampling circuit in front of a normal AtoD converter.