v1 users...watchout
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Joined: Aug 2001
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From: Santa Clara
All right moonpie, this will be my THIRD AND FINAL ATTEMPT to make you realize you are stupid. After this, I will probably become bored of the whole issue. Perhaps you have an IQ of 12 and drink from the toilet, and I shouldn't care whether you know your ass from a hole in the ground or not.
Of course, radio-silent receive is very possible for HF devices -- JUST NOT MICROWAVE DEVICES. YES, THERE'S A DIFFERENCE! And, BTW, ALL transceivers have separate transmit and receive sections.
Since you don't know what a mixer is, it's safe to assume you don't know how one works. Classic. Go find a book, and don't skip the preface.
Your knowledge is non-existent. Your experience is not applicable. It is possible to obtain virtually radio-silent reception in bands other than microwave, but, well, it's just not possible in microwave.
Where do you think this mythical military hardware comes from? Do you think the clouds part once every few months and a new radio transciever is issued forth from God's hands in heaven? The same people who design cell phones (like me) also design military hardware. After all, uh, someone has to.
- Warren
amusing...yes, you see, the HF radios we operated had a separate transmitter and receiver, so it was very possible to turn off the transmitter but still be capable of receiving a signal.
nope, and I really don't care to. I initially posted because you made a blanket statement
that is incorrect to my knowledge and experience. I know for a fact that it is capable to emit no detectable RF signals while still having the capability to receive. And yes, when we were in radio silent mode, even the microwave ovens were not allowed to be used.
You assume that all systems are equal, but this is not so. Do you think your cell phone technology is the same as military grade hardware? I think not.
- Warren
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Joined: Aug 2001
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From: Santa Clara
hecash:
Interesting concept, for sure... but as always, it's the word in quotes that screws everything up... "listen." I'm not sure how you could do this, because even your tuned antenna would be firing off all the time, just on random ambient noise, cosmic background, whatever. You'd have to wait until you get some amount of power indicative of a bona-fide transmitter, and the act of distinguishing random noise from signal would involve some amount of active electronics, which would radiate and give you away.
I'll think about it though, it's an interesting lead.
modifry:
Well put!
- Warren
Interesting concept, for sure... but as always, it's the word in quotes that screws everything up... "listen." I'm not sure how you could do this, because even your tuned antenna would be firing off all the time, just on random ambient noise, cosmic background, whatever. You'd have to wait until you get some amount of power indicative of a bona-fide transmitter, and the act of distinguishing random noise from signal would involve some amount of active electronics, which would radiate and give you away.
I'll think about it though, it's an interesting lead.
modifry:
Well put!
- Warren
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Joined: Aug 2001
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From: Santa Clara
moonpie,
What, you're giving up?? It's ok man. The design techniques for low-frequency and high-frequency communication devices are grotesquely different, and a radar detector has very little in common with your military UHF sets. There's an entire field of weirdo electronics for dealing with GHz range signals.
Perhaps some day soon we'll have truly radio-silent microwave receivers, but they just don't exist right now -- not even in the military. By then, the police will just be using photo-radar, though.
- Warren
What, you're giving up??
It's ok man. The design techniques for low-frequency and high-frequency communication devices are grotesquely different, and a radar detector has very little in common with your military UHF sets. There's an entire field of weirdo electronics for dealing with GHz range signals.Perhaps some day soon we'll have truly radio-silent microwave receivers, but they just don't exist right now -- not even in the military. By then, the police will just be using photo-radar, though.
- Warren
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From: Austin
I thought they were removing the ability to delete your posts on a thread for this reason. Someone or someones have obviously removed their posts making this thread a one sided arguement. Oh well, at least the good information is still here.
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Joined: Aug 2001
Posts: 1,607
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From: Santa Clara
Raptor,
Moonpie removed his own posts, I'd guess, because he was skooled pretty hard. It doesn't really matter anyway. I was kinda hoping Utah S2K would jump in, too, because he needed a good skooling as well.
I did a little of my own research (asking three of the 60+ year old senior engineers and staff scientists here at National Semiconductor, two of whom served in WWII) and I have determined, that, in fact, I was WRONG... or at least partly so.
It is THEORETICALLY possible to create a microwave receiver that does not need a local oscillator. It's actually the simplest kind of radio receiver, but also the most fraught with challenges. The topology is known as TRF (tuned radio frequency), and is constructed from filters and amplifiers specifically tuned for a particular frequency or narrow band of frequencies (it must be narrow because filters and amps that have high Q's also have very un-flat transfer characteristics, an undesirable trait). You'd also have to clean it heavily with active filters to prevent any of the amplifier's distortions from back-feeding to the antenna. The active filters themselves might also do a little of their own backfeeding, so you'll end up cleaning up the cleaners that are cleaning up the amplifiers, ad infinitum.
Now, because of the way TRFs work, you'd have to have one complete receiver for each radar band (so you'd need, at a minimum, three). Two of the engineers got into an argument about using one or three antennas, and eventually both decided that one antenna would almost certainly have resonant properties with one or more of the RF stages, and would be too prone to radiate. The consensus was that three independent, specially designed, tuned antennas would be required.
Then, as we go down the RF pipe, we come to the distinguishing circuitry that attempts to make sense out of the signal, and determine if a radar gun is in use. The act of distinguishing modulation characteristics with PLLs, frequency counters, and other devices was considered, but all of them would have their own harmonic radiation. The engineers, in over an hour of discussion (yes, on company time!) agreed they didn't know of any kind of distinguishing circuitry that wouldn't radiate something bad. However, even if it did radiate, it'd be anybody's guess WHAT it would radiate, so the cops probably couldn't go hunting for it like they can for superheterodyne models, which have a distinct, standard emission.
So it IS possible to make a radar detector that doesn't produce LO emission, and therefore is much harder (but NOT IMPOSSIBLE) to detect than the popular superheterodyne models on the market now. BUT, there are a tremendous number of problems with the whole affair, listed below:
1) It would be enormous (one engineer commented it might have to have its own trailer).
2) It would require very frequent retunings and trims to keep it functioning (many RF components have significant drift with time, temperature, or humidity).
3) It would draw several thousand watts.
4) The myriad of necessary custom-designed inductors alone would probably cost ten thousand dollars.
5) It still wouldn't be radio silent... just... radio polite.
- Warren
Moonpie removed his own posts, I'd guess, because he was skooled pretty hard. It doesn't really matter anyway. I was kinda hoping Utah S2K would jump in, too, because he needed a good skooling as well.
I did a little of my own research (asking three of the 60+ year old senior engineers and staff scientists here at National Semiconductor, two of whom served in WWII) and I have determined, that, in fact, I was WRONG... or at least partly so.
It is THEORETICALLY possible to create a microwave receiver that does not need a local oscillator. It's actually the simplest kind of radio receiver, but also the most fraught with challenges. The topology is known as TRF (tuned radio frequency), and is constructed from filters and amplifiers specifically tuned for a particular frequency or narrow band of frequencies (it must be narrow because filters and amps that have high Q's also have very un-flat transfer characteristics, an undesirable trait). You'd also have to clean it heavily with active filters to prevent any of the amplifier's distortions from back-feeding to the antenna. The active filters themselves might also do a little of their own backfeeding, so you'll end up cleaning up the cleaners that are cleaning up the amplifiers, ad infinitum.
Now, because of the way TRFs work, you'd have to have one complete receiver for each radar band (so you'd need, at a minimum, three). Two of the engineers got into an argument about using one or three antennas, and eventually both decided that one antenna would almost certainly have resonant properties with one or more of the RF stages, and would be too prone to radiate. The consensus was that three independent, specially designed, tuned antennas would be required.
Then, as we go down the RF pipe, we come to the distinguishing circuitry that attempts to make sense out of the signal, and determine if a radar gun is in use. The act of distinguishing modulation characteristics with PLLs, frequency counters, and other devices was considered, but all of them would have their own harmonic radiation. The engineers, in over an hour of discussion (yes, on company time!) agreed they didn't know of any kind of distinguishing circuitry that wouldn't radiate something bad. However, even if it did radiate, it'd be anybody's guess WHAT it would radiate, so the cops probably couldn't go hunting for it like they can for superheterodyne models, which have a distinct, standard emission.
So it IS possible to make a radar detector that doesn't produce LO emission, and therefore is much harder (but NOT IMPOSSIBLE) to detect than the popular superheterodyne models on the market now. BUT, there are a tremendous number of problems with the whole affair, listed below:
1) It would be enormous (one engineer commented it might have to have its own trailer).
2) It would require very frequent retunings and trims to keep it functioning (many RF components have significant drift with time, temperature, or humidity).
3) It would draw several thousand watts.
4) The myriad of necessary custom-designed inductors alone would probably cost ten thousand dollars.
5) It still wouldn't be radio silent... just... radio polite.
- Warren