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What does sync lock do?
Just wondering, as no one explains what it does or how it works.
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"atomicthumbs" ) writes: Just wondering, as no one explains what it does or how it works. An AM signal has a carrier and two sidebands. The sidebands carry the actual content (and they are identical, meaning only one is necessary) while the carrier just goes along for the ride. But at the receiver end, the carrier is needed to beat with the sidebands to translate the modulation from RF back down to audio. (Imagine a 10MHz signal, with a 1KHz tone modulating it. There's a sideband at 10.001MHz and one at 9.999MHz, plus the carrier at 10MHz. Mix the 10.001MHz signal with the 10MHz carrier at the receiver and you get the 1KHz signal out of the speaker again.) Due to propagation, there are times when the carrier can fade more than the sidebands, so it's too weak to properly demodulate the signal. You end up with a distorted signal. Synchronous detection uses a locally generated signal in the receiver to beat against the sidebands to translate them back to audio. Since this local "carrier" is nice and strong, it can never be too weak in reference to the incoming sidebands. The signal may be weak, but it won't be distorted. The problem, though, is that this local "carrier" has to be right at the spot halfway between the sidebands. An obvious reason is that if it's mistuned, you will hear a beat note between the signal's carrier and the local "carrier". A constant and obnoxious tone in your ear. But more important, if that local "carrier" is not right in the middle, the sidebands will not translate to the same audio frequency. WIth that previous example, both the upper (10.001KHz ) and the lower (9.999KHz) sidebands both translate to 1KHz because the carrier is right in the middle. But if this locally generated "carrier" is not right in the middle, one sideband would translate to 1.1KHz and 990Hz, for example. You've not only got them translated to the wrong frequency, but you suddenly have two frequencies instead of one at audio. It will sound horrible. This is where the "synch" comes in. There is circuitry in the receiver to lock this local "carrier" to the incoming signal. The incoming signal includes enough information so that exact middle point between the sidebands can be determined, and this synchronization ensures that this local "carrier" is set to that frequency. The sidebands translate to the correct audio frequency, and everything is well. If there is no lock of this local "carrier" then the modulating signals do not translate to the correct audio frequencies. And as a side issue, once you have this circuitry in place, it doesn't take all that much more to allow selectable sideband. Since both sidebands carry identical information, only one is needed to recover the modulation. With the right circuitry, the receiver can select which of these redundant sidebands are used, so if one has some interference, the other one may not and selecting that one will mean the listener will not hear the interference. Michael |
Wow, excellent description, thanks.
Mark. Auckland New Zealand. "Michael Black" wrote in message ... "atomicthumbs" ) writes: Just wondering, as no one explains what it does or how it works. An AM signal has a carrier and two sidebands. The sidebands carry the actual content (and they are identical, meaning only one is necessary) while the carrier just goes along for the ride. But at the receiver end, the carrier is needed to beat with the sidebands to translate the modulation from RF back down to audio. (Imagine a 10MHz signal, with a 1KHz tone modulating it. There's a sideband at 10.001MHz and one at 9.999MHz, plus the carrier at 10MHz. Mix the 10.001MHz signal with the 10MHz carrier at the receiver and you get the 1KHz signal out of the speaker again.) Due to propagation, there are times when the carrier can fade more than the sidebands, so it's too weak to properly demodulate the signal. You end up with a distorted signal. Synchronous detection uses a locally generated signal in the receiver to beat against the sidebands to translate them back to audio. Since this local "carrier" is nice and strong, it can never be too weak in reference to the incoming sidebands. The signal may be weak, but it won't be distorted. The problem, though, is that this local "carrier" has to be right at the spot halfway between the sidebands. An obvious reason is that if it's mistuned, you will hear a beat note between the signal's carrier and the local "carrier". A constant and obnoxious tone in your ear. But more important, if that local "carrier" is not right in the middle, the sidebands will not translate to the same audio frequency. WIth that previous example, both the upper (10.001KHz ) and the lower (9.999KHz) sidebands both translate to 1KHz because the carrier is right in the middle. But if this locally generated "carrier" is not right in the middle, one sideband would translate to 1.1KHz and 990Hz, for example. You've not only got them translated to the wrong frequency, but you suddenly have two frequencies instead of one at audio. It will sound horrible. This is where the "synch" comes in. There is circuitry in the receiver to lock this local "carrier" to the incoming signal. The incoming signal includes enough information so that exact middle point between the sidebands can be determined, and this synchronization ensures that this local "carrier" is set to that frequency. The sidebands translate to the correct audio frequency, and everything is well. If there is no lock of this local "carrier" then the modulating signals do not translate to the correct audio frequencies. And as a side issue, once you have this circuitry in place, it doesn't take all that much more to allow selectable sideband. Since both sidebands carry identical information, only one is needed to recover the modulation. With the right circuitry, the receiver can select which of these redundant sidebands are used, so if one has some interference, the other one may not and selecting that one will mean the listener will not hear the interference. Michael |
"Michael Black" wrote in message ... "atomicthumbs" ) writes: Just wondering, as no one explains what it does or how it works. An AM signal has a carrier and two sidebands. The sidebands carry the actual content (and they are identical, meaning only one is necessary) while the carrier just goes along for the ride. But at the receiver end, the carrier is needed to beat with the sidebands to translate the modulation from RF back down to audio. (Imagine a 10MHz signal, with a 1KHz tone modulating it. There's a sideband at 10.001MHz and one at 9.999MHz, plus the carrier at 10MHz. Mix the 10.001MHz signal with the 10MHz carrier at the receiver and you get the 1KHz signal out of the speaker again.) Due to propagation, there are times when the carrier can fade more than the sidebands, so it's too weak to properly demodulate the signal. You end up with a distorted signal. Synchronous detection uses a locally generated signal in the receiver to beat against the sidebands to translate them back to audio. Since this local "carrier" is nice and strong, it can never be too weak in reference to the incoming sidebands. The signal may be weak, but it won't be distorted. The problem, though, is that this local "carrier" has to be right at the spot halfway between the sidebands. An obvious reason is that if it's mistuned, you will hear a beat note between the signal's carrier and the local "carrier". A constant and obnoxious tone in your ear. But more important, if that local "carrier" is not right in the middle, the sidebands will not translate to the same audio frequency. WIth that previous example, both the upper (10.001KHz ) and the lower (9.999KHz) sidebands both translate to 1KHz because the carrier is right in the middle. But if this locally generated "carrier" is not right in the middle, one sideband would translate to 1.1KHz and 990Hz, for example. You've not only got them translated to the wrong frequency, but you suddenly have two frequencies instead of one at audio. It will sound horrible. This is where the "synch" comes in. There is circuitry in the receiver to lock this local "carrier" to the incoming signal. The incoming signal includes enough information so that exact middle point between the sidebands can be determined, and this synchronization ensures that this local "carrier" is set to that frequency. The sidebands translate to the correct audio frequency, and everything is well. If there is no lock of this local "carrier" then the modulating signals do not translate to the correct audio frequencies. And as a side issue, once you have this circuitry in place, it doesn't take all that much more to allow selectable sideband. Since both sidebands carry identical information, only one is needed to recover the modulation. With the right circuitry, the receiver can select which of these redundant sidebands are used, so if one has some interference, the other one may not and selecting that one will mean the listener will not hear the interference. Michael Then, why do they have double sideband on some rigs like the Lowe HF-150? What purpose does double sideband serve and what is it's benefits? Stronger lock?? Lucky |
Lucky wrote: "Michael Black" wrote in message ... "atomicthumbs" ) writes: Just wondering, as no one explains what it does or how it works. An AM signal has a carrier and two sidebands. The sidebands carry the actual content (and they are identical, meaning only one is necessary) while the carrier just goes along for the ride. But at the receiver end, the carrier is needed to beat with the sidebands to translate the modulation from RF back down to audio. (Imagine a 10MHz signal, with a 1KHz tone modulating it. There's a sideband at 10.001MHz and one at 9.999MHz, plus the carrier at 10MHz. Mix the 10.001MHz signal with the 10MHz carrier at the receiver and you get the 1KHz signal out of the speaker again.) Due to propagation, there are times when the carrier can fade more than the sidebands, so it's too weak to properly demodulate the signal. You end up with a distorted signal. Synchronous detection uses a locally generated signal in the receiver to beat against the sidebands to translate them back to audio. Since this local "carrier" is nice and strong, it can never be too weak in reference to the incoming sidebands. The signal may be weak, but it won't be distorted. The problem, though, is that this local "carrier" has to be right at the spot halfway between the sidebands. An obvious reason is that if it's mistuned, you will hear a beat note between the signal's carrier and the local "carrier". A constant and obnoxious tone in your ear. But more important, if that local "carrier" is not right in the middle, the sidebands will not translate to the same audio frequency. WIth that previous example, both the upper (10.001KHz ) and the lower (9.999KHz) sidebands both translate to 1KHz because the carrier is right in the middle. But if this locally generated "carrier" is not right in the middle, one sideband would translate to 1.1KHz and 990Hz, for example. You've not only got them translated to the wrong frequency, but you suddenly have two frequencies instead of one at audio. It will sound horrible. This is where the "synch" comes in. There is circuitry in the receiver to lock this local "carrier" to the incoming signal. The incoming signal includes enough information so that exact middle point between the sidebands can be determined, and this synchronization ensures that this local "carrier" is set to that frequency. The sidebands translate to the correct audio frequency, and everything is well. If there is no lock of this local "carrier" then the modulating signals do not translate to the correct audio frequencies. And as a side issue, once you have this circuitry in place, it doesn't take all that much more to allow selectable sideband. Since both sidebands carry identical information, only one is needed to recover the modulation. With the right circuitry, the receiver can select which of these redundant sidebands are used, so if one has some interference, the other one may not and selecting that one will mean the listener will not hear the interference. Michael Then, why do they have double sideband on some rigs like the Lowe HF-150? What purpose does double sideband serve and what is it's benefits? No real benefit compared to sideband selectable sync, other than the fact that you have sync. Take for example the R8 and R8A, they both have sync on both sidebands at once, compared to the better sideband selectable sync on the R8B. dxAce Michigan USA |
Thanx!
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"atomicthumbs" wrote in
oups.com: Due to people's obsession to possess things that have certain terms affiliated with them (Namely, in this case, Synchronous Detection), allow me to direct you to the following link. Concerning the venerable Icom R-75 with "Synchronous Detection", Radio Netherlands had the following to say: "Spot the Difference with the Sync What is the singular failing of this receiver? In our opinion, there is virtually no difference between synchronous AM and AM reception. The synchronous mode includes both sidebands; there is no option to choose the lower or upper sideband. The Lowe HF-150 synchronous modes and performance are far superior. We urge that ICOM correct the synchronous performance in future models and make available a retrofit ROM available to current customers. Fortunately all is not lost here. As the receiver's SSB reception is quite good, in difficult or crowded band conditions, we simply tune in the appropriate sideband of the desired signal and, if necessary, adjust the PBT controls." http://www2.rnw.nl/rnw/en/features/m...ceivers/icr75b. html As I have diatribed before, using the SSB capabilities of "quality receivers and transceivers" functions similarly to using "Synchronous Detection", or at least the uninformed reviewers at Radio Netherlands seem to think. Yes, you can survive without "Synchronous Detection". Using the Icom R-75 and the Yaesu FRG-100, I do not see any differences worthy of lavishing attention on the Sync features of the Icom. I will say that in terms of portables, the Sony 7600GR, with the Sync Detection (when the signal levels are sufficient to preclude the ghastly noise that the Sony makes as the Sync Detector locks and losses its lock), is a laudable feature making listening under "some circumstances" much more enjoyable. (avoiding the noise associated with one sideband or the other sometimes provides relief, but it seems that not infrequently the noise the infests one sideband sooner or later manages to infest the other). Oddly enough, in terms of 3.210 and 5.070 MHz, my DX-396 is more sensitive than the Sony, (this is with the antenna extended on the Sony and the antenna collapsed on the DX-396, using it's internal antenna). Of course, since Sony makes the worlds best everything (Remember the obsession to possess things with specific names from the beginning of this post), it must mean that my Sony is defective. Soliloquy. (P.S. to any poster unlucky enough to not have added me to their plonk files, I have filtered this post, please offer all the antagonism that you wish, I won't be here to read it ;-) Just wondering, as no one explains what it does or how it works. |
In article ,
"Dr. Artaud" wrote: Snip (P.S. to any poster unlucky enough to not have added me to their plonk files, I have filtered this post, please offer all the antagonism that you wish, I won't be here to read it ;-) No problem Dr. Plonk -- Telamon Ventura, California |
dxAce wrote:
No real benefit compared to sideband selectable sync, other than the fact that you have sync. Take for example the R8 and R8A, they both have sync on both sidebands at once, compared to the better sideband selectable sync on the R8B. Drake advertises the R8 and R8A as having 'sideband selectable sync' but you have to use the passband offset to select one side or the other. Certainly not as good as the R8B detector. Interestingly the RX-350 (and some other receivers) give you the choice of both sides, lsb or usb. I guess if there is no adjacent interference, the 'both' choice is OK but I still don't see what the benefit is over a choosing the sync with one sideband. -- Brian Denley http://home.comcast.net/~b.denley/index.html |
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