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#1
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Am Station On USB Also ?
Hi,
Let's say I pick up a regular HF shortwave station on AM. Should I also be able to hear this same station on USB ? If so, what would the freq. "offset" that I should increase the tuned freq. to ? Should I expect the USB freq to be clearer, or... ? Thanks, B. |
#2
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Am Station On USB Also ?
"Robert11" wrote in message ... Hi, Let's say I pick up a regular HF shortwave station on AM. Should I also be able to hear this same station on USB ? If so, what would the freq. "offset" that I should increase the tuned freq. to ? Should I expect the USB freq to be clearer, or... ? Thanks, B. yes you can listen to AM on USB by slope detecting the frequency would be 1.5khz higher than the AM frequency the audio might sound clearer as the IF filters on USB would normally be narrower than when on AM |
#3
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Am Station On USB Also ?
"Robert11" wrote in message ... Hi, Let's say I pick up a regular HF shortwave station on AM. Should I also be able to hear this same station on USB ? Yes, and also on LSB. If so, what would the freq. "offset" that I should increase the tuned freq. to ? No frequency offset. You should be able to zero beat the AM carrier at it's exact frequency. Should I expect the USB freq to be clearer, or... ? That depends on the stability of your receiver, and the quality of the product detector for the SSB signals. It will often be a bit muddier because the filters used for true SSB are narrower than those used for AM, thus less high frequency audio. |
#4
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Am Station On USB Also ?
john wrote: "Robert11" wrote in message ... Hi, Let's say I pick up a regular HF shortwave station on AM. Should I also be able to hear this same station on USB ? If so, what would the freq. "offset" that I should increase the tuned freq. to ? Should I expect the USB freq to be clearer, or... ? Thanks, B. yes you can listen to AM on USB by slope detecting the frequency would be 1.5khz higher than the AM frequency the audio might sound clearer as the IF filters on USB would normally be narrower than when on AM Should be able to zero beat right to the frequency. I think you are confusing the use of 'slope detection' to copy an FM signal with an AM detector. dxAce Michigan USA |
#5
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Am Station On USB Also ?
"dxAce" wrote in message ... john wrote: "Robert11" wrote in message ... Hi, Let's say I pick up a regular HF shortwave station on AM. Should I also be able to hear this same station on USB ? If so, what would the freq. "offset" that I should increase the tuned freq. to ? Should I expect the USB freq to be clearer, or... ? Thanks, B. yes you can listen to AM on USB by slope detecting the frequency would be 1.5khz higher than the AM frequency the audio might sound clearer as the IF filters on USB would normally be narrower than when on AM Should be able to zero beat right to the frequency. I think you are confusing the use of 'slope detection' to copy an FM signal with an AM detector. dxAce Michigan USA True slope detection can be used on FM signals not SSB It is really Single SideBand - Suppressed Carrier For SSB the carrier which was suppressed when transmitted has to be re-inserted (function of a BFO), modern receivers with USB and LSB mode selection will insert the carrier automatically. Then with careful tuning in the USB mode on modern receivers -- it should sound very clear. Also one can switch to LSB and get the same result That is the intellegence is contained in BOTH the upper and lower sideband of an AM signal. Try this -- go to WWV at 10MHz with receiver set to AM, then switch to USB, then LSB With very careful tuning, the USB and LSB and AM signal will sound nearly the same depending on filtering. No offset is required if you tuned "dead on" to the AM signal CL |
#6
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Am Station On USB Also ?
On Thu, 10 Nov 2005 17:47:19 -0500, "Robert11"
wrote: Hi, Let's say I pick up a regular HF shortwave station on AM. Should I also be able to hear this same station on USB ? If so, what would the freq. "offset" that I should increase the tuned freq. to ? Should I expect the USB freq to be clearer, or... ? Thanks, B. On some radios it works real well. On others, not so good. Unless you have a true communications receiver the tuning steps are often too crude to resove proper pitch. Makes music sound especially weird. (Back to that non-linear active device again). |
#7
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Am Station On USB Also ?
"Robert11" wrote in message ... Hi, Let's say I pick up a regular HF shortwave station on AM. Should I also be able to hear this same station on USB ? If so, what would the freq. "offset" that I should increase the tuned freq. to ? Should I expect the USB freq to be clearer, or... ? Thanks, B. You can receive the AM signal on both USB and LSB. This is a good technique to remember as listening to one sideband is not so prone to selective fading or phase distortion of the carrier. It is also useful when trying to listen to AM stations 5KHz apart. Often you can tune to one or other of the sidebands and listen to a clear signal, while the other sideband is being interefered with by the adjacent station. The sideband filter usually has a narrower bandwidth. This is not a hi fi method, but it is excellent for identifying weaker signals. Some stations do transmit on SSB only. AFRS is on 10320khz from Hawaii in my afternoons, with a very strong USB signal. Brad. |
#8
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Am Station On USB Also ?
"Michael Black" wrote in message ... "Robert11" ) writes: Hi, Let's say I pick up a regular HF shortwave station on AM. Should I also be able to hear this same station on USB ? If so, what would the freq. "offset" that I should increase the tuned freq. to ? Should I expect the USB freq to be clearer, or... ? Thanks, B. An AM signal consists of two sidebands, upper and lower, which are mirror images of each other, and a carrier (a constant level signal) right in the middle of the two sidebands. A single sideband transmitter removes one of the sidebands before the signal leaves the transmitter. Usually, it removes the carrier too, though there are some specific cases where they send the carrier along. If you tune the AM signal with a sideband receiver, then you are removing the redundant sideband in the receiver. The narrow filter will slice off the unwanted sideband. And usually, you also knock out the carrier, which in effect gives you a single sideband signal with no carrier inside the receiver. The rest of the receiver thinks it is an SSB signal, the same as if that's what had been sent by the transmitter. But since two sidebands with exactly the same content were sent, you can switch the receiver between upper and lower sideband, selecting whichever of the two sidebands is in better shape. If the receiver was taking in the full AM signal, if one of the sidebands had interference, you'd hear it and be unable to do anything about it. Michael Strictly speaking both the "AM" signal and the "SSB" signal are AM (Amplitude Modulation). The common usage of the term "AM" (other than referring to the MW broadcast band in North America) means DSB-AM (Double Side Band Amplitude Modulation) with carrier. Likewise, "SSB" commonly means SSBSC-AM (Single Side Band Suppressed Carrier Amplitude Modulation). There is also DSBSC-AM (DSB suppressed carrier is pretty rare on hf but used for the L-R channel in the multiplex for FM stereo and also written as DSSC) and SSB with carrier (not sure of the mnemonic). Between full carrier and suppressed or nearly zero carrier is the reduced carrier mode, i.e., DSBRC and SSBRC. The Canadian time signal transmissions on 3330 and 7330? kHz are USBRC-AM (Upper Side....). To answer "what would the freq. "offset" that I should increase the tuned freq.?" depends on your receiver design and, in some cases, settings that you make. For example, my DX-394 (correctly aligned and tuned to the station's frequency) needs no retuning to switch between AM (DSB), LSB and USB modes. That's because the microcontroller behind the front panel controls makes the necessary shifts in the 1st and 2nd Local Oscillators and the selection or not of one of two Beat Frequency Oscillator frequencies. This is not true of simpler receiver designs. Simpler radios may have a variable BFO and no automatic tuning. In this case, you would tune higher than the station's frequency by approximately 1/2 the passbandwidth of your IF filter to suppress the lower sideband and adjust the BFO frequency until the beat note from the carrier was near zero frequency at which the pitch of speech and music should sound right with least distortion. To select the lower sideband, you would tune lower than station freq by the same amount and readjust the BFO. My Kaito-Degen 1103 lies between the simpler radio and the DX-394. While microprocessor controlled, it does no auto tuning in SSB mode and provides no direct selection of Lower and Upper sidebands. While it has a pretty decent (for a cheap radio) narrow filter (narrower than the DX-394's!), when the radio is tuned to display the station frequency, that filter is centred on the carrier and equal amounts are passed from both sidebands. The BFO is adjustable over a range slightly larger than +/-1kHz and the main tuning tunes in 1 kHz steps so you can get some sideband suppression by tuning 1 kHz higher or lower and adjusting the BFO for zero beat/clearest signal. Off-tuning by 2kHz would be a better fit to the filter but is beyond the range of the BFO. Were it to have that range on such a small control, it would be twice as hard as the already touchiness to get close to zero beat. The DX-394 does not have an adjustable BFO; without modification, it can be off zero beat by a few tens of Hz. Receiving a DSB-AM signal with the radio in SSB mode is also known as ECSS, Exalted Carrier Selectable Sideband, and can be advantageous in reducing the effects of fading, as well as interference in the suppressed sideband. But it requires a continuously variable BFO with stable transmitter frequency and receiver oscillators to attain near zero beat for best enjoyment. That leads to automatic means of zero beating - and that's a whole other topic called Sync-AM (or Synch-AM) - join http://groups.yahoo.com/group/Synch_AM/ for more. Tom |
#9
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Am Station On USB Also ?
I think you are making this a bit more complicated than necessary. The
easiest way to keep track of AM and DSB is to look at the signal flow diagrams. If you feed an audio signal with a DC offset into a mixer, you get AM. If there is no DC offset, you get DSB. Tom Holden wrote: "Michael Black" wrote in message ... "Robert11" ) writes: Hi, Let's say I pick up a regular HF shortwave station on AM. Should I also be able to hear this same station on USB ? If so, what would the freq. "offset" that I should increase the tuned freq. to ? Should I expect the USB freq to be clearer, or... ? Thanks, B. An AM signal consists of two sidebands, upper and lower, which are mirror images of each other, and a carrier (a constant level signal) right in the middle of the two sidebands. A single sideband transmitter removes one of the sidebands before the signal leaves the transmitter. Usually, it removes the carrier too, though there are some specific cases where they send the carrier along. If you tune the AM signal with a sideband receiver, then you are removing the redundant sideband in the receiver. The narrow filter will slice off the unwanted sideband. And usually, you also knock out the carrier, which in effect gives you a single sideband signal with no carrier inside the receiver. The rest of the receiver thinks it is an SSB signal, the same as if that's what had been sent by the transmitter. But since two sidebands with exactly the same content were sent, you can switch the receiver between upper and lower sideband, selecting whichever of the two sidebands is in better shape. If the receiver was taking in the full AM signal, if one of the sidebands had interference, you'd hear it and be unable to do anything about it. Michael Strictly speaking both the "AM" signal and the "SSB" signal are AM (Amplitude Modulation). The common usage of the term "AM" (other than referring to the MW broadcast band in North America) means DSB-AM (Double Side Band Amplitude Modulation) with carrier. Likewise, "SSB" commonly means SSBSC-AM (Single Side Band Suppressed Carrier Amplitude Modulation). There is also DSBSC-AM (DSB suppressed carrier is pretty rare on hf but used for the L-R channel in the multiplex for FM stereo and also written as DSSC) and SSB with carrier (not sure of the mnemonic). Between full carrier and suppressed or nearly zero carrier is the reduced carrier mode, i.e., DSBRC and SSBRC. The Canadian time signal transmissions on 3330 and 7330? kHz are USBRC-AM (Upper Side....). To answer "what would the freq. "offset" that I should increase the tuned freq.?" depends on your receiver design and, in some cases, settings that you make. For example, my DX-394 (correctly aligned and tuned to the station's frequency) needs no retuning to switch between AM (DSB), LSB and USB modes. That's because the microcontroller behind the front panel controls makes the necessary shifts in the 1st and 2nd Local Oscillators and the selection or not of one of two Beat Frequency Oscillator frequencies. This is not true of simpler receiver designs. Simpler radios may have a variable BFO and no automatic tuning. In this case, you would tune higher than the station's frequency by approximately 1/2 the passbandwidth of your IF filter to suppress the lower sideband and adjust the BFO frequency until the beat note from the carrier was near zero frequency at which the pitch of speech and music should sound right with least distortion. To select the lower sideband, you would tune lower than station freq by the same amount and readjust the BFO. My Kaito-Degen 1103 lies between the simpler radio and the DX-394. While microprocessor controlled, it does no auto tuning in SSB mode and provides no direct selection of Lower and Upper sidebands. While it has a pretty decent (for a cheap radio) narrow filter (narrower than the DX-394's!), when the radio is tuned to display the station frequency, that filter is centred on the carrier and equal amounts are passed from both sidebands. The BFO is adjustable over a range slightly larger than +/-1kHz and the main tuning tunes in 1 kHz steps so you can get some sideband suppression by tuning 1 kHz higher or lower and adjusting the BFO for zero beat/clearest signal. Off-tuning by 2kHz would be a better fit to the filter but is beyond the range of the BFO. Were it to have that range on such a small control, it would be twice as hard as the already touchiness to get close to zero beat. The DX-394 does not have an adjustable BFO; without modification, it can be off zero beat by a few tens of Hz. Receiving a DSB-AM signal with the radio in SSB mode is also known as ECSS, Exalted Carrier Selectable Sideband, and can be advantageous in reducing the effects of fading, as well as interference in the suppressed sideband. But it requires a continuously variable BFO with stable transmitter frequency and receiver oscillators to attain near zero beat for best enjoyment. That leads to automatic means of zero beating - and that's a whole other topic called Sync-AM (or Synch-AM) - join http://groups.yahoo.com/group/Synch_AM/ for more. Tom |
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