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#8
August 31st 06, 05:01 PM
posted to rec.radio.shortwave
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Newbie - Just Purchased Etón E5
"Telamon" wrote in message ... In article , geeman wrote: "Telamon" wrote in message ... --Major Snippage of Previous Post-- The word band has a different meaning depending on context. When speaking about SSB, USB, LSB the inference is a range of frequencies below (LSB) and above (USB) a stations carrier frequency. This range of frequency is defined by the information that modulates the carrier and so it is a small range of a few kilohertz wide. Here USB and LSB are the sidebands of the carrier. When speaking about a range of frequencies that by regulation are used for a specific purpose such as aeronautical communications is a wider range of frequencies that will accommodate many carriers or stations and is more like 100 to 500 kilohertz in width. Stations that broadcast in SSB mode usually only modulate one sideband upper or lower. If your radios has a switch for USB / LSB then you will have to pick the correct sideband to hear it. If your radio does not have that switch you just turn the BFO control in one direction for USB and turn it in the other direction for LSB. -- Telamon Ventura, California You took the words right out of my mouth. : 0 Seriously, band in my example was your second definition specifically the 3400 to 3500 kHz frequency range. So, is it accurate to say with my unit, which only has a button to switch to SSB, I need only select SSB, start tuning, get a decent signal and turn the BFO up (USB) or down (LSB) to resolve the transmission? When you say BFO, am I wrong in thinking you're simply referring to the "Fine Tuning" dial I have on my unit which must adjust in finer increments (frequency readout does not change but differences in audio can be heard) than the Tuning dial itself (1 kHz increments)? Otherwise I don't know what BFO is. I looked it up and "beat frequency oscillator" seems to be a way to resolve an audio frequency signal for a carrier wave (a fancy way of saying tuner?). - If I am out of the official AM band (540 kHz-1700 kHz) should I always be in SSB? - What is the effect of the Wide vs Narrow switch and when should you use either? The manual that comes with the unit bascially identifies these controls but not necessarily their effect on reception. Sorry about all the newbie questions. I learned a ton just looking up BFO and the related references in different places so thanks for that one even if I didn't get it. I like to understand things which is why I started this damn note two hours ago and am just now finishing! The detector in most portable radios requires a carrier to demodulate the audio. AM is amplitude modulation that has this carrier along with the audio side bands (both upper and lower). SSB (usually just one side band) generally does not have a carrier so the radio needs a replacement for the missing carrier and that is the BFO, which is a local oscillator that you tune that "beats" or mixes with the incoming side band signal allowing it to be detected. Tuning this BFO is not a fine tuning operation but adjusting the local oscillator to what the carrier would be if it was present. The wide and narrow filter selection usually has to do with whether the signal you want to hear is far from other strong signals. The wider filter will allow a wider and higher range of audio frequencies to be heard in AM mode. Use the narrow filter when a near by channel is causing interference in AM mode. SSB uses a narrower range of audio frequencies so the wider filter will not make the signal sound better and just allow more noise into the audio making it harder to hear what is being said. So in AM mode you normally use the wide filter and in SSB mode you usually use the narrow filter. This wide / narrow filter selection is the final gate of a range of frequencies that get passed on to the audio stage in the radio. Tuning moves this range of a few kilohertz through the range of 500 KHz to 30,000 KHz on most radios. Short wave covers 2,300 to 30,000 KHz and consists of many band segments. There are 14 international broadcast bands that are with few exceptions AM modulated just like the regular AMBCB band you know about. There are a number of ham bands and they have digital, CW and SSB modes of transmission. There are bands for utilities, air craft, marine and military. If it is a person to person voice communication then it is usually SSB mode and if it is an international broadcast then it is usually AM mode. -- Telamon Ventura, California Thanks! |
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