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CBblackbeard
| | Posted on Thursday, January 01, 2004 - 6:16 pm: | 
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What is the difference between SSB,USB and LSB?
Also, what is a good radio for someone who wants to talk SSB,USB or LSB but doesn't know alot about radios? I want to buy one for my girlfriend but don't want to spend extra money for features that she will not use. |
Dodgeman
| | Posted on Thursday, January 01, 2004 - 7:18 pm: |
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CBbiackbeard the Uniden Grant LT is a nice radio or the TR 296GK each one 40 ch with usb&lsb. The 296 could be moded with extra ch if you would like to.Copper has both radios I thank the Grant can be moded for extra ch to hope this helps.CEF178 |
Bruce
| | Posted on Thursday, January 01, 2004 - 10:20 pm: |
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A RADIO AM SIGNAL HAS A CARRER A UPPER SIDEBAND ( CARRIER + AUDIO) and a LOWER SIDBAND (CARRER - AUDIO)
you select them by a filter that is only wide enough to pass one at a time..... |
Crafter
| | Posted on Thursday, January 01, 2004 - 11:28 pm: |
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Even a uniden pc122 would work nice and small too. |
Taz
| | Posted on Friday, January 02, 2004 - 12:02 am: |
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what about FM bruce? |
Bruce
| | Posted on Friday, January 02, 2004 - 2:03 am: |
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simply
FM is generated by changing the frequency at a audio rate and the loudness of the audio determins how large the change will be the 2 combinded is the bandwidth of the signal which is why most FM signals are much wider that SSB or AM 16 khz for a standard FM reciver on 2 meters is not uncommon ... there are SKINNY band fm also common its bandwidth is about the same as AM. FM is VERY good in high noise invirements. VERY POOR on skip because of phase distortion. |
Bigbob
| | Posted on Friday, January 02, 2004 - 7:05 am: |
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Cbblackbeard;AM is 2 sidebands plus a carrier,the side bands are superimposed on the carrier,remove the carrier and you have 2 sidebands,USB AND LSB,either one is referred to as a single sideband,ideally the am signal is 3khz wide,think of it as laying in front of you,length is horizontal,and width is vertical,the top half(1.5khz)is USB,the bottom half(1.5khz)is LSB.Take crate paper,the stuff you use to decorate ceilings of rooms for baby showers and wedding showers,lay it out flat that is what a carrier looks like,now twist the paper for hanging,that is what the carrier looks like with an audio tone added to it,it does not get any wider but has an undulating pattern,that is what the signal looks like as AM or ssb AM is twice as wide as ssb,now it gets more complicated than this,but 2600 can explain the difficult stuff better than I,it was explained to me this way by another and makes sense to me ,hope this helps.Bigbob |
Scrapiron63
| | Posted on Friday, January 02, 2004 - 10:46 am: |
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Some of the old sideband radios had double sideband. I think I heard an old double sideband radio a few days ago on channel 38. The guy was on sideband, not AM, but I could tune him on USB and LSB, strange deal. |
Ozzie
| | Posted on Friday, January 02, 2004 - 12:53 pm: |
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Bruce, I think you made an error. Isnt it the frequency of teh modulating audio that determines how much the change is?? |
Pointman
| | Posted on Friday, January 02, 2004 - 1:55 pm: |
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The Grant is a great radio and can be moded for extra channels also. I have a XL for years and it is great on SSB and is simple to operate. |
Crafter
| | Posted on Friday, January 02, 2004 - 2:05 pm: |
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I had one like that scrap years ago. Cant remember what it was called. |
Bruce
| | Posted on Friday, January 02, 2004 - 2:11 pm: |
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regency tried one double sideband can be done with a push-push amp...... heck it works! Another ssb transmitter was was phase tramsmitters like my HT-37 VERY nice but expensive to build no advantage over the 2.1khz filter method |
Bruce
| | Posted on Friday, January 02, 2004 - 4:14 pm: |
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Ozzie
BOTH DO
FM 101
Frequency say 3 khz will give a 3 khz bandwidth also the audio loudness will effect deviation also so you have to figure BOTH for final bandwidth. SO FM is a bit more complex that AM and results in a wider band width..... except for skinny band.
just a quick overview of how the receiver works ..
Now on receive the deviation is decoded as a voltage by passing it through a ballance tuned detector ...nulles at center frequency and gives a output with any change +/- of that frequency also since the change will be a combineion of audio frequency and loudness the voltage will reproduce the original sounds frequency and the loudness of them ...... since noise is amputude not frequency it is not reproduced however a limiter before the detector is used to get rid of the noise ..... the reason once you hit limiting background noise goes way down.
Thats the story.... |
CBblackbeard
| | Posted on Friday, January 02, 2004 - 5:12 pm: |
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Thank you everyone, I'm starting to understand now. Next question is:
what do people mean by "the high side" and "the low side"?
Is SSB a general term for either USB or LSB?
And what would the frequency be for channel 38 LSB? |
Tech8541
| | Posted on Friday, January 02, 2004 - 10:49 pm: |
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blackbeard,
think about your -LEFT- (remember this for later) hand as an a.m. signal. your bird finger is the carrier (all other fingers are down as if you are giving the bird). when you talk your other fingers come up and become the modulated sidebands(usb and lsb). if you take your bird finger out of the equation, you are left with the usb and lsb. now take your thumb and pointer finger out. all you have left is the lsb (pinky and whatever you call that finger beside the pinky). you have no carrier or usb, so it is less than half the bandwidth of a modulated am signal. actually about 40% the size. same goes for usb. |
CBblackbeard
| | Posted on Saturday, January 03, 2004 - 11:10 am: |
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Got it! Now if I decided to go with a TR296 and wanted to talk SSB, all I would have to do is turn the selector switch from AM to SSB? |
Mr_Rf
| | Posted on Saturday, January 03, 2004 - 7:38 pm: |
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Blackbeard, SSB (single sideband) is the general term that refers to LSB (Lower sideband) or USB (upper sideband)
2. Not to be confused with SSB...some CB'ers have their radios modified to include ILLEGAL extra channels both above and below the standard LEGAL 40 channels, sometimes referred to as "High Side" and "Low Side."
3. Channel 38 = 27.385 MHz
See link for complete list (Band G):
http://www.copperelectronics.com/frequency_chart.html |
CBblackbeard
| | Posted on Saturday, January 03, 2004 - 9:07 pm: |
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Thank you Mr. Rf
Would frequency 26.515 MHz and 27.415 MHz be examples of the other ILLEGAL channels you are talking about? |
Bigbob
| | Posted on Sunday, January 04, 2004 - 6:57 am: |
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Yes. |
Tech8541
| | Posted on Monday, January 05, 2004 - 12:16 am: |
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posted by ozzie;
Bruce, I think you made an error. Isnt it the frequency of teh modulating audio that determines how much the change is??
------------------------
tech8541's post;
the amplitude of the audio of the modulating signal determines how much the change is. we'll use narrowband(wideband narrow; 5khz deviation) fm like the police use for an example.
if 30mv of audio into the mic jack gives 5khz of dev., it doesn't matter if the audio in is .5khz or 2.5khz. the rf output will still be modulated at 5khz of deviation. the only difference is that it will be swinging/deviating from 5khz below the carrier to 5khz above the carrier at the rate of the audio applied. so with a .5khz tone it will be deviating from 5khz below the carrier and 5khz above the carrier at .5khz per second. with a 2.5khz tone into the mic the rf output will be deviating +/- 5khz above and below the carrier at 2.5khz per second. both still give your +/- 5khz of deviation.
basically just keep in mind that it is the amplitude/level of the audio that determines the change/deviation, not the freq of the audio.
--------------
and don't get deviation confused with bandwidth. while the carrier above is deviating +/- 5khz above and below the carrier, it is actually taking up 16khz of space/bandwidth due to the sidebands. there will be up to 3 sidebands with the system i used here. when finding bandwidth the audio freq -DOES- determine how much bandwidth the modulated signal takes up. you get the 16khz by finding the deviation ratio (which i can't even remember how to do right now since no one ever uses it) and then putting it into a formula known as carson's rule. for a system that has a max deviation of 2.5khz the overall bandwidth is 11khz. since this never changes you don't need to remember the formulas (that is what books are for), just the answer you get from them.
this also answers why fm is illegal on the 40ch's. even if narrow narrowband fm is used (max dev of 2.5khz) the overall bandwidth is 11khz. the ch. spacing at cb is only 10khz. the ch. spacing would need to be 12.5khz to keep one fm ch from bleeding over onto another. the max dev could be dropped to 2khz dev for cb and this just would get the bandwidth down to 10khz per ch, but then speech compressors and expanders (companders)would be needed or else the rx audio quality would not be great.
i hope this wasn't too confusing because fm can be confusing. |
Mr_Rf
| | Posted on Monday, January 05, 2004 - 6:30 pm: |
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Tech 8541, FYI...
You said: "if 30mv of audio into the mic jack gives 5khz of dev., it doesn't matter if the audio in is .5khz or 2.5khz. the rf output will still be modulated at 5khz of deviation."
This may not always be the case unless the TX mod is modulated into limiting across the entire audio spectrum. 30mV across the the entire audio spectrum may not neccessarily deviated full limiting, especially near 300hz and above 2500hz.
Many FM radios employ limiter circuitry in the TX audio path called "pre-emphasis". This circuit is designed to create a sloped rise in deviation of audio above 300hz and steep fall in deviation for audio above 2500hz when the mic input is driven with a steady input voltage. Attached are actual graphed results of such circuitry. Hope this makes since.
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Crafter
| | Posted on Monday, January 05, 2004 - 7:32 pm: |
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Black Beard 27.385. |
CBblackbeard
| | Posted on Monday, January 05, 2004 - 8:03 pm: |
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I thought it was 27.385 but I wasn't sure. Thanks. |
Tech8541
| | Posted on Wednesday, January 07, 2004 - 12:42 pm: |
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mr. rf you are exactly right. that is why i used .5hz and 2.5khz as my tones in the example (in case someone like you caught it). i did not want to go into audio response and pre-emphasis as it would add to any confusion my post would already make. so my post was as if the audio response was flat (which you and i both know is never the case) and there was no pre-emphasis.
you did a good job of visually showing this with your pictures. your graphs explain this much better than words could. |
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