wrapping my head around AM, FM, SSB

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leaf

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Hey all,

I'm new to Radio and am waiting on my BCD396XT in the mail.. and in the meantime, trying to wrap my head around a few concepts, and also messing around with my little Grundig G4...

Wondering if someone can help clarify a couple of things for me, maybe answer a question or two!

1.) The way I am understanding it is that the type of modulation defines how a signal gets "put" onto the carrier wave. So for an AM (or FM) signal, say 770 Khz, there are no "sides", right?. With your receiver you just tune to 770 Khz. Is the carrier wave the same wave that carries the information too? (770 Khz).

2.) WIth SSB, there is the Carrier wave, say 4.0 Mhz, but the information can be heard on the USB or LSB of 4.0 Mhz, therefore you have to tune up or down from the carrier wave. Is this correct??? Seems too simple!

3.) And lastly, when someone says "we will be on 6 meter band tonight", how do we know what that includes? According the the math I have learned from my ARRL book... 300 / 6 meters = 50Mhz....But according to wiki the 6-meter band ranges from 50Mhz-54Mhz. How does one know that this band is 4Mhz wide? The bands that I look up do not all seem to be the same width. (ex: 10m band is from 28-29.7Mhz).

Apologies for the long thread, but any info would really help!!! I plan on messing with my 396XT for a while and then becoming a HAM like you guys in the future :)

Thanks,
leaf
 

lep

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How do I know how wide the bands are? I memorize them. And another 'fact' to recognize is that the width of the allocation depends on the country one is in. For example, in the USA the 2 meter band is 144 to 148 MHz but in most European countries it is only 144-146 MHz. After doing it for a while it just seems second nature to have these rather obscure facts at your finger tip.

good luck.
 

QDP2012

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Welcome to RR,
Ok, scratch the first 2 questions....Still very curious about the third one though if anyone can clarify..

3.) And lastly, when someone says "we will be on 6 meter band tonight", how do we know what that includes? According the the math I have learned from my ARRL book... 300 / 6 meters = 50Mhz....But according to wiki the 6-meter band ranges from 50Mhz-54Mhz. How does one know that this band is 4Mhz wide? The bands that I look up do not all seem to be the same width. (ex: 10m band is from 28-29.7Mhz).

The answer to your question has several parts:
  • Band-boundaries: The FCC establishes the frequency boundaries in which a given radio-service is permitted to transmit. Using your question, the FCC allocated 50-54 mHz for Ham. That choice was an administrative one. To earn your amateur radio operator's license, you will simply memorize the appropriate boundaries for your license-level's permitted bands.

  • Band-Nicknames: For convenience, the bands are often referenced by short-name of 10m (ham), 11m (CB), 6m (ham), 2m (ham), etc. The band-name "6m" or "6 meters" is just a convenient way of describing the approximate location in the radio spectrum, and does itself not specify which radio service is authorized for that band or for a specific frequency-range in that band.

  • Antenna-length calculations: To do actual antenna-length calculations, please use the following equation. There are other antenna-references, including other Antenna forums on this site with much more detail about how to choose or configure the antenna best suited for your circumstance(s).

    • In general, the base-equation used to convert between frequency and wavelength is:
      • (freq in Hz)(wavelength in meters) = (speed of light in meters/second).

    • The units-of-measure matter, To use the above equation, be sure to convert inches, etc. to meters

    • A calculation-example, found in this other thread, is regarding how long a straight-wire antenna should be.
      • 103.3" is 1/4 wave for 28.58.. MHz = 10.49 m. (Ham band)
      • 108.6" is 1/4 wave for 27.185 MHz = 11.03 m. (CB band)
Hope this helps get you started,
 
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zz0468

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1.) The way I am understanding it is that the type of modulation defines how a signal gets "put" onto the carrier wave. So for an AM (or FM) signal, say 770 Khz, there are no "sides", right?. With your receiver you just tune to 770 Khz. Is the carrier wave the same wave that carries the information too? (770 Khz).

An AM signal on 770 KHz would have a "carrier" (which doesn't actually carry anything), and two sidebands, which are the sum and difference frequencies of the "carrier" and the signal modulating it. So, if you were to put just a 1000 cycle tone on the transmitter, that transmitter would be outputting out 3 separate signals - one on 769 KHz (the lower sideband), 770 KHz (the carrier) and 771 KHz (the upper sideband). These are called "sidebands". Put voice and music on instead of a single tone, and complicate the situation according to taste.

2.) WIth SSB, there is the Carrier wave, say 4.0 Mhz, but the information can be heard on the USB or LSB of 4.0 Mhz, therefore you have to tune up or down from the carrier wave. Is this correct??? Seems too simple!

With SSB, filter out one of the AM sidebands, and what's left is single sideband. Note you still have a carrier, which STILL doesn't actually carry anything. For single sideband suppressed carrier (just SSB for short), you also have to filter out the carrier. Do this at a low power level in the transmitter, and you don't have to waste a huge amount of power suppressing the carrier and unwanted sideband. You then just amplify the single sideband.

3.) And lastly, when someone says "we will be on 6 meter band tonight", how do we know what that includes?

The "meter" wavelength designations for the various ham bands are meant to represent the whole band, not a specific frequency. So, it becomes understood when someone says "meet me on 6 meters", they mean the 50-54 MHz ham band. You then need to ask them "what frequency", or else you need to search the full band.


Apologies for the long thread, but any info would really help!!! I plan on messing with my 396XT for a while and then becoming a HAM like you guys in the future :)

Well, cool. At this stage of the game, the only stupid question is the one not asked. =)
 

LtDoc

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By definition, a SSB signal has no carrier, it's only one of the side bands being transmitted (upper or lower). The carrier is put back and the received SSB signal is applied to it in the receiver, then it is converted to audio/sound that you hear.
There's also a DSB or double side band signal, both side bands still there and only the carrier removed. And there's a single or double side band signal with a suppressed carrier, the carrier isn't completely removed.
And then, a SSB signal is still an amplitude modulated type signal, it just has part(s) of the typical 'AM' signal removed. The name, SSB/USB/LSB/DSB distinguishes it from a 'complete' AM signal.
Confused yet??
- 'Doc
 

leaf

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Confused yet??
- 'Doc
Nope, Think I got it! Thanks...

Welcome to RR,

The answer to your question has several parts:
  • Band-boundaries: The FCC establishes the frequency boundaries in which a given radio-service is permitted to transmit. Using your question, the FCC allocated 50-54 mHz for Ham. That choice was an administrative one. To earn your amateur radio operator's license, you will simply memorize the appropriate boundaries for your license-level's permitted bands.

  • Band-Nicknames: For convenience, the bands are often referenced by short-name of 10m (ham), 11m (CB), 6m (ham), 2m (ham), etc. The band-name "6m" or "6 meters" is just a convenient way of describing the approximate location in the radio spectrum, and does itself not specify which radio service is authorized for that band or for a specific frequency-range in that band.


  • Ok, this makes more sense now. I was looking for some mathematical/physics reasoning, but I guess it's just the way it's been allocated.. Sounds good :)

    An AM signal on 770 KHz would have a "carrier" (which doesn't actually carry anything), and two sidebands, which are the sum and difference frequencies of the "carrier" and the signal modulating it. So, if you were to put just a 1000 cycle tone on the transmitter, that transmitter would be outputting out 3 separate signals - one on 769 KHz (the lower sideband), 770 KHz (the carrier) and 771 KHz (the upper sideband). These are called "sidebands". Put voice and music on instead of a single tone, and complicate the situation according to taste.

    OK... Is this why on an AM broadcast I can tune into 770Khz and hear the station, but I can also tune to 771Khz and 769Khz and still hear the same station, but just faintly or slightly distorted? Then when I tune to 770Khz I am hearing the sum of those 2 sides...??


    Thanks for all the great links and help guys. Such an awesome community so far.. Getting my BCD396XT in the mail tomorrow and I really want to try to hear some ham's communicating. Any suggestions for what meter band I should try first? I am in Queens, NY. I am also going to try to take it to this guy:
    http://www.nytimes.com/2011/10/30/nyregion/peter-guggenheims-life-of-fixing-radio-scanners.html?_r=0
    I'm hoping he can program all freq's in there for me :)

    -leaf
 

QDP2012

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...I was looking for some mathematical/physics reasoning, but I guess it's just the way it's been allocated...
In general, the base-equation used to convert between frequency and wavelength is:
  • (freq in Hz)(wavelength in meters) = (speed of light in meters/second).
The above equation can be rearranged as:
  • (wavelength in meters) = (speed of light in meters/second)./ (freq in Hz)
As you probably noticed already, the names "2m", "6m", "10m", etc. are based directly upon the calculations for a given frequency using the above equation.

The administrative choices regarding which radio-service is permitted to transmit in those bands is based on other factors, like which service should have priority (i.e. military/federal over civilian/business), which service is most benefitted by how a certain band propagates over certain terrain (HF vs VHF vs UHF vs microwave), or how a band-plan can be made most efficient (i.e. the NexTel-sponsored rebanding of the 800mHz frequency-block), etc.

...I really want to try to hear some ham's communicating. Any suggestions for what meter band I should try first? I am in Queens, NY....

I am not familiar with repeaters in that area, but as a place to start, you might try browsing the RRDB's NY Amateur page and visit the NY forums and the Amateur Radio forums.

Hope this helps,
 
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zz0468

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OK... Is this why on an AM broadcast I can tune into 770Khz and hear the station, but I can also tune to 771Khz and 769Khz and still hear the same station, but just faintly or slightly distorted?

What you're seeing there is mostly an artifact of the receiver IF bandwidth, which would be about 10 KHz wide. So, when you're dialed in to 770 KHz, what you're actually doing is listening to a window 10 KHz wide, centered on 770 KHz. As you tune off, one way or another, the signal starts to run into the edge of the filters in the receiver, and starts to distort.

Then when I tune to 770Khz I am hearing the sum of those 2 sides...??

Yes.
 
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