What is meant by frequecy @ decibel in SSB

[davidv555]

Hello,

I am new to sdr and radio. I use websdr sites to listen to shortwave radio.

In the bandwidth section I see this for SSB

Bandwidth:
2.80 kHz @ -6dB; 3.26 kHz @ -60dB.

What does this mean? What is meant by 2.80 kHz @ -6dB and 3.26 kHz @ -60dB?

I appreciate any feedback. Thanks

 

[majoco]

Welcome to RR - you'll find a heap of information and mainly friendly folks here.

The 'bandwidth' of a radio is a measure of how 'selective' it is and is often just called it's 'selectivity' - how well it can receive the signal you want to hear while rejecting adjacent signals. Without getting too deep, the audio for an SSB signal goes from 300Hz to 2700Hz so you need a "door" at least 2400Hz wide to get best reception but nothing is perfect so the "door" doesn't have vertical sides, they slope outwards at the bottom. "dB's" are too complicated at this time so lets just say that "-6dB" is how wide the 'door' is at half the height and "-60dB" is one fiftieth.

Hope this is helps.

 

[davidv555]

Welcome to RR - you'll find a heap of information and mainly friendly folks here.

The 'bandwidth' of a radio is a measure of how 'selective' it is and is often just called it's 'selectivity' - how well it can receive the signal you want to hear while rejecting adjacent signals. Without getting too deep, the audio for an SSB signal goes from 300Hz to 2700Hz so you need a "door" at least 2400Hz wide to get best reception but nothing is perfect so the "door" doesn't have vertical sides, they slope outwards at the bottom. "dB's" are too complicated at this time so lets just say that "-6dB" is how wide the 'door' is at half the height and "-60dB" is one fiftieth.

Hope this is helps.

Thanks for the reply. But still not sure of what you mean here

lets just say that "-6dB" is how wide the 'door' is at half the height and "-60dB" is one fiftieth.

What do you mean by half the height? Is it the width of the bandwidth or the height/amplitute of the signal? or other?

Thanks

 

[majoco]

Here you go, I've drawn you a diagram although Iv'e put the -6db line too high.

 

[AK9R]

If you are listening to a signal with narrow bandwidth, like a CW signal, if that signal is centered within the 2.80 kHz bandpass region, the signal will come through full strength. So, let's assume that your tuner is centered on this CW signal. If another signal pops up 1.40 (half of 2.80) to the left or right of the bandpass region, it will be attenuated slightly. Once the signal gets out to 1.63 (half of 3.26), it will be attenuated by a lot.

Most receivers work on this principle. The receiver has a bandpass that you slide up and down the spectrum to find signals to listen to. Once that signal is in the bandpass, you'll hear it. But, signals outside the bandpass won't be heard unless they are very strong.

 

[davidv555]

If you are listening to a signal with narrow bandwidth, like a CW signal, if that signal is centered within the 2.80 kHz bandpass region, the signal will come through full strength. So, let's assume that your tuner is centered on this CW signal. If another signal pops up 1.40 (half of 2.80) to the left or right of the bandpass region, it will be attenuated slightly. Once the signal gets out to 1.63 (half of 3.26), it will be attenuated by a lot.

Most receivers work on this principle. The receiver has a bandpass that you slide up and down the spectrum to find signals to listen to. Once that signal is in the bandpass, you'll hear it. But, signals outside the bandpass won't be heard unless they are very strong.

WOW!!! Thanks!!! This diagram and your extra explanation really helped alot. Thanks for taking your time in creating this diagram. I have a much better understanding of it now.