Author Topic: Modes  (Read 121 times)


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« on: August 28, 2021, 12:37:55 pm »
I find many CB operators these days are not familiar with the understanding between "Modes and Bands". This is more prevalent here in the UK, as most operators are only familiar with the "Straight UK 40" or "One trick ponies". Namely the 27/81 radios that where legalized.

I've also found that even explaining the difference between modes and bands is recurring topic to the same operators who may not grasp the difference in these modulation types.

This has all probably stemmed for a previous miss-conception with broadcast radio receivers, which are kind of incorrect, namely small transistor radios with a band switch marked AM/FM. Although this does in-fact switch between bands, the labeling is written in "Modes".

Firstly AM is Amplitude Modulation, where the carrier intensity is increased with the audio frequency. The modulation is transmitted in DSB e.g. "Double Side Band" The carrier in essence is only there to prop up the modulation, and the intensity change is a product of the way the audio frequency is imposed onto the carrier. There are many ways to do this that I will not go into here, as it's beyond the scope of this topic for now.

Secondly FM is Frequency Modulation which is almost identical, but the carrier will deviate in sympathy with the modulation that has been imposed onto it. In essence the carrier is only there once again to prop up the modulation, with still the same DSB pattern.

Thirdly SSB or Single Side Band is basically AM with rectified audio, this will either be the "Upper" or "Lower" side. The way this is done is very simple and yet ingenious too. However now the carrier is suppressed, and is not technically part of the transmission.

There are many types of modes, all requiring a different approach to the way they are resolved at the receiver. For AM a simple diode detector is all that is required. For FM a "Discriminator" is needed, and finally for SSB a "Product Detector" is needed.

I hope this has shed some light on the topic of "Modes" and I'd be interested to hear from others who are finding the same operators on 11m especially with the same lack of understanding regarding modes.

Here's a image below giving an example to what I've explained.

73 DE Bill
« Last Edit: August 30, 2021, 12:31:23 pm by 26AM081 »

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