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Gordon Gibby
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From: [email protected] <[email protected]> on behalf of Ashhar Farhan <farhanbox@...>
Sent: Wednesday, November 29, 2017 3:38 AM To: [email protected] Subject: Re: [BITX20] Help me understand the USB (upper side band) mod ?
Lets take a concrete example.
An lsb signal generated at 12 mhz carrier, now considee that it is modulated with a 500 hz carrier, it produces a signal at 11,999,500 hz. If the modulating carrier is at 1khz, the signal will shift further down to 11,999,000 hz.
Now, lets mix this with a? 5 mhz oscillator. The lsb signal will be subtracted from the 12 mhz signal. The 11,999,500 - 5,000,000 = 6999,500? mhz. The 1khz signal will be even lower at 11,999,000 - 5,000,000 = 6,999,000. Thus as the modulating
tone moves up, the rf moves down, it is still LSB.
Now, consider the local oscillator at 19 mhz. Here, the signal is subtracted from the 12hz signal (the previous example had oscillator subtracted from the 12 mhz if). So, 19,000,000 - 11,999,500 = 7000,500 is the frequency of the signal at 500
hz is 700.5 khz. When the audio shifts to 1000 hz, the IF is at 11,999,000 and the rf is at 19,000,000 - 11,999,000 = 7001,000 hz. That is 7001 khz. Thus, the rf frequency moves up as the audio tone goes up. We are in USB!!
On 29 Nov 2017 1:33 pm, "Dale Brooks KG7SSB" <kg7ssb@...> wrote:
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