[Elecraft] 9MHz IF +/- 5MHz VFO -- sideband inversion

[Brian Lloyd]

On May 25, 2008, at 7:50 AM, WILLIS COOKE wrote:

> It does not give the same sideband on 80 and 20.

Actually, it does.

Imagine you are generating your sideband at a 9MHz IF. In the IF you  
are generating USB, i.e. you have a 9MHz carrier and 1KHz and 1.2KHz  
tones injected to the mic jack. This produced a spectrum at 9MHz of:

9000.0 KHz - carrier (suppressed)
9001.0 KHz - first tone
9001.2 KHz - second tone.

Now we mix subtractively with 5100 KHz to produce a result in the 80M  
band:

9000.0 - 5100 = 3900.0 KHz
9001.0 - 5100 = 3901.0 KHz
9001.2 - 5100 = 3901.2 KHz

Notice that the spectral lines are above the carrier in increasing  
frequency. That is USB.

Now let's repeat this using additive mixing to get 20M.

9000.0 + 5100 = 14100.0 KHz
9001.0 + 5100 = 14101.0 KHz
9001.2 + 5100 = 14101.2 KHz

The spectral lines are still above the carrier indicating USB.

Now if you repeat the process by setting the VFO to 5500.0 KHz you  
will see that the radio would tune to a lower frequency on 80M while  
tuning to a higher frequency on 20M thus indicating that the radio  
tunes "backwards" for 80M but in both cases it still produces an USB  
signal.

--

73 de Brian, WB6RQN
Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com