[minima] Re: When is USB not USB
- From: farhanbox@xxxxxxxxx
- To: minima@xxxxxxxxxxxxx
- Date: Fri, 24 Jan 2014 17:03:52 +0000
Hahaha...
Now, a 20M signal modulate by 1 KHz carrier is 20.001 MHz. If the oscillator is
at 34 MHz, the IF gets subtracted, so the output isnow at 13.999 mhz. If the
tone increases by another khz, the if is at 20.002 and the mixer output has now
gone to 13.998!
Yes, the sidebands are inverted.
If found this by serendipity. I tuned to twenty, adjust the bfo. Then I
measured the frequency of the bfo and found that I was on the lower sideband at
the IF.
- f
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-----Original Message-----
From: Mark G0MGX <mark.g0mgx@xxxxxxxxx>
Sender: minima-bounce@xxxxxxxxxxxxx
Date: Fri, 24 Jan 2014 16:57:21
To: <minima@xxxxxxxxxxxxx>
Reply-To: minima@xxxxxxxxxxxxx
Subject: [minima] When is USB not USB
Hi Gang
I'm now in a complete muddle and have confused myself beyond belief; I
have never made a homebrew TX with a LO higher than the output frequency
before and this is causing my brain to ache.
We start with an Audio Frequency of (say) 1200Hz and a BFO of (say)
20MHz. We mix these together in our matched diode based mixer and we get
a carrier at the BFO frequency of 20MHz plus an USB of 20MHz+Audio
frequency and a LSB of 20MHz-Audio frequency. So far so good.
Then we mix this signal with the LO at (say) 34MHz and we get the
Carrier at 34-20MHz = 14MHz and my USB from above is now 24-(20+Audio)
which will be LOWER than the carrier.
So by definition it is now LSB? Am I right? Therefore when adjusting the
BFOs we need the USB BFO to retain the LSB and the LSB BFO to retain the
USB.... I need to go out more I think....
Mark
G0MGX
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