> Working the sideband part into it with a 9 MHz USB signal and a 5 MHz
> LO - Suppressed carrier freq: 9.000 minus 5.000 = 4.000 3 kHz
> modulation tone: 9.003 minus 5.000 = 4.003
No, it's 5.000 - 9.000 = -4.000 and 5.000 - 9.003 = 3.997
and it's 5.500 - 9.000 = -3.500 and 5.500 - 9.003 = 3.497
The VFO does not need to be the LO ... the IF can just as easily be
connected to the LO port.
> Just as a sanity check, take another look at your own negative
> number example, Joe, and 'splain to me how 5.000 minus 9.003 gives
> minus 3.987. OK,I'll grant you a typo and assume you meant minus
> 3.997, but you're still wrong. It's minus 4.003.
You're correct it's a typo *BUT* there is no error in the inversion
when the 9 MHz USB signal is applied to the LO port of the mixer.
All you need to do is spend some time with the historical record.
73,
... Joe, W4TV
On 11/22/2011 6:22 PM, KU4AF wrote:
> First, let's dispense with the red herring of backward tuning. The VFO does
> tune backward on 75 but it has nothing to do with sideband inversion. The
> USB/LSB business works the same way with a fixed LO as with a VFO, and it
> works as I described.
>
> When you mix a 5 MHz signal with a 9 MHz signal, there's no need to stand on
> your head and pretend that you're subtracting 9 from 5 to get minus 4.
> Instead, you go back to second grade and subtract 5 from 9 and get 4.
>
> Working the sideband part into it with a 9 MHz USB signal and a 5 MHz LO -
> Suppressed carrier freq: 9.000 minus 5.000 = 4.000
> 3 kHz modulation tone: 9.003 minus 5.000 = 4.003
>
> Just as a sanity check, take another look at your own negative number
> example, Joe, and 'splain to me how 5.000 minus 9.003 gives minus 3.987. OK,
> I'll grant you a typo and assume you meant minus 3.997, but you're still
> wrong. It's minus 4.003.
>
> John, KU4AF
> Pittsboro, NC
>
>
> On 11/22/2011 4:04 PM, KU4AF wrote:
>> Whatever the genesis of the LSB/USB convention on the ham bands,
>> this conversion scheme wasn't it. Mixing a 9 MHz USB signal with a 5
>> MHz VFO will produce a USB output on either 4 MHz or 14 Mhz. The
>> sidebands only get inverted in a mixer when you subtract the SSB
>> signal from a higher frequency
>
> Try the math again ...
>
> If you have a 5.0 - 5.5 MHz VFO and subtract a 9 MHz USB signal from
> that VFO you end up with a LSB output that tunes from 4.0 - 3.5 MHz
> in reverse. Start at 5.0 and subtract the 9 MHz carrier frequency you
> get *minus* 4.0 MHz (carrier frequency) when the highest modulating
> frequency (3 KHz or 9.003 MHz) is used you end up with *minus* 3.987
> MHz - *lower sideband*! Do the same with the VFO at 5.5 MHz and you
> will find LSB at *minus* 3.497 to 3.500 MHz.
>
> A mixer can produce F2 +/- F1 just as easily as it produces outputs
> at F1 +/- F2. If you don't believe this ... spend some time reviewing
> the early SSB transmitter and receiver articles in QST from the 1950s
> or borrow a Drake 1A/2A/2B and learn why some bands "tune backward."
>
> 73,
>
> ... Joe, W4TV
>
>
> --
> View this message in context:
> http://elecraft.365791.n2.nabble.com/US-60-Meter-Band-Changes-Approved-by-FCC-tp7011949p7022509.html
> Sent from the Elecraft mailing list archive at Nabble.com.
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