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Bernie[_5_] · October 15th 18, 08:20 AM posted to uk.radio.amateur,rec.radio.amateur.antenna

On Sun, 14 Oct 2018 23:55:27 -0700 (PDT)
Jeefaw K Effkay wrote:

On Sunday, October 14, 2018 at 11:01:15 PM UTC+1, Ralph Mowery wrote:
In article , lid
says...

On Sun, 14 Oct 2018 12:04:52 -0700 (PDT)
Jeefaw K Effkay wrote:

On Sunday, October 14, 2018 at 7:33:10 PM UTC+1, Jeff Liebermann
wrote:

It might help to understand why some bands use LSB while
others USB. In the early daze of sideband radio, the common
IF frequency was 9MHz. The radios had only one sideband
filter. With one filter, it was cheaper and easier to mix
and up convert in the transmitter. So, to save the cost of
adding a second filter, the bands below 9MHz were designated
as LSB and the band above 9MHz became USB. Eventually, radios
were built with two sideband filters, and this was no longer
important. As usual, the legacy technology remained in place
to haunt the survivors to this day.

I've seen this explanation before, but it doesn't make sense.

A 9MHz USB signal mixed with a 5.0 to 5.5MHz VFO will produce
mixing products in the 80m and 20m bands - but both will be
upper sideband.

When the 9 MHz is mixed with the 5 mhz the 20 meter signal is upper
sideband. The 80 meter signal is inverted and becomes the lower
sideband NOT usb.

Consider a 2 tone signal at the 9MHz USB IF, comprising 900Hz and
1300Hz tones.

The components will be 9.0009 and 9.0013

Subtract the VFO at 5.5MHz:

9.0009 - 5.5 = 3.50009
9.0013 - 5.5 = 3.50013

Nothing has been inverted. The 80m signal is still upper sideband.

GB3BERNIE

Ralph is posting from rec.radio.amateur.antenna and google groups
strips the crosspost - without a repeater, he's not going to answer you.

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