Re: USB rig control


Joe Subich, W4TV
 

On 2021-06-13 7:24 PM, Lou W7HV via groups.io wrote:
I think that's a tough one to pull off, even for Yaesu.
It's simple 3rd order IMD. If the carrier is at 10 MHz and the
audio is at 10.003 MHz ... 2*10.000-10.003 = 9.997 MHz. Instant
LSB.

Without a carrier it is more difficult, but say one has 200 Hz
and 2400 Hz audio present at the same time: 2*10.0002-10.0024 =
9.998 MHz. It's not a perfect LSB but it is a lot of energy
in the LSB spectrum. Remember, Sherwood measures 3rd order
IMD of many of the rigs with 12V finals in the -25 dBc range
(-31 to -34 dB pep) and fifth order no better than -30 dBc.

-30 dBc is *one watt* of IMD power with a 1KW amp (1 mW for
a 100 W transceiver) *assuming* the 1KW amplifier is *totally*
clean (and many of the LDMOS amps are as bad as a 12V rig).

73,

... Joe, W4TV


On 2021-06-13 7:24 PM, Lou W7HV via groups.io wrote:
As an unknown and disrespected engineer, I'll add the following.  The TX side band consists of ~3kHz band of RF frequencies.  Even if the carrier was present, there's no audio signal to mix with it to produce the other sideband.  The carrier would have to mix with the TX signal to recreate the audio signal, and that audio signal would then have to mix with the carrier again to produce two sidebands at the TX frequency, including the undesired one. I think that's a tough one to pull off, even for Yaesu. ;-)

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