Re: USB rig control


Joe Subich, W4TV
 

On 2021-06-13 6:30 PM, Colin Smithers wrote:

I think in TV transmitters there is still carrier present.
Yes, analog TV transmitters (NTSC) were vestigial sideband
(carrier and upper sideband with a remnant lower sideband).

*However* the IMD products in an SSB transmitter will spread
out on both sides. Given that the male voice has significant
energy in the 200-600 Hz and 1600-2700 Hz formats, the IMD
energy to +/-5.2 KHz (3rd order), +/-7.5 KHz (5th order),
+/- 9.5 KHz (7th order) and more (9th and higher) will be
significant, particularly with heavy clipping.

With many of the "12V" final rigs, the 3rd order IMD is only
-25dBc and 7th can be as bad as -40 dBc (see Sherwood's recent
writings/measurements). Icom and Yaesu are particularly
notorious but the K3/K3s is no saint.

73,

... Joe, W4TV


On 2021-06-13 6:30 PM, Colin Smithers wrote:
It can only re-appear if carrier is present for the wanted sideband to mix with in the non-linear amplifier.
In an SSB transmitter with good carrier suppression it is not possible to regenerate the unwanted sideband through poor IMD in the final stages. In my experience the K3 has negligible carrier content. Given that, It would require an inappropriate TX filter or TX filter adjustment for the unwanted sideband to truly be present.
I think in TV transmitters there is still carrier present.
73, Colin G4CWH
-----Original Message-----
From: Elecraft-K3@groups.io <Elecraft-K3@groups.io> On Behalf Of Joe Subich, W4TV via groups.io
Sent: Sunday, June 13, 2021 10:13 PM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] USB rig control
On 2021-06-13 4:45 PM, Lou W7HV via groups.io wrote:
Subsequent distortion in the rig or external amplifier can broaden
> that signal but can't create and add back the opposite side band.
Au contraire! IMD in amplifier stages *will* regenerate the missing
sideband. I saw with my own eyes (spectrum analyzer) in the days of
analog UHF TV ... in "high efficiency" Klystrode/IOT amplifiers. It
was necessary to do significant precorrection (early "Pure Signal")
to prevent the lower sideband from exceeding the "spectral mask"
requirements for protecting the next lower channel.
73,
... Joe, W4TV
On 2021-06-13 4:45 PM, Lou W7HV via groups.io wrote:
I am not a well known engineer and certainly not a respected engineer.  It is my understanding that normal superhets produce SSB by mixing audio with the LO up to the IF where the unwanted sideband is stripped off by the same xtal filters used for RX.  This is fixed and doesn't change with TX band or frequency because mixing to the TX frequency occurs after that.  Subsequent distortion in the rig or external amplifier can broaden that signal but can't create and add back the opposite side band.  So, based on that, I would think if someone is hearing the opposite sideband, there's a problem with the rig unrelated to being used outside the ham bands.

Direct conversion rigs are another matter.

Perhaps a well known and respected engineer will weight in.

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