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Another TS-850S Question

Posted: Wed Oct 01, 2014 4:38 pm
by Smooth912
Hello folks,
I am running a KA0KA modified 850s, WITHOUT the dsp-100. I am getting really great reports. Question is, are there any new improvements (filters, cap changes, etc) for this rig besides trying to locate a DSP-100? Also how wide will this radio transmit (AM and SSB) again without the DSP unit?

On AM I run the 8.83if filter off and 455if bypassed
On SSB I run 8.83if off and 455if @12khz


Posted: Fri Oct 03, 2014 1:38 pm
by BillPaul
On AM mode, with the KA0KA mods (feeding the modulator directly and bypassing the 8.83MHz and 455KHz IF filters), you should be able to get about 9KHz to 10KHz of audio bandwidth.

On SSB... well, you shouldn't operate the rig like this on SSB. You really need the DSP-100 unit. In "analog" mode, the TS-850 (like a lot of Kenwood rigs) does SSB like this:

1) An audio signal is fed into one input of the AN612 balanced modulator
2) A 455KHz RF signal is fed another input
3) The output of the AN612 is a double-sideband modulated 455KHz signal, i.e. an AM signal with the carrier suppressed
4) This DSB signal is fed through the 2.7KHz 455KHz filter to strip out one sideband
5) The 2.7KHz 8.83MHz filter at the next IF stage is used to provide another stage of alternate sideband suppression

The exact frequency of the 455KHz input signal in step 2 is varied a bit depending on whether the transmit mode is AM (right on 455KHz), USB (a few KHz lower), or LSB (a few higher). This is so that the modulated portion of the AN612's output signal always falls in the center of the filter passbands.

Normally the radio forces the use of the 2.7KHz filters in USB or LSB mode. If you bypass them completely, then you'll have a really wide SSB signal, but you'll be transmitting in double-sideband mode, meaning people will hear you on both USB and LSB at the same time.

Putting the 455KHz IF filter in the 12KHz position will help that somewhat, but I think you'll still be leaking a significant amount of alternate sideband signal, unless maybe you also tweak the carrier point adjustments.

So really, this method should only be used for AM.

If you have the DSP-100 unit, then the alternate sideband suppression at the 455KHz level is being done with digital filtering inside the DSP unit. Out of the box, the radio also uses the 2.7KHz filter at the 8.83MHz IF for added suppression when the DSP-100 is engaged, but you can turn it off and the alternate-sideband and carrier attenuation done by the DSP alone is still excellent. And when you set the DSP-100 for extra wide mode, all you're doing is changing the parameters of some of the software running on the CPU in the DSP unit so that it uses a wider passband, but while maintaining the excellent carrier and alternate sideband suppression. This means you get a wide SSB signal on only one sideband, which is what you want.

The DSP unit in the TS-950SDX works much the same way, which is why the TS-850/DSP-100 combo and the TS-950SDX are so desirable. This is also why DSP or SDR rigs (like Flex radios) are popular choices for ESSB in general.

Anyway, if you do have the DSP-100 unit, then you can expect to achieve 6KHz of audio bandwidth.

-Bill N1GPT

Posted: Mon Oct 06, 2014 10:17 am
by Smooth912
Thanks for the information!