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Kenwood SSB Filters
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by W1TFM on July 30, 2002
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Hello,
Thank you for taking the time to read this message.
I have a Kenwood TS940S HF rig and I have a question about SSB filters.
I will state "I am completely uneducated pertaining to all filters". I have heard that a lot of hams replace the stock filters as soon as the rig is out of the box.
Installed in my TS940S my manual tells me I have a "Stock" 883 MHz IF 2.4 kHz filter and a 455 kHz 2.4 kHz filter. Overall pass-bandwidth 2.4 kHz. SSB SLOPE TUNE (HI-CUT to 1500 Hz) LO-CUT to 700 Hz. and NOTCH. Being totally unknowledgeable about filters, could one of you "PRO's" give me any information for a nice SSB filter for my 940S ? I read somewhere that a ham used an IRCI 2.kHz dual SSB in his 940S and noticed a BIG difference. Also, I have heard that many hams replace the stock filter in their rigs as soon as the get it out of the box.
What I am experiencing is when I am using the HF and a station comes on the air only about 2-3 kc away the station does a song and a dance on my receive almost to the point I can not hear the station I am in QSO with. Also static crashes and all types of noises in the background. Will I benefit from a filter with these problems ? Any information will be greatly appreciated. Thank you.
W1TFM (Rick)
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RE: Kenwood SSB Filters
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by vk2cz on July 30, 2002
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I understand there are no optional voice filters that suit the TS940S - I use a fully 'loaded' unit with TCXO, Voice, CW filters, ATU and a neat after market RS232 interface.
You may want to do a USB/LSB/AM IF frequency alignment using WWV, as my 16 year old unit had the IF conversion just a bit off-centre. This meant that the filter low cut sounded very different when switching between USB/LSB, even though WWV generates a 2~3Hz beat with the cal switch on (rig in AM mode).
Make sure that you reduce the weight of the radio by removing that one diode that enables a full HF band SWR analyser feature.
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RE: Kenwood SSB Filters
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by N2MG on August 6, 2002
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Yes, there are SSB filters suitable for the 940 - but they are not "Kenwood" filters. And there's a bit of wiring to install them. Check out the International Radio (commonly called Inrad) website for more info. I have the 2.1kHz (@455kHz and 8.8MHz) units in my 940.
http://www.qth.com/inrad/
Go to the bottom of the home page, click on "Crystal Filters...", etc.
or go directly to
http://www.qth.com/inrad/TS-930.HTM
If I recall the plots, the Inrad filters are much sharper than comparable Kenwood filters (CW and SSB).
Now, to the interference issues...static crashes and close-in loud stations will still plague you even with the filters. However, there will, of course, be less of that junk in a narrower passband (assuming you install the filters).
Noise blankers tend to make some types of interference worse - try turning it on and off (in the presence of some loud stations) as an experiment. Also try dialing in some attentuation - if your front end is getting hammered, it will become non-linear making interference seem worse.
If you are operating on 80/160, try a Beverage (or other low-frequency specialty receiving antenna) - they are MUCH better regarding static crashes then most TX antennas.
Bad news: The 940 is notorious for phase noise issues with its synthesizer - these are inherent in the design and were improved with later serial numbers - but not really "fixed". Excessive phase noise can generate extra products that cause interference as well and there's not much you can do about it with filters or front-panel controls.
73 Mike N2MG
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