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[Yaesu] FT-990 mods, noise etc

To: <yaesu@contesting.com>
Subject: [Yaesu] FT-990 mods, noise etc
From: stuart@itron-ca.com (Stuart Rumley)
Date: Mon, 27 Jan 1997 12:02:16 -0800

I do not have infomation on a fix or mod for this problems.  I did want to
mention that I too have determined that the noise problem is from the 455kHz
IF stages following the filters.  This can be verified by enabling any of
the unused
455kHz filters (using the dip switches) and turning the audio gain up.  If
you use an ac 
voltmeter on the AF audio output on the rear you can compare the noise of the
2.4kHz IF selection to an unused (or narrow) filter.  You will notice that
of which filter (or any uninstalled filter location) will result in the same
noise level.

You can verify that the noise is not in the AF stages by simply removing the
IF board.
In my opinion the noise is likely to be associated with the notch filter
circuit but I 
haven't verified this as I do not have an extender card set.  (Do you have

Good luck and 73s

At 10:25 PM 1/24/97 +0000, Ian White, G3SEK wrote:
>Please can someone update me about published modifications for the FT-
>990, on or off the Internet? (The only ones I know of are the all-band
>TX mod and the one to reduce the power level below 10W.)
>Also, did the discussion about IF/AF noise in the FT-990 reach any
>conclusion? I collected some of that from DejaNews, but wasn't sure if I
>saw it all. Somebody mentioned a modification involving a second filter,
>late in the 455kHz IF stages...
>73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
>                          'In Practice' columnist for RadCom (RSGB)
>IFW Technical Services     Clear technical English - world-wide.
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Stuart Rumley KI6QP                             e-mail:         
Hardware R&D Manager                            Phone:  408/973-7024 
Itron Silicon Valley                                    Fax:    408/973-8647    
Saratoga CA

Home e-mail: stuart@ricochet.net

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