This is not exactly so. EVERY single one that I have ever seen, is biased
properly for SSB operation. In fact they had a switch on the front to
change the dealy of the antenna change over circuit for AM and SSB. I had
one during the last sun spot cycle that I used on 10m in the mobile, and it
worked perfectly.
Now there may be some that were meant for AM only, but I've never seen one.
Dan Newby
WD4LUR
At 05:03 PM 4/30/98 -0500, you wrote:
>Message-ID: <3548A62C.143A@ames.net>
To: <tentec@contesting.com>
>Date: Thu, 30 Apr 1998 11:26:20 -0500
>From: "Dr. Gerald N. Johnson, P.E." <geraldj@ames.net>
>Reply-To: geraldj@ames.net
>Organization: Gerald N. Johnson, P.E.
>X-Mailer: Mozilla 3.01Gold (Win95; I)
>MIME-Version: 1.0
>To: owen@piper.eeel.nist.gov
>Subject: Re: [TenTec] RE:Using CB amps with Qrp rigs.
>References: <46510.owen@piper.eeel.nist.gov>
>Content-Type: text/plain; charset=us-ascii
>Content-Transfer-Encoding: 7bit
>
>It will take more than a low pass filter to make a decent amp out of a
>CB amplifier. They were designed for AM and so depend on the carrier to
>provide forward bias to the transistors to make them sort of linear. For
>CW this may not be as great a consideration, but a pure class C
>amplifier can add key clicks to a marginally hard keyed signal, and will
>splatter all over when driven with SSB.
>
>The simplest forward bias circuit uses a resistor and a diode to create
>a sort of regulated bias voltage. This is unfortunately commonly used in
>VHF "linear" amplifiers and leads to lots of splatter because it can't
>control the bias when there is drive. The circuit in Motorola
>applications notes using a couple transistors (one in thermal contact
>with the RF power transistors, which can be a diode) and a 723 regulator
>chip has proven to significantly improve the intermod distortion of such
>a pseudo linear and make it as good as can be accomplished with
>transistors.
>
>Adding forward bias to a poorly constructed amplifier that neglects RF
>feedback, shielding, and adequate bypassing can create a power
>oscillator.
>
>73, Jerry, K0CQ
>
>
>
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>
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