Date: Fri, 30 Apr 93 16:54:25 EDT
From: [email protected] (Edward Pacyna)
Message-Id: <[email protected]>
To: [email protected], [email protected]
Subject: Re:  Campbell KK7B R1 DC receiver
Cc: [email protected]

Yes, I have built one. Also made many modifications to improve it. Its one of
the better DC receivers I've built. Does have excellent DR, low noise and
its the only DC receiver I've heard that actually has the tonal quality that
everyone talks about.  The filtering is really nice. A summary of the chages
are:

1. Elimated L2 and R2 from the diplexer to improve AM suppression (I live near
  an AM broadcaster). Also lowered all the high pass filter corner frequencies
  because I like to copy a lower beat note than 750Hz. As shown, there all
  above 300Hz, which is fine for SSB.

2. Rebiased the 50 ohm audio preamp for proper operation with a 13.5V supply.
  Also used a ultra low noise transistor at Q1.

3. Improved the 7th order eliptical filter. Author scaled values from another
  authors SSB design. Tightened up the filter quite a bit. See attached.

4. Improved the biasing and changed the gain distribution a bit on both U2A
  and U2B.

5. The power amp had a Icq of 100ma and gets quite hot. Don't need to generate
  this kind of heat and use this much power. Rebiased the power amp to idle
  much lower (10 -20 ma). Fidelity is still excellent.

73's Ed W1AAZ








        0 DB *   *   *   *   * <--- Fc = 850 Hz    ______ __
 A          | Ripple = .18 DB*                           |
 t          |                                            |
 t          |                 *                 Stop Band Attenuation
 e          |                                      (70 DB Minimum)
 n      50  |  S.F. = 1.4:1--> *                         |
 u          |    (6:60 DB)                               |
 a          |                   *      *           *_____|__
 t          |
 i          |                                  *      *
 o      100 |                      *  * *
 n          |________________________*___*_________________*
                      |         |         |          |
            0        500      1000       1500      2000  Hertz

                               Frequency


           Figure 1. Frequency Response (7th order E.L.P.F)







                    120.8 MH        98.8 MH        99.8 MH
                     (120)           (100)          (100)
       o--------x----UUUUUU----x-----UUUUUU-----x---UUUUUU-----x-------o
                |              |                |              |
                x-----| |------x------| |-------x----| |-------x
                |   .036uF     |     .17uF      |   .12uF      |
   Z =          |   (.033)     |     (.18)      |   (.12)      |        Z =
   500    .47uF---       .68uF---         .63uF---       .40uF---       500
          (.47)---       (.68)---         (.68)---       (.39)---
                |              |                |              |
       o--------x              |                |              x-------o
               ---            ---              ---            ---
                -              -                -              -

    Note: Values shown are calculated. ( ) are the nearest standard value.

          Figure 2  Schematic - Elliptical Low Pass Filter (7th order)

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