[Elecraft] Re: Transmitted audio distortion on certain frequency

[Walter Wilson]

Wayne,

Thanks for the great advice.  I removed the covers and checked everything
you mentioned, and did not find any problems with R19 or RFC15, and all the
solder joints looked good.  So I installed a 30pF ceramic disk capacitor
across pins 12 and 13 of U4, on the bottom side of the RF board.  After
reassembly I found no signs of transmit audio distortion anywhere, checking
every 2K both up and down from 7183 KC.  After running CAL PLL again as
recommended, I rechecked everything again, and the distortion problem seems
to be completely gone.

Big Thanks!
Walter - KK4DF
(K2 S/N 3809)

----- Original Message ----- 
From: "Wayne Burdick"
To: "Walter Wilson"
Cc: "Elecraft"
Sent: Wednesday, November 12, 2003 11:14 PM
Subject: [Elecraft] Re: Transmitted audio distortion on certain frequency


> > I have a very distorted transmit audio (listening on another receiver)
> > around 7.183 KC on LSB.  If I move up or down the band only 4 or 5 KC,
> > everything is clear again.  On USB, the problem occurs at 7.180 KC.  Any
> > ideas???
> >
>
> I believe you have an instability condition that occurs when the
synthesizer's
> reference and VCO dividers are at the same frequency; this occurs only in
the
> vicinity of 7180-7185 kHz. Try soldering a small capacitor, say 33 to 56
pF,
> between pins 12 and 13 or U4 (MC145170) on the RF board. Also make sure
that R19
> is 2.7 k, not some smaller value, and that RFC15 (at pin 16 of U4) is not
> broken.
>
> If none of this helps, consult Gary (support@elecraft.com) for other
ideas. If
> it *does* help, re-run CAL PLL to ensure that the now-stable synthesizer
tunes linearly.
>
> 73,
> Wayne
> N6KR