p.s. as I noted in my blog I have heard similar wandering birdies before but
never had them land on a band like that one did during cqww. I have been
doing other repairs on those amps so they have moved around from band to
band periodically, its possible that amp has been oscillating for a while
and it just never got caught... add in temperature sensitivity and
apparently some line voltage sensitivity and it may have just been hot
enough and the voltage at just the right spot that day. As I said, when I
tried to reproduce it I could only get it in the 20m band for a short time,
most likely it was drifting all over the place.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> -----Original Message-----
> From: d.cutter@ntlworld.com [mailto:d.cutter@ntlworld.com]
> Sent: Tuesday, December 09, 2008 10:33
> To: Ian White GM3SEK; amps@contesting.com
> Subject: Re: [Amps] Fwd: rx noise?
>
> Did the regulator have proper bypass in the first place or was this a
> problem just waiting to pop out? Capacitor-to-regulator distance is
> critical. I've never known a regulator go funny if it was properly set up
> in the first place. As Pease would say "do what the manufacturer tells
> you or all bets are off."
>
> David
> G3UNA
>
> >
> > From: Ian White GM3SEK <gm3sek@ifwtech.co.uk>
> > Date: 2008/12/09 Tue AM 08:39:07 GMT
> > To: amps@contesting.com
> > Subject: Re: [Amps] Fwd: rx noise?
> >
> > David Robbins K1TTT wrote:
> > >I think the noise in that one is solved... take a look at the scope pic
> > >for a 12v regulator with a 2v p-p oscillation on it at:
> >
> >http://wiki.k1ttt.net/2008%20Maintenance%20and%20Upgrade%20Blog.ashx?NoR
> > >edir ect=1#Bottom That's one repaired, another one tested clean for
> > >now, and 5 more to go.
> > >
> > Glad you found the problem, Dave. By coincidence(?) someone recently
> > found a similar problem with a 78xx in a GaAsFET preamp that had been OK
> > for years, but then decided to become unstable.
> >
> > Any thoughts about what changed to trigger the instability? (Aside from
> > it being CQWW weekend, and the regulator having poor stability margins.)
> >
> >
> > --
> >
> > 73 from Ian GM3SEK
> > http://www.ifwtech.co.uk/g3sek
> > _______________________________________________
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> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> >
>
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