[time-nuts] Achieving maximum performance when driving5370A/Binputs

[John Miles]

If you drive it from 50-ohm coax, you need to use the 50-ohm setting, or the
resulting reflections may cause trouble.  The 74AC04s in the TADD-2 are
happy enough driving 50 ohms, so that's the best way to go.

-- john, KE5FX

> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
> Behalf Of Dave hartzell
> Sent: Sunday, February 28, 2010 8:05 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Achieving maximum performance when
> driving5370A/Binputs
>
>
> Thanks for the tips John.  Do you use the 50 ohm or 1M ohm
> settings with the
> TADD-2?
>
> Dave
>
>
> On Sun, Feb 28, 2010 at 7:42 PM, John Miles <jmiles at pop.net> wrote:
>
> > What threshold are you using?  If you leave it set to preset/0
> volts, you
> > may find that crosstalk between outputs on the TADD-2 cause false
> > triggering.  I usually use the divide-by-10 setting with the
> threshold set
> > to about 0.25V.
> >
> > It also helps to remove the jumpers from any outputs on the TADD-2 you
> > aren't using.
> >
> > -- john, KE5FX
> >
> > > -----Original Message-----
> > > From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
> > > Behalf Of Dave hartzell
> > > Sent: Sunday, February 28, 2010 7:28 PM
> > > To: Discussion of precise time and frequency measurement
> > > Subject: Re: [time-nuts] Achieving maximum performance when driving
> > > 5370A/Binputs
> > >
> > >
> > > Today I have been trying to drive a 5370B directly from a TADD-2, with
> > > little luck (other HP freq counters seem to work OK).   I was about to
> > ask
> > > about it on this list, but noticed this thread.
> > >
> > > I guess this could explain why I am getting erroneous, random
> readings?
> > >
> > > Dave
> > >
> > >
> > >
> > > On Sat, Feb 27, 2010 at 4:01 PM, Bruce Griffiths
> > > <bruce.griffiths at xtra.co.nz
> > > > wrote:
> > >
> > > > The attached excerpts from the 5370A and 5370B manuals indicate that
> > for
> > > > best performance, that the common practice of driving the
> > > 5370A/B 1x inputs
> > > > directly from a 5V CMOS logic signal is a bad idea.
> > > >
> > > > For the 5370A attenuating the 5V CMOS signal to a 1V swing with the
> > > > threshold set to 0.5V is close to optimum.
> > > > An input signal with limits of 0V and +1.4V with a trigger
> threshold of
> > > > 0.7V is the maximum usable (for high performance).
> > > > An input signal with limits of 0V and +0.3V with a trigger
> threshold of
> > > > 0.15V is the minimum usable (for high performance).
> > > >
> > > > For the 5370A attenuating the 5V CMOS signal to a 2V swing with the
> > > > threshold set to 1V is close to optimum.
> > > > An input signal with limits of 0V and +3.5V with a trigger
> threshold of
> > > > 0.7V is the maximum usable (for high performance).
> > > > An input signal with limits of 0V and +0.3V with a trigger
> threshold of
> > > > 0.15V is the minimum usable (for high performance).
> > > >
> > > > Bruce
> > > >
> > > >
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