[time-nuts] Spectracom 8140T Line Tap Schematic

Dana Whitlow k8yumdoober at gmail.com
Thu Jun 14 11:47:31 EDT 2018


Hi Bob & Julien,

Why bother with the short on the downstream end of that DC-blocking
attenuator?  At 10 MHz I'd expect
leakage radiation to be negligible.

Dana

On Thu, Jun 14, 2018 at 10:43 AM, Bob kb8tq <kb8tq at n1k.org> wrote:

> Hi
>
> > On Jun 14, 2018, at 9:31 AM, gandalfg8--- via time-nuts <
> time-nuts at febo.com> wrote:
> >
> >
> > Hi Julien,
> >
> >
> >
> > Earlier replies that discussed removing the DC supply from the 8140
> outputs gave me the impression your requirement was to connect directly the
> outputs of the 8140 without line tap modules, which is what I was
> addressing with my recent suggestion of a series capacitor, but can see now
> that's not the case.
> >
> >
> >
> > If you were to build your own termination the same principle would still
> apply of course but perhaps another option for a reasonably compact
> solution, aside from a coaxial DC block followed by a 50 ohm termination,
> might be a DC blocking attenuator followed by a BNC shorting dust cap, as
> the latter are generally quite small.
> >
> >
> > For example, current Ebay item 332461304064 is a DC blocked 20dB
> attenuator, they are also available in pairs at a slight discount, and that
> fitted with a shorting cap would give you a return loss of 40dB, which is
> probably as good as you'd get from most 50 ohm terminations anyway and
> would save having to build your own.
>
>
> I would be very surprised if the original terminations did any better than
> 20 to 30 db return loss. They are not fancy devices.
> I’ve also seen a lot of attenuators that only make it to about 20 db of
> return loss …..
>
> Bob
>
>
> >
> >
> > The VersaTaps phase lock an internal crystal, any frequency between 4
> and 20MHz, to the 10MHz input and then provide an output at the crystal
> frequency or the crystal frequency divided by a fixed integer between 1 and
> 8,192, so in that sense yes they're a synthesiser but the few I've seen
> were still supplied preset for a specific frequency.
> >
> >
> > However, "versatile" does not necessarilly mean quick or convenient to
> reprogram.
> > Aside from perhaps needing  to change the crystal the division ratio
> needs to be set by adding or removing links across pairs of holes in the
> circuit board. Those holes are on a standard 0.1inch pitch so fitting
> headers that would take shorting links should be straightfoward enough, and
> I suspect what was originally intended, but the units I have were supplied
> preprogrammed using resistor style wire ended zero ohm links mounted above
> the circuit board and soldered from below. Reprogramming one of these would
> involve unsoldering and perhaps removing all the connectors etc in order to
> remove the circuit board, so I'd certainly make darn sure they had headers
> fitted before being returned to the box!
> >
> >
> >
> > Nigel, GM8PZR
> >
> >
> >
> >
> >
> >
> > -----Original Message-----
> > From: Julien Goodwin <time-nuts at studio442.com.au>
> > To: gandalfg8 <gandalfg8 at aol.com>; Discussion of precise time and
> frequency measurement <time-nuts at febo.com>
> > Sent: Thu, 14 Jun 2018 11:36
> > Subject: Re: [time-nuts] Spectracom 8140T Line Tap Schematic
> >
> > I'm somewhat tempted to take the schematic and see if I can fit it in
> > the comparatively tiny Pomona boxes, although I have far too many side
> > projects already, enough 10MHz taps, and I still need to do the
> terminators.
> >
> > The VersaTaps are supposed to be an actual synthesizer IIRC.
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
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