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 <kb...@n1k.org> wrote: > Hi > > > On Jun 14, 2018, at 9:31 AM, gandalfg8--- via time-nuts < > time-nuts@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-n...@studio442.com.au> > > To: gandalfg8 <gandal...@aol.com>; Discussion of precise time and > frequency measurement <time-nuts@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. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > _______________________________________________ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.