caf@omen.com said: > I have a FlexRadio 1500, Racal 1992 counter, HP 3586, Advantest U3641, and > Gigatronics 6061A daisy-chained off my Thunderbolt. Don't throw out those > BNC T connectors. I thought most boxes would have an internal 50 ohm terminator so at first, I'm a bit surprised that it works. If cables are short (which is not hard at 10 MHz), it would just be a resistive divider. If the source impedance is low, it's just more work for the driver. If the source includes 50 ohms, that's a 5:1 (1/6) divider so it probably works if the receivers are reasonably sensitive. -- These are my opinions. I hate spam.

I am using, with no problems a used modular video amp I purchased on ebay (Claimed power supply problem but actually worked fine). As is common with video, the inputs are loop through, each module has 8 outputs, with as many looped and terminated as necessary. Certainly not up to Boulder standards for noise and isolation but works fine, for me, driving counters and signal generators. BTW, two different GPSDOs, one driving a 18 GHz locked signal generator, the other driving the microwave counter at 1 Hz resolution; Counters reads bang on most of the time, occasional short walks up or down 2 Hz. Not having precise TI and Allan variance analysis, it shows me, quick and dirty, it is as good as I need. Lester B Veenstra  MØYCM K1YCM W8YCM lester@veenstras.com US Postal Address: 5 Shrine Club Drive HC84 Box 89C Keyser WV 26726 GPS: 39.33675 N  78.9823527 W (Google) GPS: 39.33682 N  78.9023741 W (GPSDO) Telephones: Home:                     +1-304-289-6057 US cell                    +1-304-790-9192 UK cell                    +44-(0)7849-248-749 Guam Cell: +1-671-929-8141 Jamaica:    +1-876-456-8898   This e-mail and any documents attached hereto contain confidential or privileged information. The information is intended to be for use only by the individual or entity to whom they are addressed. If you are not the intended recipient or the person responsible for delivering the e-mail to the intended recipient, be aware that any disclosure, copying, distribution or use of the contents of this e-mail or any documents attached hereto is prohibited.

External reference inputs are definitely not all '50-ohms.' 'Learned the hard way. You need to read the specs on each piece of equipment. Input impedances will vary all over the map, even within the HP line. -Don ---- Hal Murray <hmurray@megapathdsl.net> wrote: > > caf@omen.com said: > > I have a FlexRadio 1500, Racal 1992 counter, HP 3586, Advantest U3641, and > > Gigatronics 6061A daisy-chained off my Thunderbolt. Don't throw out those > > BNC T connectors. > > I thought most boxes would have an internal 50 ohm terminator so at first, > I'm a bit surprised that it works. > > If cables are short (which is not hard at 10 MHz), it would just be a > resistive divider. If the source impedance is low, it's just more work for > the driver. If the source includes 50 ohms, that's a 5:1 (1/6) divider so it > probably works if the receivers are reasonably sensitive. > > > > -- > These are my opinions. I hate spam. > > > > _______________________________________________ > 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.

Hi all , normally the external frequency standard input are not 50 OHms , but all the distribution amplifier have 50 Ohms of standard output impedance. This because the standard cables used to connect the devices are 50 ohms. Case one: External Zi input 50 ohm: direct connection with rg58 cable. Case two: External Zi input 1k or more (as example) use the RG58 cable with a 50 ohm as termination in parallel to the instrument input. This second setup is to avoid any standing waves on the cable that produce unwanted phase and amplitude modulation; this is a cost-less best practics to apply . Luciano www.timeok.it On Fri, Apr 19, 2013 at 2:54 AM, <dlewis6767@austin.rr.com> wrote: > External reference inputs are definitely not all '50-ohms.' > > 'Learned the hard way. > > You need to read the specs on each piece of equipment. > > Input impedances will vary all over the map, even within the HP line. > > -Don > > > > > > > > > > ---- Hal Murray <hmurray@megapathdsl.net> wrote: > > > > caf@omen.com said: > > > I have a FlexRadio 1500, Racal 1992 counter, HP 3586, Advantest U3641, > and > > > Gigatronics 6061A daisy-chained off my Thunderbolt. Don't throw out > those > > > BNC T connectors. > > > > I thought most boxes would have an internal 50 ohm terminator so at > first, > > I'm a bit surprised that it works. > > > > If cables are short (which is not hard at 10 MHz), it would just be a > > resistive divider. If the source impedance is low, it's just more work > for > > the driver. If the source includes 50 ohms, that's a 5:1 (1/6) divider > so it > > probably works if the receivers are reasonably sensitive. > > > > > > > > -- > > These are my opinions. I hate spam. > > > > > > > > _______________________________________________ > > 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. > -- Luciano Timeok visit : www.timeok.it

I think the same could be said for using 75 ohm cable. One could run quad shield rg-6 with BNC connectors in the lab. It will have lass leakage then even the best rg58. then you can terminate as required. The quad shield is foil-braid-fiol-braid and is even better then the 100% coverage conventional cable. One annoying thing about the rg6 is that it is stiff. Not good for test leads but for clock distribution being stiff is ok. If you want the best, use hardline. I picked up a little bit of this by accident when I bought a lot odds and ends. It looks like coper pipe with RF connectors on each end. I have no idea how you put the connects one put you can bend it with a tubing bender and it is not hard to work with. But seriously if you want low leakage the cable TV stuff is designed just for that. On Sun, Apr 21, 2013 at 12:22 AM, Luciano Paramithiotti <timeok.it@gmail.com > wrote: > Hi all , > normally the external frequency standard input are not 50 OHms , but all > the distribution amplifier have 50 Ohms of standard output impedance. This > because the standard cables used to connect the devices are 50 ohms. > Case one: External Zi input 50 ohm: direct connection with rg58 cable. > Case two: External Zi input 1k or more (as example) use the RG58 cable with > a 50 ohm as termination in parallel to the instrument input. > > This second setup is to avoid any standing waves on the cable that produce > unwanted phase and amplitude modulation; this is a cost-less best > practics to apply . > > Luciano > www.timeok.it > > On Fri, Apr 19, 2013 at 2:54 AM, <dlewis6767@austin.rr.com> wrote: > > > External reference inputs are definitely not all '50-ohms.' > > > > 'Learned the hard way. > > > > You need to read the specs on each piece of equipment. > > > > Input impedances will vary all over the map, even within the HP line. > > > > -Don > > > > > > > > > > > > > > > > > > > > ---- Hal Murray <hmurray@megapathdsl.net> wrote: > > > > > > caf@omen.com said: > > > > I have a FlexRadio 1500, Racal 1992 counter, HP 3586, Advantest > U3641, > > and > > > > Gigatronics 6061A daisy-chained off my Thunderbolt. Don't throw out > > those > > > > BNC T connectors. > > > > > > I thought most boxes would have an internal 50 ohm terminator so at > > first, > > > I'm a bit surprised that it works. > > > > > > If cables are short (which is not hard at 10 MHz), it would just be a > > > resistive divider. If the source impedance is low, it's just more work > > for > > > the driver. If the source includes 50 ohms, that's a 5:1 (1/6) divider > > so it > > > probably works if the receivers are reasonably sensitive. > > > > > > > > > > > > -- > > > These are my opinions. I hate spam. > > > > > > > > > > > > _______________________________________________ > > > 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. > > > > > > -- > Luciano > Timeok > visit : www.timeok.it > _______________________________________________ > 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. > -- Chris Albertson Redondo Beach, California