[time-nuts] Query about insulated coax panel connectors
The 106D DMTD unit was designed by NBS (now NIST), and the BNC connectors I mentioned were also isolated from the chassis. The shield side was bypassed to the chassis ground inside via a 50 Ohm resistor and a .1uf capacitor. I retained those when I converted to isolated SMA. The center pin and shield were then sent via coax to the various points. Cheers, Corby ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Query about insulated coax panel connectors?
On Sat, October 24, 2020 1:24 pm, AC0XU (Jim) wrote: > Having recently run into major ground loop noise > issues, I have begun reworking some of my homemade > pieces of equipment using insulated coax connectors. There is generally a trade-off between 60Hz noise and EMI when you start thinking about isolated coax connectors. > Insulated BNCs are readily available. There were BNC connectors made for telco use which have an integrated coaxial capacitor connection to the chassis mount point. The connector is isolated from the chassis by a high reactance at 60-120Hz, but decreasing impedance at RF frequencies. I haven't looked at the info for those in a while, not sure where the self inductance would cause the impedance to begin rising again, but I think it was at a pretty high frequency. > And I am not thinking about using plastic cases - that would introduce > a whole other set of problems. I think about my lab area at work where > a bundle of dozens of gigabit ethernet cables run through the roof directly > over the lab bench - the ambient noise level is quite high. If you are worried about external EMI, keep in mind that when you disconnect the cable shield from the enclosure, you make an antenna to pass external RF into the interior of your enclosure. Changing to a plastic enclosure might not be much worse from an RFI/EMI standpoint. -- Chris Caudle ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Query about insulated coax panel connectors
Corby wrote: My NBS 106D DMTD originally had all BNC connectors but after finding out BNCs are not the best for DMTD units I retrofitted it with insulated SMA connectors. I used nylon washers on both sides. See PIX. Note that this can cause problems with RF noise and interference (both ingress and egress) if it is not carefully done. The problem is that RF can get into (or out of) the enclosure on the shield of a connected cable, on the signal conductor(s) of a connected cable, or (usually) both. One needs to bypass (short/shunt) the RF energy on the cable shield and and on the signal conductor(s) to the instrument's RF shield (i.e., the conductive enclosure) *without* causing appreciable ground loop currents to flow between the instrument and other instruments and devices connected to it (DC and LF -- usually the first 10-30 harmonics of the mains frequency ). This is a much more involved topic than can readily be covered here, but there are some fundamental principles. Generally speaking, it involves (i) connecting the isolated cable shield(s) to the instrument enclosure with low-impedance RF paths (e.g., capacitors) *very close* to the connectors; (ii) introducing high-impedance RF paths in series with the signal conductors (e.g., series resistors, chokes, ferrite beads, and/or common-mode RF chokes); and (iii) bypassing the signal conductors with low-impedance RF paths (e.g., capacitors) *very close* to the connectors, on the instrument side of the high-impedance series RF element(s). As the frequencies of concern get higher, connecting the isolated cable shield(s) to the instrument enclosure effectively with low-impedance RF paths gets harder and harder. I often use two or three capacitors equally spaced radially around the connector as a useful approximation. Leads must be kept *short* to minimize the effective antenna loop -- 2mm or less for high VHF to low-GHz signals (or use SMT parts to build out the connector-to-enclosure link). There is another approach, which I often prefer. You can bond all connector bodies (cable shields) together on the smallest area of the enclosure (RF shield) possible, then make sure you don't make *any* mistakes in the entire system that create ground loops. When done correctly, this method can often provide superior results. I'll try to post a general overview of that solution in the future, modeled on the above -- but there are far more variables and opportunities to go wrong on that side of things, so the designer must be correspondingly more diligent. Best regards, Charles ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Query about insulated coax panel connectors?
If panel and connector sizes permit a small single hole panel mount connector can be insulated with a fiber shoulder washer and a flat fiber washer. https://www.keyelco.com/category.cfm/Shoulder-Washers-Bushings/Fibre-Shoulder-Washers/id/813 https://www.keyelco.com/category.cfm/Washers/Nylon-Fibre-and-Steel-Washers/p/448/id/712/c_id/714 Alternately a piece of PCB material with copper removed can become an insulating mount, with the connector poking out through an oversize panel hole. Yes, now you need to mount the PCB somehow (2-4 screws?). But one piece of PCB stock can hold multiple connectors, making that a bit easier. Bob L. > Sent: Saturday, October 24, 2020 at 2:24 PM > From: "AC0XU (Jim)" > To: time-nuts@lists.febo.com > Subject: [time-nuts] Query about insulated coax panel connectors? > > Time-nuts: > > Having recently run into major ground loop noise issues, I have begun > reworking some of my homemade pieces of equipment using insulated coax > connectors. My goal is to have one ground connection only in the cases, and > that is at the power entry point, either a power cord or the outer terminal > of a DIN. I am also installing isolation baluns on inputs and/or outputs. > > Insulated BNCs are readily available. Others not so. In some cases, there is > not room to install an insulated BNC. I am not finding any insulated SMA, > SMC, SSMA, or SSMC despite googling and searching catalogs. > > Does anyone know of a source for insulated small threaded coax panel > connectors? > > Another option would be a compact insulating bushing that an SMA panel > connector, for example, could be mounted in. I am not finding anything like > that either... In fact the ideal solution would be an insulated SMA with an > integrated 1:1 balun. > > And I am not thinking about using plastic cases - that would introduce a > whole other set of problems. I think about my lab area at work where a bundle > of dozens of gigabit ethernet cables run through the roof directly over the > lab bench - the ambient noise level is quite high. > > Suggestions??? > > The only idea I have some up with is to design something myself, possibly 3-D > printed... Any suggestions about how to get started on something like that? > > Thanks in advance- > Jim ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Query about insulated coax panel connectors?
Hi Mini-circuits will sell you the transformers already in a box. Needless to say, they do charge a bit for that. Occasionally, you can find them on eBay for a more rational price. If you are going the DIY route, incorporating a couple of common mode chokes on both sides of the transformer is probably a good idea. Once you get rid of 60Hz, the next problem is all the crud your cell phone or WiFi device is spouting ….. Bob > On Oct 24, 2020, at 6:35 PM, paul swed wrote: > > Jim > A couple of other suggestions. > A 1:1 Mini circuits transformer external to the unit They are quite small > and offer electrical isolation also. Use a small pomona box etc. > Another possibility is the typical RCA phono jack and plug. They come in > insulated models. Understanding its not 50 ohms but the discontinuity > length is pretty short. > Good luck and what you are doing does work. > I actually use the small 100 bT ethernet transformers from China. DIP size > two to a 14 pin package. Seriously does the job something like 500 Vac > isolation and no ground loops. They are inexpensive or at least were. 10 X > $2 or something silly and had been free shipping. Who knows these days. > Regards > Paul > WB8TSL > > > On Sat, Oct 24, 2020 at 4:44 PM AC0XU (Jim) > wrote: > >> Time-nuts: >> >> Having recently run into major ground loop noise issues, I have begun >> reworking some of my homemade pieces of equipment using insulated coax >> connectors. My goal is to have one ground connection only in the cases, and >> that is at the power entry point, either a power cord or the outer terminal >> of a DIN. I am also installing isolation baluns on inputs and/or outputs. >> >> Insulated BNCs are readily available. Others not so. In some cases, there >> is not room to install an insulated BNC. I am not finding any insulated >> SMA, SMC, SSMA, or SSMC despite googling and searching catalogs. >> >> Does anyone know of a source for insulated small threaded coax panel >> connectors? >> >> Another option would be a compact insulating bushing that an SMA panel >> connector, for example, could be mounted in. I am not finding anything like >> that either... In fact the ideal solution would be an insulated SMA with >> an integrated 1:1 balun. >> >> And I am not thinking about using plastic cases - that would introduce a >> whole other set of problems. I think about my lab area at work where a >> bundle of dozens of gigabit ethernet cables run through the roof directly >> over the lab bench - the ambient noise level is quite high. >> >> Suggestions??? >> >> The only idea I have some up with is to design something myself, possibly >> 3-D printed... Any suggestions about how to get started on something like >> that? >> >> Thanks in advance- >> Jim >> >> >> >> ___ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. >> > <20F001N.pdf>___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Query about insulated coax panel connectors?
Jim A couple of other suggestions. A 1:1 Mini circuits transformer external to the unit They are quite small and offer electrical isolation also. Use a small pomona box etc. Another possibility is the typical RCA phono jack and plug. They come in insulated models. Understanding its not 50 ohms but the discontinuity length is pretty short. Good luck and what you are doing does work. I actually use the small 100 bT ethernet transformers from China. DIP size two to a 14 pin package. Seriously does the job something like 500 Vac isolation and no ground loops. They are inexpensive or at least were. 10 X $2 or something silly and had been free shipping. Who knows these days. Regards Paul WB8TSL On Sat, Oct 24, 2020 at 4:44 PM AC0XU (Jim) wrote: > Time-nuts: > > Having recently run into major ground loop noise issues, I have begun > reworking some of my homemade pieces of equipment using insulated coax > connectors. My goal is to have one ground connection only in the cases, and > that is at the power entry point, either a power cord or the outer terminal > of a DIN. I am also installing isolation baluns on inputs and/or outputs. > > Insulated BNCs are readily available. Others not so. In some cases, there > is not room to install an insulated BNC. I am not finding any insulated > SMA, SMC, SSMA, or SSMC despite googling and searching catalogs. > > Does anyone know of a source for insulated small threaded coax panel > connectors? > > Another option would be a compact insulating bushing that an SMA panel > connector, for example, could be mounted in. I am not finding anything like > that either... In fact the ideal solution would be an insulated SMA with > an integrated 1:1 balun. > > And I am not thinking about using plastic cases - that would introduce a > whole other set of problems. I think about my lab area at work where a > bundle of dozens of gigabit ethernet cables run through the roof directly > over the lab bench - the ambient noise level is quite high. > > Suggestions??? > > The only idea I have some up with is to design something myself, possibly > 3-D printed... Any suggestions about how to get started on something like > that? > > Thanks in advance- > Jim > > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > 20F001N.pdf Description: Adobe PDF document ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Query about insulated coax panel connectors?
Dear Jim These, in conjunction with some M6 nylon washers, work OK for isolating an SMA bulkhead feedthrough from the case: https://www.minikits.com.au/components/hardware/washers/Metric-M6-Washers (the nylon shoulder washers down the bottom) The connector will rotate though if you try to torque up the SMA nut - you can really only make them finger tight. Otherwise, you can buy isolated bulkhead feedthroughs eg https://www.fccable.com/SMA-Female-To-SMA-Female-Bulkhead-Isolated-Ground-Adapter/2068/A1636/ or https://www.centricrf.com/adapters/sma-adapters/sma-to-sma-bulkhead-adapters-18ghz/c3150b-sma-f-f-isolated-ground-bulkhead-adapter/ I never found anything cheaper than about $US20 per connector. Cheers Michael On Sun, Oct 25, 2020 at 7:44 AM AC0XU (Jim) wrote: > > Time-nuts: > > Having recently run into major ground loop noise issues, I have begun > reworking some of my homemade pieces of equipment using insulated coax > connectors. My goal is to have one ground connection only in the cases, and > that is at the power entry point, either a power cord or the outer terminal > of a DIN. I am also installing isolation baluns on inputs and/or outputs. > > Insulated BNCs are readily available. Others not so. In some cases, there is > not room to install an insulated BNC. I am not finding any insulated SMA, > SMC, SSMA, or SSMC despite googling and searching catalogs. > > Does anyone know of a source for insulated small threaded coax panel > connectors? > > Another option would be a compact insulating bushing that an SMA panel > connector, for example, could be mounted in. I am not finding anything like > that either... In fact the ideal solution would be an insulated SMA with an > integrated 1:1 balun. > > And I am not thinking about using plastic cases - that would introduce a > whole other set of problems. I think about my lab area at work where a bundle > of dozens of gigabit ethernet cables run through the roof directly over the > lab bench - the ambient noise level is quite high. > > Suggestions??? > > The only idea I have some up with is to design something myself, possibly 3-D > printed... Any suggestions about how to get started on something like that? > > Thanks in advance- > Jim > > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
[time-nuts] Query about insulated coax panel connectors?
Time-nuts: Having recently run into major ground loop noise issues, I have begun reworking some of my homemade pieces of equipment using insulated coax connectors. My goal is to have one ground connection only in the cases, and that is at the power entry point, either a power cord or the outer terminal of a DIN. I am also installing isolation baluns on inputs and/or outputs. Insulated BNCs are readily available. Others not so. In some cases, there is not room to install an insulated BNC. I am not finding any insulated SMA, SMC, SSMA, or SSMC despite googling and searching catalogs. Does anyone know of a source for insulated small threaded coax panel connectors? Another option would be a compact insulating bushing that an SMA panel connector, for example, could be mounted in. I am not finding anything like that either... In fact the ideal solution would be an insulated SMA with an integrated 1:1 balun. And I am not thinking about using plastic cases - that would introduce a whole other set of problems. I think about my lab area at work where a bundle of dozens of gigabit ethernet cables run through the roof directly over the lab bench - the ambient noise level is quite high. Suggestions??? The only idea I have some up with is to design something myself, possibly 3-D printed... Any suggestions about how to get started on something like that? Thanks in advance- Jim ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
