BNC Cables and Connectors for Test Equipment like Oscilloscopes - Page 1
Forum section: electronics / beginners

author: radiohomebrewer2000
author_rank: Contributor
timestamp: August 05, 2022, 09:56:39 pm
content: Hello,What BNC parts would I need for various test equipment and radios?I recently paid for an oscilloscope and an arbitrary waveform generator. Nothing exciting. The used scope I got for $55. Both use BNC connectors which seem to be the standard for scopes and signal generators. But also QRP (low-powered) ham radios.I am working my way through a book named Electronics of Radio.The book in Appendix A lists variables BNC cables and adapters which are needed.I have not used anything that has BNC connectors.What is the difference between a BNC 50ohm load and BNC 50-ohm termination?Could one of them be a dummy load and the other a pass-through 50-ohm connector to provide a matching impedance?What is the difference between a BNC tee and a BNC union?I have a 50-ohm Dummy Load for 300-watts, but it has a UHF Female (SO239) connector.Now, I understand it is important to know if the cable is 50-ohm or 75-ohm. I need 50-ohm.But is it important for a connector or adapter to know if it is 50-ohm or not?I am familiar with the terms used in ham radio but not when it comes to engineering/test equipment.List of BNC and banana items to get:------------------------------------------------------ BNC to mini-hook adapter (get multiple)- BNC tee (get multiple)- BNC cables:- 30-inch BNC cable (get multiple) <-- hard to find- 18 inch BNC cable (get multiple)- 10 meter BNC cableSome of these cables are "sync".Not sure if that is just a label to indicate how it would be usedor there is something special about a "sync" cable.- BNC 50-ohm load (is this a Dummy Load? But has a BNC connector?)- BNC 50-ohm termination. Not sure what is different between the BNC 50-ohm load and the termination here?- BNC union. a different type of Tee?- BNC barrel. Just a female to female adapter or male to male adapter or coupler?- BNC to banana plug adaptor- banana test hook to minihook test leads (get multiple)- banana patch cords (red and black) (get multiple)Here are some possible items that give me a clue:Set of 4 BNC Adapters 1 (F-F-F) Tee, 1 (M-F-F) Tee, 1 (F-F) Coupler, 1 M-M UnionThey do not specify the impedance here.https://www.ebay.com/itm/224590289529?_trkparms=amclksrc%3DITM%26aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3Db564e1a6eb8b4514a9fc6854a5af9eb4%26pid%3D100675%26rk%3D3%26rkt%3D15%26sd%3D385033328062%26itm%3D224590289529%26pmt%3D0%26noa%3D1%26pg%3D2380057%26brand%3DPomona&_trksid=p2380057.c100675.m4236&_trkparms=pageci%3A70330e65-1504-11ed-8e12-4260620d042e%7Cparentrq%3A6fe19aa21820acf1b4c3272cfffd8e6e%7Ciid%3A1BNC Male Dummy Load Termination 50 Ohmhttps://www.ebay.com/itm/232945960798?hash=item363ca9475e:g:J0QAAOSwcWtbr7mN&amdata=enc%3AAQAHAAAA4MhQLmMvGoZHHgup9pYZmnDNIAYjLTAEXeveTFEDdiRnE8%2Fd9EP%2BmCSRllCfW2HSY9IXKy0WsrxlX%2Blcf7ByusRhV5%2FgRD9Z3mC9YnHM3T5K2CQxQcgs0oHnyZ6j64e0sINtMV8xRU%2BJ8B7E8fTL1xgOpOKcndmXgdV6Ec%2BiUfCW4BvAXeFMNcvNVDWnoeMH3x5KPz%2B2klBPIjy2NItvdUNkVNeOzRljmAvXDmyKgVhK4B4UJ4VgYVNeDyMNuOVhNG0IvPttcuHy2c2xkryuA5oeW9hguQYsFVaL%2Bbn2NorJ%7Ctkp%3ABFBMltGZ_s1g2X Copper Adapter 50Ohm 38.5mm Insert Type BNC Feed Through Terminator 50Ω A764https://www.ebay.com/itm/175016142413?hash=item28bfc6664d:g:vK4AAOSwvrZhi2ZoAnd of course, I will need to get lots of adapters to go between BNC and existing equipment that use UHF or SMA.The Problems (Lab Exercises) in the book has various experiments but also builds a Norcal 40A CW Transceiver. The input is 12 or 13.8VDC and the RF output is 2watts. And of course, ham radios have 50-ohm impedance. So, I think the BNC terminations or loads need to handle this.Places that I have seen these BNC parts: amazon, ebay, mouser, jameco, and allelectronics. Any others places that are good but crazy expensive?Thanks,Daniel

author: Benta
author_rank: Super Contributor
timestamp: August 05, 2022, 10:08:27 pm
content: You're the wet dream of a Test Cable Salesman/Woman.You need two oscilloscope test probes for your 'scope. Those are always BNC.Then you need a BNC...BNC cable to trigger your scope from the AWG.And then you need a third 'scope test probe to let your AWG inject a signal into your device under test.Start from there, and then see what you need additionally later on.Cheers.

author: tooki
author_rank: Super Contributor
timestamp: August 05, 2022, 10:36:16 pm
content: Yes, 50 ohm and 75 ohm BNC connectors are slightly different, see attached photo.

author: El Rubio
author_rank: Regular Contributor
timestamp: August 08, 2022, 05:56:31 am
content: Don’t go overboard with cables and connectors you won’t use very much. What do plan to work on mostly?.I have 4 BNC to mini grabber clips and have never used all of them at once. 2 would be a good start and make sure you get quality mini grabber clips like those made by Pamona.I had made up several BNC to BNC coaxial test cables. I have the tools and experience making quality test cables. I found 3-6ft is plenty long enough for my needs. I made 2-3’ and 2 - 6’. These are used from sig generators to DUT, or using a tee split to observe on scope and freq counter, or Distortion analyzer. Tee’s are 2:1 splitters. Unions are barrel connectors most often fem to fem. Godd to have several of each. I like to work on vintage audio gear and have several bnc to rca adapters both genders. Also made up left and right bnc to rca test cables.Your dummy load is probably fine for most testing as long as impedance and freq range is within the dummy load specs. A terminator provides a load typically 50ohms, but is usually rated for 1-2 watts max. Dummy load is the same thing, but handles more power. I have several and most have N connectors. Get adapters for the common connectors you use. This is a never ending acquisition. Just get what you need at the time. You will want BNC’s to so239 to connect your dummy load and to match up with the radio you are testing.Mini grabbers are great on dmm’s too. Get an attenuator or two. Something rated for at least a few watts or at least the power of whatever you intend to test mostly.You can find most of this stuff at hamfests . Large dummy loads and high quality connectors/ adapters will add ip $ quickly.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: August 10, 2022, 01:13:08 pm
content: There are innumerable posts on these topics. Look aroundYou need the correct probes for your scope. The scope usually has the capacitance of the probes marked on the input BNC,Get 10X probes.This will help preventing you from damaging the scope while providing a good scope input.Does your scope have a 50 ohm setting? If it does you will not need a 50 ohm termination for it,What freq is your scope good to? Get probes that are good for more freq than your scope's stated freq. The ones that are 1X and 10X adjustable should be avoided, IMHO. Cheap Chinese made probes are usually just fine. (Almost all probes are made in China, even the expensive Agilent etc....)I do not know what sort of scope you have, Old scopes are rated for the freq where the scope reads 80% of what is should, but usually go quite a bit higher with a visible trace. Newer scopes usually are good to the stated freq but "fall off a cliff" just beyond that.A 50 ohm input on a scope essentially turns the scope into a 50 ohm load for measuring low power outputs of small amps and such (QRP Stuff).If you put too much power in you will burn up something in your scope or your termination. If you are using a 10X probe, you are not letting in much power.A termination provides a 50 ohm load to the generator while letting a signal go thru for the scope. A load is just a fancy resistor that works at stated freq.If your scope has a 50 ohm setting the "termination" is inside the scope.The higher you go in freq, the better the coax you will need. Look at some specification charts.You can make your own BNC to BNC test coax, in the length you need.Some coax is much better than others. RG 223 (double shield) is good for test leads (there are other coaxes that are good too).You need coax that is good at the frequency you are using, Loss is less important since you are using only a few feet of coax.There are lots of BNC test coax that are made from RG58. RG58 is all over the map with some of this coax being good and some not. For HF (not VHF) this probably does not mater.There are all sorts of BNC connectors that you can buy. Most are 50 ohm. Read a little about crimp connectors and the other connectors. For crimp connectors you need a proper crimping tool, these can be expensive. Other connectors are harder to connect to the coax, if you make your own coax leads. But they do not require a crimping tool. I have tried to use crimps without the tool and the results are not inspiring.Yes you can get this stuff at Hamfests. Usually bigger hamfests have a few vendors who specialize in connectors. They can help.Sometimes there are ready made BNC test leads used, some are very inexpensive and some are quite good also. some are just awful.You can get SO to BNC adaptors. SO 239 are not very good at or above VHF"T" connectors have limited use but pick up two. They really do not "split" the signal equally. You need a "splitter" for this later.Unions or Barrels are just connectors between two BNCs. There are ones made for mounting on a chassis and ones made for "in line" connections. They are really the same thing electrically.By the way, any scope for $55 is a great buy, maybe except for some of the cheap computer based scopes, (some of which can be quite good also)Just a suggestion:Make a 50 ohm load out of a PL connector and a 1 watt (or more) 50 ohm resistor (maybe 1%), Or two 100 ohm big resistors in parallel. Big resistor for easier connection with your scope leads, not because your generator is that powerful. Make it so the resistor leads are easily accessible. Feed your signal generator into it using an adaptor. You can then attach your scope leads to the "load" to see how they work. You can compare this with just putting your signal directly into your scope with BNC jumper...compare the various freq and types of waves.Have fun getting to know your scope.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: August 10, 2022, 01:14:32 pm
content: List of Hamfests:http://arrl.org/hamfests-and-conventions-calendarEdit:I picked up a 500 watt several GHz load at a hamfest recently for $35You never know what someone want to get rid of.

author: radiohomebrewer2000
author_rank: Contributor
timestamp: August 10, 2022, 11:28:29 pm
content: Everyone, thanks for the replies.Quote from: El Rubio on August 08, 2022, 05:56:31 amHam Radios of course! LOL.Well, more specifically, QRP HF radios, accessories, and test tools for QRP HF like a z-match tuner I am home brewing to go with my QRP radios. QRP HF Transceivers like QRP-Labs QCX (not the mini or plus), 5 Watter from kitsandparts.com, and a NORCAL 40A. The NORCAL 40A transceiver is the radio that you build as part of the Problems (you can call them Lab Exercises) in the book Electronics of Radio. I even got a Kindle book that showed how to use a Rigol scope to see the output of a Two Tinned Tuna transmitter. So, I may do that too. And then you can look at the FFT to use as a poor-man's spectrum analyzer to see the harmonics.I have all the parts and boards to build the Norcal 40A and experiments for the book - except test tools like an oscilloscope, arbitrary waveform generator, and BNC cables and adapters.I recently got a scope off ebay for $55 and it is being delivered, so I will see if it works or not once I get it. If not, then I have some home work to do on how to fix it. I got a cheap Juntek 2800 arbitrary waveform generator that goes up to 60MHz for $81 on ebay which is being delivered from China. And I have in my possession 2 count of 100 MHz 1x/10x probes I got off from ebay for $15.The used oscilloscope I got was a HP 54600B digital scope. I know people on EEVBlog are no fans of this model because of the low sample rate. But, it is a beginner scope for me. Later, I may get a Rigol or Siglent scope - I am really eyeing the Siglent SDS1202X-E. I really like the FFT with its markers on the Siglent 1104X-E but way out my price range. Even the SDS1202X-E I would be stretching... that budget there. I need the 200MHz bandwidth to probe the 10m band. However, not sure what I would do with a 4-channel scope.However, down the road once I complete my learning from various books like Electronics of Radio, I plan on creating my own VFO using a Si5351A synthesizer chip and a microcontroller like the Atmel/Microchip ATmega328P. I have seen people use this to create their own home made signal generator too. But the Si5351A's output is square wave, so I would need low pass filters to create a nice clean sine wave. And possibly an RF amp to variably increase the power output.QRP being low-powered - 5 watts or less RF output. (For others reading this thread)HF being High Frequency bands (also called Shortwave) from 3 MHz thru 30 MHz.However, I am mostly interested in the bands like 80, 40, and 20 meters since they tend to be open most times of the year. However, 10meters is tempting with the E openings in the summer and with sunspots getting better in cycle 25.I was planning on buying some 2 to 3 foot BNC jumper cables. But, I could buy some BNC connectors for RG8X (also called Mini-8) for the RG8X cable roll I never used. I think RG58 is near the same diameter as RG8X. I bought this roll of coax to run lines under the house up through existing cable tv holes and then crimp some UHF connectors, but I found a different way to bring in coax for my antennas.Quote from: Wallace Gasiewicz on August 10, 2022, 01:13:08 pmNo, I think the HP 54600B only has a 1M-ohm which it says on the front. I looked through the manual and I did not find any setting.Hmmm. I think I will need to do that since most of the terminators I looked on line are a quarter of a watt or a half-watt. I already have a bunch of 100-ohm resistors. I used them in parallel for 50-ohms in my z-match. Sadly, I put SO-239 connectors on it. I should have put BNC connectors on it since this is what most test equipment have like scopes and it is what QRP radios mostly use. I did find a 10-watt dummy load with BNC male for about $20. So, if it is not too heavy, I probably could use it as a terminator on a tee?I know down the road once I worked through the book, I want to experiment building all kinds of oscillators and impedance matching networks like Pi, L, Tee, etc. Currently, I built a Colpitts Oscillator to be used as a G3UUR Crystal Tester so I can find 6 matching crystals for the NORCAL 40A transceiver. The crystals are 4.9152 MHz HC49 from DigiKey. And I hooked the oscillator up to a cheap Chinese frequency counter 8-LED green display. The frequency matches what I have hear/see on my rig for the 1st crystal I tested.So, this is what I want to do with my scope and BNC cables and adapters.Thanks,Daniel

author: EPAIII
author_rank: Super Contributor
timestamp: August 11, 2022, 11:47:28 am
content: BNC, in a nutshell:First, while BNC connectors are primarily made for coaxial cable, they are not tied to any particular type or IMPEDANCE of coax. Thus there are BNC connectors that are made for RG-58, RG-59, various miniature (1/8") coaxial cables, and probably a bunch more. And the 50 and 75 Ohm varieties are certainly common, but many have been made for use with 75 Ohm cable intended for composit video (30 Hz to 5 MHz) without having any particular specified impedance.As I more or less say above, they are made to PROPERLY fit only one or perhaps just a few types of cable. Thus a BNC connector that was made for RG-59 cable may not work well with RG-58.Oh, and they come in both solder and crimp styles. And I have seen and used some that are a combination of the two with the center connector being soldered on and the shield crimped. Oh, and then some with the shield being trapped between two parts the screw together. There are many manufacturers of BNC connectors.You asked about fittings. There are Ls, Ts, connectors, and pass throughs. Ls come with two males, two females, and one of each. Ts come with three males, three females, and two of one with one of the other. Connectors are usually called barrels and are used to splice two cables. They usually have two female ends. But I have seen connectors with two male ends. Pass throughs are for running a cable through a box or chassis and also can have two females or sometimes a male and a female. They come with two kinds of mounts: a flange with four screw holes and a threaded barrel with a nut. Some of the pass throughs are liquid or gas tight.I worked with them for over 45 years and I am sure I have not seen every variation. You can literally put a fortune into these accessories so I would suggest that you only buy them as you know you need them. Perhaps just get one or two BNC Ts of the F-M-F variety and, in your case, 50 Ohms sounds like the best.Scope inputs:With very few exceptions, scopes have BNC input jacks and often use them for outputs too. The vast majority of scopes will have a high impedance input with a 1 MOhm impedance with a few pFs of capacitance in parallel with that being the standard. Almost all scope probes sold presently and for the past 50 years will work with those scope inputs.There are a number of different types of scope probes, including 1X or straight in, 10X or with a factor of 10 of attenuation, temperature, current, RF detector, and many more. As I said above, virtually all of them are made to attach to the standard 1 MOhm inputs.Most probes will have a ground connection brought out to the tip where a ground wire or clip can be attached. Also most probes will have a number of interchangeable options for connecting to the circuit: clips, points, hooks, etc. These usually attach with a friction fit.A 1X probe is just a piece of wire or coax attached to a BNC connector. They do not attenuate the signal but they also have less bandwidth than an attenuated probe. For the most part you can not utilize the full rated bandwidth of a scope with a 1X probe (or an unattenuated coaxial connection).10X probes are the most common. They reduce the signal by a factor of 10 so a 10 Volt signal will show up at the input amplifier of the scope as a 1 Volt signal. 10X and other attenuated probes will or at least should have a frequency compensation adjustment. This is usually a variable capacitor at the scope end of the probe which is adjusted with a small screwdriver. The scopes usually have a square wave output available to allow these probes to be adjusted to properly matched to the scope's input.100X probes are available but somewhat rare. They will allow even higher frequency compensation but at the cost of lower gain. For most applications the 10X probe is the best compromise.Some scopes have special BNC jacks that allow automatic switching of the Voltage range depending on if a 1X or 10X probe is attached. A flat, ring like contact surrounds the ground shell of the BNC jack and a contact in the 10X probe grounds it to tell the scope a 10X is in use. Different numeric scales are lit via switched lamps for the two ranges. This is a nice touch but only the higher end scopes and probes have this feature. And you can always use any probe, just doing the math in your head.50 Ohm scope inputs:Yes, they exist. But, IMHO, a scope with a dedicated 50 Ohm input is a very limited scope. Not only are the regular 1X and 10X probes not useful, but the internal load will have a limited power rating so you will need to be careful not to exceed it. Such a scope is used only for RF power and other measurements and can not be easily used for normal circuit work. A 50 Ohm load placed at most places in any but RF circuits will look a lot like a short and may produce instant smoke. I have only seen one such scope in over 55 years in electronics and did not have much use for it.50 Ohm input workaround:In the pouch on my scope I keep some BNC Ts with one female and two male ends. The female end attaches to the high impedance scope input. The coax which connects the signal that needs a termination is attached to a male end and a BNC female connector with a termination resistor to the other male end. This terminates the coax just outside of the scope and is good enough for most purposes. This way loads of any impedance or power rating can be used.But here is the long form:https://en.wikipedia.org/wiki/BNC_connectorI tried to keep it as short as possible.

author: jonpaul
author_rank: Super Contributor
timestamp: August 11, 2022, 01:18:27 pm
content: We have accumulated BNC adapters, cables, probes since 1967.For one just Starting up, suggesting a minimum of....a pair of Tektronix x10 probes sélection for the scope Cin2 X BNC 50 Ohm cable 0.5 m, 2x 1.5m2x BNC 50 ohm thru termnot more!Source...Ebay, Ham fleas ( see ARRL for local chapters fleas)RéférenceProbesTektronix Circuits Concept book Oscilloscope Probe Circuitson tekwiki50..75 ohm, BNC and cables, connectors,Belden Wire app notes and papers of Steve Lampenbon courageJon

author: TimFox
author_rank: Super Contributor
timestamp: August 11, 2022, 01:30:28 pm
content: Although "N" connectors made for 50 or 75 ohms will not mate with each other, the (rare) 75-ohm BNC connector will mate with the 50 ohm connectors.Almost all BNC connectors are the 50 ohm variety, but the cable connectors are made for different sizes of coax and some will accept some 75 ohm cables: the short section of 50 ohm coaxial transmission line through the connector is not a big deal for 75 ohm systems at relatively low frequencies.BNC "Tee" connectors are useful when you need to connect a generator to an oscilloscope and to another circuit: be sure to have the 50 ohm termination at the end of the cable farthest from the source.It's generally not a good idea to put the Tee at the generator and run two cables to different places.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: August 13, 2022, 12:01:34 am
content: If you wan to see voltage at the 50 ohm test load, make some gizmo maybe using a Tee that you can attach a decent probe to.This should work fine for HF and probably VHF. There are loads that I have seen that have a "take off" at the input for connecting a BNC. Probably rare although I have something like this.You can make a pretty good load using a paint can and some resistors. Usually you put oil in the paint can for cooling. Combination of resistors in series and parallel to make 50 ohms. In my experience with these things they work nicely for HF.But although you can make one MFJ still makes them. You can usually pick one up at a Hamfest for $5-10. Some of these things have a non calibrated "take off" connector on them.Essentially when you connect your scope to a load, you are dividing the output of your transmitter. Not much power will go into a 1M ohm input relative to the 50 ohm load. Even less will go into your scope if you use a probe. 10 X less.If you use a Tee and then feed the one line into a 50 ohm termination, half the power will go to the termination and you will essentially have a 25 ohm load, And maybe a hot terminator,Really 50 ohm terminations (not 50 ohm loads) are rarely used, but sometimes you need one if your scope does not have one. I looked at your HP scope and you are correct, it seems it does not have a 50 ohm setting.I picked up a few at a Hamfest for a few bucks. I think I used them once in five years. Some calibration of something I was working on required one.I have a box of New Amphenol 50 ohm BNC loads, maybe a watt, that are available, PM me if interested. I can give you better stats if you are interested.