#626

Episode 626
Different types of SMA connectors and how to identify them
en.wikipedia.org/wiki/SMA_con...
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[@aronhighgrove4100]

8:15 this is so called RP-SMA, reverse polarity SMA. It was introduced to prevent people from using WiFi antennas that extend the range beyond what is allowed. RP-SMA was supposed to be harder to source, which is not the case anymore today.

[@OC35]

The last connectors are called rp SMA. (Reverse polarity). They are used on wifi equipment.

[@Roadrunner48]

You are right, I discovered that some years ago when I was operation with WLAN amplifiers.

[@teapot9514]

If it was RP it would have female inside and male outside. Or the other way around..

[@ismaelyu5]

@@teapot9514 it is RP-SMA, usually sex is determent by the conducting core, here its not.

[@subramanianr7206]

Yes, similarly I once got stuck with 75 ohm BNC connectors. The usual 50 ohm cables (like RG58, RG213) have a capacitance of around 30 pF/foot length. And the 75 ohm cables (RG59 or RG11) have 20 pF capacitance per foot length. The diameter of the center pin, the width of the dielectric (of course the dielectric constant of the material too matters) would decide the capacitance per foot length of the cable. Sub miniature coax connectors do have the reverse polarity types; some of the connectors on the VHF/UHF HTs do have the RP connectors and we have to look for proper interface to connect to the standard connectors we have already. 75 ohm SMA connectors are having very deceiving looks from the outside.

[@paolomonai9511]

Good evening. No, you are wrong about SMA-like connector compatibility. First of all, it is right: SMA are usable up to 18 GHz, even though there is a special type, called super SMA, rated to up 27GHz. One manufacturer is a company called SOUTHWEST inc. ; then, what you call 2.92mm it also known as K connector, originally developed by WILTRON company (nowadays Anritsu-Wiltron). It is rated for overmode free operation up to 40 GHz but its dielectric is AIR not TEFLON as in the regular SMA. K connector and SMA connector are compatible . You can join, for example, a SMA female and a K male, using a torque up to 3 lb/inch to preserve K mechanical integrity. As far as 2.4mm, this was the HP response to Wiltron K proposal and it is usable up to 50GHz. To connect a 2.4mm to a K connector (or SMA) you need a special (and expensive) adapter. If you want to increase frequency range, up to 67 GHz, the right choice is 1.8mm and to reach 110 GHz the choice is 1mm...but these are for very esoteric and limited applications. Back to SMA-like, the most important difference between K and SMA connectors is this: K is a precision connector, a professional instrument grade connector suited to situations related to determine tne exact reference plane of your VNA measurement. On thecontrary this is NOT possible with SMA connector. In fact calibration standards (I mean OPEN, SHORT or THRU) are commercially available ONLY for K connector. Sorry, for this long post but there are a lot of things to consider...regards from Italy.

[@kariputtonen]

The Signal Path went through those different connector types with other components few years ago: kzbin.info/www/bejne/bJzakqB5nZaEoac

[@dorleysflir5350]

Thank you for the video, very informative and appreciated that you were able to help me access it, Thank You. ​@@kariputtonen

[@DavidPaauwe]

You forgot only 3.5 mm connectors, which also intermate with SMA, but have an air dielectric like the K/2.92. So for SMA compatibility there are SMA, Super SMA, 3.5, and K/2.92. I believe the 2.4 and 1.85 mm connectors also intermate. I used to work at a company as a machinist, then engineer designing RF and MW connectors and adapters. I never really understood RF theory beyond determining the right line diameter ratio for 50 ohm, and figuring out how to make connectors/adapters with low VSWR via clever transitions in the dielectric material and conductor diameters. I don't remember selling too many 3.5 mm connectors now that I think of it.

[@paolomonai9511]

​@@DavidPaauwe😂 Yes, you are right! My fault...3.5 mm connector was an intermediate step, since It was rated upto 26.5 GHz. It was mainly supported by HP in equipment operating upto that frequency limit, such as RF frequency generators or test sets included into VNA (i.e. Vector Network Analyzer) systems and associated Cal Kit for Calibration procedure. They were rapidly, say forgotten, in favour of K connector whose upper frequency was over 40 GHz. Remarckably, 3.5mm and K were perfectly mechanically compatibile without any adapter in between...I mean you could connect directly a 3.5mm female tò a K male...Old good times!!! Regards from Italy.

[@W8ASA]

The connector with the smaller xmsn line diameter seemed to have a part number stamped on it. Give us the part number and maybe we can find out more information.

[@dri50]

We are in the year 2020 where there are actually 4 different "sexes" of SMA connectors. (as you have discovered). The ones with pins reversed are actually called RSMA's (for Reversed).

[@theamericans2219]

What is with you... Thinking you are suppose to know what you are ordering... I'm finding the problem being... no listings for as you say " RSMA's " Best I can do is make sure the references in the listings photos are what I am wanting... This genius didn't even look at the items detail... Which is OK... HE WILL FROM NOW ON... :)

[@PapasDino]

I made that mistake just the other day when using a BaoFeng radio as a "test set"...was also using another rig and got the adapters mixed up - the BF has a male SMA connector and the other one has a female connector. I screwed the BF adapter into the other radio and couldn't figure out why there was no movement of the Bird wattmeter needle...duh, dumb , rookie mistake! I'll second the other commenter who offered that you can put a couple hundred ohm pot on the end of the red cable to determine the impedance which I'm guessing will be 75 ohms.

[@truglodite]

FWIW, @2:50 in the video, the red cable rotates itself loose right before you install the load on the other end. Not sure if you noticed that, or if it affected your measurements. So wanted to mention just in case.

[@IMSAIGuy]

I did see that, no change

[@glaura1581]

Thanks for a wonderful detailed video, certainly it is helpful for me. In addition, Compared to SMA connectors, SMB connectors are easier to install.and elecbee connectors as well as others. it also has ic products, too. thanks.

[@choifiona3127]

i think it's really helpful for me and i will recommend this video to my friends.and have you ever used SMA connectors in luckyconnectors from China? thanks!

[@herbertsusmann986]

I ran into reverse polarity SMAs recently when ordering a 900 MHz antenna. Had to order rpsma to sma adapters. Why in the world are there two types? Just mke the regular. What purpose do rpsmas serve?

[@rfengr00]

It’s an attempt to keep people from hooking up high gain antennas to WiFi equipment.

[@ismaelyu5]

@@rfengr00 its used on gear with multi antennas and frequencies for example aircrafts, there isn't just the average consumer

[@Papa7Bravo]

I hope you can help, i'm restoring my car and got an alliscom gct puck antenna, it has 2 plugs, one being SMA and the other is what seems to be a slightly smaller version of it, it has rhe same threaded nut fitting but it has a kind of hollow pin in the middle that is kept in place by a white collar. I'm hopefully needing a simple adapter to make it SMA for a laptop dock that is said to have SMA passthrough's for wlan wwan and gps. Worst case... can i just cut the plug off and crimp a SMA on instead?

[@IMSAIGuy]

SMC connector?

[@Papa7Bravo]

@@IMSAIGuy it is, that's awesome, thanks, i don't get why my searches of "mini sma" and trying to find all types of sma connectors, never was SMC shown.

[@m0kov]

Out of interest. I've been using the NanoVNA to calculate quarter wavelength coax stubs and have found that at vhf/uhf frequencies, the stub length turns out to be quite a lot shorter than by using the published vf. The vf was measured as correct using propagation delay and a scope of known accuracy. Could this be an interesting future video? 73 Steve

[@IMSAIGuy]

I did this video: kzbin.info/www/bejne/moaspGSkq7asn9k

[@m0kov]

@@IMSAIGuy Thanks for the reply. It wasn't the vf measurements where I found an anomaly it's when I used this information to cut some quarter wavelength stubs. These quarter wavelength coax stubs were to transform 28 ohm to 50 ohm on a new Yagi build and they were not performing correctly. I used the NanoVNA to find where they were resonating and the frequency turned out to be far lower than it should have been. After searching the internet I found someone else had had similar experiences. DG7YBN Phasing and Matching Lines and Baluns, had run similar tests. Interesting stuff. 73 Steve

[@djohnsto2]

Haha yeah the RP-SMA. Somebody's bright idea to prevent people from hooking up Yagis to WiFi/BT stuff. I think it causes only a minor inconvenience to everybody except those trying to hook Yagis to WiFi/BT stuff - Because the online tutorials they follow have links to buy the right adapters.

[@npgatech7]

There is some writing on the red connector, couldn't find a frame in your video where I could read it. Can you post it? Edit: Found a frame where it says 26805. It seems like an Omni Spectra OSM connector - ofcourse top quality for military aviation use. OSM has been acquired by M/A COM. The connector you have most likely is Made in U.K. Good stuff.

[@IMSAIGuy]

so what are the specs? impedance?

[@IMSAIGuy]

the stamping on the connector: AMERICON 26805

[@zeljkoadzic1692]

The red cable is not 50 ohm. That circle is showing you that your terminator is mismatching the cable impedance. Since you like building your own test gear, build a terminator with a potentiometer, dial it to the smallest circle your can get, and then read the value with a ohmmeter. That is likely your cable impedance. Those right angle connectors are RP-SMA. They are used on routers/APs. The FCC tried to make it difficult for people to hack with their wifi gear and change the antennas to something more useful. The industry solution was to reverse the pin, so the WiFi equipment is incompatible to standard stuff. However, you can now buy just about anything in RP, so it just made things complicated for no reason.

[@subramanianr7206]

Exactly correct. The red one maybe of 75 ohm impedance.

[@galileo_rs]

VNA can easily measure the impedance of a cable, no need for a pot.

[@rjordans]

If you want to be more accurate in measuring the cable impedance at a given frequency do the following: measure z11 first with the open standard at the end of the cable and then with the short standard. Calculate the cable impedance as the geometric mean of both measured values (multiply both and take the square root of the result)

[@AECRADIO1]

Red cable might be a phase adjustment cable.

[@RyanHannaProductions]

Good idea

[@caleb7799]

ok that fidgeting is no bueno

[@chrisscott1547]

I hate 75 ohm flavors of standard connectors.

[@pinox61]

the last cable was not tide properly

[@IMSAIGuy]

I noticed that but it measured the same as when tight. I had already measured it once before the video.

[@andrewstone8999]

It's a 75 ohm cable. When you connect a cable of an unmatched impedance to a VNA, it traces a circle around the cable impedance on the smith chart. You can see in the chart the circle going through the 50 ohm center of the chart and the line marking 100 ohms, therefore, the impedance is right in the middle, 75 ohms.

[@IMSAIGuy]

I used to think the same thing. My friend did a mathematical derivation and it actually does not circle that point. I don't have the math (or understand it) but he is smarter than me. A separate measurement puts that cable at 91ohm

[@IMSAIGuy]

kzbin.info/www/bejne/p53MqGR6iqd5fdU

[@IMSAIGuy]

here it is: After slogging through the math, you can get Zo of the unknown cable by finding Rmiddle (resistance at the middle of the circle with 50 Ohm load) and then using this formula: Zo = sqrt( ( Rmiddle*3*50^2 - 50^3 ) / ( 3*50 - Rmiddle ) ) or you can calculate the resistance at the middle if you know Zo: Rmiddle= (-Zo^2*150 - 50^3) / (-Zo^2 - 3*50^2) So for 500 Ohm coax, the middle is at 146.1165 Ohms. For 90 Ohm coax the middle is at 85.8974 Ohms.

[@jimsouthall1085]

Quit moving the devices around so much. It very distracting and we can not get a good view of the devices.

[@rosswines]

stop panning in so close on the cables initially and fiddling/moving around+++ so much especially on macro , extremely annoying !!! Better editing would be good as well.