SMA vs SMA-RP

[uer166]

New to RF and I see regular SMA and "reverse gender" SMA-RP connectors which obviously aren't compatible, and there doesn't seem to be a good reason as to why. Is there any advantages of one vs. the other? I currently have random SMA, SMA-RP, N, BNC stuff and it would be nice to standardize on one kind, but equipment in the wild seems to have any and all combinations.

[antenna]

SMA-RP are typically used for wifi applications.  Why?  I have no clue.  I can only assume it was to limit the use of external antennas by those who happen to have the standard SMA cables back when these SMA to SMA-RP adapters weren't so commonly available.  Perhaps I am wrong and it was a way to prevent someone from accidentally using a baofeng antenna on the router and frying the output...  Today, the RP connectors are exclusively used just to piss people off.

[TheUnnamedNewbie]

After having ordered 50 RP-SMA's by accident at some point I went digging, and what I found back then was that this was an attempt to ensure that 'silly consumers' would use the wrong antennas or connect 'non-original' accessories to the antenna ports of their wifi routers.

But in the end the issue is the same as whenever people make custom screw heads or other non-standard components: The accessory markets takes about 3 days to figure it out and pivot to your 'custom' solution.

[ejeffrey]

Yes, RP-SMA is strictly a FCC compliance thing for consumer electronics that is approved for use in the ISM bands only as specified by the manufacturer.  You aren't supposed to attach an external amplifier or 3rd party antenna to a consumer access point.  The RP-SMA is just supposed to make that slightly more inconvenient, but of course since the companies who develop and test these things need to connect them to test equipment, adapters exist.  But it at least means that people are slightly less likely to directly plug an access point into some off the shelf 6W power amplifier.  In any case, you basically shouldn't use RP-SMA for anything.

[nctnico]

The main disadvantage of SMA vs. BNC in my opinion for lab bench gear is just that it is harder to mate / unmate the SMA properly vs. the quick half-turn and pull that is OK for BNC.  So an oscilloscope probe or function generator test lead or something using SMA would be less convenient to attach / detach than SMA for mechanical reasons.   So that and cheap / common cables is why if you are only using HF/below frequencies maybe for some instruments BNC cables can be convenient.

Actually I'm wondering why people are using SMA for bench use in the first place. They tend to get lose and ideally you'd need to torque SMA to make a good fit. I'm working on getting rid of SMA and use SMB instead. Plug & play...

[TheUnnamedNewbie]

Actually I'm wondering why people are using SMA for bench use in the first place.

For me, it's a convenient connector that goes up to 27-ish GHz, and if you get 3.5mm o4 2.92 mm connectors, which are thread compatible, you can go up to 40 GHz. SMB only goes to what, 4 GHz? In which case I would just use BNC if that is your requirement. If you want to go higher or do precise measurement, SMA is just a better, more repeatable connector.

They tend to get lose and ideally you'd need to torque SMA to make a good fit.

Yes, you should always torque those connectors. For most non-metrology stuff, a 20 buck torque wrench of ebay is fine. The actual torque doesn't matter that much in those cases - it's just that you can't finger-torque them hard enough for them not to wiggle loose, but it's very easy to absolutely destroy them with an 8mm wrench before you even realize you are putting so much torque into the connector.

[rfclown]

Actually I'm wondering why people are using SMA for bench use in the first place.

For me, it's a convenient connector that goes up to 27-ish GHz, and if you get 3.5mm o4 2.92 mm connectors, which are thread compatible, you can go up to 40 GHz. SMB only goes to what, 4 GHz? In which case I would just use BNC if that is your requirement. If you want to go higher or do precise measurement, SMA is just a better, more repeatable connector.

They tend to get lose and ideally you'd need to torque SMA to make a good fit.

Yes, you should always torque those connectors. For most non-metrology stuff, a 20 buck torque wrench of ebay is fine. The actual torque doesn't matter that much in those cases - it's just that you can't finger-torque them hard enough for them not to wiggle loose, but it's very easy to absolutely destroy them with an 8mm wrench before you even realize you are putting so much torque into the connector.

Me too. I use BNC for clocks and such, but SMA for most everything else. You'll see N to SMA adapters on most of my equipment. I have piles of attenuators, mixers, splitters, etc. that are SMA. SMA edge mount connectors are easy to use for prototype PCBs. Consistent and works well with finger tightening for <=2.4 GHz. When I do 6 GHz I pay more attention to the quality of the connector and the torque to get consistent results. Avoid really cheap eBay SMA connectors.

[tkamiya]

On DIY test equipment, I typically use N.  Occasionally BNC but rarely SMA.  Issue with SMA is connect/disconnect cycle is limited (about 300 to 400 depending on manufacturer)  I can use connector saver but then there is this long thing waiting to be bumped and snap off.  Also, brass type BNC torque spec is rather low and over torquing will result in stripped thread.