Crimping vs. Soldering RF cable to connectors

[matthuszagh]

I'd like to start making my own RF cable assemblies and would like to understand the pros and cons of crimping vs soldering the connectors to the cable, as well as any other method if another method exists. I'm mostly interested in BNC cables, but I'm also potentially interested in homemade SMA, N, and possibly other cable assemblies.

To provide some further context, I'm currently leaning toward crimping RG-400 cable based on other threads on this forum. This is intended for general-purpose test cable. It will be connected/disconnected and bent quite a bit. Admittedly, the bandwidth of this cable is probably way overkill for me. But, I like the isolation provided by the double shield. Though, I'm a bit dissuaded by the lack of flexibility.

I would expect that one of the downsides of crimping compared with soldering is the tooling cost. However, I purchased one of these pressmaster MCT frame crimpers (https://www.pressmaster.se/product_leaflet/mct_frame) and am willing to buy further dies to go along with it. If I go the RG-400 route, I'll probably purchase a die intended for RG-58, since the dimensions are very close to the RG-400. I don't currently have anything better than an xacto blade for cable stripping, but may get something higher quality if I experience difficulties using a blade.

One of the appeals of crimping to me is that it seems simpler than soldering and easier to achieve consistent results. But, besides tooling cost is there any reason I should consider soldering instead? What about for higher-frequency coaxial cables such as SMA? I'd like good, durable results. But this is for hobby, not professional use.

Relatedly, does anyone have any particular BNC connectors they like for custom cables?

It's also probably worth mentioning that I have a VNA I can use to test the completed cable assemblies.

[coppice]

With most types of RF connectors you don't really have a choice. The connectors are made for crimp assembly. Some people fudge some connectors with solder, but the results aren't good. Crimp can be a pain if you only want to make a few leads, and have to buy a crimp tool for every connector type you use. However, if you want reliable results, especially when the cables are going to be flexed a lot, that's the price you have to pay.

[Neomys Sapiens]

Well, the series N, TNC, BNC, and SMA are available in the form of soldered inner and clamped outer connector with a compression packing holding the cable mantle tight. To be precise, I even have some of those in SMC size, but I would consider their mounting a penal assignment or even a cruel and unusual punishment. The clamp-type RF connectors forgive even less than the crimped ones and the handling of the screen braid is the critical element. They have the advantage that you can redo a connector that came out crappy. I suggest the following precautions:
- only (and strictly only) use connectors from established manufacturers with available documentation. Do not use any low-cost no-name connector crap. (Suhner, Rosenberger, Radiall, Kings, Pasternack, Amphenol, Automatic Connector..)
- Get the correct mounting instruction for each connector and follow it meticously. Do not try to take shortcuts. If you do not like to look at a 0.5mm-divided ruler often, use vernier calipers.
- Finger-tight clamp won't do
- in some connectors is a special part that clamps the screen braid, in others (regardless of manufacturer or series) there isn't. Can be only checked with the abovementioned docs, especially if the cat connector is already out of the bag. (i refer to the thicker ring with the tapering cross-section.)
- if you want some additional robustness against the cable bending too sharp, you can use a piece of shrink tube. But you should install it right when fitting the connector and it has to be real flush.Use a thinner, harder type and not a soft and thick one, or the compression clamp will not work.
- check the position of the inserted center contact whether correct and retained good. In one case, it will be shoved out, in the other the counterpart will suffer.

General: you are aware that the PTFE-cables like RG-400 are somewhat less flexible than the PVC-isolated ones? If you do not need the performance, the latter might handle easier. I have to look up the suitable double shielded type, but it is not RG-223!

If you go for crimping, do yourself a favour and get a Daniels or Astro M22520 5-01 or 10-01 crimp tool.
Or the one from Suhner or a comparable one from one of the connector manufacturers. Not a Pressmaster, not a Knipex and not anything else. And of course some dies for it. In the US they are far easier to find than here. The end result will be used and still a bit more expensive (not much, although) but it makes a real difference. REPEAT: NOT ANYTHING ELSE.

You should further invest in one of the stripper tools which have two blades and depth stops. You do not want to have one end fitted ok, then cutting off the other side in pieces because nicked conductor, dielectricum etc. And do not think that a coax connection will be acceptable if, for example, you hurt the dielectric in the position where you should cut the mantle.

Also the X-acto knife is a devious tool. Change blades in time. And apply as much feeling as you would like your dentist to have when the Novocaine is out. The forward end of the dielectricum must be a flush, circular shape. No points or flakes standing out, as this will impair the seating of the center conductor. especially for the smaller series this is critical. But this means that you have to cut through all of the dielectric over the full circumference and that you must not rip off the uncut remainder. Doing so does in turn raise the danger of nicking the center conductor, which is also not good. This applies to both forms of connectors.
Do not straighten out the screen wires if not explicitly instructed to do so (by a mounting instruction). In most cases, it is assumed that the weave of the shield braid under the crimp or clamp is kept undisturbed.

And last not least: do not cut your coaxial cables with a diagonal cutter. The deformation of the dielectric is far to excessive. Use a small cable shear!

As for the special connectors: again the major manufacturers should be ok. Thore that do real RF, instrumentation and Milspec. No CATV or Network crap. and then get a ample supply of the same type. The more often you fit the same connectors, the easier it becomes.

[matthuszagh]

Neomys Sapiens, thank you for such a detailed explanation of the process and pitfalls. This is incredibly useful.

General: you are aware that the PTFE-cables like RG-400 are somewhat less flexible than the PVC-isolated ones? If you do not need the performance, the latter might handle easier. I have to look up the suitable double shielded type, but it is not RG-223!

The flexibility is important to me. I'll probably stray away from the PTFE cables then. Are you referring to the PE dielectric cables? I was only able to find PVC used as the jacket material.

If you go for crimping, do yourself a favour and get a Daniels or Astro M22520 5-01 or 10-01 crimp tool.
Or the one from Suhner or a comparable one from one of the connector manufacturers. Not a Pressmaster, not a Knipex and not anything else. And of course some dies for it. In the US they are far easier to find than here. The end result will be used and still a bit more expensive (not much, although) but it makes a real difference. REPEAT: NOT ANYTHING ELSE.

I'm following this advice. I cancelled my order for the pressmaster and will place an order for the daniels M22520/5-01 shortly, with some dies.

You should further invest in one of the stripper tools which have two blades and depth stops. You do not want to have one end fitted ok, then cutting off the other side in pieces because nicked conductor, dielectricum etc. And do not think that a coax connection will be acceptable if, for example, you hurt the dielectric in the position where you should cut the mantle.

Any product you particularly like here? Or, good manufacturers to go with?

And last not least: do not cut your coaxial cables with a diagonal cutter. The deformation of the dielectric is far to excessive. Use a small cable shear!

Same question: recommended products or recommended manufacturers?

[David Hess]

One of the reasons I like RG-400 and other double shielded cables is that clamp connectors work better with the double shield.  And I like Teflon insulated cables because soldering the center pin is so much easier to do without melting the insulation.

[Neomys Sapiens]

The flexibility is important to me. I'll probably stray away from the PTFE cables then. Are you referring to the PE dielectric cables? I was only able to find PVC used as the jacket material.

Yes, PE as dielectric. And I was wrong: RG-223 is the closest to RG-58 diameter that you'll get.

Of course, there are Sucoflex and Sucotest cables. 
I have an RG-214 size cable good for 8GHz here that feels just like a big test lead!
I suppose that it is about the same price as a chinese spectrum analyser. 

Any product you particularly like here? Or, good manufacturers to go with?
Same question: recommended products or recommended manufacturers?

As the ones which I have are made of unobtainium, I would recommend Bernstein or Knipex.
I can't find the proper entry at Piergiacomi, but they are nice too.
The others shown should be also fine. And you can have a look what Jensen or Techni-Tool throw at you.

https://www.bernstein-werkzeuge.de/produkte/produktdetails/3-0648-koaxial-kabelschneider

https://www.knipex.de/produkte/kabelscheren-und-drahtseilscheren/kabelscheren-griffe-mit-kunststoff-umspritzt/kabelscherengriffe-mit-kunststoff-umspritzt/9505165

https://www.platinumtools.com/products/cutters/cable-cutters/btp-6-coax-data-cable-cutter-10510c/

And while you are at it, get a Kronenschere (crown shears) for trimming shield braids:

https://www.bernstein-werkzeuge.de/produkte/produktdetails/5-301-schere

For stripping:
I have some which are labeled 'Radiall', but I am not sure who makes them originally.
Also:
https://www.milestek.com/p-15839-3-blade-coax-stripper-03270146-clothespin

or the 45-16x series from Ideal

But in this categogy I can't say that I tried them all. I also use a precision knife and a thermal wire stripper.

Also enclosed is an useful document.

[matthuszagh]

Follow up question on this:

I got the impression from this discussion that crimping both the contact and ferrule was the robust way to join RF connectors and cables. It seems like soldering is only done when one doesn't have access to the crimping tools. However, when I was looking through Pasternack's catalog of RF connectors almost all of them specify crimp/solder, which means crimp the ferrule, solder the center pin (contact). I emailed Pasternack and they verified that for crimp/solder connectors the contact must be soldered. Why would this be the case? I would expect that Pasternack caters to somewhat less price-conscious clients (i.e., with the right tools for the job). Is there an advantage to soldering the contact? Is it possible the Pasternack rep told me the wrong thing and the contact can be soldered or crimped? For reference, I was looking at this connector (https://www.pasternack.com/bnc-male-rg58-rg303-pe-c195-pe-p195-lmr-195-connector-pe4016-p.aspx). FYI the datasheet says both contact and ferrule should be crimped, but the rep said that was an error.

[coppice]

Follow up question on this:

I got the impression from this discussion that crimping both the contact and ferrule was the robust way to join RF connectors and cables. It seems like soldering is only done when one doesn't have access to the crimping tools. However, when I was looking through Pasternack's catalog of RF connectors almost all of them specify crimp/solder, which means crimp the ferrule, solder the center pin (contact). I emailed Pasternack and they verified that for crimp/solder connectors the contact must be soldered. Why would this be the case? I would expect that Pasternack caters to somewhat less price-conscious clients (i.e., with the right tools for the job). Is there an advantage to soldering the contact? Is it possible the Pasternack rep told me the wrong thing and the contact can be soldered or crimped? For reference, I was looking at this connector (https://www.pasternack.com/bnc-male-rg58-rg303-pe-c195-pe-p195-lmr-195-connector-pe4016-p.aspx). FYI the datasheet says both contact and ferrule should be crimped, but the rep said that was an error.

The BNC connectors on that site look odd. There are pages of crimp/solder and pages of crimp/crimp versions of a BNC connector. However, the pin looks the same in both cases. The pin for a crimp connector should look different.

[matthuszagh]

The BNC connectors on that site look odd. There are pages of crimp/solder and pages of crimp/crimp versions of a BNC connector. However, the pin looks the same in both cases. The pin for a crimp connector should look different.

Huh, you're right. I hadn't noticed that. At least one of the crimp contacts looked like:



Compared with the solder connectors, which seem to generally look like:



What is each supposed to look like?

[eb4fbz]

Whatever mounting style you decide to use, place two layers of grued heat shrink tube for stress relief.

[matthuszagh]

I found this mini-circuits page (https://blog.minicircuits.com/choosing-the-right-rf-coaxial-cable-assembly-for-your-application/) informative. Here's what it says about the different attachment methods:

Connectors are usually attached to the cable in one of three ways: crimp, clamp or solder/clamp and direct solder. A general understanding of the different assembly helps the user evaluate the performance and reliability of a given cable.

Crimp:
While occasionally used on semi-rigid cables, crimp connectors are popular for lower frequency, RG cables. Crimp attachments require less labor but may require specialized crimping tools.  They are best used on cables that are not handled frequently. Surprisingly, many suppliers opt to use crimp attachments on test cables, which is not appropriate and affects reliability. An assembly marketed as a test cable with crimp attachments should raise questions about quality in the user’s mind.

Clamp or Solder/Clamp:
Clamp or solder/clamp attachments are used more often in cable designs for military and aerospace applications. They are much more expensive and complicated to assemble, but far more reliable than crimp and will not result in latent cracked solder joints.  Mini-Circuits uses solder/clamp on its CBL, ULC and other series of test cables for superior reliability.

Direct Solder:
This method is very popular for semi-rigid and hand formable (e.g. Mini-Circuits HandFlex®) cable.  Direct solder connectors ironically are the lowest cost but are also the highest performance because they are simple and result in fewer RF discontinuities.  Within this category there are separate and no-separate contact designs.  Separate contact designs employ a variety of captivation methods depending on the maker including barb, epoxy, and mechanical shoulders.  Soldering skill and technique is very important to the performance and reliability of the finished product.  Lack of skill and proper technique in the manufacturing process will almost always result in cold solder joints or cracked solder joints either immediately or later in the field.  Field failures can obviously be expensive to remedy.

So, basically it seems that while crimping can work well on lower-frequency cables (RG + BNC, etc.) they're not generally recommended when you get into higher-frequency applications. The searching I've done seems to corroborate this view. I've looked through the catalogs of Huber+Suhner and Pasternack and most of their higher-frequency connectors seem to use clamp/solder, with some using solder/solder. I've seen very few that use crimping methods.

This is interesting, because I still don't feel like I have a good understanding of how to get a very robust connection with a solder method. Additionally, it seems that for lower-frequency cables/connectors (i.e., outside of coaxial and similar cable), crimping does seem to be the optimal method based on information I've seen elsewhere on this forum.

Curious to hear others' thoughts on this. I'm currently leaning toward using crimped connections for ring/spade terminals etc (recommendations?) and solder/solder or clamp/solder (still not sure how to accomplish the clamp part) for coaxial cable.