RG 402/405 - Can it be used like a normal coaxial testcable? - Page 1
Forum section: electronics / rf-microwave

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: January 15, 2018, 03:44:01 pm
content: Hi guys,I recently got my hands on some RG405 SMA-SMA cables for in the lab. I really like the semi-rigid nature of RG405, but was wondering how long they last. Is this similar to a rigid cable, and does every time you bend it result in decreased performance? Or can you just use them like other coaxial cables (RG58, RG316, etc), and just happily bend and un-bend away (respecting sufficiently large bend radii of course)?

author: AF6LJ
author_rank: Unknown
timestamp: January 15, 2018, 04:43:06 pm
content: If you take care not to overtighten the connectors the cables will last a long time.

author: hagster
author_rank: Frequent Contributor
timestamp: January 15, 2018, 08:32:04 pm
content: No they will degrade if you bend them too much. You find this sort of cable inside many RF test gear. Its called semi-rigid.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: January 16, 2018, 09:27:30 am
content: Hmm seems like I am getting contradicting things here. AF6LJ seems to say that it's fine, just handle with care like any other RF cable, but hagster, you claim that they will degrade...Any more details on this? Perhaps "guides" or references about the use of these cables?

author: AF6LJ
author_rank: Unknown
timestamp: January 16, 2018, 04:11:50 pm
content: All I can say is we used it at Loral Corp. for test cables, used cables hundreds of times with no ill effects. Don't make sharp bends, don't put a lot of strain on it, and don't set heavy gear on it.This is where common sense rules.

author: hagster
author_rank: Frequent Contributor
timestamp: January 16, 2018, 07:38:56 pm
content: When i say they degrade, what I mean is that parts tend to work harden and become brittle. While they work they are mostly ok performance wise. I always recomend checking all cables before you use them for any critical measuremnts anyway. For general use, i think true flexible cable is better. You can pay a lot for the really high quality cable. For most applications thats not worth the investment though.

author: AF6LJ
author_rank: Unknown
timestamp: January 16, 2018, 08:56:25 pm
content: I agree.

author: CopperCone
author_rank: Super Contributor
timestamp: January 16, 2018, 09:11:19 pm
content: There is a kinda woven semirigid and a solid semi rigid (like a copper pipe). The solid one does not put up with bends for very long.

author: AF6LJ
author_rank: Unknown
timestamp: January 17, 2018, 05:20:27 pm
content: Quote from: CopperCone on January 16, 2018, 09:11:19 pmAgreed.When we first saw RG-402 where I worked we were challenged to break it (within normal use.)The connectors will wear out before you do significant damage to the cable.

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: January 17, 2018, 06:31:25 pm
content: The solid jacket type comes in two forms. Thick-walled copper jacket needs a form to bend it along, free-form bending will damage it.Thin-walled aluminum jacketcan be bent by hand maybe twice or three times before it breaks. I'm guessing you have thetinned copper braid.For these, repeated bends along the cable will eventually cause the solder (used for tinning) to become brittle and break, or fall off leaving just the braid. Somewhat more problematic (in my experience) is that they will break at the solder joint near the connectors. This is particularly bad for cables that are jacketed or have heat shrink at the connector ends, which hides any brokenness from view. RG-405 tends to fail in this way more than RG-402.Mini-circuits makes some inexpensive (relatively speaking)test cables; these are decent for most work < 18 GHz that doesn't require phase stability, although I would avoid the quick connect (half-turn) types. They also have a new series ofultra-flexible test cables(with higher loss).RG-405 will work in a pinch, but I'd recommend a pair of dedicated test cables as your daily drivers. Treating them with some extra TLC (dust covers when not in use, always using a torque wrench instead of the AvE method) will make them last longer.