belden 8214 woes - Page 1
Forum section: electronics / rf-microwave

author: electrolust
author_rank: Unknown
timestamp: August 04, 2020, 02:58:14 pm
content: I bought a lot of belden 8214. It says "RG8" but it turns out it's actually sized like LMR400. The RG8-sized connectors I bought don't fit over the center conductor. My bad -- I should have read the actual physical dimensions before buying connectors.My first go at stripping any coax, ever. UGH. I bought an expensive tool ($60 or so) with adjustable blades. It is the kind you put your finger through and spin. I went through multiple feet of cable and multiple hours and couldn't get a clean cut. Then I started getting a clean cut every 5,6,7,8,something attempts. Way too unreliable. I eventually had an a-ha moment when I noticed that the center conductor is alternately wound in opposite directions (CW then CCW). See photo.When I was cutting on the CCW wound section, which I suppose was most of the time, the dielectric would pull away during the cut. The necessary pressure of the tool would force the dielectric against the center, forcing it to follow the winding and pull itself off. Even light hand rotation with no radial pressure does this -- there is no way at all to rotate a cut piece of dielectric and have it stay in place axially. The dielectric is too tightly bound to the conductor. So whenever I cut on a CCW section, the dielectric would pull away and the tool, having pressure against the jacket, would pull away with it, ruining the cut.But if I happened to cut on the CW section, I finally would get a clean cut. Rotating the dielectric on this section of the conductor results in the dielectric pulling itself backontothe wire, thereby staying in place, and resulting in a clean cut. See photo. (ignore that it's not a proper 3 level cut.)I then vise gripped the hanging end so it couldn't rotate off and got a clean cut, since there's no way I'd reliably find or cut only on the CW wound sections.Nowhere on the interwebs is anyone talking about the difficulty of stripping stranded coax!I've tried keeping axial pressure away from the loose end while turning, but it's not reliable.The proper way would be to secure the ends (past the blade)onlyand then have a freely rotating blade make the cuts. The handheld finger loop tools aren't able to work like this. I imagine this is more like how a CNC type machine would do the cut.I've now found the TMW LMR400 tool, and a tool from DX Engineering. The DXE tool gives a full stop to the cable end at a specific recommended length for a specific connector. The dielectric is thereby not able to move itself off the end of the cable during the cut operation. The TMW tool I'm not sure about. It appears to peel the insulation away as it cuts, in 2 steps, only making a 2 level cut. And of course, actual LMR400 has a solid conductor and shouldn't have the side effect of the dielectric rotating itself off.It will be a week before I get the DXE tool. Any comments on its effectiveness for this type of cable? I hate to wait a week, find it ineffective, and then spend more time looking elsewhere. I feel like I've exhausted google on this one.

author: electrolust
author_rank: Unknown
timestamp: August 04, 2020, 02:58:53 pm
content: photo 2

author: ArthurDent
author_rank: Super Contributor
timestamp: August 04, 2020, 04:57:52 pm
content: I don't think the stranded center conductor is alternately wound one way then the other but that you are twisting the wire with your tool.Try stripping a section a few inches long with a knife, cutting through the outer shell, shielding, and foam insulation to the center conductor (like whittling a stick) and I think you’ll find that the twist is consistently one way. With a little practice you can probably do a better stripping job with a knife than with the tool.

author: electrolust
author_rank: Unknown
timestamp: August 04, 2020, 05:41:09 pm
content: yeah you are right. i found that with dielectric cut but still attached, as i twist it the wires twist.the problem then seems to be then related to roller pressure radially. maybe it's just that the cable is basically too large for the tool, period.

author: electrolust
author_rank: Unknown
timestamp: August 05, 2020, 01:05:02 am
content: finally got a technique that works repeatedly.first i just place the cable in the tool. it doesn't go in from the end as designed (along the axial direction of the cable) because the blade sticks out too far, not leaving enough room (not designed for thick cable). instead i rotate it in from the top opening, with 2 inches extended out of the tool. spin spin spin. doesn't do much because the roller isn't engaged but the first blade does do a light cut and sets the depth, ie secures the position of the cable. that step resembles all the videos i see online. except of course the cable isn't cut yet.then i engage the roller. even the first stop is too far and it's physically quite hard to engage. then i spin 2-3 times only, holding it like a car battery cleaning tool to keep pressure against the cable axially so as to keep the blade cutting concentrically and not allowing the dielectric to force itself off the core, pulling the cutter with it. then disengage the roller and rotate the cable back out the top -- not pull it away axially as designed, as i haven't made a complete cut. the dielectric can then be taken off to expose the core, and the braid is 90% cut. i trim the remaining braid by hand and then remove the insulation where the 3rd blade almost but not quite cut through the outer insulation. then cut off the center conductor to length.it's an ok compromise between a fully by-hand razor cut and a tool cut.the DXE tool and the correct connectors should arrive at the same time, so i'll see if that tool is any better. in theory it should do the job in one step, no fuss.

author: cdev
author_rank: Super Contributor
timestamp: August 05, 2020, 01:58:11 am
content: Generally very thick coax makes very good stubs. If you want a stub to really do its job, make it out of the thick stuff.

author: electrolust
author_rank: Unknown
timestamp: August 05, 2020, 02:58:22 pm
content: The tool I am using is Paladin Tools PAL-1247. I see now the spec for that tool is max 8mm dia. 8214 is >10mm. So I suppose I'm lucky to have found a technique that works at all.Is there a smaller diameter cable with similar or better loss (11dB/100ft @1.5GHz)? 4in bend radius max. Maybe I can tolerate more loss, but eg RG58 is definitely over the threshold. Outdoor-rated is better.Everything I know about cables (which isn't much) I learned here.https://hamradioschool.com/coaxial-cable-use/It tells me I should be using RG8/U class cable, which 8214 nominally is. Looking around, it seems loss is directly proportional to diameter (makes sense) so I didn't want to overthink it. ooops, too late. BTW that page has a photo of RG8/U stripped to perfection.

author: TimFox
author_rank: Super Contributor
timestamp: August 05, 2020, 05:29:46 pm
content: Have you considered Teflon coax cables? RG 393 has a dielectric OD of 0.285 in = 7.24 mm, 50 ohms nominal, and 7.5 dB per 100 ft loss (typ, according to Pasternack; others say over 8 ). It has 69.5% velocity factor, a bit different from PE.

author: A.Z.
author_rank: Super Contributor
timestamp: August 05, 2020, 07:32:48 pm
content: well... in a past I used mil spec (cannot remember the numbers now) RG8/U coax with external neoprene (not kidding) sleeve and teflon inner insulator, it worked well for me at the time, but I never used a special "tool" to deal with it, just a pair of scissors, and had no issues with those, just place a bit of tape where you want to cut, and rotate the scissors while applying the appropriate pressure and there ye goYMMV BTW

author: electrolust
author_rank: Unknown
timestamp: August 06, 2020, 03:33:45 pm
content: many times the old methods are the best!the finger-rotating tool is essentially your method ... except that you cannot adjust (or feel) the pressure of the blade! it's like CNC where hand machining is actually called for. i do like the cut length locating aspect of the tool though. no measurements required.with that in mind, looking at the DXE tool again it is (in theory) the perfect meld of the two. it locates the cuts for you, and since you have to squeeze the blade by hand, like a scissors, you get to feel the cut.i'll have a look at teflon cable also. thanks.

author: electrolust
author_rank: Unknown
timestamp: August 08, 2020, 03:35:05 pm
content: the TMW LMR400 tool worked perfectly! had to adjust the cut lengths but otherwise absolutely perfect cuts no guessing.