[TowerTalk] BIG clamp on issue
cbrown at woods.net
Sat Jan 20 18:00:56 EST 2018
I always use 2 or 3 (depending on the size of the clamp) .25" wide black
UV rated Panduit or T&B zips for exactly this reason. So long as you
are using quality zips (high strength uv stabilized with a stainless
keeper tab) they last and hold tension. I have removed ties after 8+
years of Alaska temp cycling and UV and found them to be under so close
to original tension I could not tell the diff.
On 1/17/18 11:41, Jim Thomson wrote:
> Im in the middle of some CM experiments..using a single large clamp on, in addition
> to some 2.4 inch od cores. For interest, I connected my B+K 875-B digital lcr meter
> to the shield at each end. These large clamp ons are a six sided affair, on the outside.
> I measured 120 uh with just the torroids. That increases to 137 uh with the addition of
> one large clamp on. However, with one side of the big clamp on, firmly against the inside
> of a thermoplastic box, and squeezing really hard on the opposite side, the inductance increased
> to as much as 157-158 uh ! Let go, and it drops back down to the 137 uh region. In both cases
> the hinged section was shut solidly. Ok, so what gives here ? My plan was to use 2-3 x ty raps
> and tighten the clamp on really good.
> ## I think the issue is the mating surface gaps on the hinged portions. There is a pair of mating surfaces
> at the 9 oclock position..... and another pair of mating surfaces at the 3 oclock position. In this application, there
> is only 3 turns of RG-393 passing inside the big clamp on, so there is room for the 3 turns with no fitment issues.
> The ID of these large clamps ons is 1 inch.
> ## Is this normal for these large clamp ons ? I have never used them b4. I was thinking of 88 tape to keep em
> firmly closed, but 2-3 wide ty-raps can be cinched up a lot tighter than any tape job. Or do I use one wrap of tape
> 1st, then a ty-rap dead centered on the tape job.
> Jim VE7RF.
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