[TowerTalk] BIG clamp on issue

Christopher Brown 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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