One point of concern ... and overall I agree with what Bob is saying here.
If the mechanical/physical design between the two diameters is not correct,
meaning there is an excessive measurable difference between the OD of
the smaller element tubing and the ID of the larger element tubing .
.. and no effective manner to address that difference, such as slot(s) or ?
in the larger tubing, then we may be requiring the clamp to do something
that is outside it's properly designed function.
Meaning the effort required to close the excessive difference between the
two materials may exceed what the clamp design can provide.
These types of clamps are not by design to be used as "universal Vise-Grips"
to overcome what may have a been a poor or inaccurate joint configuration.
You can check for this by seeing how "loose" the smaller tubing is inside the
larger tubing BEFORE installing the clamp(s).
And ask yourself, "OK, exactly how or what is going to close this gap?"
So if it seems that you are stripping out multiple clamps, or are able to pull
or
twist the element section AFTER the clamp is tight ... then look closer as to
the overall joint construction ... it might save you replacement time later.
73 de Billy, AA4NU
PS ... my apology for busting KQ2M's name in the earlier email ... it's Bob!
----- Original Message -----
From: "Bob Shohet, KQ2M" <kq2m@kq2m.com>
To: john@kk9a.com, towertalk@contesting.com
Sent: Thursday, June 22, 2017 8:05:17 AM
Subject: Re: [TowerTalk] HyGain 155CA dampening rope
There are two reasons.
1) Many of the screw clamps do NOT tighten enough to keep the element pieces
from slipping. I used to test the clamps but tightening as much as possible
(without stripping the clamp) and then trying to pull out the thinnest element
piece – I succeeded ~ 50% of the time. meaning that over time and the normal
expansion/shrinking cycle due to the seasonal temperature changes (coefficient
of thermal expansion) would almost certainly cause the element tip to extend
and ultimately fall out aided and abetted by any wind.
2) The loose fit would allow the element tip to vibrate, which after a period
of time, would cause metal fatigue which could easily cause the element tip to
crack and/or break off. And, once the element tip begins to crack, moisture can
get in and then freeze which would expand any crack or possibly fracture the
element tip.
These are the two most common types of element tip failures associated with the
Hygain antennas and most other types of antennas.
Using my two Stainless Steel hoseclamp method and flattening the hoseclamp ends
and taping over them, I have never had a failure of this type in 18 years on 11
different Hygain Yagis (105CA, 155CA, 205CA). Which, given the prevalence of
ice-storms (averaging 7 per year!), Nor’easters, violent T-storms and
Hurricanes at my qth, is as good any :”real-world” antenna “test-range”. ;-)
BTW, not all stainless steel hoseclamps will tighten all the way either – I
know this from the same test that I performed on the Hygain Screw clamps. With
the hoseclamps, if they don’t tighten all the way and keep the element
completely unmovable, I replace the offending hoseclamp with one that WILL keep
the element tip completely tight.
73
Bob KQ2M
From: john@kk9a.com
Sent: Thursday, June 22, 2017 8:43 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] HyGain 155CA dampening rope
Why would the screw clamp have any effect on the elements braking? The
parts website seems to indicate that HyGain uses 0.028" wall thickness on
their 20m element tips.
http://www.hy-gain.com/Product.php?productid=174939.
John KK9A
To: "Bill Parry" <bparry@rgv.rr.com>, <towertalk@contesting.com>
Subject: Re: [TowerTalk] HyGain 155CA dampening rope
From: "Bob Shohet, KQ2M" <kq2m@kq2m.com>
Date: Thu, 22 Jun 2017 07:47:51 -0400
Bill,
Did you use the stock Hygain screw clamps at the end of the telescoping
elements or did you use stainless steel hoseclamps like I do?
73
Bob KQ2M
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