I ran into a different failure mode on a right angle UHF M-F adapter.
Several years back, while at Visalia, I found some new, very
nice-looking, nicely-machined, apparently-well-built, adapters from one
of the several vendors there; I don't recall exactly but they were
probably less than $5 each. I snagged a handful. I've been using them
with no problem until recently, when I was able to up my power to more
than 600 or 700 watts. Suddenly, one night, SWR shot sky-high on a few
dits, then seemed to return to normal. Ten or so minutes later, the same
thing happened again. Then it began happening every few minutes; the
high SWR condition would persist for a couple words then disappear, only
to reappear again after awhile. Examination of my coaxes didn't reveal
anything untoward. But awhile later, I had occasion to swap a couple
antenna coaxes to my tuner (where I was using several of these adapters)
and when I pulled on one that was screwed into one of those "new" right
angle adapters, I could tell it was loose. Removing it, I was astonished
to find the female center insulator and socket pin just pulled straight
out of the adapter!
It turned out that this manufacturer (whoever they might have been) made
the center conductor of their right-angle adapter by maching a male UHF
pin from a rod; the inner part of the rod then necks down in diameter
and feeds back into the body of the adapter to the region of the
right-angle. There, at the end of that rod, they drilled a small hole
through the rod. On the female end of the adapter, the UHF female pin is
another machined rod that, on the inside of the adapter at the right
angle, is machined down to a small diameter pin that fits into the hole
in the rod that becomes the male pin. I don't see any solder or a weld
joint joining the two rods and indeed, since there is no access to the
junction of the two rods inside the adapter, you can't get inside to
solder it, anyway. (You could, however, if so inclined, carefully drill
your own hole through the right-angle squared-off body to stick your
iron's tip inside to attenpt to solder them together.) It appears that
the small-diameter pin is supposed to be a force-fit into the hole in
the rod that forms the UHF male pin. Perhaps it is; but movement of
either or both of any cables or connectors on either side of that
adapter will eventually cause that force-fit to loosen up and hey, el
presto: a broken circuit causing high SWR.
My high-SWR fault was caused by that small pin end becoming loose inside
the hole drilled through the larger rod used to form the UHF male pin.
These are nicely-machined and very-well-fitting adapters; too bad
they're so unreliable and virtually useless for any serious application.
I have a bunch of UHF-to-type N adapters from the same vendor; I wonder
what failure mode they're going to present?? I have no doubt that they,
too, will catastrophically-fail at some point.
Steve, K0XP
On 11/25/2023 12:28 PM, Ron WV4P wrote:
Amphenol connectors are Banned at my station. They are Not what they used
to be...
100% of all Up the tower jumpers are DXE RG213 and DXE Crimp ons.
Ron, WV4P
On Sat, Nov 25, 2023, 1:57 PM Jack Brindle via TowerTalk <
towertalk@contesting.com> wrote:
The problem isn’t so much resistive buildup, but rather arcing and
flash-over. The reason the right angle connectors are such a problem is
that the center conductor can either move or is bot well-placed to start
with. At 100 watts it is OK, but at 500 it may arc. This tends to be
destructive to the amplifier. Good amplifiers will protect themselves,
leaving you to wonder why it just shut down.
Similarly, coax in semi-tropical environments exposed to the sun will see
migration of the center conductor over time, changing the coax
characteristics (which a TDR should see), but ending in contact between the
center conductor and shield, which again will be problematic to the driving
amplifier. I have seen this take less than a year in South Florida.
With hamfest-variety connectors and adapters there is not much care taken
in assuring the center conductors are both well-placed and secure in their
positions. Add to that the insulators used (phenolic or something other
that Teflon) will weather and age with time, breaking down to
allow center-conductor movement.
All this is why we use really good connectors. Most of the suggestions are
for UHF family connectors, but there is junk even in type-N and BNC
connectors as companies push to lower costs to increase sales. These are
easy to find, unfortunately.
Also note that for mismatched lines, which we all use, things get far
worse. The scenario here is an ATU driving coax to a wire antenna. The ATU
will make the transmitter and amplifier happy, providing a good impedance
to those devices. But beyond the ATU you will have very high losses in
everything from the ATU components, connectors and coax. A lot of power
will be dissipated in these things, with surprisingly little being radiated
from the antenna. N6BV did some excellent work in this area, which can be
found in his published articles and the ARRL Antenna Book, which Dean
edited during his time at ARRL. His presentations show how much the
components in the antenna system are stressed.
73,
Jack, W6FB
On Nov 25, 2023, at 12:51 PM, Scott Townley<scott@nx7u.net> wrote:
If that's the case, then wouldn't an insertion loss test reveal such an
issue?
For example, I was deconstructing the power handling of a Charter
Engineering B5-series coaxial relay (N-female connectors). If I map "max
insertion loss at x GHz" to the average power rating on their published
chart, at every point the dissipated power comes out to 11 watts. That
tells me that "good" N-connectors can dissipate 5 watts, and for that
mechanical form factor I should be able to derive a power limit based on
measured insertion loss.
Or are the physics of power handling in "not-so-good" connectors
different from what would be revealed by an insertion loss measurement?
Assuming of course that we are not in the realm of high voltage breakdown
of the dielectric (or maybe that's exactly the difference?).
On 24/11/2023 17:29, Jack Brindle wrote:
One of the big problems with off-brand connectors and adapters is their
power handling capabilities. This is especially noted in the right-angle
adapter. We see a lot of arcing when higher power is applied.
Higher power in this case is anything above just a few hundred watts.
Whenever I see an amplifier log report with a lot of high reflected power
or PA Dissipation faults, I immediately start looking at the
connectors and feed line for problems. These are usually found in one
of several places - right angle adapters, and baluns that were meant for
low power, but have been over-stressed with high
power.
My advice? If the right-angle adapters aren’t Amphenol, throw them out.
73,
Jack, W6FB
On Nov 24, 2023, at 12:59 PM, Scott Townley<scott@nx7u.net> wrote:
Say I have a pile of coax adapters on my bench (we all do, right?).
How do I separate the wheat from the chaff? I have a fully equipped
bench...I would think the go-to would be a TDR measurement. Any
better/additional suggestions?
TIA,
--
Scott NX7U
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