[TowerTalk] ...and another coax adapter question

[Ron WV4P]

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 at 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 at 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 at 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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> >
> > --
> > Scott NX7U
> >
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