Very interesting, Jim - I have been using Ideal connectors from Home
Depot, and they have no color band at all (nor do they have decent
instructions for installing). I will try to find some of the
black-banded ones (I have red-banded ones for RG-59).
73, Pete N4ZR
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On 5/4/2013 11:13 PM, Jim Garland wrote:
I'm sure most of you know this already, but there are different compression
F-connectors for ordinary RG6 and for quad-shield RG6. I use "Ideal" brand
connectors with matching compression tool, and there is a color-coded band
for the two types of cables (blue for RG6 and black for quad-shield). It is
not always easy to find the installation instructions, but for quad shield
especially, it is very important to follow the directions so as to make sure
the multiple aluminum foil and braided shields make appropriate contact at
the connector, just as Tom cautions.
73,
Jim W8ZR
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Tom
W8JI
Sent: Saturday, May 04, 2013 6:08 PM
To: Topband@contesting.com
Subject: Re: Topband: Problem with compression F connectors on Quad RG-6
I'm having a repeated weird problem with compression F connectors on
quad-shield RG6. When I connect a short length (say 4 feet) of cable to
my MFJ-259B, I would expect R>650. Instead, when I wiggle the coax,
occasionally I see the display change to R=0 and X= several hundred ohms
at 1.8 MHz. This makes no sense to me - the R implies ashort, but
where's
all the X coming from?
R doesn't come from a short, it comes from no loss resistance, or more
correctly very low loss resistance.
It sounds like the connector you have is not contacting all the shields.
This is typical for mismatched connectors and cable, or improperly
manufactured cables. It could be somewhere else also, but I've seen this
before with quad shield. That's why I avoid it.
The problem seems to vary with the same
connector and different PL-259 to F adapters, which makes me wonder what
might be happening inside the adapters, but I can't imagine anything
producing this result. I have also been unsuccessful in detecting a
short
using a simple DC multimeter.
Remember how RF current flows. It flows on the outside of cables, unless
it
has a connection path to the inner shield. If you have cable with Mylar on
the inside of one or more shield layers, and a connector that only
contacts
the outside of the outer shield, the inner shields that carry nearly all
of
the desired transmission line currents will be insulated and isolated from
the shield at the connector. Every shield has to be contacted at the
connector, or at least the inner shield does.
This might not be it, but it is a common issue with quad shield. Dual
shield
is much more forgiving of connectors. You'll never detect the leakage in
dual shield in outside runs. If you have nasty common mode problems, a
thicker shield will help. It is also just as simple to add a few dozen or
few hundred ohms of common mode choking to regular dual shield cables and
knock down CM ingress to levels that cannot be noticed.
I;'m wondering if I should go through my RX antennas and replace all the
F
connectors and particularly the F to 259 adapters with something else,
but
what? BNCs?
BNC's are worse yet, as a general rule. They rely on spring pressure for
the
shield path. Look into a type match error between the cable you have and
the
connectors, or a connector installation error.
73 Tom
All good topband ops know fine whiskey is a daylight beverage.
_________________
Topband Reflector
All good topband ops know fine whiskey is a daylight beverage.
_________________
Topband Reflector
All good topband ops know fine whiskey is a daylight beverage.
_________________
Topband Reflector
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