Topband: Problem with compression F connectors on Quad RG-6
4cx250b at miamioh.edu
Sat May 4 23:13:14 EDT 2013
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.
> -----Original Message-----
> From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Tom
> Sent: Saturday, May 04, 2013 6:08 PM
> To: Topband at 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
> > 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
> > using a simple DC multimeter.
> Remember how RF current flows. It flows on the outside of cables, unless
> 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
> the outside of the outer shield, the inner shields that carry nearly all
> 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
> 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
> > connectors and particularly the F to 259 adapters with something else,
> > what? BNCs?
> BNC's are worse yet, as a general rule. They rely on spring pressure for
> shield path. Look into a type match error between the cable you have and
> connectors, or a connector installation error.
> 73 Tom
> All good topband ops know fine whiskey is a daylight beverage.
> Topband Reflector
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