Topband: Chokes for Beverages

[Bill Wichers]

> I noticed something recently about at least one of my spools of
flooded
> quad-aluminum-shield "RG-6". Since the flooding compound is only in
the
> outer shield (the braid right under the outer jacket), it seems
possible
> that under certain circumstances, water could still wick its way along
the
> inner shield and cause degradation of the inner braid and the foil
> surrounding the dielectric.

The flooding compound is intended to protect the cable against *minor*
defects in the jacket such as *small* punctures or nicks. The general
idea is to protect against the kinds of very minor damage a cable would
get during installation or over time (such as rocks abrading the jacket
underground or tree branches abrading an aerial cable in the wind).
Large areas of damage will still harm the cable. 

If a big critter gets a taste for coax some night you're still going to
have problems regardless if it's flooded cable or not. There is just no
way to protect against LARGE punctures or severe damage aside from
conduit.
 
> I'm thinking that the aluminum foil shields are plastic coated. If
that's
> the case, then only the inner braid would oxidize.

The inner foil usually has a plastic backing on the "inside" (the side
away from the braid). In the case of quad or tri-shield cable the outer
foil does not normally have a plastic coating. Remember that the outer
foil is between the braids in the case of quad-shield cable so there
needs to be electrical continuity between the various shields. Plastic
layers would prevent this.

> In this scenario, the coax would have one intact (outer) braid, and
one
> oxidized (inner) braid, at least for some distance from where the
water
> entered. Any thoughts on the consequences if this should occur?

I would expect this to be minor unless it got bad enough to start
increasing the loss of the cable. You might get some extra noise on
receive though. If you're running DC powered things like preamps or
relays with the cable the DC current may exacerbate the problem with the
oxidation of the shield.

> And is all quad-shield flooded coax manufactured with just the outer
braid
> flooded?

As far as I know, yes, and this goes for all other cables too since the
floodant is only intended to protect against water ingress due to damage
to the outer jacket. The only type of cable I'm aware of that
essentially has flooding compound all around is loose-tube fiber optic
cable where the glass strands reside within buffer tubes that are
literally filled with the flooding compound. I've never seen any kind of
electrical cables manufactured this way.

   -Bill