DIYbanter - View Single Post - RG-6 QS, top brands?

Ian Jackson

In message .com,
writes
On Apr 6, 2:27 pm, "Ralph Mowery" wrote:
"Ed Nielsen" wrote in message

. ..

Hex-crimp fittings have 6 points where the connector is pinched into the
cable creating small impedance mismatches. Impedance mismatch creates
reflection. If the reflection(s) is(are) severe enough, whatever is at
that(those) frequency (frequencies) may not work. Plus, their return loss
is a fair amount lower than that of compression connectors (~18dB as
compared to 30dB).

I've replaced hex-crimp fittings on DirecTV systems because of hex-crimp
fittings which were causing some channels to not work.

Funny how it works where a bad connector will blank out just a couple of
cable chanels. First time this hapened to me about 20 years ago the cable
guy came out and said it was a bad connection. Almost laughed at him,but he
replaced the connector at the outside of the house and it cleared right up.

Very good info. The interesting thing is since my original post I
went and bought a 500 ft roll of Carol Brand RG-6 QS from Home Depot,
and made some cables with the crimp-on connectors I already had. When
I swapped these new RG-6 QS cables with ones I made a while back with
regular RG-6 with the same crimp-on connectors, I got surprisingly
horrible results. A couple of analog channels don't come in at all
(ch 28 and 56), where they used to come in with a fairly good picture.
Yet other channels on lower frequencies, such as VHF appear to be the
same. I inspected the connectors and they appear to be OK, but I am
guessing there must be an issue with these connectors and the RG-6 QS,
where it's causing the issues that were described above with loss. Is
this possible?? It seems to be affecting various UHF channels (ch.
28, 56, 62).

Thank you very much for the help.

--
Chris

I've worked in the cable TV industry for nearly 44 years, and have NEVER
found that a certain type of male F-connector is, in itself, responsible
for 'horrible results' in terms of RF throughput. Provided that (a) the
shell makes good contact with a few strands of the braid, (b) you
haven't managed to wind a strand of the braid around the inner
conductor, and (c) you haven't left a thin film of the dielectric on the
surface of the inner conductor (yes, I've done all of these!), the
connector WILL appear to work normally. All that suffers is the
screening effectiveness and mechanical reliability.

Regarding whether some male connectors create a significant mismatch due
to crushing of the dielectric, even if this does happen, is not going to
be significant in normal use (up to at least 2GHz) until the outer
conductor is almost touching the inner. You can easily prove this for
yourself by looking at the RF throughput of a piece of coax, while
progressively crushing it with a large pair of pliers.

The thing which causes the most noticeable impedance mismatch is
normally the female part of the connection. Connectors with a
'duck-bill' inner (two parallel fingers) tend to be more capacitive than
those with a 'tulip' (three or four fingers). They are also likely to
make a less reliable ohmic contact.

Don't get me wrong. I do not advocate sloppy practices when fitting
connectors. In the UK, the compression and 'snap-and-seal' types are the
de facto standard. However, I would not hesitate to use crimp or
screw-on types for home use, provided you know how to fit them properly.
And I do.

Ian.
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