On 11/18/2010 12:13 AM, Jim Brown wrote:
> On 11/17/2010 12:18 PM, Bill NY9H wrote:
>> The ONLY problem with Belden is that they are setup to ONLY go thru
>> multiple levels of distribution....causing multiple levels of profit
>> margins,,, and unnecessarily high prices....
>>
>> the Davis folks and a FEW others buy&/or have built quality
>> product,,,,and can profitably sell it for 1/2 to 2/3s the price with
>> NO cut in quality....
>>
>> THE BELDEN STUFF IS VERY GOOD....NO PROBLEM THERE..
> EXACTLY the problem.
>
> For advice on coax, see
>
> http://audiosystemsgroup.com/Coax-Stubs.pdf
Very nice addition Jim. At least I think it's an addition as I didn't
see it when reading the tutorial a year or so back, which could speak
more to my attention span than contents.
There are several things I'd like to add.
You did a great job of covering the electrical characteristics of the
cables however there are some physical characteristics of cables that
could be important.
CNT 240 and I assume LMR240 ( I have a lot of experience with the CNT240
but none with LMR240) can be a bear to install connectors and get a good
shield connection. The cable is quite stiff and the wires making up the
braid are tiny and VERY *fragile*. I used to use CNT240 to feed my 40
meter slopers as they are located in an area where the wind funnels
through the yard and between buildings making a coax with a low cross
sectional area desirable. CNT240 does not tolerate a lot of movement
and flexing well. I was having to replace the connector at the antenna
end of the coax every few months and I had them reinforced. I have also
found the jacket on the LMR Ultra Flex, or UF versions to be fragile,
sensitive to UV, and difficult to use standard cable strippers on. OTOH
the old "Box Cutter" stripper works very well on the rubber like jacket.
That jacket being rubber like also tends to stick to or catch on metal
where it slides over edges. IIRC it's lifetime rating is about half that
of the standard LMR cables, but it is the most flexible cable for a
given size that I've used.
As you already mentioned, the larger cables are better for station
interconnections rather than the small ones. OTOH RG-8X using braid +
foil is very flexible and fairly rugged. That does make it
handy/convenient if not ideal for interconnect cables and also feed
lines to my 40 meter slopers. It also handles the legal power limit if
the SWR is not high. As I operate the entire 160 and 75 meter bands the
very high SWR encountered at the band edges pretty much eliminates the
use of RG-8X
Although you didn't list it, LMR-600 can be found at pretty reasonable
prices and not a lot more than the premium Belden cables of 15 to 20
years ago. I paid $1.29 a couple years ago and I believe it is presently
on the order of $1.50 to $1.60 per foot. Typically it is thought of as
one of those coax cables for UHF, but for price Vs IR loss I find it
ideal for 160 and 75 as well. I use it for all runs to and up the tower.
I find that important as my overall runs from the rig to antennas are
roughly 228', but that includes the rotator loops and feed lines (and a
lot of connectors) from remote coax switches to the slopers where I now
use either LMR-400 or Davis BuryFlex(TM)
There are two drawbacks to using LMR-600 and the larger coax cables for
the average ham. One is its size/weight and the other is the price of
connectors. UHF can be found, but for the most part they are
*extremely* expensive. (on the order of $80 to over $100 each), BUT
Davis found some for me quite reasonable. They are "off brand", but
they were sent to me on an approval basis. Testing showed them to be
viable unlike many of the off brand hamfest connectors. N type
connectors are, or were on my last purchase, on the order of $13 (give
or take a tad) I've found N type connectors do not tolerate the high
SWR at the band edges of 160 and 75 when running the legal limit. I've
also had them blown out from nearby lightning strikes. A double female
connector cost me a lot of time and money as I tore every thing in the
system apart before it dawned on me that the connector might be bad. It
still looks brand new, but an ohmmeter shows a dead short from center
conductor to outside. I keep it for illustration, but it has a band of
red around the middle just so it won't get reused.
They may be a bit more money, but I think I'd go with 7-16 DIN
connectors on the LMR-600 in the future....after I use up the stock of
connectors I have on hand.
73
Roger (K8RI)
> At the end of the section on coax, there's a table of various cable
> types, with costs listed. It's intended to help you answer exactly this
> question.
>
> 73, Jim K9YC
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