[TowerTalk] Andrew CNT-240-FR

[Roger (K8RI)]

Sorry, the screwed up posting format ended up with me just sending this 
to Don initially.

On 11/2/2010 6:18 PM, n8de at thepoint.net wrote:
> The '240' specifies the outer diameter of this 50-ohm coax  .240 inches.
>
> http://awapps.commscope.com/catalog/andrew/product_details.aspx?id=1257
>
> The specifications say 1.5 db loss in 100 feet at 30mhz.
>
> Looks like it's better than most 50 ohm stuff being used by the average ham.
That would not be my take except for loss Vs size.  I chose CNT-240 over 
8X, but after using a 500 foot spool of CNT-240 I've changed my mind.
However it is good coax.

   I have used a lot of CNT-240 and would not consider it for an 
interconnect cable, or one that gets much movement/flexing.
CNT 240 is a semi rigid coax, or perhaps I should just call it a rather 
stiff coax, the same size as RG-8X, but *NOWWEHERE* near as flexible.  
Also the braid over foil shield is very fragile as far as the braid 
goes. That makes installing connectors be they UHF, N, crimp, or clamp a 
bit problematic. You do not cut the jacket off, you score it *lightly* 
with a sharp knife or box cutter, then flex it slightly until the jacket 
separates at the score mark, then pull the end piece off. It takes very 
little to break the shield wires. IF you cut the jacket the braid wires 
will just fall off.    I have used CN240 as feed line from the remote 
switch to the balun at the antenna and run the full legal limit on 40 
with a low SWR. I did this for two reasons. One is the low cross 
sectional area of the cable which is important in windy areas.  The 
other is the light weight and small size allow the end of the cable to 
be incorporated into 5 or 6 turns on five, 2.4" cores for a relatively 
light weight balun.    However I found that the rigidity of the CNT-240 
was just too much and it would end up breaking at either end at the 
connector. I replaced it with RG-8X, LMR-400, and Davis BuryFlex (TM).  
The 8X is flexible with a low enough cross sectional area that I've had 
no breaks yet.  Although not very flexible the LMR-400 is strong enough 
I've had no problems with it either. Davis BuryFlex(TM) is both strong 
and flexible although not as flexible as 8X. It's also very rugged, but 
a bit heavier than the LMR-400.  Due to the hostile environment I have 
picked the Davis BuryFlex(TM) as the cable of choice.  Although it also 
makes a great interconnect cable, the 8X is just so much easier to work 
with in tight places 8X with foil plus braid is my choice for the low 
power interconnect coax. I do run Bury Flex from the amp to the patch 
panel. From there to the tower and antennas it is mostly LMR-600 with 
the exception of from the remote switches to sloping dipoles.  I do use 
the 600 all the way to the feed point on the 160 half sloper.

I've found the characteristics (rigidity, fragile center conductor and 
shield) to make it unsuitable for most ham use ...at least for me.
Yes, 8X has a bit more loss, but 8X with shield plus braid is very 
flexible, rugged,  and easily handled. It's also much easier to install 
connectors on 8X than CNT-240 and once installed they stand up better.   
RG-8X makes a great interconnect cable with good shielding in an area 
where loss is not usually considered very important. Loss is also 
negligible on HF as long as the SWR is kept low.  I'd not use it on 160 
where the SWR rises quickly as you move from resonance.  Nor would I use 
8X on 75 unless operating with a very low SWR, or no more than a couple 
hundred watts.

I've blown out N connectors on 75 including one double female due to low 
impedance and high SWR at roughly 1200 PEP.  The same conditions that 
cause antenna tuners to be derated

But, but back to the original question. Yesm CNT-240 is good coax, 
but... No, I don't think CNT-240 is a good coax to use for station 
interconnect, BUT if I had a bunch of it I'd not hesitate to use 
it...even as much as I've sworn at it because of that braid.

73

Roger (K8RI)
> 73
> Don
> N8DE
>
>
>
> Quoting Eugene Jensen<eugenejensen at nyc.rr.com>:
>
>> I have came by 2 spools of Andrew CNT-240-FR new cable and was thinking of
>> using for all my interconnect in my station and on to the outside box that
>> has all the runs of Hardline out to the tower. No run's would no longer than
>> 30 feet. Comments pro or con and anyone use thing this cable. Thanks Gene
>> K2QWD
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