[BC] RG-8

[Gregory Muir]

Choice of cabling is often found out to be inadequate after the job has been 
completed.  It tales careful consideration before you start to choose the 
cable for your application.  If you look closely at cellular sites you will 
often find 214 in use within the building.  Then it is Heliax up the tower. 
The same applies to trunking sites.  But there I have even seen RG8 in use.

LMR400 is effectively solid.  It's a foil tape covered with a tinned copper 
braid.  Times touts shielding effectiveness 50 dB greater than single layer 
braid.  In the past I have had 100% success of its use at co-located sites. 
And I currently have tenants at one of my sites utilizing both RG214 and 
LMR400 on their receive sides in the presence of several high power LMR and 
digital paging systems plus my two 100 KW FMs, a 50 KW FM and a 35KW 
television transmitter with no problems at all.  Turn out the fluorescent 
lights when you leave and they stay lit.  That tells me about the RF 
presence at that site.

One must also use care in terminating smaller cables.  The "quick-spin" 
cable stripping tools nearly always cut off a significant amount of shield 
strands reducing the contact area with the connector outer shell.  Variation 
in crimp pressure can mean the difference between good and bad when putting 
crimp connectors on cable.  I have performed post-mortems on trouble cables 
and found that excessive pressure literally pinches the braid connection to 
a point where it breaks off inside the ferrule.

Andrew Heliax cable is excellent.  Although it would be great to do, I would 
have a problem trying to use it in 100% of my applications in light of the 
numerous cables and tight spaces they are located in.  Besides, I would hate 
to have to adapt from Heliax down to BNC and SMA connectors on the 
equipment.

Greg


----- Original Message ----- 
From: "Broadcast List USER" <Broadcast at fetrow.org>
To: <broadcast at radiolists.net>
Sent: Thursday, April 03, 2008 7:23 PM
Subject: Re: [BC] RG-8


> Really, double shielded or quad shielded cable is CRAP!
>
> You should only use 100% shielded cable, like LDF-4.
>
> I have built all kinds of combined land mobile sites, and they all  bitch 
> about the 100% shielding requirement until it is on the air.   100% 
> shielding is really great, and makes the sites work well.
>
> RG-8 really blows.  So does 213, 214, and LMR-400.  If it isn't  solid, it 
> isn't 100%.
>
> --chip
>
> On Apr 3, 2008, at 6:00 AM, broadcast-request at radiolists.net wrote:
>> Message: 11
>> Date: Wed, 2 Apr 2008 23:31:49 -0700
>> From: tony dinkel <tonydinkel47 at hotmail.com>
>> Subject: Re: [BC] RG-8
>> To: <broadcast at radiolists.net>
>> Message-ID: <BAY127-W48C4B2CB93108F2D10145DC1F70 at phx.gbl>
>> Content-Type: text/plain; charset="iso-8859-1"
>>
>>
>> Agree with the LMR comment.  I am using LMR-400 cable where ever I  would 
>> spec RG-8 or 213 now.  RG-214 is mandatory for more critical  situations 
>> that involve flexing or full duplex mode.  And if you  think 214 is 
>> expensive, try RG-393.  A customer had me replace all  of his jumpers in 
>> a tx rack not too long ago.  Really expensive and  stiff stuff but its 
>> double shielded, silver plated everything and  teflon dielectric.  Not 
>> good for areas with UV exposure though,  unless you give it a good 50% 
>> overlap wrap with Scotch 88.  Done  that too but not for a run to a 
>> tower!
>>
>> td
>> wb6mie
>> microwave frequency services
>>
>>
>>> If you have the inclination to use a more inexpensive grade cable as
>>> compared to Andrew products, you might try looking at the Times 
>>> Microwave
>>> LMR series cables.  They have an overall foil shield (100%  coverage) 
>>> and are
>>> very robust for most applications at a much cheaper cost.  The  only 
>>> minor
>>> problems is that it is a significantly stiffer cable as compared  to RG8 
>>> and
>>> that it possesses possess a foam internal insulation which is a  bit 
>>> tricky
>>> to manage at times if you need to solder the center conductor.  RF
>>> Industries makes crimp-style connectors for this cable (again at 
>>> reasonable
>>> prices) but, after attending a RF connector symposium at NIST, I  still
>>> solder the center conductor contact in lieu of crimping whenever 
>>> possible.
>>>
>>> But if you want a super high-grade RG8 braided shielded cable, go  with
>>> RG-214 which has a double silver-plated braid shield and will put  you 
>>> in the
>>> poor house before your project is completed.
>>>
>>> Greg
>
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