[TowerTalk] TowerTalk Digest, Vol 181, Issue 6

[GEO Badger]

The Times cable book sez the RG 6 and 6A have a max voltage rating of 2.7kV. The 6A has a 0.9 dB lower loss than the 6 at 400 MHz.
Do you have a reel of 75Ω cable you want to use? 
>Anyone have an idea of the 30MHz power handling capability for RG6A/U >and Belden 9104?---  
 Ciao baby, catch you on the flip side.    
 GEO     

 http://www.w3ab.org

Time flies like an arrow, fruit flies like a banana.

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 Sent: Saturday, January 6, 2018 9:02 AM
 Subject: TowerTalk Digest, Vol 181, Issue 6
   
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Today's Topics:

  1. 75 ohm cable power handling ? (Martin Sole)
  2. Re: 75 ohm cable power handling ? (Jim Brown)
  3. Re: 75 ohm cable power handling ? (jimlux)


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Message: 1
Date: Sat, 6 Jan 2018 16:41:41 +0700
From: Martin Sole <hs0zed at gmail.com>
To: towertalk at contesting.com
Subject: [TowerTalk] 75 ohm cable power handling ?
Message-ID: <cabcbb10-fc8a-e121-6653-0a38a02d2314 at gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed

Definitely not feeling the Google love today!

Anyone have an idea of the 30MHz power handling capability for RG6A/U 
and Belden 9104?

I have some RG59A/U as well but having seen RG58 melt I'm not inclined 
to try it at 1kW.


Thanks

Martin, HS0ZED



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Message: 2
Date: Sat, 6 Jan 2018 02:09:28 -0800
From: Jim Brown <jim at audiosystemsgroup.com>
To: towertalk at contesting.com
Subject: Re: [TowerTalk] 75 ohm cable power handling ?
Message-ID:
    <fa034306-9371-6758-313e-c1be2d29b579 at audiosystemsgroup.com>
Content-Type: text/plain; charset=utf-8; format=flowed

On 1/6/2018 1:41 AM, Martin Sole wrote:
> Anyone have an idea of the 30MHz power handling capability for RG6A/U 
> and Belden 9104?

RG-numbers are essentially meaningless -- the tell us nothing more than 
approximate size and Zo. The Belden data sheet

https://catalog.belden.com/techdata/EN/9104_techdata.pdf

tells us that 9104 is a CATV cable, CCS center, shield is Al braid and 
Al foil. Your guess is as good as mine for power handling. It's designed 
for low power CATV systems where the signals are mostly UHF. It tells us 
that DCR (resistance at DC) of the center is 4.45 ohms/100 ft, and 1.2 
ohms for the shield. These values will increase (a lot) with frequency.

My WAG (Wild Assed Guess) is that these cables will be OK for 100W into 
matched loads, but I'd be cautious with high power or poorly matched 
loads. And remember -- the match that matters is that between the 
antenna and the line.

73, Jim K9YC

73, Jim K9YC



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Message: 3
Date: Sat, 6 Jan 2018 04:51:26 -0800
From: jimlux <jimlux at earthlink.net>
To: towertalk at contesting.com
Subject: Re: [TowerTalk] 75 ohm cable power handling ?
Message-ID: <6aa2c20d-d066-78e2-7b14-66520a9a2128 at earthlink.net>
Content-Type: text/plain; charset=utf-8; format=flowed

On 1/6/18 2:09 AM, Jim Brown wrote:
> On 1/6/2018 1:41 AM, Martin Sole wrote:
>> Anyone have an idea of the 30MHz power handling capability for RG6A/U 
>> and Belden 9104?
> 
> RG-numbers are essentially meaningless -- the tell us nothing more than 
> approximate size and Zo. The Belden data sheet
> 
> https://catalog.belden.com/techdata/EN/9104_techdata.pdf
> 
> tells us that 9104 is a CATV cable, CCS center, shield is Al braid and 
> Al foil. Your guess is as good as mine for power handling. It's designed 
> for low power CATV systems where the signals are mostly UHF. It tells us 
> that DCR (resistance at DC) of the center is 4.45 ohms/100 ft, and 1.2 
> ohms for the shield. These values will increase (a lot) with frequency.
> 
> My WAG (Wild Assed Guess) is that these cables will be OK for 100W into 
> matched loads, but I'd be cautious with high power or poorly matched 
> loads. And remember -- the match that matters is that between the 
> antenna and the line.
> 

0.9 dB/100ft, so 0.009 dB/ft - that's about 0.2% 1000W * 0.002 is 2W/ft

As Jim noted, that's in a matched system - Think of it as a series of 
little resistors - 2 W/Ft is about 0.2 watts/inch.  I think that will 
get noticeably warm.

Another way to look at it is that the center conductor is 20 gauge 
(copper coated steel).  1 kW at 75 ohms is 4 amps rms.  Are you 
comfortable running 4A through a steel 20 gauge wire with 1/8" of 
polyethylene foam insulation?


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End of TowerTalk Digest, Vol 181, Issue 6
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