Topband: 50 ohm direct burial coax cable

[Carl]

Ive been using that CATV RG-11 since the late 70's as jumpers to the 
hardline from wire antennas, in the house, and as phasing lines for 160 and 
80M verticals. Never a hint of heat at 1200W but someone with a 3CX15000 
might have a different opinion. Measured loss at 2 MHz was .17dB/100' 
Several lengths are over 35 years old, reused several times MF to UHF, and 
pass regular sweep tests.

Carl
KM1H




----- Original Message ----- 
From: <mstangelo at comcast.net>
To: "Donald Chester" <k4kyv at hotmail.com>
Cc: <topband at contesting.com>
Sent: Friday, June 13, 2014 3:49 PM
Subject: Re: Topband: 50 ohm direct burial coax cable


> Don,
>
> You bring up some good points. I got a couple of hundred feet of Flooded 
> Commscope 75 ohm "RG-11" type at a good proce. I don't have the part 
> number handy. I've been very happy with it at 100 watts. I'm thinking of 
> running 500 watts. The center conductor is copper clad steel. I'm 
> concerned about RF current losses because of the skin effect on 160 
> meters. Does anyone have any experience with this type of CATV cable at 
> high power?
>
> A 1:5 maimatch may be an issue at the amplifier but I guess I can place a 
> L matching circuit between the amp and coax to get the SWR down.
>
> I like Flooded cable not because it is anti-fungal but to keep out 
> moisture. My coax runs 45 feet underground and 20 feet under my deck. I 
> had some groundhogs visiting us under the deck and fortunately they didn't 
> have a taste for the coax. The visitors have been relocated.
>
> Mike N2MS
> ----- Original Message -----
> From: Donald Chester <k4kyv at hotmail.com>
> To: topband at contesting.com
> Sent: Fri, 13 Jun 2014 19:17:59 -0000 (UTC)
> Subject: Re: Topband: 50 ohm direct burial coax cable
>
> I think you're being overly picky. The 75-ohm cable would be at worst a 
> 1.5:1 mismatch. Probably a fraction of a dB loss at most, particularly 
> with foam type hard line. If you have a source of good, low-loss 75-ohm 
> coax that will safely handle the power you intend to run, and which will 
> hold up for an extended period under direct burial, use it. The most 
> likely consequence might be a slight re-adjustment of your matching 
> network.
>
> From my experience, the greatest problem even with direct burial cable has 
> been rodents chewing on the plastic outer jacket, but moisture 
> infiltration and corrosion may be a problem as well. I am not aware of any 
> fungal problem. I started out with a 140-foot run of RG-213 direct burial 
> rated cable to the base of my series-fed 160m vertical. When I first 
> tested with fresh coax, it was running about 93% efficiency to a dummy 
> load at the far end of the transmission line. After about a decade I 
> re-tested it using identical measuring procedure, and the efficiency had 
> dropped to slightly less than 80%. I replaced the cable and once again the 
> reading came up to the original 93% efficiency, but after only three years 
> it had dropped to around 83%. The second time I didn't find any evidence 
> of rodent damage as in the previous case (however I didn't pull up and 
> inspect the entire length), but I ended up erecting poles, installing 
> fresh cable, and running it elevated, 8' off the ground.
>
> I no longer use coax with this antenna at all. I eventually replaced it 
> with a run of 440-ohm balanced open wire line, #8 copperweld conductors 
> spaced 2 1/2" apart, elevated using the same poles. Comparing rf ampere 
> readings at the base feed point using a thermocouple meter, with the same 
> DC input to the final, the reading was noticeably higher at 1800 kHz with 
> the OWL system, and about the same or just slightly higher at 2000 kHz. 
> These are overall efficiency readings that include likely variations in 
> losses with the different types of matching networks used at each end of 
> the two types of transmission lines.
>
>
> Don k4kyv
>
> -----Original Message----- 
> From: mstangelo at comcast.net
> Does anyone know of a source for 50 ohm "RG-8" type direct burial coax 
> able.
>
> I can find many sources for CATV and Satellite 75 ohn cable but not 50 
> ohm.
>
> Direct burial cable is coated with and anti-fungal compound. I''ve had
> success with 75 ohm cables for receiving and want to purchase 50 ohm 
> direct
> burial for transmitter feeds.
> Thanks,
>
> Mike N2MS
>
> _________________
> Topband Reflector Archives - http://www.contesting.com/_topband
>
> _________________
> Topband Reflector Archives - http://www.contesting.com/_topband