Topband: 50 ohm direct burial coax cable

[mstangelo at comcast.net]

Frank,

That is true but a 1/2 wavelenght at 160 meters is quite long, about 260 feet; shorter with the velocity factor.

Mike N2MS 
----- Original Message -----
From: donovanf at starpower.net
To: topband at contesting.com
Cc: jim at audiosystemsgroup.com
Sent: Fri, 13 Jun 2014 20:01:13 -0000 (UTC)
Subject: Re: Topband: 50 ohm direct burial coax cable

You can easily make the 75 ohm coax essentially "invisible" in a monoband 
application by using some RG-11 to extend the total length of the 75 
ohm feedline to any multiple of 1/2 wavelength. 

73 
Frank 
W3LPL 

----- Original Message -----

From: "Jim Brown" <jim at audiosystemsgroup.com> 
To: topband at contesting.com 
Sent: Friday, June 13, 2014 8:33:35 PM 
Subject: Re: Topband: 50 ohm direct burial coax cable 

On 6/13/2014 12:17 PM, Donald Chester wrote: 
> 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. 

Yes. Assuming a suitable matching network at the transmitter, worst case 
excess loss due to a 1.5:1 mismatch is 0.18 dB, no matter how long the 
line. Curves showing this have been in every edition of the ARRL 
Handbook since I've been a ham (59 years). 

73, Jim K9YC 
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