[TowerTalk] Coax cable economics. (was Mosley Antenna Question)

[Earl Morse]

Coaxial cable here is bought in quantities of 500'.  Scraps less than 100' get hauled off to the hamfest.

Looking at price per foot of 3 popular types of 1/2" coax we have:

LMR400  $1.18/ft  or  $589.99/500 ft roll
RG213   $0.83/ft  or  $412.99/500 ft roll
9913    $1.12/ft  or  $559.99/500 ft roll


Loss/100 ft of these @ 30MHz is:

LMR400  0.7 dB
RG213   1.2 dB
9913    0.7 dB

At this frequency the loss in a 500' run (@30 MHz) would be:

LMR400 3.5 dB
RG213  6.0 dB
9913   3.5 dB

Crunching these numbers, 2.5 dB can be gained from spending either an extra $177 for the LMR400 or $147 for the 9913 over the RG213.  This is just for 30 MHz and a 500 foot run.  Losses would be lower at lower frequencies and higher at higher frequencies especially when the dielectric loss properties of the cable kick in.  Your run may be shorter, hopefully not longer.  It starts to add up and an amplifier starts to look like a good deal where you can get 10 dB on all bands for the same price.

These cables can all use the same cheap (but not too cheap) PL259 connector.  You might get a chunk of free 50 ohm 7/8" Heliax and spend $150 for connectors.

There are tons of other cables available.  They all have different properties.  They all have advantages and disadvantages.  Your application may need direct burial or need to be very flexible.  You may be phasing something and require something that needs a specific phase velocity.  I have seen guys use aluminum jacketed 75 ohm CATV hard line where connectors are soldered to it with a pigtail and the shield is clamped to the aluminum jacket with a hose clamp then the whole thing gets a milk jug or bleach bottle shoved over the top of it.  Hey, the cable is free.

As with everything in life.  Check the fine print.  Figure out your cost/Bel.  Take into account the frequency you are using and what exactly it is you want to do.

If price/Bel is no object, then get your bank book out, give me a call, and I will build you a dream station.  Heck, if we are talking contract I will even come over and operate it for you.

Oh yeah, someday you will probably have to replace all that coax, probably around 10-15 years when the rest of the station starts breaking down.  (I'm at 12 years now and over due especially after a well meaning neighbor hit the coax bundle going to the tower with a mower.)  Then start saving up again for the rebuild as soon as you complete the station.  (Are they ever really completed?)

Earl
N8SS  





>----------------------------
>
>Message: 1
>Date: Tue, 17 Feb 2015 18:37:51 -0800
>From: Jim Brown <jim at audiosystemsgroup.com>
>To: towertalk at contesting.com
>Subject: Re: [TowerTalk] Mosley Antenna Question
>Message-ID: <54E3FAFF.8020406 at audiosystemsgroup.com>
>Content-Type: text/plain; charset=windows-1252; format=flowed
>
>On Tue,2/17/2015 1:30 PM, Ed Sawyer wrote:
> I can tell you one reason to spec RG213 over LMR400 to feed your Mosley
> tribander, or any other tribander for that matter.
>
>There are some misconceptions here that are the result of advertising. 
>Loss below about 500 MHz is entirely due to the resistance of the 
>conductors at the frequency of interest. The dielectric does not 
>contribute to loss below that frequency unless it's wet, and if it's 
>been wet, the braid is probably degraded, increasing copper loss. :)
>
>If you really want low loss, use hard line. I'm feeding my SteppIR with 
>350 ft of 7/8-in. :)
>
>73, Jim K9YC
>
>
>------------------------------