how to find characteristic impedance

Printed From: the12volt.com
Forum Name: Cellular and Communications
Forum Discription: Cell Phones, Hands Free Kits, Bluetooth, Two Way Radios, CBs, Pagers, Wireless Internet, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=131429
Printed Date: April 25, 2024 at 5:15 PM

Topic: how to find characteristic impedance

Posted By: --weezl--
Subject: how to find characteristic impedance
Date Posted: May 17, 2012 at 8:06 PM

i realize this is an odd place for this post, but it seemed most fitting.

I am going to be buying a HAM radio tomorrow, (most likely) yes, i am licensed, don't worry. With my install, i am thinking very seriously about installing it where the stock radio antenna is on my truck, of course the transmission line from the stock stereo to my antenna is coax, and naturally, i am hoping it will work... only problem is, i can't find ANYWHERE, how to calculate or find characteristic impediances for things, nor what it is for the line that I have... if anyone can answer me how to calculate/find it, or what it would be for my line, i would be forever grateful!

my truck is: a 2007 ford ranger supercab.

the wiring had a sticker on it, identifying it, best i can see, it reads:

6l5t-18812 ** pn150
w289m 2406
made in mexico

the stars are characters i can't make out, they are smugged too badly now...

ford lists this part as "18812"

thanks in advance!

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Replies:

Posted By: the12volt
Date Posted: May 17, 2012 at 8:29 PM

The factory radio antenna coax is too small and will not work properly. If need be, use it to fish the new coax to your HAM radio.

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the12volt • Support the12volt.com

Posted By: --weezl--
Date Posted: May 17, 2012 at 8:34 PM

good enough! thanks for the reply!

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Posted By: the12volt
Date Posted: May 17, 2012 at 8:46 PM

BTW, the impedance of the factory radio antenna cable is probably 90 ohms. Typical coax for HAM radio is 50 ohms.

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the12volt • Support the12volt.com

Posted By: howie ll
Date Posted: May 27, 2012 at 1:53 AM

Personally I was brought up to use the (metal roof), nice big ground plane.
Oh do I remember the early cellular days of climbing on to the roof of the big trucks or the aluminium foil glued to the inside of a plastic van roof.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Posted By: oldspark
Date Posted: May 27, 2012 at 6:48 AM

Ditto.
And fwd or rearward for more directionality....

Posted By: --weezl--
Date Posted: June 08, 2012 at 7:28 AM

thanks again for the replies, for the purposes of what i am going to be doing, the only time i'm going to be transmitting more than a few km, is in an emergency situation, which i plan never to have to deal with... as it is, from my driveway, i can two different repeaters, which are 12miles (20km) and 11miles (18km) both on 5w transmit power, and this of course is urban, and not level terrain...

with the 55w i have at my finger tips, i would imagine that i don't have a whole lot to worry about for range... i should post some pics of how i have it mounted...

this is the antenna, with a little cover that went over the base of the stock radio antenna, i had to modify it to fit the large coil through...

posted_image

an early pic of the mount, since this pic was taken, i have shaved it down to get about double the threads out, i will also be filing it down more to make it thinner, and then fitting a shim under it, as it sits on an angle as it is...
posted_image

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