coax length

Oh happy day!!!! No more having to weed through posts from CJ, He is gone, his posts are gone etc. Bout time!!!!!

 

I wondered why CJ didn't call me stupid for asking the question about coax. Good move admin.

 

Wow, it's like he never even existed. That's a little scary...

 

18 feet is relatively close to being a single 1/2 wavelength of 11 meters, which is the general wavelength of the frequencies of the CB band. Using a 1/2 wavelength multiple of coax will present the radio with a mirror of the impedance at the antenna feedpoint. This means that your SWR meter built into the radio will now show the actual SWR at the antenna feedpoint.

It's a bit more complicated than that; to be completely accurate, you'll need to adjust the final length after accounting for the velocity factor of the coax that you're using.

Just get the SWR low enough that it won't damage the radio and keep on truckin'.

 

Talk about some poop slinging.....WOW! When I was in my last truck I ran a 102" stainless whip mounted on the grab rail on the back of a PETE 387. The radio is a Kenwood TS 440 SAT. It has a built in tuner. I have literally work the world on 11, 10, 20, 40 and 80 meters with a piece of Ratshack RG8X coax just long enough to get from the radio to the antenna (who knows how long that is) and had no issues. I think the point that most miss is that most internal SWR meters are about as accurate as a trebuchet loaded with a BB at 30 feet. Most "antenna warning" lights are pretty much the same. If you're paying attention, your warning light is on in the morning when the dew is covering your truck and it goes away as soon as it warms up and the dew goes bye bye.
If you don't have an accurate SWR meter, pay someone to use theirs and check your system. Keep in mind that if it under 1.5:1 you're GOOD! even 2:1 won't hurt the radio. You still won't talk more than a few miles anyway. 3 or 4 watts doesn't go very far. I can load up my TS 440 SAT which has been modified to work on 11 meters on the 102" whip which is an electrical length 1/4 wave for 11 meters with an SWR of 1.3:1 and 80 watts and still only talk 4 or 5 miles. Yet I can load it up on 20 meters (through the tuner and a loss of about 30 watts) and work 9YU stations in Trinidad all day long.

1 antenna is better if it is placed correctly. You can't even "co-phase" antennas unless they are at least a 1/4 wave electrically apart from each other and EACH ANTENNA IS TUNED AND OPEATING CORRECTLY. For short communication capability, you are wasting your time and money. Another problem that some miss is that the truck manufacturers have now installed units in line with the CB antenna system to allow TV reception. This opens up a whole new can of worms!

I have worked Russia, Australia and Japan on a piece of wire 48 feet long supported by stand-offs on the top of a trailer which had a fiberglass roof. It wasn't "tuned" for any freq, just a random piece of wire ZEP fed and the ground (shield) tied to a screw on the sheet metal of the trailer.

In a nutshell.....ya'll worry about too much crap.

N5DAR (General Class licensed in 1976)

Have a great evening!

 

For you maybe, up until past couple weeks i liked reading his postings.... didn't understand 'em but it was food for thought. Then he seemed to get mean for no reason.
This part of the forum is my fav. i learn so much from all of you all

Now back to our regularly scheduled program

 

What I meant was that his posts completely disappeared - not even a 'post has been deleted' like with others that were banned by the mods.

 

It has been quite.....

 

A better length would be 11.34798 feet. That would be closer to a 1/2 wavelength for 11 meters using RG-58 coax.

Leon
(kc0iv)

 

Thanks. It's Sunday and I didn't feel like doing the math.