18' of coax??

Shaking my long held beliefs?
Why oh Why?

 

Because the feedline is separate from the antenna.

If you want to have a true swr reading, it is at the antenna.

The changes you see on the meter when you ad the feedline is because the added load of the feedline that throws the reading off.

i think I posted a lot of why swr reading are worthless.

 

Yes you did.
I read all your posts religiously.
And I learned a lot from them.
That's why my antenna tune-up will be done
with a help of a tool. NanoVNA H4 is on order.
It should arrive next week.
The tune-up will be done at the antenna to be as closed to good
at 27.185 Mhz.
Then the shortest coax cable will connect with the transceivers.
I will use President McKinley for the overhead location.
And I will use the Texas Ranger TR 966 located
in the sleeper area with an extension coax.
I'll post the results as soon as I have them.
If I get in trouble, I'll ask for help from the
CB Radio community right here on the forums.
I'll tune-up a 10K Predator first.
Then I'll replace it with a Wilson 2000 Trucker for the normal operation.
That's the plan, at least.
Thank you for your post.

 

You lost me with the ranger, but anywho … get rid of the 10k, forget the 2000 and get yourself a good …



Light bulb!

 

Ok I was just remembering something about swr.

can anyone tell me what the swr is for a resonant antenna using a 600 ohm feedline?

I am using a small zepp right now, turned to 28.500 and it is using a balanced feedline, so I know the answer to this, wondering if anyone can calculate it.

 

Light bulb!
They are illegal in AB.
I'm sorry that I lost you.
Should I convene a Search and Rescue party?
Where were you last seen?
Do you remember? /s

 

I may need a little more info. Since this is an end fed zepp antenna (I assume), is your balanced line 1/4 wave, or longer? You may have an impeadance as high as 6000 ohms. So 6000 x 50 = 300,000 ohms, and the square root of 300000 = 547..72 ohms which is perfect for your 600 ohm feed line. Of course the point where the balun is attached, the voltage is very high, on the antenna wire and the current is low. Since an SWR meter reads voltages, the SWR could be as high 12:1 if your using a 1:1 balun, and if the antennas impeadance was around 50 - 75 ohms like a dipole, although it won't be. Hmmm, that's a good question, I've never built a zepp antenna, so I'm really not sure what the input impeadance is. But like most end fed antennas, I'm sure it's pretty high and may require a transmatch. Of course I'm probably over thinking this like usual. Ha.

Edit: okay I just realized if this an end fed zepp, this antenna is basically a J-pole antenna. The impedance at the balun should be around 2000 ohms, so the SWR could be 3.3 (not necessarily resonant) with a 1:1 balun. I assume you are using a 4:1 balun with this antenna?

 

I wouldnt say swr reading is worthless...
Yes i agree that they are not overly important but in my eyes its a tuning aid at best....
You can be way off your impedences and have an acceptable swr but not likely to happen the other way around..

 

You’re right, I don’t have my notes with me about the impeadence. right now I have a 8:1 swr with the setup. I am using a cb conversion to ten meters for digital with open 600 ohm line from the radio to the antenna, no balun. No coax.

it is worthless until there is a balance in the system. You know the grounding is important and without it, you can have a great swr but the rf signal can be prevented from traveling more than a few hundred feet.

 

in theory that should work fine if you have a purely resistive 50 ohm load. That's rarely the case in a mobile application.