ARRL

Secure Site Login

Forum Home - Rules - Help - Login - Forgot Password
Members can access, post and reply to the forums below. Before you do, please first read the RULES.

What do I trust, my tuner or my analyzer?

Jan 26th 2016, 18:49

AF9U

Joined: Nov 5th 2014, 18:48
Total Topics: 0
Total Posts: 0
Hello friends,

Here's the setup: I have a simple homebrew 20 meter dipole up in the attic (no balun). Off the feedpoint, I have 100 ft of RG8X going to the tuner in the basement. There is about 20-30 feet of extra coax than I need, but it's what I had and I figured cutting and putting my own PL-259 on there would have been worse than leaving it long. (If this is a big issue...let me know)

I can tune my SWR to about 1.4:1 around the band. Not much better than that, but I'm not a full half wave off the ground either. So that's a factor. It's up about 26 feet.

My question is. Why does my MFJ-949E give me a 1.4:1 SWR, but if I connect my MFJ-259C to the output of the tuner I am showing about 1.7-1.8:1 on the same frequency? Which should I trust?

Thanks,
Drennen, AF9U
Jan 26th 2016, 20:35

WA0CBW

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
You connected the MFJ-259C to the output of the tuner? That doesn't sound right. Shouldn't you connect the MFJ-259C to the antenna?
BB
Jan 26th 2016, 21:39

AF9U

Joined: Nov 5th 2014, 18:48
Total Topics: 0
Total Posts: 0
Well, I have tuned the antenna for a particular frequency. And that is what I am trying to analyze. I'd like to know if what I am showing on the tuner is confirmed with the analyzer. Wouldn't the output of the tuner (I am referring to the coax that goes from the tuner to the radio) be a different SWR after it's been tuned? Or is it an unreliable SWR because of the tuned? That is what I am trying to understand?

Thanks,
Drennen
Jan 27th 2016, 03:49

WA0CBW

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Remember the tuner does nothing to change the antenna. The antenna SWR remains the same with or without a tuner. The tuner matches the impedance of the antenna to the radio's 50 ohm impedance. Therefore the SWR between the radio and the tuner should be near 1:1.
Also the connection on the tuner that goes to the radio is the tuner INPUT and the radio OUTPUT. Remove the radio and connect the MFJ-259C analyzer to the tuner input and you should see nearly the same thing the meter on the tuner shows.
Bill
Jan 27th 2016, 13:22

AF9U

Joined: Nov 5th 2014, 18:48
Total Topics: 0
Total Posts: 0
Thank you Bill for the reply again. I must apologize for my input/output labeling in my post. I had it connected correctly, I just called it the wrong thing. In fact, on the actual tuner it doesn't say input/output. It says Transmitter and Coax1 or Coax2 depending on which you have selected. But good catch...that probably would have fixed my problem. I'll keep researching, based on your description above I should be seeing about a 1:1 match on the transmitter side coming off the tuner and I am seeing around a 1.8:1. Something isn't right.

73,
Drennen. Af9U

Jan 27th 2016, 14:26

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Since you don't have a balun, the outside shield of the coax is another antenna element. Presumably, when connected to the tuner, the tuner grounds the shield. You need to duplicate this connection when using the antenna analyzer--otherwise you are really measuring two different antenna systems.

Zack W1VT
Jan 27th 2016, 16:33

AF9U

Joined: Nov 5th 2014, 18:48
Total Topics: 0
Total Posts: 0
Ok, that is very helpful Zack. Maybe I'll add a balun and see if my readings are closer between the tuner and the analyzer. I wanted to get a balun anyway. Thank you very much!

Drennen, AF9U

Back to Top