Tuner acting crazy when attached to a anylizer - Page 1

[ARCHIVED THREAD] - Tuner acting crazy when attached to a anylizer

Posted: 8/30/2014 10:30:59 AM EDT

Setting up a new antenna and was going to see how broad banded it was. Put a tuner in line with my MFJ259 to see how it tuned and everything went crazy. I can get a good tune and lose it just by tapping on the tuner. Tuner is not grounded but I am having no issues when he tuner is in line with a radio. Ideas? Fwiw new tuner as I have a internal tuner and am trying to dip into the 160m band.

Posted: 8/30/2014 11:42:46 AM EDT

[#1]

Are you using the MFJ 259 as a signal generator? I'm having a hard time understanding what you are describing.

Posted: 8/30/2014 12:10:21 PM EDT

[#2]

I'm not quite getting it either. Is it a manual tuner?

Posted: 8/30/2014 12:28:33 PM EDT

[#3]

Ground your analyzer or tuner.

The tuner, and thus antenna coax, were all grounded to the radio chassis via the coax braid on the jumpers. That is IF the radio was grounded.

You've taken the radio out of the system and now it is all "floating". You need to ground the analyzer and/or the tuner.

Posted: 8/30/2014 2:46:44 PM EDT

[#4]

If it's an auto tuner, the analyzer is probably not putting enough of a signal into the tuner for it to get a useable reading. Most analyzers only put out a few milliwatts, if that much.

Posted: 8/30/2014 4:59:55 PM EDT

[#5]

Quote History

Quoted:
If it's an auto tuner, the analyzer is probably not putting enough of a signal into the tuner for it to get a useable reading. Most analyzers only put out a few milliwatts, if that much.

View Quote

I'll build off of FrankB's post: Take the autotuner out of line. Check the natural SWR and X of the antenna. It isn't important what the SWR is through the tuner. It is more important to check the SWR of the antenna to see what the autotuner has to work with.

Posted: 8/30/2014 5:18:09 PM EDT

[#6]

With the tuner out of the circuit and the analyzer connected to the feedline, the SWR the analyzer indicates is very likely not the SWR on the transmission line.

"What?" you ask, "I have this fancy-smancy antenna analyzer and it's lying to me?"

Read these links on antennas, transmission lines, and SWR. They blow away a lot of myths and urban legends about this fascinating subject.

http://www.hamuniverse.com/n4jaantennabook.html]http://www.hamuniverse.com/n4jaantennabook.html]http://www.hamuniverse.com/n4jaantennabook.html

http://www.astrosurf.com/luxorion/qsl-transmission-line2.htm

http://www.angelfire.com/electronic/funwithtubes/T-Lines.html

Posted: 8/31/2014 8:05:44 AM EDT

[#7]

Thanks for the replies. Turned out to be a bad solder junction on the antenna connector inside the mfj259. Was using a manual tuner and tapping on the case of the tuner would change swr. Sure it was some wild random ground loops or stray rf.

Posted: 8/31/2014 9:46:32 AM EDT

[#8]

Turned out to be a bad solder junction on the antenna connector inside the mfj259.

View Quote

From what I understand, a very common problem on the MFJ analyzers.

Posted: 9/1/2014 1:57:34 AM EDT

[#9]

Quote History

Quoted:
Thanks for the replies. Turned out to be a bad solder junction on the antenna connector inside the mfj259. Was using a manual tuner and tapping on the case of the tuner would change swr. Sure it was some wild random ground loops or stray rf.

View Quote

How did you verify? Pop the case of the MFJ open, or google?

I still think you should measure the SWR of the antenna only. Whatever it is naturally, the tuner "should" make it appear better to the transceiver.

Posted: 9/1/2014 2:46:20 AM EDT

[#10]

I suppose you could use a regular radio and transmit until the tuner locks then unplug it. The tuner should have latching relays that hold the position of tune. Then you could hook up the MFJ and see what it reads.

Posted: 9/1/2014 3:53:12 AM EDT

[#11]

Quote History

Quoted:

From what I understand, a very common problem on the MFJ analyzers.

View Quote View All Quotes

View All Quotes

Quote History

Quoted:

Turned out to be a bad solder junction on the antenna connector inside the mfj259.

From what I understand, a very common problem on the MFJ analyzers.

Very common problem with MFJ anything. Good designs well priced, but always remember to treat them as 95% complete kits out of the box. Check for wire clippings and solder balls, all major connections and loose fasteners before putting any MFJ unit into service.

Posted: 9/1/2014 5:22:26 AM EDT

[#12]

Quote History

Quoted:
If it's an auto tuner, the analyzer is probably not putting enough of a signal into the tuner for it to get a useable reading. Most analyzers only put out a few milliwatts, if that much.

View Quote

^^^ this.

and:

bad solder joint or not, even at 10:1 the reflected power will be at most a few milliwatts, and the autotuner is not going to care about that.

and:

with a reasonable antenna attached, the input to the tuner should look more or less like 50 ohms resistive. all the time.

so:

what exactly are you trying to measure/analyze here? as a start, take the tuner out and measure/analyze the antenna.

ar-jedi

[ARCHIVED THREAD] - Tuner acting crazy when attached to a anylizer

Outdoors » Ham Radios

Win a FREE Membership!

Sign up for the ARFCOM weekly newsletter and be entered to win a free ARFCOM membership. One new winner* is announced every week!

You will receive an email every Friday morning featuring the latest chatter from the hottest topics, breaking news surrounding legislation, as well as exclusive deals only available to ARFCOM email subscribers.

Warning

Confirm Action

About AR15.COM

Stay Connected

Newsletter

Contact Us