MFJ259 B........Found problem!

[DXman]

A strange thing is occurring when I am checking my mobile antenna.

I am using a 14' piece of RG8x (electrical is 14'4") which the best I can get the Predator down to is R=44 & X=5 with SWR 1:2. Now if I use a 3' jumper of the same coax the SWR drops to 1:0 and R=51 & X=2.



Now this pretty good right? Well, when I add a 6' jumper (which this is what I will be using to make everything meet) the R=52 & X=0 and SWR is 1:0, but, when I move my hand towards the meter to adjust it, all the reading go "crazy". Except the SWR, it will only move to 1:2 but the R & X goes sky high. I take my hand away from the meter and everything is back to normal.



So what is causing this with the 6' jumper and not the 3' piece?



----------------

DXman


</p>Edited by: <A HREF=http://pub86.ezboard.com/bworldwidecbradioclub.showUserPublicProfile?gid=dxman@worldwidecbradioclub>DXman</A> at: 10/2/03 5:14 pm

 

[Dealer]

Re: MFJ259 B........

DXman, When tuning a antenna with the MFJ 259 !

You do not need anything but a antenna, the coax that

you are going to use and the analyzer..



No Radios, Amps, Meters or anything else.



Once it is tuned and set then thats it. Not anything else

that you do will change it.



That 14 foot piece of coax is invisable to the antenna at

least in theory, and the meter is hooked directly to the

antenna as if no coax was there.



The 259 can be used to check the input impeadence of

the amplifier, But thats on the bench with a dummie load

at amplifier output.



Take a regular SWR meter and put it last in line after the

amplifier and it should read the same.

If it dosnt then ALL problems are at or before that meter.

Do Not hook the MFJ back in line as it has already

done its job. The antenna was tuned and Not Anything will

change that.



Sliding hands around the ccoax and seeing a difference in

SWRs is a sign of common mode currents on the feed line,

and in the case of a mobil install I would guess bad jumpers

and or a terrible mismatch in the system.



You can use the MFJ to check your jumpers one at a time,

just dont ground them by handling the ends while doing so.





Hope I am reading these problems right ?? as I was confused

about your testing with the different length jumpers using

the MFJ ?

That lead me to believe that you were using a barrel connector

and adding length to your antenna feed line ? Maybe Not but

simple way is when I do a antenna I check and set the antenna and then put MFJ back in storage as it has done its job at least in just this One Aspect. That is to tune a antenna

to its point of resonance, and or adjust it to the place where

it is You want it to be.



Hope I am being of some help here....





Regards,

</p>Edited by: <A HREF=http://pub86.ezboard.com/bworldwidecbradioclub.showUserPublicProfile?gid=dealer@worldwidecbradioclub>Dealer</A> at: 10/1/03 9:59 pm