mfj 259b x= /R=

[hotrod]

with the nice weather ive been playing around with mobile antennas
im still kinda new to the anylizer idea. but i tested 2 antennas with
very different results yet both work good. heres results
sirio z180 R=86 x= 3 -4
wilson 5k - R=52 x= 26
what has me stumped is the radio jack is 50 ohms the coax is 50 ohms
so when i tune the antenna i should try to get as close to 50 ohms as possible ?right
or am i missing something.in the manual mfj claims the x is the imaginary part of all this
hmm????? both antennas were on wilson mag mount same location ,same vehicle,coax,ect

 

[Captain Kilowatt]

Ideally you want R=50 X=0 for a perfectly tuned antenna. The R represents the radiation resistance of the antenna system while the X is any reactance in the system caused by an amount of capacitance or inductance present. The X value is called reactance and in layman's terms determines how well the antenna will actually accept power from the transmitter.The less reactance the better. When X=0 the antenna is considered resonant at that frequency. Far too many people think that resonance means 50 ohms exactly when in fact some antennas are resonant with other values of R especially some wire antennas on some of the ham bands. In your case of the mobile antennas you want to tune for as close to R=50 X=0 as you can get. Don't worry if the R is a few ohms off as long as you can get the X value as close to zero as you can get it.

 

[hotrod]

well that was my understanding of it . but if you look at the wilson 5k
the x= 20 something sounds kinda high moving whip up lowers it a bit but
only 3-4 numbers lower before i run outta whip
on the sirio z180 the x is close to zero but the ohms is off the charts at 80 something
is this typical for the ohms to be off like this.

 

[boomer111]

I used to have r50 x0 but now I can only see r58 X0, so I guess I am good to go but I do wonder about the ohms increase. I did change coax and have tried several others to no avail. Same brand and also another made up from a different vendor. I use the ring terminal to attach to my predator 10K mobile mount using a tri mag.

These readings are on my intended channel.

 

[The Jerk]

well that was my understanding of it . but if you look at the wilson 5k
the x= 20 something sounds kinda high moving whip up lowers it a bit but
only 3-4 numbers lower before i run outta whip
on the sirio z180 the x is close to zero but the ohms is off the charts at 80 something
is this typical for the ohms to be off like this.

I guess I would be interested in knowing how those number relate as well...what happens when they are that far apart?

 

[The DB]

well that was my understanding of it . but if you look at the wilson 5k the x= 20 something sounds kinda high moving whip up lowers it a bit but only 3-4 numbers lower before i run outta whip
on the sirio z180 the x is close to zero but the ohms is off the charts at 80 something is this typical for the ohms to be off like this.

I know you used to be able to get longer whips from Wilson, I would assume you still can but am not sure, that would help lower X a little more. If that whip has ever been cut that will also not help your current situation. Unfortunately I don't know of any mobile antennas that lets you tune for R and X separately, so you typically get to choose tuning one or the other. Of the two, X is the one to tune for. R isn't as picky as X. As long R is between 25 and 100 (while X = 0) you will be ok.

The 80 ohms you were referring with the Sirio, that is off of which chart? Was that the R reading or something else? As far as impedance is concerned that MFJ can measure up to 600 or 650 ohms...


The DB

 

[hotrod]

I know you used to be able to get longer whips from Wilson, I would assume you still can but am not sure, that would help lower X a little more. If that whip has ever been cut that will also not help your current situation. Unfortunately I don't know of any mobile antennas that lets you tune for R and X separately, so you typically get to choose tuning one or the other. Of the two, X is the one to tune for. R isn't as picky as X. As long R is between 25 and 100 (while X = 0) you will be ok.

The 80 ohms you were referring with the Sirio, that is off of which chart? Was that the R reading or something else? As far as impedance is concerned that MFJ can measure up to 600 or 650 ohms...


The DB

well after going thru my antenna stuff i did find a 66 inch whip ,the other was a uncut 62 inch whip. also tried a 1k coil which tuned better ...hmmm? reading now are R=80 X=0-2
which strangely is very close to the z-180.i still had to pull the 66 inch whip about 1/4 inch -1/2 inch up. when i said the ohms [R] was off the chart i meant itread higher than
what i thought/expected.now to add more to this as i added lenth my swr slightly increased
from a 1.6 to a 1.7 -1.8.has me rethinking about tuning for lowest swr

 

[kt4ye]

now to add more to this as i added lenth my swr slightly increased
from a 1.6 to a 1.7 -1.8.has me rethinking about tuning for lowest swr

Re-think your re-thinking.

The important number is the SWR. The lower the better. It doesn't matter whether the R is Higher or the X is Higher. It's the combination that is important.

Bill

 

[W5LZ]

where's the popcorn... dang have'ta go to the store for more... Wait! I got 'Rice-Chex', that'll do...
Okay, carry on...
- 'Doc

 

[Robb]

Since you are using the MFJ meter . . . OK I'll bite . . . Where is the SWR at the best lowest point/best impedance? What is the X= at that proper SWR point?

Perhaps your antenna is either too short or too long still . . .

 

[hotrod]

the lowest swr ive seen was a 1.5 -1.6 for my freq. range R=60 ? X= 20 something
as i raised/ the whip from the bottom position the X lowered into single digits
which is what i understood to be desired for a mobile install.but i started watching
the others and the R went up to =80 swr went up 1.7-1.8 [not very much actually]
but the X went down considerbly . for kicks i checked my z180 and its very close to same

 

[Robb]

the lowest swr ive seen was a 1.5 -1.6 for my freq. range R=60 ? X= 20 something
as i raised/ the whip from the bottom position the X lowered into single digits
which is what i understood to be desired for a mobile install.but i started watching
the others and the R went up to =80 swr went up 1.7-1.8 [not very much actually]
but the X went down considerbly . for kicks i checked my z180 and its very close to same

Sooooo . . . doesn't seem to be so much of antenna problem as it does an installation problem if both antennas are getting the same readings . . . I would check the coax, PL-259, solder joints at both ends, and even the antenna mounting location/choice . . . gotta be something like that . . .

 

[hotrod]

Sooooo . . . doesn't seem to be so much of antenna problem as it does an installation problem if both antennas are getting the same readings . . . I would check the coax, PL-259, solder joints at both ends, and even the antenna mounting location/choice . . . gotta be something like that . . .

both antennas read the same [or close] AFTER i made adjustments and added the
66inch whip. the standard wilson 62 inch whip the reading were much different
between the two.

 

[Captain Kilowatt]

Re-think your re-thinking.

The important number is the SWR. The lower the better. It doesn't matter whether the R is Higher or the X is Higher. It's the combination that is important.

Bill

To a point. Any value of X reduces the ability of an antenna to accept power from the transmitter. When X equals zero the antenna is resonant regardless of the R value. There are cases where an SWR of greater than one to one is actually more efficient. I am thinking aboit a 1/4 wave over a perfect (or close to it) ground plane. It also depends at what point that SWR is measured if using tuned feeders.

 

[The DB]

Re-think your re-thinking.

The important number is the SWR. The lower the better. It doesn't matter whether the R is Higher or the X is Higher. It's the combination that is important.

To a point. Any value of X reduces the ability of an antenna to accept power from the transmitter. When X equals zero the antenna is resonant regardless of the R value. There are cases where an SWR of greater than one to one is actually more efficient. I am thinking aboit a 1/4 wave over a perfect (or close to it) ground plane. It also depends at what point that SWR is measured if using tuned feeders.

I can confirm this. Before I got my first analyzer I used a field strength meter to tune antennas. The peak field strength was rarely at the 1:1 SWR mark. In mobile setups I don't think I ever remember seeing it peak at 1:1 SWR, it was always somewhere else. I would always tune until it peaked and then began to drop off, then set it back to the peak. Later when I bought my first analyzer I noticed that the field strength peaked near as makes no difference to the X=0 reading.

Yes, SWR can make a difference, no argument there. However, once you get past a certain point gains to your signal from making it lower drop out significantly. If I get x=0 and R between 25 and 100 (2:1 SWR) I'm generally happy. If R is outside of that range on a mobile antenna I look for a potential antenna problem, be it positioning or an issue with the coax or antenna itself...


The DB