I-10K TUNING

[bob85]

since i did not even get a jaypole comment from my buddy MC i thought i would try posting in here,

i moved and lowered my 10k recently while i play with other antennas, the feedpoint is only about 15feet from the ground,
while playing with the minivna i hooked it to the 10k to see what if anything had happened to the vswr,
i took a screenshot to see if jay or anybody else can give some insight into what to do next with the tuning as XS and vswr min are not even close,
the min vswr point has only moved up slightly from where it was set at the feedpoint with the vswr meter but whats happening with the XS,
i feel i need to get the XS zero point up where i want to use the antenna,
can anybody point me in the right direction??

thanks.

 

[W5LZ]

Bob,
Not being familiar with the measuring device used/program, and not knowing what frequency you want the 'best' results at, you want to take this as an honest question (not trying to 'catch' you at anything sort of deal).
It appears that the 'best' results are around 27.6 Mhz. Slightly higher than the 'US-CB' band. If that's where you want it, I really don't see where anything is 'wrong'. To be honest, I don't see much being 'wrong' with the bottom end of the test range. SWR might be a bit 'off' from the 'ideal', but considering human error, it's still not bad.
What am I missing?
- 'Doc

PS - Nice program! The information is presented a bit different than what I'm used to seeing, but nothing unusual about that. What do you use to do the measuring? I'm afraid to ask what the cost is...

 

[bob85]

doc it is a minivna, not as expensive over here as a mfj £130,
im just learning how to use it so maybe i am reading it wrong,
you get no instructions at all on how to use it,

it looks to me like the best vswr is at 27.6 but its not resonant there,
XS=0 or almost down at 26.9,
i want both XS=0 and min vswr at around 27.580 if thats possible,
am i reading this correctly or not,

when i first errected it the antenna was set to the tuning chart with a little precision guesswork calculator and a tape measure then i fiddled a little to see if i could get it working any better and maintain a low vswr,
i ended up right about where i started,

now i moved it and lowered it the vswr min point has moved up a little in frequency but not much,

its the XS thats bothering me, i want to bring that up towards the min vswr point and maintain a low vswr,

not sure if i can do that with just the trombone or do i also need to shorten the antenna,

i guess i will have to alter things one at a time and observe the effect,

i figured somebody that has tuned one with an analyser would be able to point me in the right direction :?:

thanks.

 

[ken white]

Well since your reactance went up with an increase in frequency, the X is inductive.

However, the phase angle and R are almost perfect at 27.6 MHz => R is about 51 ohms with an angle of less that one degree.

I would call it good enough.

But if you can't, you might be able to shorten the electrical length some to reduce the inductive part, which may also reduce the resisitive part and make the antenna appear like the 26.9 MHz sweep, which isn't as good...

 

[Jay in the Mojave]

Hello Bob85:

Ok sorry I am not framiluar with your measuring machine or program there. So I a don't know what the measurement traces are, SWR?
I have a hard enoght time working with a Network Analyzer, at times.

Send me a web site explaning the data.

Any antenna will have some change to SWR when it heigth is changed. The SWR smile trace measurement curve, will indicate (for all antennas) Capactive Reactance Xc to the left of the smile, or below in frequency the SWR lowest point, and Inductice Reactance Xl to the right of the lowerst SWR point, or higher in frequency.

Hope this helps.

Jay in the Mojave

since i did not even get a jaypole comment from my buddy MC i thought i would try posting in here

 

[W5LZ]

Bob,
Well, I would think that shortening the antenna very slightly would shift the resonant point up in frequency and make that '5.8' smaller. (I also think that '5.8' isn't all that 'bad', sort of doubt if you'd 'realize' any benefit from making it '0'.) That 'very slightly' means exactly that, a -very- slight change in length. If you have to move the antenna again, it's something you might try. If or until then, I seriously doubt if it's something to worry about.
After using that "minivna" for a while I think you'll see that resonance and minimum SWR seldom fall on the same frequency. No idea what the 'average' spread on that would be, but would be willing to bet on there being one. And in most cases, it just doesn't make any practical difference. Oh, it could, but if the 'spread' isn't much, neither if the difference.
- 'Doc


(As for coming with instructions, who ever reads the dang things until you get totally lost?)

 

[bob85]

hello jay.
i dont know of anywhere that does explain the data, all i can tell you is what the graphs are,

the colored boxes at the lower right sellect the different curves to be displayed,

red horizontal line is the vswr curve from 26 to 28mhz

purple horizontal line is Z curve 26 to 28mhz

green horizontal line is reactance curve 26 to 28mhz

the boxes on the left sellect the 2 user moveable vertical markers and the green automatic min vswr point marker,

i can move the red and blue verticals to anywhere on the graphs then read the information at that point on the graph in the two lines of data, red marker upper line blue marker lower line,

the bottom min vswr data line corresponds to the green marker that automatically finds vswr min and displays the relavent data for that point on the graphs,

the red Xs+j as far as i know is reading inductive reactance in ohms
the Xl to uH is reading the equivalent inductance in uH that is = to the Xs+j at the indicated frequencies,

when the load is capacitively reactive the red Xs and Xl turn blue and read
Xs-j
Xc to pf
which i take to be capacitive reactance in ohms and the capacitance in picofarrads that is = to that reactance at the indicated frequencies,

heres a link to the instructions online, i will have a read and see if i can understand it.

http://f1.grp.yahoofs.com/v1/UBzzRX...0hP9YIa2N-4XiPZ175mEra0DrQ/manual_minivna.pdf

 

[distortion]

I don't know much about tuning antenna's, but I know mine was a little off on tuning at a 1.1 with an x=5 and 53 ohms.

Next thing you know.. 40-50 feet in the air, it was 1.0, with x=0 and exactly 50 ohms.. talk about lucky.

I don't know EXACTLY what your looking for, but keep in mind if you get really close, you might be spot on when you get higher in the air.

Peace,
Josh

 

[distortion]

Never plugged straight into the antenna.. used a 36 foot piece, and a 150 foot piece.. was about the same each time, could never get ohms dead on 50 or the X to = 0. 60 feet higher in the air, it sure did drop tho.. it was close enough as it was though, but in the air it was flat out perfect.

I'm a newb tho.. might be other variables involved. This was also with a mfj handheld, not a high tech computer software program that plots shit out

Josh

 

[C2]

First, tell us what frequency you want.

I'll assume you want it at 27.165:

There is more inductive reactance than you need. Mess with the trombone a bit (make it smaller).

The resonant element is too short, make it longer.

Also, you should be using a phase matched section of feedline for this measurement (electrical 1/2 wave).

If you could put a marker at the freq. your after, that would help know what your trying to do.

It would be interesting (for me anyway) to see the Smith plot.

Have you figured out the resolution of this measuring device?

 

[Marconi]

Hey distortion, do you think something was close to the antenna when tuning near the ground that affected your tune?

 

[bob85]

hey marconi i want it dialed in for 27.580,
the feedline was cut to more or less 1/2 wave multiples but i will use just one electrical 1/2wave when i get the analyser working on the laptop,
i am going to move first the topside of trombone and see what it does then the bottom then the radiator and observe what they each do and hopefully work out what i need to do,
resolution? i have not tested to see how much i need to alter the load before it changes the reading,
it sees changes that a mfj does not see if thats what you mean, most of my loads read close to perfect on a mfj but this shows them all to be slightly different, untill i get a calibration load i cannot check it out,

ps.the job is on hold due to the loss of a close family member in a cars smash but i will get back to it when i can,

thanks for your interest

 

[bob85]

well i flashed the bios on my old laptop and got it ti take windows xp and the minivna software,
it works great but the screen dont refresh nearly as fast as my clocked amd tower,

i cant take the i-10k down on my own untill i cut half the 2 apple trees down so i just played with the trombone sections for a good houre before the old battery in the lapi went flat,

i managed to get x=almost zero and 1.05:1 vswr on the same frequency according to the analyser,
just my luck it was below 27mhz,
at the low height its mounted at now the antenna needs shortening,

im pretty sure i can get resonance and vswr min at near enough the same frequency once i make a bit of clearance to lay it down and shorten the radiator

 

[Beetle]

Bob - sorry to hear of the loss. Wife and I will remember you and your family in our prayers.