Just put up I-Max 2000

[2RT307]

I think I'd be happy with the SWR that you posted. And, as always, I see some very good advice from the fellas here, too!

More detail on common mode currents:
http://www.k0bg.com/common.html

73,
Brett

 

[Dipole]

Just a note...

There is far less difference in going from 1:1 to 2:1 SWR than there is to make an s-unit worth of difference. To increase your signal by a calibrated 1 s-unit on the receiver's side it takes 400% more power to be transmitted, and to drop 1 calibrated s-unit on the receiver's side takes a 75% drop in power. the difference between 1:1 and 2:1 SWR, and this is making the common mistake of assuming all of the reflected power is lost, is 11%. This 11% figure is a worst case scenario, not a typical occurrence, and even if it would happen, it would take almost 7 times as much reflection to get that 1 s-unit difference.


The DB

I was distracted and made a Typo I meant" < 1 s unit" thnaks for catching it

 

[Dipole]

Just a note...

There is far less difference in going from 1:1 to 2:1 SWR than there is to make an s-unit worth of difference. To increase your signal by a calibrated 1 s-unit on the receiver's side it takes 400% more power to be transmitted, and to drop 1 calibrated s-unit on the receiver's side takes a 75% drop in power. the difference between 1:1 and 2:1 SWR, and this is making the common mistake of assuming all of the reflected power is lost, is 11%. This 11% figure is a worst case scenario, not a typical occurrence, and even if it would happen, it would take almost 7 times as much reflection to get that 1 s-unit difference.


The DB

I was distracted and made a Typo I meant" < 1 s unit" thnaks for catching it

 

[Heavy Metal]

Ok got home from work and reading about running coax the rf I realized grr that stupid piece of wire I used to ground the bottom might be my culprit guess what...


My SWR's are now as follows
Dead flat 24.435.00 to 26.770.00 --- 1.5:1 and under 18.830.00 to 28.580 2.0:1 and under 18.465.00 to 28.955.00
At 18.000.00 to 29.650.00 @2.5:1

Was that wire I used to ground grr the whole time, if wasn't might be were I have it and that's on a 5' tall 8"
Thick corner fence post lol


So I take it I will have to insulate the pole I use when I put this in the air?

 

[M0GVZ]

The antenna is > halfway long and is voltage fed so you don't need a ground wire. Insulating the pole isn't sufficient as you'll have capacitive coupling. Just run the coax away from the pole instead of securing it to it. And use a RF choke at the antenna feed point, preferably one made with a ferrite core rather than an air wound coil of coax.

 

[Heavy Metal]

The antenna is > halfway long and is voltage fed so you don't need a ground wire. Insulating the pole isn't sufficient as you'll have capacitive coupling. Just run the coax away from the pole instead of securing it to it. And use a RF choke at the antenna feed point, preferably one made with a ferrite core rather than an air wound coil of coax.

Why not air wound? ( curious )

 

[wavrider]

Air wound will work.

I have run full legal limit through my imax on 10/12/15 meters and no tvi rfi noticed, my PC sits on the desk in the shack with the amplified speakers always on. Nothing heard on the PC speakers.

 

[Heavy Metal]

Air wound will work.

I have run full legal limit through my imax on 10/12/15 meters and no tvi rfi noticed, my PC sits on the desk in the shack with the amplified speakers always on. Nothing heard on the PC speakers.

I run a dish for tv, so far none that I know of. But i am running RG8x and want to run @100-125 feet of either 9913 or lmr400 Prob 9913 and solid and stranded versions for 3' to 9' jumpers inside. But also do an air wound one but I do have a line isolator from hy power antenna a GULI 6-160-5kw...
Was thinking of using it on a homemade veritical multiband like the I-Max 2000 except not so narrow top sorta longer mid section and about 36-40' and add maybe 6 or 7 wires in it for. 6, 10, 11, 12, 15, 17, 20... 6/10/11/12 being .64 then 5/8 then 1/2 for rest... And a air wound coil and use the isolator for that. Just an idea I am floating around in my mind but dunno were to get the fiberglass tubes in 10-12 foot sections.

 

[AudioShockwav]

""BTW Jeff, aside from a really bad physically damaged feed line...have you ever worked a feed line that had very high losses due to deterioration from "old" water in the feed line?""


Yes Eddie, in fact when I got my I10K from Jay and put it up I was using some old, questionable quality coax that had been up in the air for some time.

I was plotting bandwidth/SWR on the chart that Jay provided with the antenna and I was seeing a plot that started high, below where I had set the antenna, dipped like I expected it to do, then a gradual rise in SWR , hit a peak somewhere around 3:1 then dropped again with another rise as I went up in frequency.
The band width was too wide, so much so that I called Jay on the phone to talk to him about it.
He was the one that called my coax into question.
Next weekend or so I pulled it down with the intention of re-working the connectors on the ends, but no matter how far I stripped back the outer jacket, the braid was tarnished and oxidised all to hell.
I replaced it with new coax ( 213 I think) and new ends , and the SWR plot fell right in line with what Jay told me it should be.
Weird thing is that during this time I was still using the radio and antenna and it seemed fine other than the strange SWR results.
I may have even posted the plot of the antenna on the forum, but I think that was way back in the EZBoard days.....all of that got lost long ago but I do remember it.

73
Jeff

 

[Marconi]

""BTW Jeff, aside from a really bad physically damaged feed line...have you ever worked a feed line that had very high losses due to deterioration from "old" water in the feed line?""


Yes Eddie, in fact when I got my I10K from Jay and put it up I was using some old, questionable quality coax that had been up in the air for some time.

I was plotting bandwidth/SWR on the chart that Jay provided with the antenna and I was seeing a plot that started high, below where I had set the antenna, dipped like I expected it to do, then a gradual rise in SWR , hit a peak somewhere around 3:1 then dropped again with another rise as I went up in frequency.
The band width was too wide, so much so that I called Jay on the phone to talk to him about it.
He was the one that called my coax into question.
Next weekend or so I pulled it down with the intention of re-working the connectors on the ends, but no matter how far I stripped back the outer jacket, the braid was tarnished and oxidised all to hell.
I replaced it with new coax ( 213 I think) and new ends , and the SWR plot fell right in line with what Jay told me it should be.
Weird thing is that during this time I was still using the radio and antenna and it seemed fine other than the strange SWR results.
I may have even posted the plot of the antenna on the forum, but I think that was way back in the EZBoard days.....all of that got lost long ago but I do remember it.

73
Jeff

Very good observations Jeff.

I got an old 100' foot run of RG8x from a friend that had it attached to an A99. I put it on a new Starduster I got from another buddy without knowing the line had old water in it.

The A99 has a drain hole in the bottom, but that does not stop water from still going thru the PL259 into the feed line. This is why I now use "Stuf" from Cross Devices to help prevent water in my feed lines. See this product on www.Aesham.com

My Starduster antenna got very broad banded with a very low and flat SWR from 10-20 meters. The antenna had ears like a cat...and never had noise like all my neighbors often complained of. I use to tell them it was the nature of my SD'r, but I was wrong.

It just goes to show, that more often than not, we don't need a lot of power to work DX, because I never missed a contact that any of my neighbor's were able to make...even though I did make less of a signal and sometimes guys, far away, told me they could hear me, but I did not give them a signal.

Another buddy of mine told me he removed his coax from his radio because he saw his SWR change, and then he noticed water dripping form the line...so fresh or old water that does not evaporate or drip out can ill-effect your SWR results at certain times in your coax, so be aware.

The RG8x coax I had also used air impregnated foam dielectric, and that too can aggravate water type problems.

Jeff, did Jay ever suggest to you to use 50' feet of feed line or multiples...if you had any problem tuning the I-10K?

 

[Justme]

An aircore has a very limited range where it produces enough resistance to choke rf.
The right choice of ferrite and number of windings mostly produces enough choking over a much wider frequency as an air core choke.

I'm using the Imax 2000 as well for 18 - 10 meters as one of the antenna working there, it is not the only one.
I opted for 4 x 15 feet wires on the roof as groundplane, works for me.

Why not air wound? ( curious )

 

[Heavy Metal]

An aircore has a very limited range where it produces enough resistance to choke rf.
The right choice of ferrite and number of windings mostly produces enough choking over a much wider frequency as an air core choke.

I'm using the Imax 2000 as well for 18 - 10 meters as one of the antenna working there, it is not the only one.
I opted for 4 x 15 feet wires on the roof as groundplane, works for me.

One I doubt I will use a ground plane but air might be better since the ante be is limited.

Also care to share your SWR's if you had a reading before installing a groung plane vs after installing it? Just for an FYI before and after. And anyone else that cars to share as well as with a ferrite core isolator vs air wound and if air wound how many feet of coax, coax type solid or stranded and how is it doing.

Thanks .


So
Far I turned up rings a little and shifted it higher up and so far I pleased but it's only @5, in the air for now.

 

[AudioShockwav]

To answer your question Eddie, no Jay never suggested any certain length of coax, just that I might have a problem with the coax itself.

73
Jeff

 

[M0GVZ]

Why not air wound? ( curious )

Because you can't guarantee its actually going to be doing the choking at the frequency you want unless you measure it with a Grid Dip Oscillator. They're very narrow banded so get it wrong and it'll be doing nothing at best and at worst could actually increase common mode as the choking is reactive, not resistive.

By using a ferrite core of specific mixes we know for certain what the choking will be and that it will be resistive. Its also wider bandwidth so being slightly out in its manufacture isn't going to make that much difference whereas with air wound the sizing and number of turns is critical.

 

[Marconi]

To answer your question Eddie, no Jay never suggested any certain length of coax, just that I might have a problem with the coax itself.

73
Jeff

Jeff, here is why I ask. If your manual doesn't show the statement in the 1st paragraph...then let me know.

What do you think of his comments below?