Just put up I-Max 2000

[Captain Kilowatt]

""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

I found the same thing several years ago with a mobile HF antenna. The bandwidth was just too wide to make sense. Water and salt/road grime had entered the cable at the antenna end and thru capillary action had crept half way back to the radio end. The braid was black and the insulation was black/green. I replaced the coax cable and the SWR bandwidth was much narrower however the performance definitely improved.

 

[Marconi]

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.

I tend to agree with M0GVZ.

I've used several air type coils that I wound myself on my computer lines to speakers and my mouse, but none did a thing to stop RF.

I use clamp on ferrets and the problems with RF are eliminated. Just put the clamp on the line and slide it up and down until you see the ill-effects disappear. I my case the ferret was right at the computer end of the device wire.

I got my clamp on ferrets at Radio Shack...and I do not know the specific mix for their ferrets.

 

[Heavy Metal]

What size around and legnth of coax to use for an air wound one for 13 MHz to 55 MHz?

 

[The DB]

What size around and legnth of coax to use for an air wound one for 13 MHz to 55 MHz?

There are some web sites that will try and tell you that that is possible, but its not. It is simply to wide of a bandwidth for any air choke to handle. Air chokes work well for a single band, but that is about it.

If you are using RG-213 or a coax that is about the same thickness use four to six FB-31-1020 totoids strung on before you put the antenna connector on and held in place near the antenna feedpoint, that will cover most of the bandwidth you seek to use.


The DB

 

[AudioShockwav]

I do not want to hijack...Yes it is there, but I read that as Jay explaining "I used a MFJ, 50 feet of coax so on ......." never thought of it as a recommended length.
And when talking to jay on the phone I don't remember him stating that 50 feet was necessary.

73
Jeff

 

[Marconi]

I do not want to hijack...Yes it is there, but I read that as Jay explaining "I used a MFJ, 50 feet of coax so on ......." never thought of it as a recommended length.
And when talking to jay on the phone I don't remember him stating that 50 feet was necessary.

73
Jeff

Jay sent me a tracking chart of his analyzer results once in the from of a bandwidth curve. If I can find it I will post it. It had a note in the margin about using a 50 foot length of coax when using his 259B on this report. He also talked about the radials being asymmetrical and the antenna would produce a match less than perfect no matter what one did to tune. He only said his idea was to compromise with the tune at the best point in the tuning, and would not explain further. He treated me just like my old radio mentor (Al) use to, and I payed attention to those words...just like I did with Al.

I tried to talk to Jay in more details, but he was reluctant, and told me to just follow his instructions. I never did that until much later when I saw what Hunt said in his report on chokes...noted below.

Later on when I read this report http://www.karinya.net/g3txq/chokes/ by G3TXQ and saw the chart at the bottom...I was convenience that Jay knew something that I did not understand at the time. When I realized this idea...I went straight out and setup my I-10K and used a 50' foot foam coax with a high Velocity Factor of .82 similar to the LMR 400, just like he suggested...and finally the tune was near perfect and the resonance was resistive at the same point on the antenna. Check the details for the different coax lengths and whether a choke is need or not.

Prior to this I could get a very low SWR, but the best SWR value was never at resonance, by at least close to a 40 channel difference even using Jay's math. This also allowed me to see a bit more bandwidth up near 2.00 mhz <2.00:1 SWR.

I hope I made sense so that you can understand.

 

[Heavy Metal]

Kinda... Question velocity factor on coax? higher the better or lower the better?

 

[Marconi]

Kinda... Question velocity factor on coax? higher the better or lower the better?

HM, I don't think the VF matters just using our radios.

I gave the details...just to be precise as to what Jay in the Mojave was claiming in his I-10K Manual. I was making note of the statements between these two men, Jay and G3TXQ relative to feed line length they noted.

 

[Beetle]

Kinda... Question velocity factor on coax? higher the better or lower the better?

Not a question of better or worse; it is what it is. BUT when you're working with antennas it can be critical to know the vf of the particular cable you're working with. An antenna analyzer can help you measure an "electrical" half or quarter wavelength, and it takes the velocity factor into consideration automatically.

Essentially, a "mathematical" wavelength multiplied by the velocity factor of the feedline equals the "electrical" wavelength at that frequency.

 

[Heavy Metal]

Talking HF 1 to 30 maybe 54/55.

9913 vs LMR-400 is it worth the extra cost as well as solid vs stranded center conductor. Was thinking 9913 solid. But what do you all think and should I keep to same for short cable runs radio to tuner to meter ect or if go with 9913 use lmr 400 for the 3' 6' 9' or 12' runs? And use stranded / or ultra flex on those?

Thanks again...

 

[Robb]

VF is not a critical factor for what you are doing. You might want to concern yourself with the overall quality of the coax itself instead. As this will make a difference for its life span due to UV exposure and internal insulation integrity. In the HF range, loss is not a huge factor unless the coax is junk. But not as critucal as it would be for 6m or VHF/UHF losses, which can be considerable if poor coax is chosen. Even 10m can be affected with a poor coax choice. IMO, buying decent coax the first time around is cost effective over the long and short run. Not something that is worth trying to save a few extra dollars over . . .

 

[The DB]

The only time you need to know the velocity factor is when cutting a coax to a specific electrical length, which you really only need to do under certain circumstances.

The higher quality types of coax tend to have higher velocity factors, but that is not a universal truth.

The velocity factor, by itself, tells you nothing about the performance characteristics of a piece of coax. If you have two different types of coax with the same amount of loss for a given length, and one has a higher velocity factor, you will not be able to tell the difference between the two.


The DB

 

[Heavy Metal]

As I said before I am using @97' of RG8x but will run @100-150' of either 9913 or lmr400 but also wondering if I can mix it 9913 and lmr400 solid also going out and upto antenna and stranded versions for going to meter/tuner and by the way it is a LDG AT-200Pro II Autotumer.

 

[Robb]

You can mix the LMR-400 and Belden 9913 if you must, so long as a barrel connector is used to join them and that you seal it up properly. It is also important that you use only enough coax as needed to make the distance from shack to the antenna. Extra coax is just going to add extra line loss, which is as unwelcome as a shark at a shipwreck. I'd run either coax exclusively if I had the choice, just to keep the continuity of the coax complete. But not that big of deal unless the barrel connector union isn't textbook clean.

At 100ft length or greater, coax loss becomes an issue depending on what freq it is operated on . . .

 

[Heavy Metal]

You can mix the LMR-400 and Belden 9913 if you must, so long as a barrel connector iss used to join them and that you seal it up properly. It is also important that you use only enough coax as needed to make the distance. Extra coax is just going to add extra line loss, which is as unwelcome as a shark at a shipwreck. I'd run either coax exclusively if I had the choice, just to keep the continuity of the coax complete. But not that big of deal unless the barrel connector union isn't textbook clean . . .

Actually was mixing as in using 9913 solid from inside to outside and my connections from switch box to meter to tuner to radio run either 9913 flex and or lmr400 ultra flex for between those components, as well as wondering that mixture as well as what's the best legnth for
Those runs 3' 6' 9' 12'? Reason ask on that is I remember back in late 70's certain lengths might give you mixed readings on part of SWR's? So just wondering on things like that.