A99 VS. I MAX CHOICE AT IMPROPER HIGHT

[Stellasstillarat]

Wow! I knew I left something out. I usually switch once a month between four to six amplifiers. Palomar 300a, maco 300, dnA phantom and a couple pf (4 x 1446's Palomar shooting star and no name 500's. All.three 1446's are exactly the same except for the name printed on the front (most likely the poorest built and dirtiest of all the amps I own. My reson for switching between the tubers
is amps or those ages like to be fired up as not to let the caps and whatever else can go bad from sitting around dry up. I've been hearing this for the longest time. Wheather this is true or not I'm not sure. It may also be I like to change the scenery every now and then anyway. The maco 300 and Palomar 300a are close in output with about 400 on AM and above 500 on ssb. The phantom about 850 AM and 1000 + on ssb. This is with 11/2 on AM and 12 - 15 on ssb. I very rarely run them on any position but high. Now when I say no rfi that's with the a99 with one of those amps on and as I mentioned with it on high. This is my reason for not taking a chance that might hve a bunch of nabour's looking like flesh starved zombies chasing me as my vehicle pass is their houses shouting "I hear your voice coming through my waffle maker'!! I must also add thar I'm a fairly private person and beyond a good morning, afternoon or evening there's not much conversation. I should also mention that I'm a transplant from a Brooklyn nabourhood which has been unfairly judged for having a supposedly large Italian American "sub culturer". I also happen to be of Italian decent. I should also mentio that two weeks of living here in my new home six agents of a certain government agency knocked On my door warrent in hand so i quietly left with them and returned home lees than 24 hours later. I emedietly began to notice my nabour's acting oddly strange in a shaky friendly kinda way. A week latter the guy I hired to come to my home and detail my vehicle told how ficked up that the local news paper printed the story of my a rest.. I was taken back by his notification. I onlyn purches the ny daily news which is sold locally hear in nj so I didn't see the story. My auto detailer told me it basically said I was being held for questioning on a crime that apparently happened in 1991 (over 14 years had passed). The aticle mentioned the false hood that I may have been associated with this Italian American sub culture and listed my name and street adress. Wheather this is why my a99 gives off no rfi I dont know but since I've had my station up and operating not a singal complaint and id have to belive it to be true because it's my hose that's the closest to my antenna and with the phantom on high (or as ny one of the amps) I get zero absolutely, zero rfi and would like to keep it that way.

My Imax is out back, sets in the corner of my porch and is 12ft from the power lines, and my living room wall is on the other side of my antenna, and no problems with it messing anything up, or anything....but I'm not running alot of power either, just a hf radio and 30 watts....and it's a few ft from our dish antenna, no choke on it, nothing....using RG 213 coax, and some LMR 240 coax on it, thats all.....good as it was talkiing on 10m can't complain with it.......

I have read a bunch of stories on the A99 and the Imax 2k....

My neighbor down the road runs a A99 and he has problems running a HP radio on his messing up his neighbors stuff...he talks late at night now, lol..

 

[Heavy Metal]

Single wide banded is always one with a ferrite. Narrow banded is possibly the air wound.

However the ferrite based one is going to be better 9/10. First of all its choking is mostly resistive - if you've read the G3TXQ page he mentions how reactive choking can actually increase common mode making it worse. Secondly its more tolerant of discrepancies in the building due to the wide almost 20MHz bandwidth of it. Because of how narrow banded the air wound one is, the only real way to guarantee that an air wound one is going to be choking where you want is to use a GDO to measure the resonance of the choke you've built.

Like using Ferris Mix 31 for broad banded vs single? 10 or 15 or 20 as close to the PL-259 connector on down under antenna SO-239. See below...

palomar-engineers.com/ferrite-products/ferrite-beads


VS





I used the bottom two 5T for the IMAX 2000. So far have not had it come over speaker's or anything else... ect... like it was doing before the 5T air coil. And I am up only 21 feet off ground.

 

[Needle Bender]

Dangit! - I was off by 1/2 turn & .25" from memory

 

[Stellasstillarat]

Needlebender. I'm assuming that if the chart showing those mesurments are indeed correct, your stated being off a bit didn't make any difference what so ever. And if this is the fact why couldn't it be the chart dimensions thst are off? P.s. am I detecting a bit of sarcasm?

Dangit! - I was off by 1/2 turn & .25" from memory

...



I'm not sure what you have or have not read on the subject, but an air choke is, at best, a third rate attempt at replacing the functionality of a current balun. A current balun can be used on any antenna, and it has the effect of fully isolating and removing common mode currents, among other benefits. A choke, on the other hand, simply attempts to attenuate said common mode currents. In the case of the choke some CMCs always make it through.

Also, a well made current balun works over a much wider frequency range than even a ferrite based RF choke, while an air choke that was made wrong (intentionally or otherwise) can actually make a common mode currents issue worse on some parts of the frequency range (hopefully not the part you are using it on).

Now here is the bad news, the MFJ-915 is not actually the current balun they say it is...



Taken from http://www.mfjenterprises.com/Product.php?productid=MFJ-915. What this is telling us is it actually is nothing more than a ferrite based RF choke, and because of this it is actually nothing more than a more advanced version of an air wound choke. By more advanced I mean it is more resistive instead of reactive in nature, which has certain advantages. Plus you can make one yourself without having to worry about the break in the coax stuff, just by some FB-31-1020 beads, 10 will work well, and string them on the coax before you put an end on, and then find something that will hold them in place near the antenna end of the feedline (I personally use heat shrink tubing for that).

Now about that break in the coax business. I'm sorry to have to say this, but what you have learned about this is a load of crap. Yes, there is an amount of loss going through such a connection, but it is insignificant to the point of being well beyond irrelevant. To put this loss in perspective, my AIM 4170 VNA can barely measure the difference a single PL-259 connection has. These connections have so little loss that I had to string a bunch of them together to get a meaningful measurement and make any useful calculations. You can have well more than 20 of them on your run and (assuming they are all properly connected) you won't notice the difference.

If we were talking UHF frequencies, then yea, these connectors would be a problem, but we aren't talking about UHF frequencies here are we...


The DB

Dangit! - I was off by 1/2 turn & .25" from memory

 

[M0GVZ]

Its quite possible it worked with him being a little off. It may not be peaking exactly where it is in that chart but he could've had a level of common mode that even 1k Ohm would've been ample enough to choke off. 2k and above is really only needed if you run power and have a fair amount of common mode.

In most situations where you're running say up to 100W and have a reasonably decent installation then 1k is going to be plenty. If you're running a lot of power, 500W, and have a lot of common mode, i.e you're breaking through people's speakers, wiping out their OTA TV signal and other things then 1K is probably not going to be enough.

In regards to the chart dimensions being off, if you're referring to the chart above by G3TXQ it was done by someone who is highly regarded worldwide in amateur radio when it comes to antenna design and his chart was created by him actually building every single RF choke individually and testing them with a 2 port vector network analyser. Here's the method he used:


"Fortunately, a 2-port Vector Network Analyser can measure both the magnitude and the phase of the attenuation introduced by the choke, and that allows us to fully determine the choke's complex impedance. I use a VNA2180 in the arrangement shown. The jig typically adds the equivalent of 0.2pF or less of parallel capacitance.

The ports of the VNA are connected to a test jig via two short lengths of coax - long enough that the choke is physically well-isolated from anything that could cause stray coupling and affect the measurements. The test jig comprises two BNC sockets mounted on a small piece of PCB material; "crocodile clips" soldered to the BNC centre pins allow the choke to be connected in line. A 50 Ohm resistor on the jig ensures that the impedance "seen" by Port A of the VNA never becomes extreme.

The VNA is first calibrated with the two coax leads removed from the jig and connected back to back. Then they are re-connected to the jig, the choke clipped between terminals A and B, and a VNA measurement scan made between the required frequencies. The resulting S21 Amplitude and Phase data is then transferred to a spreadsheet to calculate the choke's complex impedance. The derivation of the choke resistance (R) from S21 Amplitude and Phase is shown in the attached notes. The choke reactance (X) is then easily calculated from R and S21 phase."

So its not just done with a multimeter and I trust what Steve G3TXQ says above anything I'd see from Random Joe on a forum.

 

[M0GVZ]

I used the bottom two 5T for the IMAX 2000. So far have not had it come over speaker's or anything else... ect... like it was doing before the 5T air coil. And I am up only 21 feet off ground.

Good. Looks like its working for you then. Nothing more annoying than breaking through on speakers and wiping out the TV.

 

[Heavy Metal]

Good. Looks like its working for you then. Nothing more annoying than breaking through on speakers and wiping out the TV.

Nope, tried 8" 8T did not work followed the chart and boom worked.


Am pleased

 

[bob85]

steve's chart has worked for me in curing friends rfi in multiple installs at different locations.

 

[Heavy Metal]

Is the A99 and the Imax 2000 base the second if you were to round the Imax 2000 to look like the A99 base would both be same.dimensions as far as rounded?

 

[Heavy Metal]

What is the best height off ground vs ideal height off ground vs most effective height off ground? For local vs dx as well.

 

[wavrider]

HM every QTH is different as for height.

May be some buildings in the near field or far field, obstructions etc etc.

You just going to have to install your antenna at different heights and see what works for you.

Rule of thumb is at least 1/2 wl for decent toa.
Local as high as you can get it within reason,

 

[Heavy Metal]

Use to be 1060 plus feet above sea level and up 10' pole now @45 feet above sea level and up about 21 feet of pole. Just curious. Thinking of a 36' push pole or 50' push pole. Maybe adding @15 more usable feet bring it to 65 feet tall and put the antenna on top of that.

 

[Needle Bender]

Use to be 1060 plus feet above sea level and up 10' pole now @45 feet above sea level and up about 21 feet of pole. Just curious. Thinking of a 36' push pole or 50' push pole. Maybe adding @15 more usable feet bring it to 65 feet tall and put the antenna on top of that.

I seem to get the best performance by cutting my coax at a multiple of a full wavelength (about 434") then multiply by the velocity factor of the coax, (66% for RG8 / RG213 and 85% for LMR400) then elevating the antenna so the point 18' from the top is at a multiple of 1 wavelength (36') above ground.
My coax (LMR400) is 92' 3" (3 wavelengths) and the antenna (Penetrator500) is currently at 31.5' at the radials. Seems to perform better to most 30-plus mile contacts by about .5 - 1 S-unit compared to when it was 11' higher.

Hard to say what height an A99 should be, (again, as already addressed, for what distance and conditions?) but I'd certainly try the bottom at 1, 2, 3 wavelengths, etc...

 

[Heavy Metal]

I seem to get the best performance by cutting my coax at a multiple of a full wavelength (about 434") then multiply by the velocity factor of the coax, (66% for RG8 / RG213 and 85% for LMR400) then elevating the antenna so the point 18' from the top is at a multiple of 1 wavelength (36') above ground.
My coax (LMR400) is 92' 3" (3 wavelengths) and the antenna (Penetrator500) is currently at 31.5' at the radials. Seems to perform better to most 30-plus mile contacts by about .5 - 1 S-unit compared to when it was 11' higher.

Hard to say what height an A99 should be, (again, as already addressed, for what distance and conditions?) but I'd certainly try the bottom at 1, 2, 3 wavelengths, etc...

Ok now in this calculation do you take in affect for an air coil?


So 434 * .84( 9913f7 ) / freq = ......

Correct on how to calculate?

 

[Heavy Metal]

Was talking with someone and they asked this:

What if property height as in rule of thumb as well as proper distance between antennas smirk, say someone puts up 2 iMax 2000's or a99's or whatever vs fan type dipole( vert, hora ect ). Be it same height or just a little higher than other. As well as min height above a structure that the post holding it is up against?