common mode currents/decoupling

[bob85]

can it be done effectively on vertical antennas,

if we isolate the antenna from the mast, add 4 or more 1/4wave radials at the feedpoint and an ugly ballun?,
i have read that doing that is not nearly enough to attenuate counterprductive currents flowing on the mast and the outside of your coax spoiling your theoretical radiation pattern,
my own tests using the a99 showed a notable increase in signal reports after isolating the antenna and using an ugly balun with just 2 wire 1/4wave sloping radials, it also seemed to significantly lower rfi in my friends shack,
has anybody else here experimented with similar ideas?

is there a more effective method of minimising the effect of the mast and feedline?

 

[freecell]

"i have read that doing that is not nearly enough to attenuate counterproductive currents flowing on the mast and the outside of your coax spoiling your theoretical radiation pattern...."

the facts and experience prove quite the opposite is true, it makes for quite a noticable improvement in gain, pattern and current balancing betweent the radial system and the radiator. prior to these changes very little current actually flows in the radial system at all.

"has anybody else here experimented with similar ideas?

i've researched and measured the changes and as a result i don't sell or install a ground plane antenna without a radial system and a 1:1 current balun.

 

[bob85]

its good to hear the results of my test are not just my wanting it to work getting the better of me,
what type/brand of current balun do you suggest i try?
is there much to gain in going from 4 to 6 or 8 1/4wave radials?.

 

[Moleculo]

Just a W2DU type current balun should do the trick in addition to the radials. The difference between 4 and 6 radials? I doubt much at all, but it's worth experimenting with.

 

[Marconi]

its good to hear the results of my test are not just my wanting it to work getting the better of me,
what type/brand of current balun do you suggest i try?
is there much to gain in going from 4 to 6 or 8 1/4wave radials?.

Bob, maybe I wrote about my work with my Marconi a couple of years ago before
I got sick and had to stop, but not sure. I have an old signal report that I would
list RX signal reports on from the guys around me locally. If I did write about it, I
probably attached all the photos too. Might do a forum search for the word
Marconi, 1/4 wave antenna, or bazooka and something will turn up. If you can't find
it, let me know and I will post or email directly to you if you send me your email
address @ edromans@comcast.net

In looking at this report I show my antenna with 3 and 6 radials at about 35' and it
showed a difference in maybe 10 reports of about a 2 S-unit improvement when all
I did is add just 3 more radials. I tested with 3 elements and the compared it to 6
elements. I did not do much if any follow up as I recall because I was getting sick.
But that is what is on my report. To me that was a significant difference and I was
amazed.

I know it is not the same antenna as you are talking about, but maybe you will see
some good results by adding GP radials too.

Keep us posted.

 

[freecell]

Bob,

the Francis CB50 Amazers make great radial system elements.

"what type/brand of current balun do you suggest i try?

i use the W2DU 1:1 Current Baluns for most installations but i prefer Array Solutions and Cal-AV Labs for high power and/or application critical systems.

 

[bob85]

marconi i have seen the signal report list in the past, when i look at it im not sure what the arrows at the top indicate nor am i sure im reading it correctly, maybe you could shoot me an email of the list and add some explanation of how i should be reading it, i will email you with my current email address,

nice pic, i was going to ask you to post that back up to remind me what it looked like,

thanks.

 

[bob85]

jack i missed the boat with the cb50's, i saw the 4 cb50 groundplane kit advertised at a good price, sounds like a good idea, i had triquad flashing in my minds eye too, as usual they were out of stock,

i looked at the w2du balun using Amidon no. FB-73-2401 beads and rg303,
whats the deal with the 2 tails sticking out, can you make or buy one that has regular size coax sticking out for ease of connection to so239 antennas?, i could make the tails fit the i10k and the vertical portion of the avanti saturn but some antennas would be a problem,

the array solutions baluns look nice and expensive, as much as i would like one i can't justify that for my low power station,
these are the only ones i have found over here so far,

http://www.nevadaradio.co.uk/acatalog/Trident_W2DU.html

edit, after looking on eham, it seems that some of the array solutions baluns are cheaper than the ones nevada sell.

 

[Marconi]

marconi i have seen the signal report list in the past, when i look at it im not sure what
the arrows at the top indicate nor am i sure im reading it correctly, maybe you could shoot me an email of the
list and add some explanation of how i should be reading it, i will email you with my current email address,
nice pic, i was going to ask you to post that back up to remind me what it looked like,

thanks.

Bob that signal report was never intended to be used that way. I sent that report simply because it had a
several tests on it. I did not really consider the likelyhood of confusion. It looked perfectly clear to me.
I put the arrows on there hoping that the guys could connect the dots, but now I appreciate your concerns.
It is a mess, and I will try to explain it so maybe you can figure out some of my tackyness. :thumbdown:

Basically the arrows connect the two AT's that I was switching between to get signals on at any one point
in time. In order to get a fair number of stations however, the test were run over the course of a few days.
I made some errors of notation and with a couple of the arrow connections I took a little liberty and made
comparisons a pior reading that was not done at the moment of testing. Without explaination that would be
considered unfair and unethical, but I re-checked every time to make sure that the data from the prior test
was the same and to make sure nothing had changed. If there was no change then I recorded new test AT
signal. If I found a difference, I did not show the data for either AT and went on to another station. Kinda
messy I know, but that is it. I will still try to be more specific and explain my madness on that report straight
away.

I got your email. I sent you a blurb on the 1/4 wave bazooka type balun I use on my Marconi. It is probably
better to follow Jack's advise here, because he knows his business, and I'm not sure just how is the best way
to determine if your balun is really working, and for sure to what extent.

I guess you saw something that gave you a clue when using the Ugly balun. Maybe you could tell us more.
Maybe you already know what I do to try and find out if I am doing any good at trying to stop CMC. Jack you
could help us struggling young youts' in our efforts to figure this all out again.

 

[Marconi]

Sorry for the picture that is too big.

 

[Moleculo]

Bob, DavisRF (look on their website) has some with SO-239's on both ends. I've seen them around on other sites for sale, also.

 

[bob85]

marconi i got the email

thanks mole i will have a look on their website.

 

[freecell]

"I'm not sure just how is the best way to determine if your balun is really working, and for sure to what extent.

besides the obvious improvement in performance you need to have a way to measure rf current balance between the radiator and the radial system as well as the attenuation or absence of rf current on the outer shield of the feedline and the support structure. an rf current probe is what you need to make those measurements.

 

[Bushmaster]

This is a subject that has confused me in the past, and I still don't think I understand this correctly. I've heard the term, "isolate the antenna from the support mast", many times before, but never understood HOW this is intended to be done. What do you do? Wrap electrical tape around the end of the mast before you clamp the antenna base to it? How else does one ISOLATE the support mast from the base of the antenna? Obviously, if you do not put something between the mast and the antanna base, you will have continuity between the radials and the GROUND (via the mast), which is apparently undesireable (because of pattern skew and ground loss).

This is what I am most interested in resolving. Does "isolating" the mast from the antenna base merely refer to using some kind of insulator between the two?

I am about to install an ELEVATED 43' Zerofive multiband vertical (10M-160M). I will be using an Array Solutions "Tuner" balun at the antenna base. Are these "Tuner" baluns considered a "current" type balun? Should I also add the dozen big (#73 material) beads (I have on hand) at the feedpoint as an extra common mode suppression tactic?

And if I isolate this antenna from the mast, and do not run a ground cable, then what about lightning protection? Is there a cheap way to either create a spark gap (of sorts). If not, where would I obtain an INEXPENSIVE lightning arrestor to hook a ground cable to? I am only going to be running 100 watts (for now).

 

[W5LZ]

"How else does one ISOLATE the support mast from the base of the antenna? Obviously, if you do not put something between the mast and the antanna base, you will have continuity between the radials and the GROUND (via the mast), which is apparently undesireable (because of pattern skew and ground loss)."

If you're talking about a groundplane antenna, where the radials take the place of earth ground, there's really no point in doing that isolation thingy. The mast/support would only be adding to the ground, which ought'a be a good thing. That assumes that the mast/support does not extend above the antennas radials, in other words, is on the top of the mast.
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"This is what I am most interested in resolving. Does "isolating" the mast from the antenna base merely refer to using some kind of insulator between the two?"

That's certainly what it sounds like. Just to make sure, why not ask the manufacturer?
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"I am about to install an ELEVATED 43' Zerofive multiband vertical (10M-160M). I will be using an Array Solutions "Tuner" balun at the antenna base. Are these "Tuner" baluns considered a "current" type balun? Should I also add the dozen big (#73 material) beads (I have on hand) at the feedpoint as an extra common mode suppression tactic?"

Why not see if you need any 'additional' suppression first? they shouldn't hurt anything, but may not 'help' anything either.
No idea what those "Tuner" baluns are, voltage/current.
---------

"And if I isolate this antenna from the mast, and do not run a ground cable, then what about lightning protection? Is there a cheap way to either create a spark gap (of sorts). If not, where would I obtain an INEXPENSIVE lightning arrestor to hook a ground cable to? I am only going to be running 100 watts (for now)."

If the mast is a continuous 'conductor' going to ground, and if you isolate the antenna from the mast without adding a ground wire of some kind, no, you have no lightning protection. If you then add a ground wire from antenna to ground for that lightning protection, it seems like a complicated way of doing things to me. Why not just use that mast since it's already there? Makes me wonder about the use of 'isolate' and 'insulate', doesn't it you?
There is no 'INEXPENSIVE' way of arresting lightning. 'Spark-gap' type arrestors do not work fast enough to provide any practical protection. Since current follows the path of least resistance, and a 'gap' will always have more resistance than a conductor, it won't be lightning's first choice. By the time the current builds to a level large enough to jump that 'gap', it's already at the other end of that conductor...Zzzz Ouch!
Probably the 'best' lightning arresting scheme is that used by broadcasters. Not the simplest solution, or the cheapest sometimes, but most effective. (Ask 'QRN'.)
- 'Doc