Worldwide DX Amateur Radio Forums - Ham - CB - HF - VHF - UHF

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.

marconi i got the email

thanks mole i will have a look on their website.

__________________
The importance of an antenna having good radiation characteristics cannot be overemphasized.

"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.

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).

"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.
---------

"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?
---------

"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

you can't make any common mode current measurements if the antenna is still in the box or not up in its intended elevated mounting location.

you can't make any common mode current measurements if you don't have access to an rf antenna current probe, although there are some symptoms that have been long established as the result of the presence of common mode currents in the system, which by the way are seldom if ever a problem in properly installed ground mounted arrays.

Quote:

"which by the way are seldom if ever a problem in properly installed ground mounted arrays."

This particular installation is not ground mounted. The base of the antenna is going to be 20 feet off the ground.


Quote:

"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's just it! I keep being fed contradictory information. I keep seeing this same thing being stated, over and over: That it is "NOT a good thing" to have your mast ADDING to the ground. I've seen it stated over and over, that if you do not "isolate the antenna from the mast", then you distort the pattern of the antenna, and introduce more "ground loss".

I've seen it time, and time again. People saying "keep an elevated vertical isolated from the ground". "Do not ground the radials".

So which is correct?

Is it a "good thing" to have your mast act as another "radial", or is it better to PREVENT continuity between the antenna base (on an ELEVATED antenna) and the ground? And if it is better to ISOLATE the antenna radials from ground, HOW does one do this? Electrical tape wrapped around the mast top? And if so, then how does one ground this antenna against lightning?

This question (and the answer I received) is why I am STILL confused about this. I'd really like to put this question to rest in my mind, because I still don't know which is correct, and HOW to isolate the antenna from ground (if that is the way to go).


Anyone??

doc, my buddy was pulling his hair out trying to stop the rf,
the a99 was mounted on a 21ft aluminum scaffold pole,
i isolated the a99 from the conductive pole then added 2 wire 1/4wave radials and an ugly balun at the feedpoint,
it gave increased signal strength comparable to a doubling of transmitter power on my jrc signal meter and a marked reduction in rf in my buddies shack, its hard to believe even for me and it was me that did it,
i had a brainwave and it seemd to work much better than anybody local expected, rf problem gone and locals saying your signal has gone up what have you done, nothing scientific just an observation from several local stations including my own, i dont get it so i went looking for answers,

i dont know how much this guy knows but he seems to agree, what i did met his criteria,

Summary

The cure for common mode problems caused by less-than-perfect grounds is inserting a 1:1 choke balun in the system at the antenna feedpoint. The coax should also be kept away from the radials as it exits the area of the radials and the antenna. An antenna with a poor ground using few radials cannot have a support mast grounded to the radial common point (at least it shouldn't if designed properly). There is no exception to this!

http://www.w8ji.com/verticals_and_baluns.htm __________________

if hes got it right then the vast majority have got it wrong.

__________________
The importance of an antenna having good radiation characteristics cannot be overemphasized.

W8JI knows a bit about radio. He designed a lot of the amplifiers formerly and currently in production at Ameritron, including the AL-811 and -811H. He knows what he's talking about, and you can take it to the bank.

__________________
If you're like everybody else,
you're about average.
73 de K7KBN

Bob and Beetle, read the following which preceeds the Summary notation and text that follows in Bob's post.

"Longwire and Windom antennas really aren't much different than verticals. They are a form of Marconi antennas, and require a counterpoise or ground of some sort. As with verticals, common mode current flowing into the antenna must be balanced by current flowing into a ground system.

Instead of bringing the longwire directly to an antenna tuner, a better solution is using an RF ground system independent of the station safety ground, and keeping that ground isolated from the station safety ground."

Then read the summary below again and tell me if the article is suggesting that a grounded mast should be insulated from the radials or that a grounded mast should be independant (insulated) from common point ground for the station? Could it be that the word radial in the text below should not be there?

Summary

The cure for common mode problems caused by less-than-perfect grounds is inserting a 1:1 choke balun in the system at the antenna feedpoint. The coax should also be kept away from the radials as it exits the area of the radials and the antenna. An antenna with a poor ground using few radials cannot have a support mast grounded to the radial common point (at least it shouldn't if designed properly). There is no exception to this!