Really any difference at height?

[RadioDaze]

First post mentions dipoles at height?????

Radio Daze quote"He still says these are horizontal plots. We are talking about verticals."

Fair observation, polarization was not mentioned. I just made an assumption the IMAX also mentioned was not going to be horizontal.

 

[RadioDaze]

Here are two pics for you.

The first picture is simulating the length of said tube on the imax and the second is using a much shorter lower tube than the imax. As you can see, in both cases, the current on said element drops to nothing at the tip.

The shorter element has more low angle gain. Its not much in this case, but it is there. If you lengthen the lower tube or use a coax to simulate a choke 1/4 wavelength below the antenna as many people recommend for this antenna this gets much worse...


The DB

I am not sure I have read about this specifically.Does this mean a coiled coaxial choke is not recommended for use on the IMAX2000 near the SO-239 connection or does it mean it is not recommended to coil choke the coax 1/4 wavelength down the coaxial feeder.
Interesting stuff.

I just put the MJF 1:1 current isolator in line, thinking this was a better solution. It had pretty good write ups so I invested in one. No negative RF in "shack" issues experienced thus far.

 

[Heavy Metal]

Really I use I coiled choke see,

It has done wonders on home electronics I would come over on, now nada

 

[222DBFL]

The 1:1 current isolator can be used at the feedpoint or as close to it as you can get. No magical numbers needed for where to place them. From my own experience, they can be placed anywwhere along the feed line and should work. But should work best at the feedpoint or a close as you can get to it. It should be more effective than the air wound choke you have, but if it's not broken why mess with it!! If its working and making contacts leave it be. JMHO.

 

[RadioDaze]

Thanks, I apply the 1:1 ferrite choke as a precautionary measure really. I have no RF current meter so just put it in line "belt 'n' braces" to be sure. That way at least the pattern from the antenna should be as good as it can be given the height on the day and not negatively affected by CMC on coax.

I have even popped it inline when feeding the Gain Master despite it having a built in choke (as I read here air core chokes are no guaranteed CM solution) The only issue I have experienced on occasion with both antennas is a little break through on my external speaker which was cured with 3-4 turns on a split ferrite.

As I set up slightly differently each time including QTH some places seem to provoke slightly more break through than others. it is far from a problem to live with now though. With the 1:1 ferrite isolator at the linear end I never hear anything when I key from the external speaker.

Sometimes I put it at the antenna end, but not if I don't want a top heavy pole. If I stick 5/6 poles up (29 feet) I put it at the linear end.

 

[222DBFL]

Anywhere is better than nowhere at all!! Mine is placed about 40ft from feedpoint and it works. I keep my coax isolated from the mast pipe anyway using 1/2" grommets and snap ins zip tied to my mast. This keeps coax off the mast and totally isolated from it. Don't know if it helps but it doesn't seem to hurt it any.

 

[Heavy Metal]

As shown I use a coil but maybe use one as it comes into the place. Then from it to equipment.