Extended double Zepp help..can't tune it properly...

[VE7 Kilohertz]

Hi guys,

I extended my 160M dipole (240') to an extended double Zepp for 75M (320'). It's at about 35' high on the center and 50-60' at the ends. Home brewed ladder line with Johnson ceramic spreaders, ~4". Feedline length is about 40'.

My balanced antenna tuner is Richard Measures type, 2 identical 22uH roller inductors and 7-1000pF vacuum cap. 30' of RG-213 wound on 5" ABS for the low impeadance balun.

I couldn't get the antenna tuned anywhere in the ham bands with this length so I shortened the antenna by 6' on either side and now to get the antenna matched to 50 ohms, the roller inductors have to be completed shorted (minimum) for 75M and full inductance (22uH) for 160M. Somewhere around 600pF on the ladder line side of the inductors for 160M and ~200pF for 75M.  75M works fine and is fairly broad banded, i.e. can move from 3870 to 3890 without retuning. However on 160M, it is VERY sensitive and only a 1/8 turn on the vacuum cap makes a world of difference, and there is huge voltage on the cap. So much so that I had a spark show and fire last night on the tuning knob insulator...duct tape sure doesn't smell good when it burns. Glad I wasn't tuning it at the time.

So, who here has experience with EDZ antenna's and how can I get this antenna system working again? I think the tuner is okay, could feedline length be an issue?  Should I shorten the antenna a bit more?

Help help.

Thanks

Paul



http://www3.telus.net/radioboy/DSCN8699-1.jpg



http://www3.telus.net/radioboy/DSCN8700-1.jpg

[KF1Z]

Could be the feedline length....

Try adding 25 feet or so, and see what happens..

[VE7 Kilohertz]

Could be the feedline length....

Try adding 25 feet or so, and see what happens..

I'd like to try but the antenna is right over the house and I would have to find some place to extend the ladder line to, tie it to the roof or run it alond the ground. The driveway comes up right beside the house so I can't run it out away from the house. Could try it just to see what happens but I would need to find more spreaders and make up more line.

Thanks

Paul

[KF1Z]

You might find this helpfull.....

http://www.bloomington.in.us/~wh2t/zepp.html

[WA1GFZ]

Paul,
I have been running antenna simulations and find lengths that are very hard to match. Sometimes you have to flip the network around to get a step up. My Fugly tuner is also very sensitive on 160. I just turn the cap a few degrees to go from 1885 to 1945 22 UH is not enough l so the Q is kind of high. I've had similar problems with the flash box and ended up making a 2 wire antenna with the ends spread a bit to lower the Q. You can trim the antenna or make it longer which ever works for your tuner. You may consider adding another cap across the input to give you more range. That is the low voltage side of the network so doesn't need to be a vacuum variable. Making it longer suspect you need to go about 45 degrees or about 60 feet. You could drop vertical leads off the end.

[VE7 Kilohertz]

Well I added another 12' of ladder line (all I had) and now get flames (high voltage) on 75M and not on 160M. removed 4' at a time and found that it ended up best right where I started ( which means I need to play with different values or type of tuner.)

Amazing the difference in tuning with just feedline changes.

I found some bigass fixed coils I picked up years ago from a broadcast station, but I need to figure out what value they are, and will try a tapped inductor tuner instead of the balanced roller inductor tuner.

Let's see some of your tuners that you are using. The latest wave is the big fixed coil center link coupled type??  I have been away from the board for almost a year.

Cheers

Paul

[WA1GFZ]

Paul,
Learning a simulation program is easier than cut and try. Look at the feedline as a series connection to the antenna so if you have a odd quarter wavelength then you have a low Z. If you have an even quarter wavelength then you have a high Z. This is for the length of 1/2 the antenna plus feedline length.You might consider flipping the tuner around so the cap is on the balun side to drive a low Z. I done some vee simulations the past couple days and you can come up with some off match values. Some I have done needed more than 100 uh inductors some no inductors at all just 4 caps. You might consider adding 60 feet off the ends to see what happens.

[ab3al]

food for though...

I aint no expert but your tuner is designed to match up to a 2000 ohm load with the values stated.  the 230 degree center fed double zep antenna you constructed has an impedance of 6000 ohms.  zooorch

your feed point being almos half as high as your end points puts your take off angle @ 90 degrees..  Even if you can only get it up 40-50 feet make it flat or high in the middle and low at the ends.

all of this effort for a theoretical 1.9db of gain over a half wave flattop on 80 in free space.  thats about 55 percent gain.  wont move the old s meter any.  but your antenna modeled at the hights you gave compaired to a 80meter dipole @ 45ft are


your ant
8db of gain at 90deg  straight up  bad
-6 db @ 50 degrees  really bad

130 ft flattop 40 ft above ground
6db @ 90 degrees  straight up.. not good
+2.22 db @ 50 degrees..

these  gain or loss figures are over a 1/2 wave ant 1/2 wave above fair soil..

like everyone says and i have learned.. unless you want to kill some time.  just put up a 1/2 wave as flat and as high as you can and enjoy.

but thats just my opinion.
nobody flame me  if im wrong tell
me

[VE7 Kilohertz]

Thanks guys!!

What modeling software are you using? Interesting numbers. No wonder I can't get a decent match.

Yesterday, I moved the antenna 12' to the east, so that the feedpoint is right over the shack. Sure reduced the RFI on 160 and 75M.  I guess I must be right under a null now.  Matches are the same.

I think I will leave the antenna for a while and either try a new tuner, or find/learn some antenna modeling software.

Cheers

Paul

[WA1GFZ]

4nec2X works great!

[Steve - WB3HUZ]

NEC Win Pro and GNEC