Antenna Advice

[ka4koe]

I've about decided that this inverted L is not living up to my expectations. Due to my situation, I really cannot install a decent enough ground radial system to do it justice. So, I'm thinking about going back to the classics (not Greco-Roman) and putting up a high dipole of sorts. If I build an OCFD, it will be easier to tune multi-band, but then I have a balun to worry about burning up, not to mention losses. OR, put up a standard all band 80-10 doublet fed with twin lead and use a link coupler. I really don't have room to install a 160m doublet unless I route the wire ends down the supports (in this case, trees).

Using high duty cycle modes @ 200W carrier makes we worry I'll burn up any balun I use, despite claimed power handling capabilities.

If this works, life will be better for everyone as folks won't have to strain to hear my PW signal.

Tnx!

Philip

[W2VW]

Center fed doublet as long as you can fed with open wire line not crappy brown stuff.

Junkston Matchbox IS a balun. Some baluns don't burn up.

[K1JJ]

Phil,

You will be much happier replacing the L with a high, center-fed, flat dipole using a link coupled, balanced tuner. Forget the toroidal balun.

Twin lead is lossy for high swr, multiband use  - use homebrew openwire if you can.

If you really want 160M, consider a 180' long dipole with the ends sloped down. This will be a good compromise and let much of the current on 75M stay up in the air.  160M will work FB too.

T

[ka4koe]

180' indicates resonance at 2.6 MHz? Sloping the ends down adds top loading which makes it resonate lower? Am I on the correct track here?

P

[WD8BIL]

180' indicates resonance at 2.6 MHz? Sloping the ends down adds top loading which makes it resonate lower?Huh Am I on the correct track here?

It doesn't have to be resonant to work.

[K1JJ]

180' indicates resonance at 2.6 MHz? Sloping the ends down adds top loading which makes it resonate lower? Am I on the correct track here?
P

The reason for the longer length (180' vs: 123') is to make the dipole more efficient on 160M.   Any time a dipole's size approaches 1/4 wavelength or less, (123' on 160M) its impedance drops so low that losses in the tuner and feedline can get significant.

The dipole as a 180' "skirted dipole" (flat with ends dropped down) will work well on 75M.    180' is about 3/8 wavelength on 160M and will work well there too, but as a slightly shortened dipole.  It's a small compromise given your space restrictions.  No ground radials are needed.

The higher bands on 40M and above will have cloverleaf and octopus radiation patterns, but will still be reasonably efficient.

T

[ka4koe]

T:

Roger on that. I think this is what I'm gonna go with. Now I just have to figure out the particulars of running balanced line to my shack. Having an upstairs shack will complicate my lightning reduction system (I never say "lightning protection system") grounding provisions. However, there is plenty of open attic space to run the twinlead.

tnx.

P

[K1JJ]

T:

Roger on that. I think this is what I'm gonna go with. Now I just have to figure out the particulars of running balanced line to my shack. Having an upstairs shack will complicate my lightning reduction system (I never say "lightning protection system") grounding provisions. However, there is plenty of open attic space to run the twinlead.

tnx.

P

Sounds good, Phil..  You will be vely bery happy wid that antenna.   BTW, maybe you hear Bob / K1KBW on 75M down your way. He is running this same antenna, a skirted dipole.  He is very loud on 75M and also on 160M.

Maybe you already know this, but just to be sure, "twinlead" is that 300 ohm solid type brown feedline used with TV sets. There is also some for ham transmitting use. You do not want to use that.  Make your own 4" spaced openwire line with #10, #12 or #14 copper wire, that uses spacers every 2'-3' or so.. Plexi, Teflon and many other materials can be used for the spacers.  Also, stay away from the commercial brown plastic openwire that has the punched squares.  Making your own openwire with a good link coupled balanced tuner is what you need for an efficient multiband dipole antenna.

T

[Steve - K4HX]

The antenna wire does not have to be of resonant length. But the system (antenna wire, feedline and tuner) does have to be resonant.

[steve_qix]

Open wire works well, but if you're lazy (like me), you could use coax.  I use coax fed dipoles everywhere; on Rattlesnake Island, and at home.  For multiband, I connect more than one dipole to the same feedline, and put the antennas as close to 90 degrees apart as possible.  This is very easy to do with 2 dipoles.  With 3 dipoles on the same feedline, you can't get all of the antennas 90 degrees from each other, but you can get to 60 degrees.

Or use a separate antenna for a band that isn't to big (wavelength wise).  I do that on 40 meters - use an individual antenna.

This is a personal preference as I've never had good luck getting the line to be balanced and getting a tuner that won't arc over.

If you're concerned about antenna currents on the coax shield, put a bunch of type 43 toroidal  doughnuts up at the center of the antenna and run the coax up through the middle.  The inductance created by all of those cores will break up the antenna currents and eliminate coaxial radiation.

Dirt simple and practical.  That's why I use it!

[ka4koe]

Found this after looking around...

http://www.73cnc.com/category_s/42.htm

[K1JJ]

Found this after looking around...

http://www.73cnc.com/category_s/42.htm

Sure, those will work FB for making openwire.   You can get the 500' spools of #14 THHN stranded wire at Home Depot, as they said.

As Steve said, coax feedline is a great solution too using separate dipoles or multiband fan dipoles.

 For years I ran five separate ant tuners with #10 open wire for quick band switching. But for the last 20 years I have run 75 ohm hardline coax for all antennas. It is buried underground in 4" PVC piping.   Flexible coax wound on a 4" to 6" pvc pipe can be used as a choke at the dipole feedpoint to supress shield currents.   (As well as using ferrite cores)

The advantage of using separate coax-fed dipoles is that you get control of your radiation pattern. It will always be a predictable broadside figure 8.  With a multiband single legged dipole with ant tuner, the number of pattern lobes increases with frequency.  So a 160M dipole used on 40M will have four lobes...  a 160M dipole used on 10M has sixteen lobes - and as many sharp nulls. Pot luck.

Good luck with the project.

T

[W8EJO]

This thread has caused me to think about my situation

I have about 200' of space between two 60' trees and I want to work 160 - 10. Currently I have a 140'+ doublet fed with open wire & a link coupled tuner.

Results on 75 are OK, 40 so-so & the higher bands iffy based on lobe direction.

Would there be any theoretical (and hopefully practical) advantage to lengthening the wire to say 190'-200', and also adding additional (fan) dipole wires for higher bands of interest while keeping the balanced feed.

I would think that this would give me the desired addition of 160 but would the addition of fan dipoles for the higher bands help, hurt or have no effect?

Has anyone used and or modeled a fan diople fed with open wire?

[K1JJ]

Hi Terry,


As you thought, adding length to the 140' dipole will increase its impedance up to 40 ohms or so and make it more efficient on 160M - as a figure eight pattern.

Now as for adding the extra dipole legs for the higher bands using coax....    A set of dipoles on the same feedpoint will approximate separate dipole radiation patterns, but not exactly.  On some frequencies certain legs may hog more power than others and distort the pattern from a perfect figure 8.   But in general, multiple legs is a way to control the pattern into a figure 8.   You would need to model it to see the variations on various freqs.   For example, you may find that the lower band dipoles hog a lot of power on 15 meters and start to produce  multiple lobes. The "even" bands should fare much better.  

For an open wire fed fan antenna,  let's say we have 450 ohm line and multiple fanned dipoles...  The normally 70 ohm dipole legs will not be a match for the 450 ohm line at the desired freq.  How will that affect the radiation pattern if at all? Will the proper leg still take power at the desired frequency compared to the other legs which may be a better match for 450 ohms?  I'd have to model that to see or maybe someone else knows the answer.

The bottom line is that we want the proper 1/2 wave dipole leg to take most of the power at the desired frequency to produce a nice figure eight pattern.  A similar problem occurs when we use 450 ohm open wire rather than low impedance 50 ohm aluminum angle or a double boom  to feed a log periodic.

T

[Steve - K4HX]

On 160 meters, with a height of 60 feet, the azimuth pattern will be omnidirectional. The antenna is too low to yield a figure-8.

[K1JJ]

On 160 meters, with a height of 60 feet, the azimuth pattern will be omnidirectional. The antenna is too low to yield a figure-8.

Yep, true.  160M pattern optimization is almost a mote point. (And 80M too)   160M  efficiency increase would be the reason for lengthening it.  Though, at 60' high the ground losses are beginning to increase to significance, like using an 80M dipole at 30' high.  Good reason to get it up to 90' or more if possible.

T

[ka4koe]

The configuration you mentioned "skirt dipole" is also termed an "inverted U". The rational for its operation was that the highest current region (and radiation) is near the center. Operational characteristics by folding down 33-50% of the ends doesn't affect things all that much.

[W8EJO]

On 160 meters, with a height of 60 feet, the azimuth pattern will be omnidirectional. The antenna is too low to yield a figure-8.

Yep, true.  160M pattern optimization is almost a mote point. (And 80M too)   160M  efficiency increase would be the reason for lengthening it.  Though, at 60' high the ground losses are beginning to increase to significance, like using an 80M dipole at 30' high.  Good reason to get it up to 90' or more if possible.

T

so
Well 60' is my max height so I guess I'll forget 160.

Maybe a loaded verticle this fall, but I hate radials.

[ka4koe]

Possible drawback at my qth is only 60' height available and it will be impossible to run the stuff from the feed point entirely clear of foliage. Lots of trees on my property.

[K1JJ]

Terry,

Don't sweat it - I know of guys running 160M dipoles at 30' who do very well.  For local work, most of us will have omni-directional patterns, which is probably a good thang.   To get a good >600 mile DX signal on 160M under average conditions, we need either a well radialed vertical in the clear or a very high dipole.

So you will be fine on 160M at 60' using a skirted or inverted U dipole out to 300-500 miles or so.
The regular AM group here on 1885 Thursday nights are all within 300 miles, so low dipoles do FB here.


K1KBW runs a skirted dipole at ~ 70' fed with openwire.  Two weeks ago he was loud on 1885 - at times within 5 dB of Chuck / K1KW who runs a dipole at 140' at the apex.  Running similar power that night.  Bob is closer to me, but still, it's a tremendous antenna system for local 160M work.

T

[ka4koe]

Wow, just read this analysis using windowed polyethylene dielectric twinlead.....

http://users.triconet.org/wesandlinda/ladder_line.pdf

[W7TFO]

Not intended as a hijack, but a shot for opinions:

About 400' length dipole @ 60' AGL. 

Made up from #6 hard drawn copper, center fed with same on 6" porcelain insulators to husky HB balanced matching unit.

??

73DG

[W8EJO]

Terry,

So you will be fine on 160M at 60' using a skirted or inverted U dipole out to 300-500 miles or so.
The regular AM group here on 1885 Thursday nights are all within 300 miles, so low dipoles do FB here.


K1KBW runs a skirted dipole at ~ 70' fed with openwire.  Two weeks ago he was loud on 1885 - at times within 5 dB of Chuck / K1KW who runs a dipole at 140' at the apex.  Running similar power that night.  Bob is closer to me, but still, it's a tremendous antenna system for local 160M work.

T

Thanks Tom.

By a "skirted dipole" I assume you mean i should let the ends drop down vertically to make up the additional length necessary to get to full size 1/2 wave?

In my case that would be about 25' of vertical on each end. The bottom of the vertical wires would be about 35' off the ground.

Or should I just leave the wire at 200' in length and keep the ends 60' high - as far from the ground as possible?

[ka4koe]

Here are some MMANA GAL test runs. 60 foot horizontal, 30 foot vertical each leg, 60 foot height horizontal section.

[ka4koe]

Continued...