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Author Topic: seeking antenna suggestions for this space  (Read 987 times)
CHRISDX
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Posts: 244




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« on: February 18, 2013, 09:11:09 AM »

hey all,

I have a limited space on my 40x80 property for an antenna.

originally I had a G5RV with one leg bent 90 degrees about halfway because it ran into the back fence property line.

the chimney that was holding up its mast fell apart and I had to remove it.

my house occupies most of the back end of the property and right behind that are 2 tall oak trees.

one tree has a pulley on a limb about 20ft from the rear lot line and at the side lot line that i can hoist something up on. (I had a tree climber install it when he was doing my pruning)

I *could* just hoist the center of the G5RV about 32' up and use that again but i was wondering if there is another antenna design that would work better than that G5RV.  I thought of a vertical but ground radials would be very limited to a couple directions along side the house side and back. no my neighbors wont let me install radials either. they are cool but i think they see me as a mad scientist with all these antennas and stuff.  (the G5RV mast had a discone on top, a tv antenna halfway up and a FM broadcast beam, and next to it was a Antron 99 tuned for 10M)

I always wondered if all that affected the G5RV at all. Now I'll put a mast on the back of the house probably, and a rotor for all those. The Antron never really worked better than the G5RV on 10M as far as I could tell, so I may just leave that one out.

So, any suggestions, vertical, keep the G5RV or run something else that can benefit from the extra height?

I saw this one, says it works on 160M - 10M, (but not 6M) interesting:
http://www.kr1st.com/hfcoath.htm?

I also wonder if the ladder line can be smaller than what he made?

-chris





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N4FBW
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Posts: 34




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« Reply #1 on: February 18, 2013, 09:39:43 AM »

A lot of folks get frustrated with G5RV antennas as they feed them with coax attached to a balun at the antenna. The coax has  a lot of loss at high SWR and so results are often mediocre. The original way to feed a G5RV is with ladder line to a balanced antenna tuner. This antenna plays much better this way.

The ladder line pictured in that homebrew stealth antenna article is home-made 600 ohm ladder line. There are kits out there to make your own 600 ohm ladder line or you can buy it. However, 450 ohm ladder line would work just fine. DX Engineering sells a nice center insulator kit that takes the strain off the ladder line where it attaches to the antenna wires. The wireman sells 450 ohm ladder line.

If you can swing it, it's best to bring the ladder line to a remote balanced tuner installed outside under the eaves of your house. A short run of low loss coax connects the tuner to your rig. Another way to do this is to bring the ladder line to a 10kw 4:1 DX Engineering balun outside the house and run a short length of low loss coax to your tuner inside the house. Why 10kw? The balun is going to 'see' a lot of high SWR and it needs to be pretty stout to handle this; a 5kw balun would work if you don't plan on running lots of power. The run of coax is kept short so that losses in the coax cable are kept to a minimum. Ladder line CAN be brought inside the house, it just takes a bit of care to keep the ladder line away from metal and sometimes RF can make its way into the shack. Do a search on 'a balanced, balanced, antenna tuner' to find examples of good balanced antenna tuner designs.

The higher you can make the apex of your antenna, the better. It sounds like your lot is rather small, so a dipole would be much too low at 80 and 40 meters.  The inverted v will give you more of an omnidirectional pattern.

Here's a good article by L.B. Cebik, W4RNL (SK) on wire antennas: www.users.on.net/~bcr/files/backyard%20wire%20antennaes.pdf

HTH!

N4FBW
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WH7DX
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Posts: 1029




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« Reply #2 on: February 18, 2013, 10:10:26 AM »

How about a Hex Beam or Spider Beam on the Chimney (paint it all black).   Put it on a metal pole - galvanized for fencing and painted black found at the hardware store and used with a rotor.    Then put a couple dipoles in the trees for 40M and 80M.  Maybe use one of the combo dipoles and get 40-80M on both and go E/W - N/S.   Use the Ameritron RCS-8VL Remote Switch to control the antennas and bring only 1 coax back into the shack.
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CHRISDX
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Posts: 244




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« Reply #3 on: February 18, 2013, 10:22:54 AM »

thanks... those are some good ideas, I'll re-read this later and prob have a few questions.  I did also ask what about the ladder line running up alongside the metal support pole in a G5RV or for that matter, other design that uses ladder. does the metal support mast absorb or otherwise spoil the antenna performance?
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KF7Z
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Posts: 36




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« Reply #4 on: February 18, 2013, 11:03:33 AM »

I’m a big fan of loop antennas. You might consider mapping out the largest "loop" antenna that might fit within your available space.  Even three supports, in any kind of triangular shape, having the loop fed at one corner with ladder line, can make a decent "loop" antenna.  It will probably be difficult to operate 160M with a loop of the size within your lot, but you are going to face that problem with any alternative antenna - without enduring high losses.  You can probably make a quite decent antenna for 80M, and up, if you can string a triangular loop that is about 130 to 150 feet total length.  A loop for 160M needs should be twice that long for good results.  The exact length isn't especially important, but it is desirable to enclose the largest area possible within your loop.  (Some lengths will be less easy to "match" at your tuner.)

An advantage of the loop is that they seem to operate a bit better than many antennas when the height is low. For 80M, the loop strung at a low height above ground (35-feet is low for any 80M wire antenna) will have a more favorable take-off angle than the G5RV, or dipole, at the same height.  They also tend to be more omni-directional than most other wire antennas, although your specific layout will result in some favored directions.  The radiation patterns for the higher frequency bands will have many complex higher-gain nodes, but since you might never know the exact direction to a future QSO, any antenna other than a vertical, or rotatable beam, will have similar potential disadvantage.  

The loop needs to be fed with balanced feedline. It is a simple and interesting project to make your own ladder line.  There are many possible spreader materials, including pieces of plastic coat hanger rod that is notched with a Dremel abrasive cutoff disk, and wire secured with hot melt glue.  The exact impedance of the ladder line also isn't very important.  It can be about anything from 300 to 600 ohms and still function in most cases.  The balanced line should stand off of your metal mast, but not much spacing is needed.  Four-inch stand offs will work.  Six-inch stand-off might be better, but I am not sure.  Others might know better. You can fabricate those from 1/2-inch PCV pipe glued into a PVC "T" having an ID close to the OD of your mast. Split the back side of the "T" with a saw so that it will snap over the mast, and secure to the mast with hose clamps.

It is desirable to have a transmatch that is designed for balanced line, in order to eliminate the losses in the balun. The old Johnson Viking 250-watt unit works well, although it's not especially pretty when compared to modern stuff.  They can be bought for $75 to $200 these days.  It can also be a fun project to rebuild that old unit into a new enclosure if you want nicer aesthetics.  At the same time, you can modify to add coil taps for the WARC bands, although that is often not needed.  You could even further modify to add tuned input.  Antenna tuners are good home-brew projects to create real value that is sometimes hard to buy.

I have a three-sided "loop" strung with 18-ga solid copper-clad wire, fed with home-made ladder line made from 12-ga "flexweave" and spreaders made from clear 3/8-inch Plexiglas rod with about 2-1/2 inch wire spacing.  My loop is about 550 feet in total length, up 45 to 55 feet, and my Palstar balanced tuner works fine to match it with the nominal length of feedline to my transmitter.  In many ways, this is the best wire antenna I have ever put up.  The light weight of the 18 gauge wire reduces the caternary sag of the wire without huge tension on the wire and mast supports.    

The EZNEC program will pretty easily model the radiation pattern, and take-off angle, of a prospective loop of any shape layout and height. This program can be a big help to you in evaluating the trade-offs between your limited choices.  You can also input the impedance of your feedline, and your feedline length, and the program will calculate the apparent impedance at your transmatch at any frequency.  If you don't have EZNEC, you can send me a potential loop layout, and I will run it for you.
« Last Edit: February 18, 2013, 12:04:02 PM by KF7Z » Logged
WB6BYU
Member

Posts: 13333




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« Reply #5 on: February 18, 2013, 11:18:18 AM »

You can make the line much smaller - I have some commercial open
wire line with about 1" spacing, and I've used two separate wires
under a bit of tension to make a long span without insulators.  The
old 300 ohm TV twinlead will also work.

The G5RV has a reasonably low SWR on 80m, 40m, 20m and 12m so
the coax losses are low.  Losses can be much higher on the other
bands.  With the antenna you linked to the losses should be low
across the HF spectrum, and also on 6m if you have a suitable tuner.

Note, however, that stringing up a long (in terms of wavelength) wire
in an inverted vee configuration reduces performance on the higher
bands.  If your primary interest is 20m - 6m then you probably will be
better off using a shorter antenna, depending on the angle of the
wires relative to the ground.


Some of the first questions I always ask when someone wants an
antenna recommendation are things such as:

What bands are of most interest to you?

What distances are you most interested in?

What do you have available for supports?

because these are important to know if the recommended antenna
is to meet their needs.
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KF7Z
Member

Posts: 36




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« Reply #6 on: February 18, 2013, 11:43:21 AM »

Yes, and if you don't want to fuss with a transmatch "antenna tuner", some otherwise good choices are eliminated.  Everyone has different priorities, and it is exactly right that you can set your own.
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