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Author Topic: Select a multi-band vertical  (Read 751 times)
KI6LXT
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Posts: 13




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« on: March 30, 2010, 01:52:06 PM »

I currently have a 10-meter vertical pole mounted with the base at 28 feet. I want to replace this antenna with a multi-band antenna but most advertise ground mounting. There is little room for radials unless I lay them on my roof. Any suggestions will be appreciated.
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K0BG
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« Reply #1 on: March 30, 2010, 02:08:14 PM »

First, you might want to read the radial articles on this site: http://www.antennasbyn6lf.com/

The issues with elevated radials are two-fold, as the articles point out. They almost have to be resonant, and then there is the problem with supporting them. While more radials are needed for equal performance when the antenna is ground mounted, the need to make them resonant goes away, and they are, after all, easier to install even if it does take more of them.
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NT2F
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« Reply #2 on: March 30, 2010, 06:37:28 PM »

There are several multi-band verticals out there which do not require radials. MFJ, Cushcraft, GAP, Hustler and Hy-Gain all advertise such antennas. But be aware that some of their verticals DO require radials - so read the description carefully. You can download the manuals and verify the details for a specific model.

In the distant past I have used Hy-Gain ground mounted verticals which required radials. I thought the Hy-Gain product was a good one.

More recently I have used the Cushcraft R-7 (zapped by lightning) and the R-8. Both of these verticals operate without radials. I looked very carefully at the MFJ-1798 (80-2 meters) but decided against it because it appears to need serious tweeking and you really need an antenna analyzer to set it up. Also I wanted something quick to put together and the MFJ looks to be a minor science project for someone as mechanically challenged as myself.

I am pleased with the R-8 but I realize that others have valid opinions to offer. Also checkout the reviews here at eham.com.

The purest will say (and rightfully so) that you need the radials/counterpoise for best results. Yes, but sometimes one has to settle for less than an optimum antenna system. Nevertheless I have had some pleasant surprises running 100 watts using the R-8 (mounted about 6 feet above the ground). Worked New Zealand and then the very next contact was Latvia. If I had been using a beam I would not have been able to hear and work them back to back - so there is sometimes an advantage to be had from an antenna that is omni-directional (but yes I wish I had a 100 foot tower with the Step-IR Dream Beam).

All of these verticals tend to be sensitive to nearly structures so move it well away from any structures (follow manufacturers recommendation). Or if possible get it up in the air above any structures.

Although the manufacturers say these are self-supporting I recommend you buy the guy kits or otherwise provide guying for them.

For the Cushcraft R-7 and R-8 I found the initial set up dimensions were pretty close. I slapped it together, got some friends to help raise it and got on the air. The internal antenna tuning unit on my FT-2000 gives me better than 1:1.5 SWR across the entire 40-6 meter bands.

I wish you good luck in your choice and great DX!
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AD6KA
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Posts: 2238




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« Reply #3 on: March 30, 2010, 08:12:30 PM »

"I currently have a 10-meter vertical pole mounted with the base at 28 feet. I want to replace this antenna with a multi-band antenna but most advertise ground mounting. There is little room for radials unless I lay them on my roof. Any suggestions will be appreciated."

So if I am reading this correctly, you have a rof with the peak at 28 feet, and are using a 10 foot aluminum pole, mounted in the center of the roof, and loading it as an antenna, right? But there isn't enough roof space to attach and keep in the air, in a straight line a 33 foot radial which would be for 40m?
I assume the shoter radials for 10-15-20m (16.6' longest) wouldn't be a problem? Everyone says "4 per band" but two full sized radials per band on an above ground vertical designed for radials will work better than one of those "No radials needed, but has a 4 foot counterpoise with a magic matching box" verticals, IMHO.

I have a couple of longer roof mounted radials that "take a dive" off the side of the roof, and I keep the ends supported about 8 feet off the ground with PVC so no one walks into them. If you keep them away from metal they work fine. (Watch out for metal flashing on the eges of roofs, as well as rain gutters, if you use this method).

I'd go with a a roof mounted HF6V, 4 or 5BTV, or DX-88, all with a nice set of roof mount radials. If you find you MUST go with a "counterpoise" vertical, I'd go with the Hy Gain DX-77A.
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KA2UUP
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Posts: 388




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« Reply #4 on: March 31, 2010, 10:32:53 AM »

I have had a MFJ-1798 for ten years at my QTH.  As a previous poster said, an antenna analyzer is a must.  I tuned my roughly and worked well for 8 years until I decided to get serious.

I can't tell you about 2 meter performance because I do not use the antenna on that band.  However, durability and performance are as advertised if you assemble the antenna properly and tune it IAW the manual.

Be aware of a couple of things:

1)  The 17 meter stub is also used to tune the 6 meter band.  So, you will have to make some compromises.  6 meter coverage in my area is spotty so I have my antenna optimized for the 17 meter band and have a beam (not assembled yet) for 6 meters.

2)  Your coverage in the 80 meter band is limited to an SWR ratio of 2:1 in a bandwidth of 150 kHz.  So, you need to tune to the upper or lower part of the band.

10-20 meter coverage is great, with 40 being good and 80 being decent in the tuning range you select.

As always, multiband antennas are "compromise" antennas.

Good luck and 73 DE Bert @ KA2UUP
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KI6LXT
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Posts: 13




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« Reply #5 on: March 31, 2010, 10:39:07 AM »

My current antenna configuration starts with a 30 foot crank up tower set at 18 feet with an 18 foot 2" steel pole mounted at the top and a 24 foot 10-meter vertical with four 9 foot radials mounted on top of the pole. The base of the 10-meter vertical is 36 feet and extends to 60 feet. The vertical is unguyed and has been up for several years through some very high winds. I have a G5RV just above the roof that performs very well.

My plan is to replace the 10-meter vertical with a multi-band vertical at the same height and run an inverted V from the base of the vertical to replace the G5RV.
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N4EWS
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Posts: 11




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« Reply #6 on: March 31, 2010, 07:26:39 PM »

As far as the radials or counterpoise selection goes... Take a look at the ButterNut HF6v manual if you can find it on the web. They have a really trick little counterpoise diagram that you can make from 300ohm twin lead or 450ohm ladder line ! The 300ohm Twin lead is a really neat and cheap solution !!

73

Joe  N4EWS
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AD6KA
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Posts: 2238




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« Reply #7 on: March 31, 2010, 08:09:56 PM »

N4EWS
"As far as the radials or counterpoise selection goes... Take a look at the ButterNut HF6v manual if you can find it on the web. They have a really trick little counterpoise diagram that you can make from 300ohm twin lead or 450ohm ladder line ! The 300ohm Twin lead is a really neat and cheap solution !!"

Some Important Notes:
You can find that multiband stub tuned radial diagram and dimensions here:

http://www.bencher.com/pdfs/00366IZV.pdf

Do NOT make it out of just any twin lead. Velocity factor is *critical*.IN fact, DON'T MAKE IT OUT OF TV TWINLEAD AT ALL! Eventually wind & WX will shread the twin lead stubs to bits. Make it out of DX Engineering 300 Ohm copperweld (copper coated steel wire) Ladderline, which has a velocity factor almost identical to the flimsy Columbia 8230 twin lead Butternut uses.(If you can find it, hah!) You can find that DXE copperweld window line here:

http://www.dxengineering.com/Parts.asp?ID=924&PLID=170&SecID=93&DeptID=36&PartNo=DXE%2DLL300%2D1C

Much, much stronger. You can take your chances with 450 ohm ladderline. Personally, I would stick with what I know works. Have not tried the 450 ohm ladderline yet. Please let me know if it works for you.

David, AB0Z, turned me on to the fact that the DX Engineering 300 ohm ladderline WILL work with the Butternut stub tuned radial dimensions. (It's just a couple notches cut in the ladderline. The parallel end wires are soldered together. One end has a round lug for attaching to the antanna base. The other end includes  3 feet of plain wire, then a regular dog bone insularot. Total length about 33 feet or so. He also a uses a 3/32" dacron "Pilot line" run though every few windows and zip tied in place as a wind and strain relief for the radials.

Butternut now charges $160 for 4 (FOUR!) of those twin lead stub tuned radials (including enuf cheesy thin soft copper gray insulated wire for 2 80m radials. Butternut also now ships the HF6V with the wire 15m matching stub (an integral part of the antenna) made out of that cheap thin gray insulated copper wire, whereas before that 15m wire stub was hefty copperweld.
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