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Author Topic: HF Antennas  (Read 442 times)
KC9JKK
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Posts: 3




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« on: March 25, 2007, 08:38:38 AM »

I have a Hustler multi band vertical for which I can only run radials in two directions right along a chain link fence. It works fair, but no DX yet.  Granted I am not on very often.  I took am MFJ SWR anlyzer to it and EEKS.  Well, it is also close to the house and garage.

My question, however is this: What would work better, a lousy vertical, or a dipole laying on the ground?  Well, it would not be on the ground, but fairly close to it.

73
Kevin
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W4WNT
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Posts: 30




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« Reply #1 on: March 25, 2007, 09:05:51 AM »

Get out the manual for the vertical.  Adjust the section lengths for best SWR starting with the highest band, most likely 10m, then the next band down, etc.  Then use TV rotator cable for radials, cutting one of the wires for 20m, one for 40m and one for 80m, which should act well for most bands.  This allows more radials in less space.  We are at a sunspot minimum, but there have been 15m openings during the WPX contest this weekend.

Good luck, the DX is out there.

Bill Turner, W4WNT
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K0BG
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« Reply #2 on: March 25, 2007, 09:24:18 AM »

Whether or not you can work DX hasn't any bearing on the merit of an antenna's performance. I just means the band was open.

A vertical antenna is one half of a dipole. The missing half is the radial system. I wouldn't make much difference if you do use radials cut for each of the bands, the ground losses are still great.

You didn't say why you can't run radials in other directions, but radials can lay on the ground, as it makes little difference if they're on it or slightly under it.

And remember, the close proximity of the fence will effect performance too.

Alan, KØBG
www.k0bg.com
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AC5E
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Posts: 3585




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« Reply #3 on: March 25, 2007, 09:35:48 AM »

For DX - a poorish vertical will beat a very low dipole because most of what radiation there is will be at low angles and come back down far from your location. Most of a low dipole's radiation will go almost straight up, and come down in the next county or state.

But there are things you CAN do to help that vertical! Starting with the fact that ALL of the current flowing in a radiator (antenna) must come from somewhere. That somewhere is the other half of a dipole, radial system, ground, etc.; depending on the antenna.

If you are elevating your radials you may be able to resonate them. Three or four resonant radials will do a decent job for you.

But if you are running them on the ground or burying them proximity to ground and the difference in ground during different temperature and soil moisture conditions makes resonating radials an exercise in futility. So make the radials you put down as long as you can. Paralleling your radials, even a few inches of separation will look like another radial to the antenna, also works fairly well.  

I have even seen radials go up and over a garage that worked well. So see what you can do to get more active wire to serve as "the other half of the antenna."

73 es gud DX  Pete Allen  AC5E
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WB2WIK
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Posts: 20601




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« Reply #4 on: March 25, 2007, 11:43:14 AM »

That wasn't much information ("it EEKS").

If you posted exactly what the SWR measured at a few points in each amateur band, and exactly which model Hustler vertical you have, that would have been more useful for remote diagnosis and troubleshooting of any potential problems.

I can't offer much help and apologize for that; but in general, if someone makes a post looking for advice and that relates to an existing installation, providing all the specifics of that installation is the only way to go.

Example:

"I have a 5BTV installed 18" above ground near the corner of my 60 x 40' yard.  Adjacent to it on two sides, 15" away, is a chain link fence 60" high.  I can't run radials through the fence, as that would mean using my neighbor's property.

"The measured impedance for each band is as follows:
3.5 MHz R 33 X -41.2
3.7 MHz R 33 X -39.4
3.9 MHz R 34 X -22.6
7.0 MHz R 51 X +12.9
7.3 MHz R 53 X +20.0...(etc, for the rest of the bands)"

That kind of data is much more useful than "it EEKS."

And I agree with Alan K0BG, "working DX" is mostly a matter of picking the right frequency to use, and having good timing, with a dash of good operating practice.  It has little to do with your rig or your antenna.  However, "working DX an hour before (or later than) anybody else does" is another story altogether, and can mean you have a truly superior station.  A very good antenna system might permit you to work DX on more bands, longer, than a poor one.  But even a poor antenna system will work DX if your band choice and timing is good.

WB2WIK/6
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KC9JKK
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« Reply #5 on: March 25, 2007, 11:59:35 AM »

Sorry about lack of detail, but I read thru some QnA's about the antenna and tuning and decided I need to monkey with one of the traps or take a hacksaw to it.  My actual question was about Verticals vs Dipoles. More than that, a low mounted dipole as I doubt I could get it much higher than 15 feet.  

I do plan on throwing a long wire over the house and into a tree just to see what it can do on 80 and 160.

The Isotron antennas look interesting, if anyone would give them a thumbs up?
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N6AJR
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« Reply #6 on: March 25, 2007, 12:32:41 PM »

the Isotron  makes a great bird feeder, and an interesting sculpture, but is quite minimal as an antenna.  Look at it like a large capacitor with a coil across it. Tunes nicely, but not real effective as a radiator.  save your $$$ and put up a fan dipole...Smiley
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K2QPN
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Posts: 70




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« Reply #7 on: March 25, 2007, 02:58:16 PM »

I am a fan of verticals. My experience shows that a vertical will beat a low dipole - but you need as many radials as possible. Recently I had a 30 meter dipole @ 20 ft. The vertical beat it every time. I took the dipole down.

My vertical is a Hustler 4BTV with the 30 meter trap. The SWR is fine on every band with out a tuner. I didn't have to fiddle with it. My radials are spread in a 200 degree arc because of location. I have worked 241 countries with the vertical in 3 years at the bottom of the sunspot cycle.

I would very wary of cutting a trap. A mistake would be costly. Good luck.

73, Bob K2QPN
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W7ETA
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Posts: 2527




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« Reply #8 on: March 25, 2007, 05:09:52 PM »

Its easy to make a dipole and try it out.  Then you'll know what it can do 15 feet off the ground, compared to your other antenna.

If you'd like to see how height effects a dipole, you can download a free trial copy of EZNEC.com.

If you'd like to learn more about verticals, monopoles, dipoles, radials, counterpoises, capacity hats, W4RNL's site has GREAT info.

73
Bob
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KC9JKK
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Posts: 3




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« Reply #9 on: March 25, 2007, 05:26:00 PM »

Maybe I should change the topic of this post to "trouble with my 6BTU".

I put it up last fall, and I use a tuner to get the SWR down to next to nothing which I can do on all the bands thanks to the good people at MFJ.  I have talked all over the country with it.

Now for specifics.

It sits near the property line a few inches away from a chain link fence. The feed point of the antenna is just a few inches above the fence which makes it about four feet above the ground.  The coax runs along the top of the fence and makes a turn and then into the basement. My shack is on the other side of that wall in what used to be a cistern (the coax runs thru where the downspout was.)

Although it is off to the side by about a foot and a half, the antenna is about 15 feet from the house and 15 feet from the garage. In between the house and the garage is the cement patio, which my better half would not be so happy about me covering with radials.  I did try it and it made no observable difference anyhow (only tried with 40M).  

Not too far away from the antenna (10 feet or so) is a Martha Stewart Patio Set with umbrella. I did move that away once for grins, also nothing.

I have 2 radials for 10, 15, 20, and 40 meters running
along the fence towards the house and garage (one in each direction, the 40 meter ones run next to the house and garage.

Now for som emeasurements.  When I was taking them, the wind was blowing, and I did notice fluctuations, not by anything drastic, but by .1 or.2.

10 meters   28.000   2.8
            28.750   3.2
            29.700   3.7  lowest 2.7 at 27.420

15 meters   21.000   3.3
            21.225   3.5
            21.450   4.0  lowest 3.0 at 20.496

20 meters   14.000   2.6
            14.175   3.3
            14.350   4.0  lowest 2.4 at 13.866

30 meters   10.100   4.2  SWR does not get any lower
            10.125   4.4  around this frequency.
            10.150   4.4

40 meters   7000     3.8
            7150     2.6
            7300     3.0

And that is about all I can say about that.  The radials are virtually on top of each other because there is only a few feet in that strip before it runs into the neighbor's property. So they are seaperated by inches.  I did not get around to making any for 30 meters because the radio I had at the time did not have that band.

I guess I could run a couple of ropes from the house to the garage and drape the radials over the patio, they would then be about at half the overall height of the antenna (well a bit less than that).  I could possibly tell the wife they are for the grape vines I planted last year.

73 and thanks to everyone.
Kevin

I am now going to read about fan dipoles before I ask how high they need to be off the ground.  :-)
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N5YPJ
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Posts: 642




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« Reply #10 on: March 25, 2007, 06:24:02 PM »

Can you have both mentioned antennas? It's interesting what you CAN work with a less than optimum antenna if you are patient and catch band openings. I have vertical and horizontal for 40 & 20, it's interesting to switch antennas and see how one will outdo the other plus a low dipole will let you work local stations on 80 much better than the vertical.
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KE4WLE
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« Reply #11 on: March 26, 2007, 11:08:40 AM »

What is considered a "low" dipole - and how does that compare with a "low" G5RV Jr.?

I am running a G5RV Jr. and the bottom of the ladder line is only two feet off the ground, which that making the top about 20 feet off the ground.

I am running 100W and have made numerous DX contacts since I got my general about three weeks ago.  (Europe, SA, all over NA and the Carribean)  The contacts have come mainly on 40 and 20, but also on 15 and 17.

Thoughts?
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WB2WIK
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Posts: 20601




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« Reply #12 on: March 26, 2007, 11:09:15 AM »

Looks to me like there's nothing wrong with the 6BTV and everything wrong with the way it's installed.

A ground-mounted 6BTV needs to be really on the ground (feedpoint within inches of the ground) with lots of radials.  An elevated mount 6BTV works best when it's at least 0.1 WL above ground, which on 40m would be at least 14 feet above earth, and has at least three resonant radials per band.

What you have is a bit of a mish-mosh and it's not surprised the system isn't resonant in any of the ham bands.  However, that doesn't mean it won't work.  Based on your measurements, it's simply resonating "below" all the ham bands, and that's not a big surprise since the vertical probably sees the chain link fence as part of the antenna, and that would be in series with the antenna.

Since your 6BTV is tuned below the band on ALL bands, even 10 meters, that means it's too long.  Always tune a 6BTV or similar design beginning with the *highest* frequency.  That's easy, since the highest frequency band tuning is right at the bottom!  Loosen the clamps for the lowest tubing section and make it shorter.  Tighten them again and re-measure.  The goal is for the SWR "dip" to occur in the 10m band, obviously, and preferably around wherever you choose to operate.  If you work CW and phone, and even FM on 10 meters, pick a frequency around 28.7 or 28.8 and try to adjust the tubing length so the SWR dip is there.  It may never be 1:1, and I wouldn't expect that it should -- but it should be lower than 3:1, and probably lower than 2:1.  The goal is to achieve the dip.

Then, work your way up the bands adjusting the tubing sections as required (they may all need to go "shorter").  The 80m resonance is tuned by the whip length above the RM80S resonator at the top of the antenna.  Obviously this can't be reached from the ground, nor can the 40m or 30m tubing sections (you might reach the higher frequency ones using a ladder), so you'll have to tilt the antenna over or take it down for adjustments.

I have a 6BTV of a fold-over 4-legged roof tower that makes it *very* easy to lower and adjust -- I can do it myself in less than 15 seconds.  The DX Engineering "hinge base" mount is handy for this.

In any case, based on what you've written, I'd say nothing at all is wrong with the antenna.

WB2WIK/6
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W0FM
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Posts: 2055




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« Reply #13 on: March 27, 2007, 02:15:44 PM »

JKK: <decided I need to monkey with one of the traps or take a hacksaw to it.>

Hi Kevin,

Careful there!  I've had to cut the element length of some of the BTV's I've owned on occasion to obtain the best tuning.  But (big BUT) it is the tubing of an *element* that sometimes needs to be shortened a bit NOT the length of a trap.  Never cut the length of a trap on that antenna.  Perhaps that's what you meant but I thought a clarification might save you (or others) some grief.

Have fun!

Terry, WØFM
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