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Coil Loaded Dipole build - photo diary

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  #17  
Old 10-31-2008, 06:44 AM
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Hello Doc: How have you ben doing?

Doc said:
I'm afraid not. That coil is a loading coil for 80 meters, has nothing to do with the 40 meter antenna which is located below the 80 meter antenna.

The 80 and 40 meter antenna is one wire, with the loading coils are for 80 meters. Thats why I believe the 40 meter antenna has a wider bandwidth than the others. And I looked over the coils and did not see any capacitor so the coils are loaded coils not traps.

The antenna has three wires, the 80 / 40 meter wire, the 20 meter wire and the 10 meter wire. Mole has a pictire there showing the three wires and loading coil arrangement.

Intreresting to note that a lot of the dipole antennas are not supplied with Baluns. A older gentelmen in Mojave asked us locals for help on a dipole antenna for the ham bands. We installed a Balun and tuned the antenna for 80 and 40 meters and it significantly increased the antennas performance.

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  #18  
Old 10-31-2008, 07:24 AM
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Jay,
If that coil is in the 80 and 40 meter dipole, then it isn't a simple coil, it's a trap. If it's a trap then it has not only a coil, but a capacitor, making it a tuned circuit. That tuned circuit is tuned for somewhere in the 80 meter band (bottom end) and presents a very high impedance to a 40 meter signal, thereby acting as on open switch cutting the wire off at that point. Just like any other 'trapped' antenna.
There are a couple of things that lead me to believe that that coil is just that, a coil, or loading coil. From what Mole' says, there's not much wire on the outer end of it, so it's not 'enough' length for 80 meters, so that coil is providing the needed inductance to make up for a shortened antenna. Another thing is that there is no apparent capacitor associated with it, so it isn't gonna act like a trap.
I think you might wanna re-think the thing about which/what the other 'elements' in that antenna are for. Keep in mind that 'even' multiples of harmonically related lengths are 'bad', but 'odd' multiples are 'good'. (For example, an 80 meter dipole is terrible on 40 meters, but works out well on 15 meters. "Works well" is relative, certainly doesn't mean is better than, or equal to a 15 meter antenna, just 'workable', sort of. Terrible way of putting it, ain't it?)
The 'Alpha-Delta' series of antennas work with harmonically related segment lengths. Some are shortened with loading coils. I honestly can't remember ever seeing one that used a trap (which doesn't mean a lot since I certainly haven't seen them all).
- 'Doc

(By the way, I'm doing as fine as possible considering the conditions. Which means that there are somethings much worse than they used to be, and something I can't tell any differences in. Not sure if my memory is in that first group or the second... Oh well, I'm having fun so who wants to worry about it, right? Went back to work, found I like it. Not the 'work' part, but the part about 'getting out of the @#$ house'! They even pay me!)

Oh, one last thing.
Baluns are great for their intended purpose, making the change between a balanced antenna and an un-balanced feed line, which can make a difference. They also have some very limiting characteristics, as in they are designed for use at particular frequencies. Get much away from those design frequencies and things go to 'pot' very quickly. I've found that for typical HF use, they just are not all that necessary, and are definitely NOT a 'cure-all'. Biggest difference is that using them or not using them affects the radiation pattern more than anything else. For antennas that depend on a particular radiation pattern, changing it ain't exactly the best idea in the world. For a typical dipole, they can certainly be done away with and not really be missed. As far as impedance transformation is concerned, they are misused to a very great extent. If you just 'gotta', then use a 1:1. Depending on a huge number of things, most people have no idea of what the actual impedances involved are (what they are supposed to be, sure, but the key words there are "supposed to be"). Oh well. If it works, good. If not, try something else...

Last edited by W5LZ; 10-31-2008 at 07:36 AM.

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  #19  
Old 11-01-2008, 06:39 AM
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Hello Doc: Good to hear your doing well. And you enjoy the work.

The Alpha Delta Antenna that I have has no capacitor in the coils, so I am thinking the manufacture made the coils to have enough inductive reactance to act as a choke to the 40 meter RF Energy, and a loading coil to the 80 meter RF Energy. Not being real happy with the antenna, I am looking at an antenna tuner feeding a balanced transmission line to a longer dipole for all the bands. The Barn is about 100 or so feet away from the house. So the Ladder (Balanced) Line will has minimum loss, and its cheap.
I just get a few more knobs to turn.

The Dipole, Quad, Yagi, and Loop antennas I have used and worked on have all showed improved performance when a Balun is installed between the Balanced antenna and the coax. No Balanced antennas have left here without a Balun. I have not tested dipole antennas from 160 to 10 meters to see how effective the Balun is. I would make a 160/80/40 meter dipole with a Balun with a few extra winds as I use with the higher HF Frequencies. The Balun costs so little vs its perfomance increase, in applying balanced current to the antenna and choking off unwanted RF Energy down the coax.

Jay in the Mojave

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Old 11-01-2008, 07:48 AM
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Baluns
Have to say I just don't like them. Probably more my fault than the balun's but they've just seemed to be another point of failure than useful for the antennas I use. They do work if used for their intended purpose, going from a balanced state to an unbalanced state. 'Nuff of that.

If you couldn't tell, I'm a fan of parallel feed lines, ladder line, whatever. I have a very nice tuner that will handle just about anything I've hooked to it, which is really saying something sometimes. The one in the HF radio ain't no slouch, but isn't as versatile as the big one. I've noticed that the amount of stuff I hear using ladder line typically increases from when using the same antenna with coax. Especially when using an antenna where it wasn't designed to be. The biggy with any type of parallel feed line is that it has much less loss and can withstand much more electrical 'abuse' than coax can. A high SWR can destroy coax, I haven't seen an SWR harm parallel feed line...yet. Got a 20:1 SWR? Who cares. You still have to stay sort of reasonable, but that 'sort of' has a much wider range...sort of.
Best advice for a multiband antenna using parallel feed line and a tuner is make it as long as possible. More/several wave lengths at the lowest frequency works very well @#$ near anywhere.
Then there's the qwerks, or down side of using parallel feed lines. Should be careful of what it's near, can't lay it on the ground or coil it up, it ain't 50 ohms. All of which can be 'got around', and is just different, not all that difficult. It typically doesn't like wet or snowy weather. (Open the window, whack it a few times with a broom stick, most of that goes away, sort of.)
Oh well, 'nuther who cares, just have fun with it!
- 'Doc

(Psst - just a lump of inductance ain't gonna make a 'trap'. Take another look at them wire segments.)

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  #21  
Old 11-01-2008, 10:17 AM
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Update:

Well, work all week prevented me from getting any testing/completion done on this. Now it's Saturday and it's raining. Stay tuned...

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  #22  
Old 11-02-2008, 06:39 AM
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Hello Moleculo:

Look at your Alpha Delta Dipole Antenna Coils; is there a Capacitor inside the coil assembly? Making it a tuned trap? Or is it just a Coil. Again the Antenna Analyzer connected to the coil would tell you this by being resonate somewhere in the 40 meter band. But you would have to disconnect from the antenna. What I am thinking is that, is it possible for my Alpha Delta Antenna to not have the capacitors in the coils, as it was only 20 dollars at the TRW Swap Meet, causing me more grief that I deserve?

I bought a 500 Ft Roll of 12 gauge stranded insulated copper wire from Home Depot some time ago at a real reduced price. I don't think they understood just how low the price was, but us you can imagine they said the price was good to go. Ok then.......

I agree with Doc in using a long Dipole Antenna that is feed with open type Ladder line, or Balance Transmission Line, being feed by an Antenna Tuner. But I don't got no Antenna Tuner that will take legal limit and tune insane SWR ratios. So maybe I need to build one with all the other work I need to do. Or even buy one.

Yeah its raining here to in the Mojave Desert, kind of puts the kibosh on antenna work. But I think it would be ok for you to measure those coils. (humor)

Jay in the Great Mojave Desert, ....just down the road ah ways from the fillin station

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  #23  
Old 11-03-2008, 11:40 AM
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Quote:
Hello Moleculo:

Look at your Alpha Delta Dipole Antenna Coils; is there a Capacitor inside the coil assembly? Making it a tuned trap? Or is it just a Coil.
It's just a coil, wound with insulated bus wire: 68 turns on 1 3/4" OD pvc

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  #24  
Old 11-06-2008, 07:18 PM
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Hello Tim :

Let me offer something to consider for your project.

If by chance you have a copy of ARRL Handbook 2000 I would direct
you to Chapter 20, page 20-13 and read the W8NX coaxial-cable traps.

Better yet Google W8NX Coaxial Cable Traps for a antenna I believe would
be just the right fit.

Total length 83.6.... A few extra dollars for some coax, But when only the Best will do

Let me know what you think..


Best Regards,
John
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