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Author Topic: Looking for 80/40m vertical (160 maybe?) ideas  (Read 1183 times)
SP5QIP
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Posts: 84




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« on: October 06, 2009, 03:56:20 PM »

Hi.
The goal is to have best possible performing vertical antenna for 80/40m. If it will work on 160m would be great.
I already have 40m vertical with radials on the ground. I have k9ay for RX.

What I can do:
1. I can put around 20m high vertical in those place.
2. I can use variable inductance coil at the bottom of the vertical (0-80uH)
3. I can put a few 20m long radials on the ground.
I can lift antenna 2m above the ground and use resonant radials if it will do the trick.

Limitations are: I don't have high supporting trees or tower to hang wires from that.
Garden is not so large, so I can have as many 10m long radials as I want, but longer ones only a few.

Is there any way to have good performing, low angle radiating antenna for those bands?
Thanks, Mike
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K0OD
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Posts: 2558




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« Reply #1 on: October 06, 2009, 06:21:31 PM »

DX Engineering is bringing out a big 40/80 meter trap vertical. It uses 3" diameter thick-wall aluminum tubing at the base. Self supporting in moderate winds. Tilt winch base is available. I think it's about 18 meters tall. No provision for 160 yet.

How much power are you going to run? The same vertical is coming out without the trap (monoband 80 meters). You could use a remote tuner with it to get on 40, 80 and 160.

http://www.dxengineering.com/Parts.asp?ID=3597&PLID=275&SecID=113&DeptID=22&PartNo=DXE-8040VA-1
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KA1YUW
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Posts: 43




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« Reply #2 on: October 06, 2009, 07:50:45 PM »

You want the best than get the HyGain 18ht. 160-10.
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SP5QIP
Member

Posts: 84




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« Reply #3 on: October 06, 2009, 11:35:33 PM »

I will put 500W in it. Forgot to mention clearly: I want to build that antenna.
Mike
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WX7G
Member

Posts: 6136




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« Reply #4 on: October 07, 2009, 09:41:50 AM »

There are many ways to do this and have a great antenna. Here is one:

A 20.5 m vertical (35 mm diameter used in simulation) is directly driven against ground. This is resonant at 3.5 MHz.

A 10.5 m grounded wire is spaced 40 cm from the vertical. It is parasitically excited and is resonant at 7 MHz. The spacing from the vertical determines the 7 MHz input impedance.  

The ground consists of sixteen 10 meter radials.

A 31 uH series inductor at the base resonates the antenna at 1.8 MHz. However, the radiation resistance at 1.8 MHz is 7 ohms and with the ground you describe the radiation efficiency could easily be 33% or less.

To improve this the vertical can be top loaded using a top hat and a top inductor. The base inductor can be used to fine tune it. Perhaps 5 uH at the base. If this sounds good I will model a top hat for you.
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SP5QIP
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Posts: 84




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« Reply #5 on: October 07, 2009, 03:19:43 PM »

>A 20.5 m vertical (35 mm diameter used in simulation) is directly driven against ground. This is resonant at 3.5 MHz.
I can do it.
You mean ground rod or radials?

>A 10.5 m grounded wire is spaced 40 cm from the vertical. It is parasitically excited and is resonant at 7 MHz. The spacing from the vertical determines the 7 MHz input impedance.
You mean paralel to the antenna? Where will be the feed point?

>The ground consists of sixteen 10 meter radials.
I already have more of them.

>A 31 uH series inductor at the base resonates the antenna at 1.8 MHz.
I can use remote controlled variable inductance coil and tune that with VNA.

>To improve this the vertical can be top loaded using a top hat and a top inductor. The base inductor can be used to fine tune it. Perhaps 5 uH at the base. If this sounds good I will model a top hat for you.

Do that please. Thanks a lot for your time.
Mike
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WX7G
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Posts: 6136




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« Reply #6 on: October 07, 2009, 07:37:49 PM »

Mike,

here is a vertical that is directly fed with coax and works on 1.8, 3.5, and 7 MHz. Description:

*A 23.0 meter mast for 80 meters, 35 mm diameter
*A 10.5 meter grounded wire spaced 30 cm for 7 MHz
*A top hat and loading coil for 160 meters:

Four top hat spokes 1.5 m long, 15 mm diameter with a 118 uH inductor directly below.

BW on 160 meters is 50 kHz given a 15 ohm GND and a loading coil Q=300.

The reason the top hat is fairly small is to keep the inductor value high. If the inductor value is much lower it interacts heavily with the 80 meter performance.

The 160 meter top hat and coil do not affect the 80 or 40 meter performance much. Likewise with the 80 meter length affecting 40 meters. The easiest tune-up procedure is to put up the mast and tune the 160 meter top hat spoke length for resonance at 1820 kHz. Then adjust the mast length for 3520 kHz. Then touch up the top hat if it needs it. Then adjust the wire for 7020 kHz.

VSWR at resonance will be roughly 1.5:1 but may be as low as 1:1 or as high as 2:1.

Diameters are not too important. The antenna needs to be tuned anyway.
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SP5QIP
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Posts: 84




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« Reply #7 on: October 08, 2009, 02:41:44 AM »

So If I want only 80/40 tophat and top coil is not needed and antenna will be a little shorter?
Can you calculate dimensions for SSB part? Mailny I will use that antenna between 3750 and 3800.
On 40m between 7 and 7.2MHz mainly around 7.1MHz.
Thank you, Mike
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WX7G
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Posts: 6136




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« Reply #8 on: October 09, 2009, 05:21:07 AM »

For 3.775 kHz and 7150 kHz:

Vertical tube 19.0 meters tall
Grounded 10.25m wire spaced 40 cm

The lengths may have to be adjusted a bit but this will get you close
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SP5QIP
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Posts: 84




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« Reply #9 on: October 09, 2009, 06:55:30 AM »

10m long radials?
Should I use ground rods also or not?
Thank you, Mike
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WX7G
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Posts: 6136




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« Reply #10 on: October 09, 2009, 10:27:03 AM »

I'd put in a ground rod for a small measure of help with indirect lighting stikes. On my verticals I've connected and disconnected the ground rod and measured very little difference in input impedance.
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SP5QIP
Member

Posts: 84




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« Reply #11 on: October 11, 2009, 03:52:57 PM »

Last question before I will start building.
Can I lift antenna 2m over the ground and use elevated radials? How this will affect antenna performace and radiating angle? Or maybe it will be better to leave it as it is on the ground level.
Mike
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WX7G
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Posts: 6136




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« Reply #12 on: October 13, 2009, 06:11:49 AM »

Determining the increase in signal due to elevating the radials 2' is a job for NEC-4, which I do not have.

Using NEC-2 we can explore the change in gain of a dipole as it is placed at different heights above GND beginning at 0.1'. This can give us a feel for how elevated radials will perform.

If I had but 4 radials I would elevate them, even if only 2 feet. If I could lay down a couple dozen radials I would ground mount it.
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W4VR
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« Reply #13 on: October 15, 2009, 12:18:36 PM »

why don't you tie an 80 meter wire vertical in parallel with the 40 and tie the far end to a tree if you have one.
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KC9CHG
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Posts: 3




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« Reply #14 on: October 17, 2009, 05:54:24 AM »

Hi Mike,

If you are interested in a bit of gain over a vertical on 40/80 and are willing to use something else for 160m, you might look at the 40m half-square described in ON4UN's Low Band DXing (pg 14-6 4th ed.).  Using a voltage feed at the bottom corner makes it very easy to switch matching components to use the same wire configuration for what ON4UN calls a "2 element close-spaced top-loaded array" on 80m.  The benefit of this antenna is ~3.8 dBi gain on 40m, 1.9dBi gain on 80m.  The down-side is directionality so you trade higher gain in two directions for lower gain in the other two.  

If interested, you need a single element that rises about 10.4m from the ground, continues horizontally at this height for about 22m, then comes back down to the ground at the far end - an upright rectangle with the bottom leg missing.  You will want decent radials under both vertical members.  The bottom of the far end vertical member is connected to ground when operating on 80m.  The matching circuit is a parallel C/L tank on 40 and a normal L-C (I did series L parallel C) on 80m.  

I modelled and built one and I can tell you that it is forgiving on dimensions, easy to feed (with the correct matching components - beware the HV) and robust against high wind.  It is noisy on receive but I too have a K9AY so that is not a big deal.  I unfortunately have a lot of very nearby trees so I suspect I am not getting the gain that the design is capable of, but that did not sound like a problem you have.

Not to say you won't have lots of fun with the antenna already being discussed in this thread.

Barrett
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