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Author Topic: Fine-tune this dipole (or OCF?)  (Read 5498 times)
K7RNO
Member

Posts: 279




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« on: September 14, 2013, 10:44:29 PM »

I have this dipole in mind to install at my one-story home:



Feedpoint will be 15' high, the two halves can be 60' and 63' long max. or shorter and will be angled as shown.
The direction of the left half is fixed, the right half can direct more to the east (right) but would then be shorter (length is limited by the fence there).
The end of the left half will be approximately 10' high in a tree, the right end will be 6' high on top of a vinyl fence.
The wires will be AWG 14 stranded copper. I can feed with coax or window line and have a 1:1 balun available, if needed.

My QRP rig has a built-in ATU.
I would like to use it on 30m and higher bands (40m if tuneable)

My questions are:

Should I keep the halves as long as possible and then tune it or what shorter length should I use for one or both of the halves?

What kind of directivity (if any) can I expect? There are no high structures around, only other one-story homes.

What should I use to feed this antenna? Coax and/or window line? I can reach my shack with about 45' of cable.

Thank you for your suggestions (and your rationale).


« Last Edit: September 14, 2013, 10:46:48 PM by K7RNO » Logged

73,
aRNO
NAQCC #6870, SKCC #11131
WX7G
Member

Posts: 6328




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« Reply #1 on: September 14, 2013, 11:48:38 PM »

For 30 meters and higher the antenna need be no longer than 46 feet end-to-end. Longer will produce more lobes (peaks) and nulls (minimums), which can be good if the station you are contacting is in a lobe and bad if it's in a null.

For 40-10 meters 50' or longer will work and as-shown in your diagram the antenna will cover 80-10 meters. Center feed will reduce feedline radiation while off-center feed will increase feedline radiation.

For all bands 30-10 meters ladder line is the preferred feedline and you QRP radio will require a 1:4 balun.





« Last Edit: September 15, 2013, 12:11:06 AM by WX7G » Logged
W5WSS
Member

Posts: 1783




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« Reply #2 on: September 15, 2013, 09:02:20 AM »

The antenna you show is more a quadrant doublet 90 degree angle at the apex to sort of a more open angle and will work as a multi band arrangement.

 15 ft of feed point low height is going to dominate the horizontally oriented horizontally radiating antenna pattern development towards the zenith regardless of the impedance excursions that the tuner can handle.

At 15ft of low height except for 6M to 10M the pattern will be higher and higher towards the zenith as you progress down in bands.

This is true with any horizontally oriented horizontally radiating antenna.
The pattern of the antenna you designed will be a ballooning sort of Omni directional coverage from 15m and downwards.

Mine is low but My expectations are in alignment with what it produces and the quadrant antenna offers utility and transfers, extracts signal strengths of a low dipole doublet.

I like mine from low height and during the sunspot cycle enhancement I can and do work longer range sky wave dx with mine when the angles are compatible with it.
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K7RNO
Member

Posts: 279




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« Reply #3 on: September 15, 2013, 09:46:39 AM »

Thank you for the responses so far.

WX7G, if I understand correctly, keeping both halves at the same length (of 60') will reduce feedline radiation and have it cover 80 - 10m. In such a case, would you still prefer ladder line for such a design, and if so, should that ladder line go all the way to the ATU/XCVR or how long should it be before it goes into a coax. Where should that 1:4 (or 4:1?) balun be placed?

WSS, if I understand correctly, this antenna would have most of its use within a regional range. For my QTH being Utah, that would mean surrounding states?

In any event, unless I have a better idea, it looks like this is about the best I can set up in my specific situation (XYL and other factors included  Wink).
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73,
aRNO
NAQCC #6870, SKCC #11131
W5WSS
Member

Posts: 1783




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« Reply #4 on: September 15, 2013, 12:24:07 PM »

Looking at your layout I see a feasible second antenna so that you can have two types a vertical antenna that you could consider.Having a vertical type antenna of the following design will benefit your system to be more compatible more of the time to various sky wave conditions for longer distance communications such as DX outside of North America. Rather than depending on one low horizontal antenna.

At the location where the 15 ft horizontal doublet can be set, one could also use this location or nearly so, to install a telescoping non conductive push up type pole such as the type that uses nested non conductive tubes with a lock twist to hold in the extended position.

When the push up non conductive pole is Installed and properly secured a vertical wire can be fastened to it using non conductive tying wraps and brought down from the near top of the pole such as a 32 ft length of wire and form a junction and add some sloped radials these radials are shielding driven type radials that can slope downwards from say a 5ft high base height just out about say 5ft from the shack entrance radials from the junction to anchors driven into the ground but do not ground the radials but rather leave them insulated at the anchors one may opt for non conductive anchors or use a dog bone insulator and a messenger rope attached to metallic anchors. One could locate the pairs of 1/4 radials per band both traveling in opposite direction while both are parallel to the wall the longest above the progressing shorter pairs 2 for 40 above 2 for 30 above 2 for 20 etc. Visualise the antenna to look like a peace sign.

Yes you can fit two antennas the one that you are considering and a vertical Hyrid omnidirectional antenna that a tuner can be placed just indide the feed line entry point for good efficiency then a coaxial feed line to your equipment beyond your tunersuch as a wide range switched-L auto tuner , this way you can press the single length vertical into multi band service since it is center fed with the inclusion of the elevated slope radial pairs per band.

Weather proof the feed point junction and incorporate strain relief.

73
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K7RNO
Member

Posts: 279




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« Reply #5 on: September 16, 2013, 12:09:37 PM »

Please help me regarding the feedline from the CFD (120'). Window line (and how long?) or coax? I would prefer coax as it will be easier to run down from the antenna, while the window line would need to be held at a distance (top two feet are a steel pipe and house has siding with aluminum bits).

Also, regarding the balun I am not sure where to put it and if I still need it with this final design.

I am aware that I could try out different setups but I don't have the cables yet and would like to buy the right material only.

WSS, thank you for suggesting the vertical option. I am following your design idea and need to see if I can get something like that done.

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73,
aRNO
NAQCC #6870, SKCC #11131
KC8Y
Member

Posts: 271




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« Reply #6 on: September 16, 2013, 06:14:20 PM »

I have an OCF dipole that covers 80/75, 40, 20, 17, 12, 10 & 6 meters.
It's used with about 50-feet of coax & a Palstar tuner.  With my tuner can get  the SWR setpoint readings below 1.7:1 on all of these bands PLUS I
can also tune it for use on the 30 & 15 meters. I never go above 70-watts; don't need to, operate 95% digital modes.

My antenna is only (total=135-feet; 90-feet one side & 45-feet other side);
mounted about 30-feet high in a horizontal position

Ken KC8Y
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