Configuring the DX Flagpole Antenna System | Balun, Remote Tuner, Radio Antenna
How to Correctly Configure the Greyline Flagpole and Vertical Dipole Antenna Feed System: Hint: RF Choke, ATU (Remote Tuner), HF Antenna
We do get a fair number of inquiries that start out saying, "How do I feed the Greyline Flagpole correctly?" and it's easy to understand why, as the answer certainly is not intuitive.
Most of us think we can plug a 50 Ohm coax into an antenna out of the box and we're off to the races breaking pile-ups and feeling loud! Well, high-end plug-and-play is the general goal of our product design but it doesn't work quite that simple, but it's close!
There is a sequence to the "feed system" that is required for higher performance. Tune in below for more information from one of the antenna sages of our time, Mr. John Portune, QST Award-Winning Author and career engineer who was kind enough to share his wisdom on the topic.
"Correctly Configuring the DX Flagpole Antenna, Tuner, and Balun"
It is a common belief that one must “ground everything.” This is NOT true for the Greyline DX Flagpole Antenna System. The antenna must “float” electrically above ground. The reason is basic. Like a common wire dipole, the flagpole antenna is a balanced antenna.
Most verticals work against ground radials and are fed unbalanced at the base. The flagpole must not be fed unbalanced. It is an electrical-half-wavelength vertical dipole. Both ends are insulated from the ground and the off-center (OCF) feed point must be provided with a balanced feed.
Therefore, the tuner must also have a TRUE balanced output.
However, most modern tuners are unbalanced by design. The main output is grounded via the shield of the SO-239 output connector. Some commercial tuners do have an output labeled as balanced. In most cases, a balanced output is only simulated by an internal voltage balun. This method cannot be used with the flagpole antenna.
The ONLY satisfactory way to provide a true floating balanced output from an unbalanced tuner is to insulate it from the ground. Then to make it “float,” a 1:1 current choke must but placed in the coax directly ahead of the tuner.
Figure 2: An example that works well is this "balun", or RF Choke more appropriately, by Palomar Engineers called the BA-2 ferrite sleeve, 1:1 current choke balun, with 5 Mix 31 Ferrite Beads in series, installed on a short coax pigtail. (Heat-shrink tubing is removed for viewing).
Update: It's believed this model is discontinued by Palomar, but you get the idea. Also, for more than 100 Watts, consider 7-9 units of Mix 31 beads of this size as a good starting point.
Tip: Greyline offers RF Choking as well, from the two versions of the 3500 Watt military grade Maxi Choker, the 500 Watt Mini Chokers popular for both Choking and QRN mitigation, and several DIY Ferrite cores and snap-on cores for your parts needs. Free shipping on those prices.
Any true commercial or home-brew current balun of sufficient power-handling capacity is acceptable. Make sure, though, that it is a current balun; many are not marked.
Lastly, it is essential to mount the tuner with the balun on an insulated surface or pole nearby. Do not lay them directly on the ground or connect them to the ground. Many of our customers find success 6 inches or more above ground mounting on a wooden stake or PVC pipe next to the antenna.
Thanks, John for your perspective. That makes things much easier to understand.
Customer Install Series: Rob in Colorado's Journey with a Greyline 20' DX Flagpole in his HOA. A solid guide for anyone wanting a walk-through of the installation steps with commentary and photos.
Pro Tip: Building Sections, from the ground up
The thicker wall sections are installed lower and the lighter for the upper sections.
- The lowest section is meant for ground insertion. It matches the length of the PVC
- The Lower Dipole, with slotted insulator
- The Feed-point Section with the two round holes in the insulator (for your separated ladder line wires, one per hole. Connect one wire to the bolt upward on one side, and the same downward on the other side)
- The Flag Cleat Section is next. This one exhibits 2 holes used for the Flag Cleat (if applicable)
- The Middle Sections are all the same going up the pole with the transition sections on the upper side of the tubing.
- The Top Section's upper side has no bolt holes
Pro Tip: Feeding the Dipole sections
Separate the two ladder line wires at the feed point with approximately 6 inches of now single wire each and pull them through, one per hole left and right, for example. This is a great time to be certain that you know which wire is which. You'll want to connect the Upper Dipole sections (the longer radiator) to the center coax conductor. You can do this by eye and marking the wire on each end or by using an Ohm meter to check continuity for those areas.
Reminder: If you are using an ATU at the base of the vertical antenna, please consider raising the tuning circuit at least 6 inches off of the ground, as well as the ladder line feed, and RF Choke as they too must be above ground. This is all part of the antenna system until we reach the RF Choke and Coax back to the shack.
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