Configuring the DX Flagpole Antenna System | Balun, Remote Tuner, Radio Antenna
How to Correctly Configure the Greyline DX Flagpole Antenna and HF Vertical Dipole Antenna Feed-System: Balun, ATU Remote Tuner, Radio 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! That's the goal here but it just doesn't work quite that way. 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 DX Flagpole Antenna. 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 balun 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, installed on a short coax pigtail. (Heat-shrink tubing is removed).
Update: It's believed this model is discontinued by Palomar, but you get the idea. Also, consider 7-9 units of Mix 31 beads of this size are a good starting point.
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.
Again, thanks John for your perspective. That makes things much easier to understand.
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