EA7EER

Before changing over to using EFHW antennas, all of my HF antennas were 9:1 UNUNs. Using the chart below, I had great success with the 175-foot and the 124.5-foot UNUN back in my QTH in Potomac, Maryland. At the time, I was also using the 53-foot version of this with the non-UNUN end of the wire supported by my 33-foot telescoping fiberglass mast. The UNUN end was typically only 4 or 5 feet off the ground. If you have limited space, these are really ideal and much better than a "random" wire because you end up with resonance on most bands. The table shows typical SWR relative to installed wire length. SWR will vary based on topography, wire orientation, and ground or counterpoise use. For best results, use the longest wire shown on the table that will fit your installation constraints. Installing the antenna wire as an Inverted L can change the feed point impedance and may require tuning (changing the overall length of the wire) for the best coverage of all HF bands. Rows in color are the best overall lengths to use for optimum HF spectrum coverage. Experimenting by slightly changing the wire length (+ or-) is encouraged to provide the best overall performance for individual installations. By design, UNUNs are wound in such a manner that they provide little or no RF choking. Although not necessary, a 1:1 isolation/choke balun at the transmitter end of the feedline will stop RF from entering your equipment and reduce receiver noise caused by common mode currents. Installing a 1:1 choke balun at or near the unun will not allow the coax shield of the feed line to be used as a counterpoise! Read this last sentence twice! Note: I plagiarized the chart and most of this text from the fine folks at Balun Designs. I bought three UNUNs from them, and they worked flawlessly for me. I still have one of them that I use for some of my portable operations, as described above. Check out their website at: balundesigns.com/