|Practical Applications for End-Fed Antenna Transformers
and Safe, Effective Grounding
|Transformer coupling and properly grounding your end-fed antenna will offer you four benefits: (1) Greater signal levels across a larger bandwidth (impedance smoothing), (2) Less electrical noise pickup from local sources (common mode rejection), (3) Greater protection to your equipment (constant static bleed and near-strike shunting), (4) Enhanced lightning protection by removing positive charge build up which would otherwise provide an attraction for a strike.
Shown here are 4 possible ways to connect your transformer (balun wired as an unun) to the antenna and the radio. (Note that the first example uses a coax connector at the unun and the subsequent figures show the coax as being hard wired - both are acceptable and are options for your particular requirements.) The sketches are pretty much self explanatory. Technically, they are shown in the order of functional preference.
If you have trouble reading these sketches, you may "right click" them to your clipboard and paste them to a .jpg viewer. Please give full credit if reused elsewhere.
|Here is a graphical illustration of a typical installation. The details will be different, but the principles are the same.The primary point is to mount the xfmr as close to the system ground as possible. Mounting it directly to the first ground rod is text book-ideal. An alternate would be to eliminate the vertical component of the antenna and mount the xfmr to the insulator above it and run a heavy ground up to it. This will depend on how much the vertical wire is exposed to near-field electrical noise from your home.|
|Here is an example of good RF "ground farm" practice. As opposed to many socio-religious beliefs, in this case, more is better! There will be a point of diminishing returns, but generally speaking, one ground rod is not going to be optimal. Experimental and empirical testing is the only way to determine what will be best for you.
You may get a relative ground conductivity test as shown below. Most electrical service entry points are grounded to the fresh water (cold water) feed pipe. Homes with plastic well pipes
|will have some other code-complient grounding system. Either way, you should consider "bonding" your ground farm with the house/utility ground. (And you'll need a licensed electrician to properly perform this kind of system upgrade.) Regarding RF grounding: some soils will indicate a few dozen ohms/foot and others will offer thousands of ohms. You'll have to do some measurements with an ohm meter to get a "feel' of what your ground farm will be like.
Disclaimer: Remember, you are dealing with earth (signal) grounds only. Never tamper with, or intrude upon, or compromise your electrical service grounds in any way. If in doubt, consult your utility company and/or a licensed electrician for bonding information. Also, lightning is completely unpredictible. A direct strike or a close near-strike may damage your equipment, start fires, or cause personal injury, or death. Use common sense and be careful !