Don’s Antenna talks by N4DJ

  The image below shows the current on a wire. The curve is the standing wave of current on the wire while the arrow represents the direction of the current. When the arrows point in the same direction the current is in phase and where the arrows point in opposite directions the currents are out of phase . Note on the half wave wire ( figure 2.8 B) there is only one arrow and that indicates the current is in phase. Where there are two half waves (a full wave long wire) the currents in each half wavelength section will be out of phase if the wire is end fed ( Figure 2.8 A) If, however the antenna is center fed (Figure 2.8 C ) currents in each half wave section will be in phase. If a receiving station is broadside to the full wave end fed wire , it will receive equal strength signals from each half wave section but these signals will be out of phase and tend to cancel each other. There fore there will be a null broadside. In the case of a full wave center fed wire, the receiving stat...

 Radiation from Antennas Evaluating radiation from antennas is not widely understood. My intention is to attempt to simplify this misunderstood concept. I will use the term wire but it could actually be any conductor normally used in antenna construction . I will also use the term amp or ampere to be current flow.  Radiation from a piece of wire (antenna) is simply proportional to the amount of current flowing in that wire. It is also proportional to the length of that wire. If the wire length is measured in feet and the current in amperes we can do some comparisons.  I will start very basic to introduce what may be a new concept to many. First of all , if one amp of current flows in a piece of wire one foot long that will result in less radiation than if we have one amp flowing in a wire two feet long. I think that is easy to understand. We have a term for current flowing in a wire. That is feet-amperes . If you take the length of the wire and multiply it by the amount...

  Notes on Parasitic Antennas There are some basic principles about parasitic antennas that I quickly wrote up thinking it may help a few people understand parasitic antennas a bit better. No one resource seems to have it all. Sometimes it’s hard to understand. I hope to simplify it as much as I can. I will concentrate on only two element arrays here. I hope I do not have any significant errors but if I find any I will make necessary corrections. The date of this paper is December 4, 2024.  First there is a driven element approximately 1/2 wavelength long as well as at least one parasitic element that receives its energy from the driven element.  Assuming the driven element is resonate on some frequency, it will have an impedance that is resistive as the reactance will be zero. The resistance will be near 75 ohms. The exact value will vary with the height above ground so it could be anywhere up to 95 ohms. We will just use 75 ohms here as a nominal value.  Whe...