Tech Articles

This article explains why the use of mix 43 for HF applications is almost always a mistake.   Selecting the best toroid material or "mix" for baluns and ununs.Transmitting balunsOccasionally errors are made regarding core selection and this especially includes baluns, where on occasion some very strange ideas surface. One rather odd but somewhat popular idea is that adding a mixture of core types will allow both high power operation and high choking impedance in baluns by sl …

This is a partial reprint (with permission) of an excellent series of articles published by KV5R on shortwave antennas. His full series can be found at www.KV5R.com As previously stated, a ½ wave antenna radiates off of the sides, perpendicular to the wire. Longwire antennas radiate toward the far end of the wire. Let’s look at what happens to the directivity pattern of our 94-foot wire. As we dial up the frequency, the pattern of the antenna changes. The following diagrams show r …

Reprinted with permission of Hamuniverse, this is an excellent explanation of SWR and how to best measure it.What is SWR?SWR or Standing Wave Ratio is one of the most misunderstood terms in amateur radio. Even though every antenna and transmission line book that I have seen is quick to point that out, it still is the source of many misconceptions. To most hams with an SWR meter, SWR is whatever the meter reads and if the meter says there's no problem, then all is well. That simply isn't true. In …

Matching Problems using a tuner and high impedance feedlineMost matching problems occur when the antenna system presents an extremely high impedance to the tuner. An antenna system should be considered everything from the tuner to the tip of the antenna. High impedance feedline is usually considered that which has over 300 ohms impedance and are typically are 300 ohms, 450 ohms and 600 ohms in impedance. When the antenna impedance is much lower than the feedline impedance, an odd quarter-w …

We occasionally receive emails from customers who feel their balun is defective because they are unable to replicate our test results. This is due in large part to the effect of stray capacitance picked up by the testing method they use. For Common-Mode chokes used in RF applications, stray test-fixture capacitance (which might be only a few pF) can resonate with the choke's inductance and greatly change impedance measured. As you can see below, this is especially noticeable at …