I was looking for coax to replace the Quarter wave transformer in a commercial VHF Folded Dipole Antenna. Calculations for coax required to match 300 ohms to 50 ohms revealed that a coax with an impedance of approx 120 ohms is required. Z= √300 x 50 equals 122 ohms. RG63 has an impedance of 125 […]
Posts in category Antennas
Have you ever wondered why most of our Amateur Radio equipment is designed for 50 Ohm transmission lines? The following graph was originally produced by two researchers, Lloyd Espenscheid and Herman Affel, working for Bell Labs in 1929. The graph shows the power handling and voltage handling ability of various coax impedances.
Measuring Complex Impedances using the HP8405A Vector Voltmeter and a Return Loss Bridge Measuring complex impedances above 1000Ω is usually not possible with the average Antenna analyser however using a return loss bridge and a Vector Voltmeter this becomes possible. With a return loss bridge the amplitude and phase reading of the Vector Voltmeter represent […]
The tools required for calculating the vales in an L Network come from the following equations that can be found in the ARRL Handbook. XS = QRs and Xp=Rp/Q Q=Xs/Rs and Q=Rp/Xp Rp=Rs(Q^2+1) Rs=Rp/〖(Q〗^2+1) Q=√(RP/Rs-1) The L network is based on a technique known as series to parallel transformations.
After reading a number of articles by the late Walter Maxwell W2DU ARRL technical adviser, I was prompted to carry out some of my own experiments with mismatched loads. I carried out a couple of similar experiments that Walter described in chapter 19A of his book “Reflections”. My experiments were not as comprehensive as those […]
Probably the first question that should be asked is, what is SWR? Simply put, SWR is the ratio of the maximum voltage (resulting from the interaction of incident and reflected voltages along a transmission line)to the minimum voltage. In a correctly terminated line (that is where the load is equal to the characteristic impedance of […]