Permeability for variation in coil length versus rod length is: Tubes affect the effective permeability of these devices. Please note that thereĪre many variables and that the inductance will vary according to windingĬoil placements and the length of windings on the rods, bars, plates and The rod and covering nearly the entire length. These figuresĪre based on a closely wound coil of #22 wire, placed in the center of Of A L and NI values for various types of rods in the above table should be used as a guide only. The best 'Q' willīe obtained with the winding covers the entire length of the rod.īecause of all of the above various conditions it is very difficult Greatest inductance and A L value will be obtained when the winding isĬentered on the rod rather than placed at either end. At other times, just the reverse will be true. In some cases, the effective permeability of the rod will be influenced more by a change in the length to diameter ration than by a change in the initial permeability of the rod. These are: (1) Length to diameter ratio of the rod, (2) Placement of the coil on the rod, (3) Spacing between turns and, (4) Air space between the coil and the rod. There are several factors that have a direct bearing on the effective permeability of a ferrite rod, which in turn will effect inductance and 'Q', as well as the A L value of the rod and its ampere-turns rating. The material 61 is most suitable for the 7.5-30 MHz (10-40 meters band) range.ĭue to the open magnetic structure of the rodĬonfiguration, considerable current can be tolerated before these rod cores will saturate. Both material 77 and material 33 rods are also often used in speaker cross-over networks. The material 33 has a somewhat narrower band, and is suitable for the 3.75 - 7.5 MHz (40-80 meters band). It is suitable for 1 Mhz to 30 Mhz in the amateur radio band. The material 77 has a wide suppression frequency range. As a general rule, the highest permeability rods are used to suppress the lowest frequency range.
Chokes and filters application is in a way, similar to the antenna application. In a choke and filter application, the design objective is to get the highest impedance over the frequencies to be suppressed. When the windings occupied the entire rod (when N is largest). It can be seen from the equation that the highest induced voltage occurs Strength, F (in uV/m), provides the loop-induced voltage (in uV). Loop antennas have a height factor calledĮffective height, h e (in m), which when multiplied with field Therefore, optimum l/d ratio is from 10 to 25 for a rod antenna. On the other hand, for very short rods where the l/d is less than 5, the effectiveness of the antenna is also diminished. When the l/d goes over 35, the rod behaves more like an toroidal cores, and the close loop effects kicks in making these rods ineffective as an antenna. However, the efficiency of the rod as antennas degrades as the rod overall length versus the diameter ( l/d) increases. Rods, bars and plates have open loops and are thus suitable as radio receivers. Toroids cannot be used as receivers as they have closed loops. Material 77 is typically used in receiver application below 10 Khz. The material 77 (u i = 2000) rods are most suitable for very low frequency (VLF) receiver application. As a general rule, the higher the operating frequency, the lower permeability of the rod cores are needed.
The table above shows the recommended frequency rangesįor different materials. The material 33 (u i = 800) rods are more suitable for lower frequencies in the 100 Khz to 1 Mhz or the low frequency (LF) ranges. Material 61 (u i = 125) rods are also used by radio amateurs in the 2 MHz to 30 The material 61 (u i = 125) rods are mainly used in the 550 Khz to 1660 Khz commercial AM Receivers, airborne navigation receivers, AM, FM and VHF receivers. Widely used as loop antennas such as broadcast-band receivers, low and medium frequency direction-finder >for more information on custom blocks of ferrites and material availability.įor antenna application, the design objective is to get high Q at the center of the design frequency of operations. The table below shows the material characteristics of the various types and of NiZn and MnZn ferrite rods, slugs, tubes, strips, plates and bars. They are available in materials from permeability of 7.5u i toġ0, 000u i in both Nickel Zinc (NiZn) and Manganese Zinc (MnZn) compositions. These rods are available from 0.25" to 1" in diameter. The advantages are small size, high Q and compactness.įerrite rods and bars are available in standard lengths up to 12" long. In radio antennas, ferrite rods are useful from VLF spectrum to VHF spectrum. Ferrite rods, bars, slugs, plates and tubes are primarily used as magnetic cores in radio antennas, chokes, inductors and filters.
0 kommentar(er)
