Having determined the minimum R. Modern radio receivers of the super-heterodyne type have an input sensitivity of less than 5 microvolts per meter and, with the standard height of the antenna set at 4 meters, we find that the absolute sensitivity will be about 20 microvolts a microvolt being one-millionth of a volt.
Thus, if we desire a receiver as shown in Fig. As a certain amount of amplification can be, and is, obtained by one or more stages of conventional T. If there are two stages of T. The reader will recognize the necessity of using pre-amplification before the modulator as this phase has been covered in many excellent articles on the subject. Now, let us see just what the final figures will be with the added gain obtained in the pre-amplifier. If the input to the receiver is 0. The 4 volts required by the detector, divided by the 0.
The input to the receiver is 0. As it will he impossible to obtain a gain of In the example cited above, the amplification due to the modulating tube is ignored, as various conditions develop which cause the gain of this portion of the circuit to vary over wide ranges.
The sensitivity and output will be affected by the strength of the received signal, by the power output of the local oscillator, and by any change in operating potentials which may take place as the receiver is functioning. The check for the correctness of the calculation can be made by multiplying the gain in the pre-amplifier by the gain in the I. Figure 5 shows a skeleton circuit with the voltages developed in the various circuits.
Two stages of I. Knowing the value of either a coil or a tuning condenser, the other may be determined, for any wavelength by reference to the chart.
If an actual condition exists where the gains and voltages are measured and found to be as indicated in Fig. If the pre-modulator amplifier is limited to one stage, it will be necessary to increase the gain of the I. Unlike the conditions which exist in T. Thus, the inductance of the I. As the frequency of the I. To obtain the greatest percentage of the "mu" of a vacuum tube, it is necessary that the load in the plate circuit be as large as possible.
It will be noted that the effective impedance increases as the square. A handy rule to use in the design of such circuits is that. The condition of resonance is the same, no matter what the frequency may be, and the old L.
Most of the readers will be interested in kc. Examination of such a chart shows that The Radio-Craft readers, who have followed the articles by this author on the calculation of R. There are several types of semi variable condensers with capacity ranges running up to mmf. Earlier; we discussed the added gain to be obtained by the use of a large inductance provided the R. So, for the tuning: Now 5, microhenries is considerable inductance to put in a small space, but a good coil can be had by using any of the commonly-known methods of winding, such as diamond weave, duo-lateral, honeycomb, etc.
Most of us do not have the equipment on hand to wind a coil in this manner, so it would be practical for us to increase the size of the tuning condenser to 0. FM and television broadcasting with their narrow channel widths, as well as more modern telecommunications services such as cell phones and cable television , would be impossible without using frequency conversion. In special purpose receivers other frequencies can be used.
A dual-conversion receiver may have two intermediate frequencies, a higher one to improve image rejection and a second, lower one, for desired selectivity. A first intermediate frequency may even be higher than the input signal, so that all undesired responses can be easily filtered out by a fixed-tuned RF stage. In a digital receiver, the analog to digital converter ADC operates at low sampling rates, so input RF must be mixed down to IF to be processed.
Intermediate frequency tends to be lower frequency range compared to the transmitted RF frequency. However, the choices for the IF are most dependent on the available components such as mixer, filters, amplifiers and others that can operate at lower frequency. There are other factors involved in deciding the IF frequency, because lower IF is susceptible to noise and higher IF can cause clock jitters. Modern satellite television receivers use several intermediate frequencies.
The downlink signal is received by a satellite dish. One of the two blocks is selected by a control signal from the set top box inside, which switches on one of the local oscillators. This IF is carried into the building to the television receiver on a coaxial cable. Further processing selects the channel desired, demodulates it and sends the signal to the television. An intermediate frequency was first used in the superheterodyne radio receiver, invented by American scientist Major Edwin Armstrong in , during World War I.
Armstrong's solution was to set up an oscillator tube that would create a frequency near the incoming signal, and mix it with the incoming signal in a 'mixer' tube, creating a 'heterodyne' or signal at the lower difference frequency, where it could be amplified easily. After the war, in , Armstrong sold the patent for the superheterodyne to Westinghouse , who subsequently sold it to RCA. The increased complexity of the superheterodyne circuit compared to earlier regenerative or tuned radio frequency receiver designs slowed its use, but the advantages of the intermediate frequency for selectivity and static rejection eventually won out; by , most radios sold were 'superhets'.
During the development of radar in World War II , the superheterodyne principle was essential for downconversion of the very high radar frequencies to intermediate frequencies. Everyone who loves science is here! What is an intermediate frequency transformer? Feb 10, 1. Feb 10, 2. Can intermediate frequency transformer be classified as a variable inductor? An IF transformer usually has two windings in it so it does contain variable inductors, but these may be tuned to a fixed frequency by placing capacitors across the inductors.
If you have two parallel tuned circuits close enough to each other, then they will pass energy between them but only at a very limited range of frequencies. Other frequencies are mostly rejected. A common IF frequency is KHz. IF transformers like that were mostly used for valve amplifiers because they had high impedance inputs and fairly high output impedances. IF transformers for FETs can have a low impedance input winding and a tuned secondary.
This has the advantage that there is a voltage step-up and a lot of the voltage gain of the amplifier can come from this step-up What is its actual use in radio? A signal is mixed with an oscillator in a MIXER and the output of this will usually be the difference of the two frequencies.
This will be a lower frequency than the input signal or the oscillator. An IF amplifier is used then which is only tuned when the receiver is built.
Feb 11, · Can intermediate frequency transformer be classified as a variable inductor? An IF transformer usually has two windings in it so it does contain variable inductors, but these may be tuned to a fixed frequency by placing capacitors across the inductors.
Definition of INTERMEDIATE-FREQUENCY TRANSFORMER: One specially designed for coupling components and providing selectivity in an intermediate-frequency amplifier, the pass band being determined by anti-res.
In communications and electronic engineering, an intermediate frequency (IF) is a frequency to which a carrier wave is shifted as an intermediate step in transmission or reception. The transformer used at the input and output of each intermediate-frequency amplifier stage in a superheterodyne receiver for coupling purposes and to provide selectivity. Abbreviated i-f transformer.
Design of an I.F. Transformer. Most of the readers will be interested in kc. intermediates, so a design will be developed for this frequency. Examination of such a chart shows that kc. is the nearest frequency to kc. and will be satisfactory for our purpose. Custom manufacturer of frequency transformers, medium frequency transformers & intermediate frequency transformers. Standard insulation of transformers is V with high voltage insulation optional. Current transformers manufactured with current ratios from to , VA rating ranges from 2VA to15VA, & accuracy ranges from to