Which diode is used in am detector

Square law diode detector utilize nonlinear portion of dynamic current-voltage characteristic of an electron device and is used for detecting modulated carriers of small magnitude. Linear diode detector uses the rectification property of a diode.

The current in the rectifying diode flows in the form of pulses. A linear relation exists between the detected output voltage and the carrier amplitude. Linear diode detector uses rectification property of a diode. Linear diode detectors are extremely properly used in commercial radio receivers. However, a linear diode detector for satisfactory operation requires a carrier voltage of 5 volts or more. With such a high value carrier, the cutin voltage V V of the diode may be neglected and the operation may be considered to be taken place over basically linear region of the dynamic current-voltage characteristic of the diode.

Figure 1 give the basic circuit of a linear diode detector. The modulated carrier voltage is applied to the series combination of diode and the load impedance consisting of resistor R in shunt with capacitor C. The circuit operates in the following manner. The diode has been reversed, so that now the negative envelope is demodulated. This has no effect on detection, but it does ensure that a negative AGC voltage will be available, as will be shown.

The resistor R of the basic circuit has been split into two parts R 1 and R 2 to ensure that there is a series dc path to ground for the diode, but at the same time a low-pass filter has been added, in the form of R 1 — C 1.

This has the function of removing any RF ripple that might still be present. Last edited: Feb 17, Willen said:. All thee do work, and allow demodulation of local stations.

The Si diode can clearly deal with fewer stations I found only 1. I would not recommend itwhen building a AM radio for the first time as it will take a lot of tuning to find out whether it works or not. The Schottky en Ge diode deliver approx the same results, although with the Schottky diode the tank circuit needs to tune to a higher frequency to receive the same station kHz instead of kHz.

The selectivity of the circuit at this stage is not very good, stations appear to overlap. Should i increase selectivity by adding a resistor in the tank circuit RLC , at the cost of some signal.

Or is there a better approach for this? Should i increase selectivity by adding a resistor in the tank circuit. JimB, Thanks for your reply. I'll have a look at your suggested videos. I figured adding a resistor would reduce the amplitude of the reception, but would narrow down the bandwidth. Requiring more amplification, but giving a better selectivity. OK I see where this is coming from. Try it if you like, but I suggest that you will be somewhat disappointed.

The detector circuit will still load the tuned circuit, leading to poor selectivity. The mathcad analysis takes no account of a load on the output. When crystal radios were used a long time ago there was only one or two AM radio stations in town. Now there are many radio stations in my town and many more AM radio stations in towns all around me. No wonder the stations overlap.

You need a REAL radio circuit today to have good selectivity. So a regenerative receiver should be the way forward for more selectivity.

Thanks for the tips, i'll give it a go. I tried adding a resistor before the LC circuit, didn't do much but kill the signal.

Similar threads. How to use transistor as switch.. Replies 27 Views 8K. Jul 29, audioguru. How to use an LDR as a switch. Replies 9 Views 4K. Sep 14, Rexlan. Please help me to understand how to use a zener diode. The AM diode detector can be built from just a diode and a few other components and as a result it is a very low cost circuit block within an overall receiver.

In the early days of radio, these signal detectors were made using discrete components, but modern radios will use integrated circuits with inbuilt detectors. As a result of its cost and convenience, the AM diode envelope detector has been widely used for many years in transistor portable radios.

Not only is the basic AM diode signal detector used for AM envelope detection, but is also widely used n RF circuits in general for signal level detection. The AM diode detector is an envelope detector — it provides an output of the envelope of the signal. As such the diode detector or demodulator is able to provide an output proportional to the amplitude of the envelope of the amplitude modulated signal.

The circuit typically has a relatively high source impedance.