Soundcard Interface

Coming soon

Multiple Feedback Band-Pass filter

Band-pass filters are filters that are designed to let only a certain set of frequencies pass through. Overtime a myriad of different topologies have been developed by some very creative designers. Passive vs active, RC-filters vs LC filters, combinations of low pass and high pass filters, with gain and without gain, etc. One of the topologies that are often used for CW filters in receivers is the multiple feedback band-pass filter :

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40m DC-receiver – What’s next?

Now that the basic receiver is working, what do I want to add to consider the receiver ‘complete’ ? This is the current set-up :

The following things I would like to add:

  • S-meter : shows the strength of the received signal. Based on AF signal
  • CW filter : Multiple Feedback Band-Pass filter, 1 or 2 stages, centered around 750Hz
  • Audio Amp – current the bench utility amp is used with a gain of 20 dB.
  • Keypad – Add 3×4 Keypad much like the K-225 keypad as found in Lowe HF-255 receivers

40m DC-receiver – VFO

So the receiver is alive and kicking and I have received amateurs from The Netherlands, UK and Italy on a simple 10m wire antenna. However, the VFO is comprised of a Siglent SDG1032X function generator from work. Hardly a self-contained solution!
After an article by Bill Merea in the GQRP Sprat magazine, I’ve decided to go for a digital VFO. The clock generator is based on a Si5351 module. The I2C interface is controlled via an Arduino Nano board together with a Groove I2C LCD.

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An attenuation network is often used in devices like a (digital) voltmeter, in oscilloscopes, etc. It offers the possibility to expand the input range of the measurement tool and thus makes it more versatile. Usually the attenuation network is build with a couple of resistor as shown in fig. 1. If the input resistance of the rest of devices is considered indefinite (as for example with a J-FET) the voltage is Vo=Vi*R1/(R1+R2). This works very well with DC-voltages.

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