by JIHAI ZHANG @ edn.com:
The purpose of a PLL is to generate a frequency and phase-locked output oscillation signal.
To achieve this goal, prior art essentially functioned by frequently changing the PLL output frequency according to the phase error (i.e. the faster/slower phase relationship) to generate a momentary, but not static, frequency and phase locked output oscillation signal. This frequent back-and-forth change in VCO frequency creates significant Jitter and a longer settling time because when phase is correct (locked), frequency is likely wrong (unlocked), or when frequency is correct (locked), phase is likely wrong (unlocked).
Frequency and Phase Locked Loops (PLL) - [Link]
Among the signals below 550 kHz are maritime mobile, distress, radio beacons, aircraft weather, European Longwave-AM broadcast, and point-to-point communications. The low-frequency converter converts the 10 to 500 kHz LW range to a 1010 to 1550 kHz MW range, by adding 1000 kHz to all received signals. Radio calibration is unnecessary because signals are received at the AM-radio’s dial setting, plus 1 MHz; a 100-kHz signal is received at 1100 kHz, a 335-kHz signal at 1335 kHz, etc. The low-frequency signals are fed to U1, a doubly-balanced mixer.
Transistors Q2 and associated circuitry form a Hartley 1000-kHz local oscillator, which is coupled from Q2’s drain, through C8, to U1 pin 8. Signals in the 10 – 550 kHz range are converted to 1010 – 1550 kHz. The mixer heterodynes the incoming low-frequency signal and local-oscillator signal. Transistor Q3 reduces U1’s high-output impedance to about 100 Ω to match most receiver inputs. Capacitor C15 couples the 1010 – 1550 kHz frequencies from Q3’s emitter to output jack J3, while blocking any dc bias.
Inductor L6 couples the dc voltage that’s carried in the rf signal cable from the receiver/dc adaptor. The dc voltage and rf signals don’t interfere with one another; that saves running a separate power-supply wire, which simplifies installation at a remote location. Capacitors C14 and C13 provide dc supply filtering.
Low-Frequency Converter - [Link]
Freq Show: Raspberry Pi RTL-SDR Scanner is a new guide in the adafruit learning system:
Have you ever wondered what’s in the radio waves zipping invisibly around you every day? Software-defined radio (SDR) is a great tool to explore radio signals using a computer and inexpensive radio tuner. With SDR you can examime many radio signals such as FM radio,television, emergency & weather radio, citizen band (CB), and much more.
Although dedicated SDR hardware like the HackRF allow you to tune an immense range of the radio spectrum, you can easily get started with SDR using a Raspberry Pi and inexpensive RTL-SDR tuner. Inspired by the HackRF PortaPack, this project will show you how to build a small portable SDR scanner using a Raspberry Pi, PiTFT, and RTL-SDR radio dongle. With the Raspberry Pi Freq Show RTL-SDR scanner you can visualize the invisible world of radio!
Freq Show: Raspberry Pi RTL-SDR Scanner - [Link]
by Mark “hiddensoul” Clohesy @ hamshack.org:
I was looking at a low cost way to build a 10Mhz frequency for my electronics lab. I had a few options that I could pursue, these were…
GPS Disciplined Crystal Oscillator (GPSDO)
Rubidium atomic standard (RbXO)
Caesium atomic Standard
Oven Controlled Crystal Oscillator (OCXO)
So to make a choice on what I should use I had to come up with design parameters for my frequency standard, these were as follows.
Had to be low cost
Had to be portable
Had to work inside of a building
Had to be stable, better then +/- 0.5 hertz drift over 2 minutes
Low Cost 10Mhz Frequency Reference - [Link]
Kerry Wong writes:
DS3232 is an extremely accurate RTC with a guaranteed accuracy of 2.5 ppm (0 °C to 40 °C), which translates into an error of just 80 seconds over the course of a year under the worst case scenario. I had done a few projects using this chip before (you can read about them here).
While by default DS3232 is already very accurate, we can push its accuracy even higher by adjusting its aging offset register (8bit). This adjustment works by adding or subtracting the corresponding capacitance to or from the oscillator capacitor array. The adjustable range is represented as 2′s complement (-128 to 127) and each LSB change corresponds to roughly 0.1 ppm of change in frequency. So the overall adjustment range can be achieved programmatically is roughly ±13 ppm.
DS3232 clock frequency calibration - [Link]
IQD frequency products have introduced a new range of temperature compensated voltage controlled crystal oscillators (TCVCXO) in a miniature 8-pad 5 x 3.2 mm outline. The IQXT-210 series TCVCXO, offers frequency stability down to ±0.14ppm over the full industrial temperature range of -40 to 85ºC.
Powered from a 3.3V supply the IQXT-210 has a typical current draw of only 12 mA (dependent upon oscillator frequency). The frequency can be specified between 10 MHz to 50 MHz. Initially there are 11 standard frequencies available including 12.8 MHz, 19.2 MHz and 26.0 MHz. Output can be specified as either HCMOS, 15pF load or Clipped Sine, into 10k Ohms load.
Tiny TCVCXO gets close to oven–controlled crystal stability - [Link]
fowkc published his latest project the mains frequency display:
I wanted to make a display that could show the mains frequency to 3 decimal places. I’d be using the same seven-segment display modules that I used in my UNIX clock, so all I had to do was design the part that would work out the frequency.
Mains frequency display - [Link]
Harrymatic @ instructables.com writes:
I am in the process of designing a function generator and I needed a frequency counter to check it against. This project uses a minimal number of components for a very economical and compact design. A bare-bones Arduino clone is at the heart of this project and the measured frequency is shown on an LCD display. The maximum frequency that this can measure is about 8 MHz (at a 50% duty cycle). Despite the fact that this counts the frequency on one of the digital pins, I have found that it will quite happily measure sine and triangle waves providing that they have a suitable amplitude.
8MHz Frequency Counter - [Link]
This AVR-based Frequency Meter is capable of measuring frequencies from 1Hz to 10MHz with 1 Hz resolution. The hardware of this project consists of seven 7-segment displays, AVR ATtiny2313 uController, and a few transistors and resistors. The AVR counts input pulses for a precise 1 second interval (generated using the built-in Timer) and displays the result on the multiplexed seven segment LED displays. [via]
1Hz to 10MHz frequency meter using ATtiny2313 - [Link]
Sergei Bezrukov writes:
My goal was to design a simple and user-friendly frequency counter which would be capable to handle radio FM frequencies and have an autonomous power supply. Powering it from batteries benefits to the device portability and makes working with it more convenient by eliminating a mess of power cords in a home lab. I use it just occasionally and a small size is a bonus simplifying its storage in a table drawer.
Most of similar devices I have found on the Internet use an LCD module with a built-in controller. Such a device draws pretty much current. Also, many high-speed counters use power-hungry ICs which makes it difficult for a battery operation. Finally, many projects are poorly documented which makes any modification unnecessary difficult. So, I started my own design which uses modern high speed and low-power ICs and can work from a single AA cell.
150MHz PIC Frequency Counter - [Link]
Fast Frequency Counter - [Link]