Sunday, 20 November 2011

Guess it's time to start blogging

I've been thinking about this on and off and finally decided to start blogging.

Mainly because it helps me to keep track of the time line of the designs I do at home but also to have some kind of place where I actually can present projects, including documentations etc.

One of my hobbies has always been electronics. My first bigger projects when I was younger were classics like a power supply and a voltmeter. As I grew up and started as an apprentice at Motorola I did other projects  involving an Intel 8030/8050 microcontroller and I²C, a digital Thermometer, a device that measured the internal resistance of Li-Ion batteries and a switch-mode power supply. Later on I got exposed to the wonders of RF circuits and had the great opportunity to work in Motorola's EMC laboratory.

Today, I'm studying electronics at a university in Helsinki and although I still have about two years to go, I was wondering what topic I should pick for my thesis.

Building your own measurement equipment is something really satisfying but I also managed to pick up some gear over the years as I started to earn money. So although one can never have enough power supplies, I guess I was looking for something a little more useful.

Spectrum analysers are incredibly useful but also very expensive. Even several decades old equipment rarely costs less than 800 EUR so even when you find a steal, shipping costs generally kill any deal from outside the EU.

Why not build a spectrum analyser?

After a lot of research and browsing the internet for inspiration I settled on a design that supplemented the Spectrum Analyser with a Tracking Generator and the ability to measure phase properties, thereby effectively describing what is also known as a Vector Network Analyser.

Schematic of the Vector Network Analyser

The idea is to have all stages as individual modules so that the design may easily be improved or supplemented with additional modules. As you can see in the schematic above, the analyser features two receivers of which one is used internally to measure the phase difference between the Tracking Generator and the Test Channel after down conversion. This means that the receiver for the test port must be used for both transmission and reflection measurement by making two measurement passes.

A rough list of the specifications:

  • Dual Conversion Topology
  • 1st I.F.: 1013.3 MHz
  • 2nd I.F.: 10.7 MHz
  • Frequency: 10 kHz...3 GHz
  • Sensitivity: -110 dBm
  • Dynamic range: > 85 dB
  • Amplitude resolution: < 0.04 dB
  • Frequency resolution: < 6 Hz
  • Phase resolution: < 0.1°
  • Resolution Bandwidth Filters: 30 kHz, 15 kHz, 7.5 kHz, 1 kHz

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