The Cranky Sysadmin A world of technology, fun, and ignorant rants.

April 12, 2013

Antenna Analyzer Progress Part 2(ish)

Filed under: Electronics,ham radio — Cranky Sysadmin @ 9:42 pm

I’ve been studying detectors for antenna analyzers and trying to land on one which will be effective. If you’re interested in detectors, read past the fold.

As I’ve said in a previous post, an antenna analyzer has 3 major components.

  1. A signal generator
  2. A detector
  3. A calculator

I’ve settled on an AD9850 DDS for the signal and an ATmega328 as the calculator. The detectors I’ve looked at are listed below with a brief description.

The Anderson Loop is the simplest detector. Most hams don’t refer to it as an Anderson Loop, and I’ve only seen the loop described as such by the folks who patented it. A good example of an analyzer that uses this detector is the VK5JST Aerial Analyzer . Below is a basic schematic of the detector.
andersonloopAnother popular detector is the Wheatstone bridge. The RigExpert AA-520 uses a wheatstone bridge as do several other popular analyzers. I’ve included a schematic of the bridge below even though you can find it in countless places on the web.wheatstoneThe directional coupler is also popular. The two popular ones that I see are the transmatch and the Bruene bridge. There are also stripline directional couplers for VHF and UHF. I’ve not tried the stripline couplers on HF, but they may work fine. Most folks seem to wind some turns on toroids or binocular ferrites. Below is a schematic of a transmatch coupler.directional_couplerAnother coupler which I didn’t study in depth, but which looks promising is the direct conversion detector. PA1ARE’s antenna analyzer is an example.

Each of these detectors needs some extra circuitry like diode detectors and opamps to sample and amplify the signal.

I am settling on a transmatch directional coupler and an AD8302 combination. I have several AD8302 chips (less than $2 from china), and I want to use this as a launch-pad to build a more capable Vector network analyzer later on. I’ve worked out the math I need to use with the AD8302. I hope to have something put together over the next few weeks.

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