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

February 21, 2013

First Phase in Building an Antenna Analyzer

Filed under: Electronics,ham radio — Cranky Sysadmin @ 5:02 pm

What I have is probably a case of “Make a problem as hard as possible before solving it”-itis. I’ve been looking up at my G5RV-lite antenna and considering a replacement almost since I bought it. The antenna seems to perform well enough on 20 meters and up, but at 35 feet high, I mostly hear local traffic on lower bands. I’d like to solve that problem by building a new antenna. This leads me to the fact that I would like to measure said antenna. Since I’m looking for solutions for ARRL Field Day, I’d like something more portable than my Atten AT6011 spectrum analyzer.

If I were really motivated to build an antenna, I suppose I could just build it and trim it to low SWR via my transceiver. Because I’m not motivated to actually build an antenna, I decided to make the problem harder by looking into building an antenna analyzer. There are tons of options out there for building a homebrew antenna analyzer and I’ve spent many hours reading about them. Here is a list of some interesting ones:

  • VK5JST has a nice design which measures SWR and impedance,but not the sign directly.
  • The Tenna Dipper measures SWR with an LED. This is as simple as it gets and isn’t complex enough to put off my antenna building long.
  • The N2PK VNA is also a candidate. There is a stand alone version which just measures SWR, but the version which hooks into your PC builds Smith charts and SWR / frequency graphs among other things.
  • The PA1ARE antenna analyzer measures SWR, impedance, and can tell you whether there is capacitive or inductive impedance. It measures voltage in current in two signals which are 90 degrees different in phase to calculate the sign. It uses some obsolete parts, so it may be difficult to build as-is.

If I create an original design, I’ll probably use an arduino or bare AVR microcontroller, one or two of those cheap AD9850 modules from ebay or amazon, an encoder, and some form of detector. I may start out with a simple resistive bridge to get going, but the PA1ARE synchronous detector or something based on that seems like the most functional thing if I can wrap my head around the math. Even though homebrew analyzers are documented well elsewhere, I will post information on my attempt. I hope to capture everything necessary to build an antenna analyzer so that you, dear reader can criticize my awful design and hopefully drive me to make it better.

4 Comments »

  1. I would very much like to build the PA1ARE analyzer (I went as far as sourcing all the components), but after a bit of research, could not find the source code for the micro. As I am not into programming, and the OM who wrote the software has passed on, and not left the code with anyone contactable, I decided to build the VK5JST version. I have just finished making the pcb and will be assembling it soon. Wish me luck, and then I can put up an antenna at my new QTH. Best regards, Alf

    Comment by Alf Watts — April 9, 2013 @ 2:23 am

  2. The Vk5JST analyzer has great docs, including a good description of the math. A similar analyzer was built by yd1chs. His pdf document has a great description of the math. Both of these use a resistive bridge that I’ve seen called an Anderson Loop.

    Comment by Cranky Sysadmin — April 12, 2013 @ 8:41 pm

  3. I built the Fox Delta antenna analyser kit, it uses a PC for display, works on HF bands only and can only display SWR and return loss. But it is VERY cheap, its a kit, it is sensitive and works very well for what it is. I recomend it! ZL3DW

    Comment by Andrew — July 4, 2013 @ 8:14 pm

  4. I Just wanted to say good luck and I sure would appreciate an email when you get it done..
    Tnx

    Comment by Bill wb7pnc — June 5, 2014 @ 4:31 am

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