Antennas

[olsenn]

Just thought I'd share this reference I found for helping to understand the basic types and operating principles on antennas. It uses the minimum amount of math and it seems to cover a very broad range of related topics.

Here's the site: http://www.antenna-theory.com/

On a side note: does anyone know of any places to find a high quality VSWR bridge; preferably with N-type connectors (BNC or SMA would also work)? I recently got into HAM radio, and I would like to use my spectrum analyzer to measure some different antennas to visualize their performance.

[JackOfVA]

Check Mini-Circuits for bi-directional couplers. (I assume you will use this with a tracking generator, not a transmitter.)

Mini-Circuits' model ZFBD-61HP for example is 1-60 MHz, rated at 25 watts main branch power, 20 dB coupling loss. Price with your choice of SMA or N connectors is $67 plus a few bucks for shipping.

Or, you can make your own.

[olsenn]

Thanks. Haha, yes; I do plan on using the TG of the spectrum analyzer, not my transmitter. As for your recommendation, I would like something that can go to much higher frequencies than 60MHz. I mainly use VHF/UHF and I would like to use the full range of my SA which is 1.5GHz. I'm willing to spend a few hundred dollars on this if it's neccesary.

[kg4arn]

You can use the SA with a Tracking Generator and a Return Loss Bridge.  The SWR relates to the return loss and there are many published tables.  I keep the table from Minicircuits on my work bench. 

If you are careful you could build your own Return Loss bridge with good directivity up to the gigahertz range.  But this requires some experience (and skill).  I have built my own (HF) and I also use one from Amtronix (1.2GHz).  it is $189 and has good (40dB directivity) at lower frequencies and 35 dB.  http://www.amtronix.com/sw1200n.htm   

You need to be aware that as the SWR measurement errors increase as the SWR gets closer to 1.0 (higher return loss).  There is a web site by Sam Wetterlin http://www.wetterlin.org/sam/, somewhere on it he has some articles that explain the errors that are inherent with these measurements.  If you are interested I can send send you a plot of the measurement uncertainty vs the directivity of the Return Loss Bridge.