Since I had a few minutes after the XYL went to bad (after a *very* busy Saturday for both of us), I went into the basement and played with the antenna analyzer.

This isn't the most ground-breaking post on my blog, but they don't really teach much about antenna analysis in traffic engineering classes!

Scop'd

2013-05-18 22.00.08

The first thing I did was drop the frequency of the analyzer to something low and see how much power the analyzer puts out.  4V peak-peak.

SWR Check - 25 Ohms

SWR is based on the mismatch between the impedance of the source and the load.  So a 2:1 SWR could mean that the load is twice or half the source impedance.  So I decided to put a few resistor arrangements on the analyzer and see if what happens is what I thought would happen.

2013-05-18 22.02.54

So I had these terminators from way back when they used BNC token ring networks. I've never worked with anything but Ethernet (using RJ-45 connectors), so I'm not sure how I got these, but they came in handy for this.

2013-05-18 22.04.50

This one is 50.3 ohms. Within a 1% tolerance.

2013-05-18 22.05.14

This other one is 49.4 ohms. Just around 1% off. For what I'm doing, close enough.

2013-05-18 22.02.46

This was my redneck arrangement. This basically put the two 50 ohm terminator resistors in parallel.

 

2013-05-18 22.03.35

This doesn't quite have the resistance I was expecting, but the SWR is correct. Of course, there's all sorts of stuff going on with the open end, the many connectors, and the 4 foot piece of RG-58.  Given the fact that I had two 50 ohm resistors in parallel, I think I should be seeing 25 ohms R and (ideally) 0 ohms X.

2013-05-18 22.03.08

This seems a little more like it. Still a nearly 2:1 SWR and close to 25 ohms R, with very little reactive ohms.

SWR Check - 100 Ohms

Since I couldn't figure out a way to make my two BNC terminators in series, I pulled a resistor out of my parts bin.  It was really a 98.3 ohm resistor, according to my non-lab-grade Radio Shack meter, so I figure that's close enough!

2013-05-18 22.10.37

Close enough to 100 ohms.

2013-05-18 22.11.18

This is how I did it.

2013-05-18 22.11.34

Hey look, exactly as expected. 100 ohms resistive, and 0 ohms reactive.

Other Dummy Load Test

I had a dummy load I built for QRP uses (specifically the Softrock).  I built it a while back, which is why the callsign is wrong.

 

2013-05-18 22.15.43

Just pretend it says "KE8P Dummy Load" 🙂

2013-05-18 22.15.53

70 and 4? SEVENTY AND FOUR? WTF, it should be 50 and 0!!! I'll just blame the extra resistance and all the reactance on the cable...

2013-05-18 22.16.59

Maybe this is why it isn't perfect. My coax isn't exactly Belden or Times.

Capacitance Checks

So the MFJ-259B has a capacitance check on it.  This is really for the capacitance of an antenna, not for what I did in the pictures below.  I basically took a ceramic disk capacitor and clipped one end to the ground and the other I held into the center conductor of the antenna port. This is a 10,000 pF capacitor.

2013-05-18 22.17.38

On 80m, this capacitor has 6,298 pf.

2013-05-18 22.19.22

Up at 91 MHz, there's only 8 pF of capacitance.

I figured the stuff above was a little more fun than me talking about how I tested every antenna I own... again.

-73-


Category: Equipment

About the Author

Andrew is the owner of this blog and enjoys computer programming, building things, and photography. He’s a pretty busy guy, which explains why updates to this blog are so infrequent.


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