Tag Archives: antenna analyzer

I recently had the need to check a transceiver to ensure that it was on-frequency.  This is easiest done with a frequency counter, which is included in an MFJ Antenna Analyzer.  I use an inductive coupler made from some coil wire around a small (1/2 inch) piece of CPVC, with the coil connected to a BNC connector.

Inductive Coupler

Inductive Coupler

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Radio set frequency (28.5 MHz)

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Frequncy (28.499 MHz, or close enough considering the potential error in the antenna analyzer)

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Category: Equipment

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.

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

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

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

 

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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!

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Close enough to 100 ohms.

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This is how I did it.

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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.

 

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Just pretend it says "KE8P Dummy Load" 🙂

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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.

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

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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.

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Category: Equipment

Oh crap, that probably sounds bad.  Ah well.

2013-05-17 09.35.06 2013-05-17 23.23.43

So my first find was a key.  It's nice, heavy, and probably has a history, which I added "purchased for $35 by KE8P" to.

2013-05-17 11.59.44

 

I found this.  For $165.  Like any normal ham that likes to push buttons and turn knobs, I turned it on, just to be greeted with it flashing "LOW VOLTAGE 6.5V".  I figured that was a sign that it probably works.

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And when I got it home, I found these in it.  Ten Energizer rechargeable batteries.

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So I removed the batteries and plugged in a wall wart.  I was greeted with "VOLTAGE OK 15V" and something like the display in the picture above.  I did check my dummy load, it claims it is around 50 ohms at 1-1.3 SWR.  Guess it works!

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Also included were these.  They are coils to use the analyzer as a dip meter.  I didn't really need these, as I built one (they're really quite simple).  My built version worked quite well for the coax traps on my attic trap dipole.

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So I did try it with my HF and 2m antennas...

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Not bad for the severe destruction of 5 clothes hangars

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My HF antenna isn't too bad on 2m...

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...and it does okay on 20 meters, too...

The third purchase was a case for my SoftRock

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The last thing I got was some fiberglass mast.  I didn't take a picture of that.

 


Category: Equipment
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