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Author Topic: MR100 Analyzer shows weird readings  (Read 692 times)

Henry

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MR100 Analyzer shows weird readings
« on: April 03, 2017, 06:22:30 AM »
After watching Gil's videos about the MR100 I bought one, calibrated it and started the WIN-PCC-Sark100-Software. Everything works fine, but when I scan my 50-Ohm-Dummy (homebrew bundle of 1/8W resistors in oil) from 1-52 MHz it shows a strange picture: from 1-4.6 MHz it's SWR 1:1, Z=R=50 Ohm, as it should be. From 4.6 MHZ until 52 the SWR increases in a zig-zag-curve up to 1:5.5, Z remains at 50 Ohms and R goes down to 12 Ohms. Very puzzeling.

Then I scanned a small 47-Ohm-resitor, and the reading are weird ups and downs in SWR, R and Z all over the frequency range. Shouldn't it stay in a line? How can I trust the MR100 when checking my antennas? What is your experience if you own the MR100 or the SARK100?
Please help!

73     Henry

P.S.: Can I post the graphics here (bmp)?
 

gil

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Re: MR100 Analyzer shows weird readings
« Reply #1 on: April 03, 2017, 07:10:08 AM »
Hello Henry,

I had trouble with calibration too. I suspect it was from a so-so contact with the calibration resistors. I soldered the resistors and it worked better. Still, the calibration routine might not work so well... I might build a box with a switch for the three resistors and a BNC hoping that it will result in a better calibration...

Gil.

Henry

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Re: MR100 Analyzer shows weird readings
« Reply #2 on: April 03, 2017, 01:19:08 PM »
Hello Gil,

thank you for your quick response. I don't refer on calibration itself since I had the strange result with the Dummy before calibrating, too. Meanwhile I checked a mobile CB-antenna (the only one nearby because I'm not at home), a Sirio HI-Power 4000 N, which should have an VSWR < 1.2:1, but MR100 measures more than 3:1 and ~70 ohms on the CB-Band. Same with a short whip from ALAN 95plus, it shows ~150 ohms while the manual sais, it should have 50.
I suspect the new MR100 is damaged. But how could I check it if it were so?
Has anyone measured a small resistor over the whole frequency-range?

gil

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Re: MR100 Analyzer shows weird readings
« Reply #3 on: April 03, 2017, 03:23:33 PM »
Hello Henry,

Please do post the graphics. Host the images somewhere and use the photo button with the link.

I also did get some puzzling readings on some antennas, didn't try a sweep with a 50ohm resistor, something to try next... A lot of things can affect SWR. Where was your CB antenna mounted? Even though the company might say 1.2:1, it depends on many factors like the quality of the ground, counterpoise, radials if any, coax length, environment, and whether your shirt had green in it... Well, not quite, but you get my drift... Did you do a sweep on the antenna? What about checking SWR on a fixed frequency?

I'll play with mine a little bit more... Anyone has one here too? Comments?

I wouldn't ditch it quite yet... I'm pretty happy with mine. It's a pretty simple device so there has to be a simple explanation...

Gil.

Henry

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Re: MR100 Analyzer shows weird readings
« Reply #4 on: April 03, 2017, 07:51:51 PM »
Hi Gil,
I followed your advice and soldered the 47-resistor to a short coax (before I connected it with two alligators), and the graphic is smoother now as you can see but still not the horizontal line like in theory. Just for fun I let the MR100 sweep over the whole range with open input (nothing connected).

The CB-antenna was mounted on my car where it used to work quite well (I never measured SWR there). Unfortunatly the car is a Berlingo with plastic roof, so I put two stranded wires on both sides downwards to ground it with the metal chassis. Maybe not the best solution. I just measured the values without the computer, but I will repeat it with laptop and software.

It's very interesting to play around with that nice little gear and wonder how to interprete the results it shows. If the results are real and not artefacts we can learn a lot about our antennas and I would like to discuss the experiences with anyone who checked anything that may work as an antenna.

73 to all who want to understand how it works.