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Author Topic: RigExpert AA-30.ZERO HF Antenna Analyzer (0.6 TO 30 MHZ)  (Read 424 times)

Offline ChrisSmolinski

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RigExpert AA-30.ZERO HF Antenna Analyzer (0.6 TO 30 MHZ)
« on: January 08, 2019, 1308 UTC »
I just picked up one of this on Amazon. Here's the link: https://www.amazon.com/gp/product/B077B9D18K/ref=ppx_yo_dt_b_detailpage_o00_s01?tag=blackcatsyste-20

It's the guts of the hand held version for a lot less money, you connect it to your computer via a cheap USB to TTL serial adapter. Very cheap, like a 3 pack for $10.99: https://www.amazon.com/gp/product/B07D9R5JFK/ref=ppx_yo_dt_b_detailpage_o00_s01?tag=blackcatsyste-20

The software runs on both Windows and macOS. Don't be intimidated by all the connector pins on the PCB, it plugs into an Arduino CPU board to run stand alone. You only need to connect 4 wires from the USB/serial adapter: GND, 5V, RX data, TX data.  The board is powered off the serial adapter.

The board has an SMA RF connector, you may need an adapter, Amazon has this SMA to UHF pigtail adapter: https://www.amazon.com/gp/product/B00COW5E3A/ref=oh_aui_detailpage_o00_s00?tag=blackcatsyste-2

I like these little SMA to F adapters as I mostly use coax with F connectors here: https://www.amazon.com/Male-Type-Female-Adapter-Connector/dp/B00BIMTGXQ?tag=blackcatsyste-2

The main use of these is to measure the impedance of your antenna over a range of frequencies, plotting it out. But in this post I want to talk about the TDR (Time domain reflectometer) mode.  A TDR measures discontinuities in a cable, it can be used to find faults, as well as measure the length of a cable.  Some background here: http://www.dg8saq.darc.de/HamRadio/HamRadio_DG8SAQ_2018_English.pdf

A performed measurements on a few coax cables, the plots start below the AA-30.ZERO image:

First, the plot with nothing connected to the analyzer:

You'll see the impulse response (green line) has a peak at zero feet, indicating the cable length is zero. Note that you need to tell the software what the velocity factor of your coax cable is. You may know this from the manufacturer data, or you can take a known length of good cable, and adjust the value until it is correct.

Next the plot with a short at the analyzer input:

Now you see the peak is negative, and still at zero feet.

Next an 8 ft piece of RG6, I used a velocity factor of 0.86 which seems to work well for this brand of coax:

Very good!  Next the same cable, but shorted on the far end:

Slightly off, but still good.  Now a 100 ft piece of coax, open at the far end:

And now shorted at the far end:

Next a 57 ft piece of coax open at the far end:

Wait, that doesn't look right. The peak should be positive not negative.  And if we short it:

It looks the same.  Let's connect the other end of the cable:

Yes, looks like a dead short. Checking with an ohm meter, this end measures 1.5 ohms, the far end 3.2 ohms, so this end must be shorted.  I cut off the end and crimped on a new connector, and measured again:

Looks good!
« Last Edit: January 08, 2019, 1310 UTC by ChrisSmolinski »
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 58 ft T2FD / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop