Measure – NT1K

As I get deeper and deeper into designing and building antennas, I figured I need something better than a SWR meter to make sure that my antennas are performing well. Since I am also publishing the antennas that I’ve designed and built here on this website, I would feel more comfortable knowing that it was done correctly. I needed some kind of antenna analyzer.

There are so many choices out there today that I was not sure what to get. The most popular antenna analyzer for amateur radio use is the MFJ-259B. You’ll see it or a model similar in a lot of shacks around the world. I’ve used and enjoyed them but I felt that it was “Old School” considering technology has improved greatly. It was between the RigExpert AA-150 and the MiniVNA PRO. I purchased the MiniVNA as I felt it had more to offer. Being able to use Bluetooth to pair it up with an android device is what won me over. I found a used unit on QRZ for the price I was willing to pay. Wasn’t entirely sure about buying used test equipment but it ended up working out for me in the end.

Mixed Reviews at First

The reviews for the MiniVNA and the MiniVNA PRO were mixed. A lot of people had a hard time getting it to work with their computer and a lot of people commented about poor documentation and how it was not “User Friendly”. Some claim to receive DOA Units. When it comes to reviews from hams (or anyone really), I don’t take them all for face value because I’ve seen people who are so called “Computer experts” fail to perform the simplest tasks like installing a driver. Instead of fixing possible problems with their computer/equipment, it’s easier to blame someone or something else. You also have those who have egos that are so big that anything they touch is the best because they only buy the best. Then you have those who give honest reviews that detail how good or bad the product is. It’s hard to know who’s reviews should be trusted.

First Impressions

Before the unit arrived at my house, I’ve read the 135 page manual about using the MiniVNA PRO and it’s software (vna/J ). I can see why people would think the manual is confusing. However I never used a VNA and I have no idea what any of the measurements mean other than SWR and impedance. I have a lot of learning to do so I can take full advantage of the VNA. Other reviews claim that the manual is NOT user (ham) friendly and geared toward experienced users but I feel that’s a challenge to learn more about the numbers I’ll be seeing. It will hopefully give me more insight into what’s happening with my antenna. I didn’t see much issue with the manual other than the order which topics were discussed.

Arrival

I’m lucky that the unit arrived right when I had some time to tear into it. Since it was used, I wanted to make sure it worked. It came with calibration slug/jumper cable and the seller even included a bluetooth module to hook up to almost any computer. Before even hooking it up to the computer, I went to FTDI’s website and made sure that I downloaded the latest drivers. Once installed onto my Windows 7 X64 OS, I hooked the VNA to the computer and the OS automatically recognized the VNA and assigned it a com port. So far so good!

Using vna/J

After downloading the latest vna/J (2.8.6f as of March 7th, 2015). I noticed it was a .jar file which tells me that it runs on the Java platform. Before running vna/J I made sure to update Java. Software started up with no issue and it was asking for a calibration file. First thing I did was go to the Analyzer menu > Setup. In the new window I highlighted the MiniVNA pro as well as the com port that is associated to the miniVNA. Once the proper unit/com port is selected, press the “Test” button. If successful, the status bar will turn green and “Update” button will come active. After pressing “Update” the screen will go away. You will still need to calibrate the unit.

First Calibration

Calibrating the VNA is easy if you ask me. All you would have to do is go to the Calibration menu and choose “create”. A box will pop up and if you have the calibration kit (SMA connectors), hook the “open” connector to the DUT port and press test. Then hookup short and then the 50ohm load. Once the calibration is done, save it and then press the Update. You are now ready to use the VNA. Whenever you load the vna/J software it will recall the last calibration file used. You can make different calibration files in case you’re adding adapters and cables you don’t want factored into the test. When you go into transmission mode, you will be asked to do a calibration using the jumper cable from DET to DUT. Similar to the reflection calibration.

Navigating around vna/J

I found it not to be confusing at all to use. The layout to me is simple and easy to use. Choose what you want to see (SWR / Reactance in my case), choose the frequency range by typing it in manualy or making a list, choosing reflection or transmission (reflection in the case) and pressing the “Single” button. I guess reading the manual helped but just messing around with stuff helped me out even more. I ran a quick test leaving the 50ohm test plug on the DET port and the results produced a nice flat line at 50ohms and the SWR was 1.0:1

I’ve made a video showing the MiniVNA as well as installation and the first calibration.

First real test

Since I’m hot to trot, I grabbed whatever was nearby and tested it. It happened to be my Butternut HF9V located in my backyard. It’s 100ft away from my house fed with LMR 400. There is currently 7 radials in the ground.

If the VNA is correct, I need to go out and re-tune my antenna. From this plot I can see 75M has very narrow bandwidth (as mentioned by Bencher) and I’m off on a bunch of other bands.

Tried re-tuning the antenna outside but it was so cold I decided it can wait for another day.

Bluetooth

One of the main reason why I wanted this unit is because it’s truly wireless. There is an application for the Android that allows the miniVNA to be used with a smartphone or tablet.
You could also use a laptop or desktop computer as long as it supports or could support bluetooth.

I decided to try it wirelessly on a 10M dipole I had in my attic.

If this is correct, then I need to shorten my antenna. It’s better than having too long instead of too short.

The application “BlueVNA” was developed by Dan, Y03GGX. For a free program it’s really nice.
I do have issues where the program force closes or stops working at random times on my Samsung Galaxy S3. It’s a minor annoyance but I can’t complain. reload the app and you’re back in business.
There is a claim that the miniVNA pro can transmit up to 100 meters which I would guess that would be under best conditions. Obstructions and quality of the other bluetooth module is a major factor. I’ve had it lose communications withing feet of the unit. I also tried it outside and worked well.

Measuring Transmission Loss

Someone gave me a low pass filter over and wanted to use the vna to measure it. An low pass filter allows “Low Frequencies” to pass through but attenuate or “block”

I was able to see how the filter reacts through a range of frequencies.

Here some other stuff I measured

Here is a video of it hooked up to a 1:1 current choke

The Diamond X510 on my roof. Not bad, it was as expected.

Rubber duck antenna that is on the TYT . I added a counterpoise to see what would happen as I feel that the chassis of the radio makes up the “other half” of the antenna. Very very weird results.

Overall experience

After a few weeks of using the MiniVNA PRO, I’m quite impressed in what it can do for the small package it comes in. It was easy to setup (I think) and it was easy to use considering I never really used test equipment. Understanding what all the results mean is a different story but that means I have a lot more learning to do. I’ve tested basically everything I can hook it up to.

If I were to get nit picky and they were going make a new version, I would ask for a metal enclosure, SMA connectors to be off the board and possibly an LCD screen with control buttons to make which would alllow to me to use the unit without the need for a computer or android device.

I think I made a wise purchase and I would recommend the MiniVNA to others that need something more than just looking at SWR

Thanks for reading!

Even though I have yet to participate in any type of Radio Direction Finding (RDF) event, I find myself buying and building stuff for it. This time I decided to build an offset (active) attenuator as I think it’s a must need for RDF. When I was testing out my 3EL tape measure Yagi, I placed a transmitter on my property and tried to find it with a Yagi and found that it was near impossible to pinpoint the source as my radio was showing full scale and dead full quieting no matter where I went.

Since I’ve been reading a lot about fox hunting, I knew I needed an attenuator. However there are different kinds of attenuators that you can make or buy commercially. I wasn’t sure what to get at the time. I narrowed it down to the offset attenuator and the step attenuator. I went with the offset attenuator because it appears to be cheaper, easy to make and better than a step attenuator.

The attenuator that I went with was found on HomingIn.com’s Website. The article was writen by Joel Moell (K0OV) and explained in detail about the attenuator. What the offset attenuator does is “Offset” the received signal by 4MHz using a diode, oscillator and some other passive components. You are now listening to the signal away from it’s transmitting frequency. Your antenna and radio is no longer being overloaded and you’ll be able to get even closer to the signal.

It appears to be quite easy to build, even for me! So I went with it. The parts that are listen in the article are a little outdated

Here is an updated list of parts that I purchased. I usually use Mouser for components but I wasn’t satisfied with their shipping to the North East so I used Digi-Key with better results

Qty	Desc	Price	P/N	Source
1X	CAP CER 470PF 2KV 10% RADIAL	$0.23 ea	1286PH-ND	Digi-Key
2X	CAP CER 4700PF 50V 10% RADIAL	$0.30 ea	BC2683CT-ND	Digi-Key
2X	RES 2.2K OHM 1/4W 5% CARBON FILM	$0.10 ea	2.2KQBK-ND	Digi-Key
1X	RES 4.7K OHM 1/4W 5% CARBON FILM	$0.10 ea	4.7KQBK-ND	Digi-Key
1X	DIODE SMALL SIG 100V 200MA DO35	$0.10 ea	1N4148TACT-ND	Digi-Key
1X	OSC 4.0000 MHZ FULL SIZE	$2.49 ea	CTX774-ND	Digi-Key
1X	BNC FRONT MT RECEPT SHORT	$4.67 ea	ARF1064-ND	Digi-Key
1X	5K Audio Tape Pot	$3.49 ea	#271-1720	Radio Shack/In-Store
1X	Perf Board/PC-Board	$2.49 ea		Radio Shack / Instore
1X	SPST Swith	$2.49 ea		Radio Shack / Instore

Total project cost: Approx $8.00-$18 USD

Making Sure Everything Works

Before putting it on any type of board I wanted to make sure that It works. I never really messed around with making electronic devices from a pile of parts. I put the entire project onto a breadboard following the schematic as close as possible

Here it is being tested out on the breadboard It went together pretty easy. I used a voltage meter to make sure the correct voltage is coming out of the LM7805 regulator. I was seeing around 5V

Here is a video of it in action

Now that I know it works, it’s time to transfer the design to a more permanent home. I wanted to compact it as short as possible to get it to fit into a small PVC box. Since I had a PVC box I wanted the board to go into, I measured a piece of perf board and cut it up

After cutting the board, I laid out all the components and attached all the wiring I could from underneath the board

Here its with most of the stuff attached.

Here is the Top view of the board. I had to use some jumpers (red and green wires) to get some of the components to make contact.
The black wires you see leading away from the board are for power and the adjustable resistor. I tried to test it out at this point to make sure it works before adding the coax and other things but It turned out not to be worth doing. But I did check the circuit wiring a couple times to make sure.

Final Assembly

Getting it jammed into the small box was going to be difficult. I knew right away that I wouldn’t be able to fit the 9V battery and the circuit board into the same compartment without using a larger box.

Here is the PVC junction box with the circuit board, switch, POT and cabled jammed into it. I had to have shave some of the flange off on the cover as the Pot is almost the same size as the Inside dimension of the box.

To solve the battery issue, I fabricated a small aluminum box that can hold a 9V battery. I drilled a small hole in the side of the PVC case to route the power cable through. In the above picture you can also see the on/off switch and adjustable pot. I mounted the switch sideways to avoid any accidental switching even though it’s still possible.

Here is the fully assembled antenna. The PVC junction box is also used to mount the grip handle. This way most of the weight is sitting on top of my hand instead of out on the boom. I also didn’t want to put any kind of electronics/metal between the reflector and driven element. Not sure if it would make a difference but I think it’s better off this way

Lessons Learned

I learned a lot while making this attenuator. The circuit was simple enough to where I can understand what is going on.

If I were to build another one, I would make some changes to make it even better. The big problem is that the coax runs from the driven element straight into the attenuator from inside the PVC. This doesn’t allow me to swap out antennas. What I would do is put a BNC connector sticking out of the PVC box and have the coax come out the boom to make the connection. I could just make an attenuator that is seperate from the antenna but that is just another bulky piece of equipment to carry around. I wouldn’t want to attach it directly to the radio because I think it would put strain on the connector that is in the radio.

You also can’t TX using this antenna. If you do, you can kiss the diode and possibly other parts goodbye. I would try to install some kind of switch that would allow me to TX but I’ll just carry an extra antenna or extra radio for now.

Hopefully it will see a lot of use.

Thanks for reading!

73,
Jeffrey Bail (NT1K)

Tag: Measure

Introductory look into the MiniVNA PRO.

My Offset Attenuator Project