The N2PK is a serious SMD soldering exercise - over 300 components on the main PCB and over 700 solder joints. The blank 4.3 PCB was ordered from VE3IVM. All parts are from Digikey. The only additional components were the Valpey Fisher Master Oscillator and the Minicircuits transformers. The VP XO is a very difficult component to find! There is an alternative with Connor-Winfield MO, available from Digikey but I was lucky to find the Valpey Fisher part. I installed all components on one side of the PCB and then moved to the other.
The N2PK VNA is an advanced project - high part count / desnsity on both sides, some fine pitch ICs (not very easy to solder pin-by-pin) and some components in very small packages. Good soldering skills are a must as well as a good set of tools, soldering materials and soldering iron with fine SMD tips (I used Weller WESD51 with ETP / ETH tips). I worked on the board for about 2 weeks spending a couple of hours almost every evening. I could have done it much faster but I was taking my time, double-checking and making sure that there are no mistakes. Troubleshooting is difficult with SMDs and the capacitors are not marked which can cause a lot of headaches should one makes a mistake with the components. My approach was to install all components (small-to-large size order, but starting with the ICs) of the same type/value together, while working on the top side first. After the top side was completed, I did the same thing on the bottom side leaving all connectors for last. I made sure that there is only one type/value components out on the bench at a time to prevent confusion. How well I've done we will see once it is powered up.
I have also prepared custom heatsinks for the MO, DDS and ADC chips. The only thing left to do on the main PCB is the RF shielding cans for both detectors. I need to make screening boxes out of tinplate. After I am done with the power supply / power conditioning board and the wiring harness I'll be able to finally test the VNA.
4 comments:
Does this VNA do Polar Plots such as for an antenna radiation pattern?
vk6bmt@iinet.net.au
The software (MyVNA) is capable of Polar Plots of measured values and both detectors are sensitive enough so in theory you can use it for antenna radiation pattern plots but this functionality is not offered "out of the box" so to speak and it will require some extra work.
In order to plot an antenna radiation pattern you'll need to perform a number of field strength samples with another receiving antenna. Since the pattern represents the distribution of power in space, you should be able to rotate the antenna under test (if it is directional like Yagi) and use fixed receiving antenna to take the power samples. If the antenna is not rotatable (wire antenna) or Omni-directional (vertical) you must be able to move your receiving antenna in circular fashion around the tested (transmitting antenna) while taking the measurements. The VNA is portable and you could do this with a laptop or netbook, but the process is not going to be very automated.
If you are dealing with Yagi antenna, I'd look into Telepost LP-100A (www.telepostinc.com) This unit works also as a field strength meter, it costs less and there is a software integration with Polar Plot software for antenna radiation patterns. (Same limitations though - you can only test rotatable Yagi)
Which program(s) do you use to design your frontal panels? They look very nice & professional.
I used Corel Draw to design the graphic layout but other Vector Graphics software such as Adobe Illustrator will work fine too. This is a general graphics software and works great for almost anything graphical - it is not specifically made for panels so you'll need to learn how to use it.
Details on the front panels can be found in this post:
http://blog.kotarak.net/2009/09/n2pk-vna-power-supply-and-enclosure.html
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