Thursday, July 26, 2012

For sale - N2PK Vector Network Analyzer

UPDATE: SOLD! Thanks Bob! This unit has found a new home at Tufts University, but most importantly, it will be used for scientific research - I just couldn't wish for a better new owner.
If you are looking for a "cheap VNA", "just anything that will plot a Smith Chart or "an incredible bargain VNA", please don't waste your time reading this post. There are other, less expensive solutions out there and some cover even wider frequency range than N2PK VNA.
Coming here, while searching to buy an N2PK VNA in particular, you probably have a good idea why you want this specific VNA design and what it is capable of. Then, if you are handy with the soldering iron, worked with SMDs before and have plenty of time and patience, I'll encourage you to try to build one yourself.

I have for sale a very high-quality, custom built with an extreme attention to detail, no-expense-spared, no-corners-cut "kind of deal" VNA. This an absolutely completed N2PK VNA set ready to be connected to a computer and DUT - not a bit of additional work is needed. It is for somebody who wants to quickly get a hold of a fine N2PK VNA and own a superb, completed unit and a set of accessories, without the hassle of the DIY project. This is not something, quickly slapped together and shoved in a box - it is an accurate and capable instrument, built with passion and skill. It is probably as good as it gets, short from a CNCed enclosure or an "oven"-ized unit.

Included in this sale:

 - N2PK VNA based on Ivan Makarov's v4.3 PCB, ALL of the components are from Makarov's/Paul's original BOM (no substitutions), Master Oscillator is by Connor-Winfield (not the VF pictured). Both detectors are shielded in separate RF cans. Inputs and outputs of each detector are also internally shielded from each other inside each RF can. Both DDS chips and the MO are all heat-sink cooled (MO is using separate heat-sink). Everything is hand-soldered, component placement and soldering work is impeccable (30 years of  experience). High-quality MA/COM gold-plated SMAs on the main PCB.
There was no rework during the building process whatsoever or any need for troubleshooting - everything worked the first time.
The Internal Multi-voltage Power Supply module is custom made (I have designed the PCB layout) using switching and linear voltage regulators. Shielded in a separate RF can and with extra noise filters, over-current and over-voltage protections - provides highly regulated and clean power.
The thermal design is using the extruded aluminum enclosure as a giant heat-sink, stabilizing the internal enclosure temperature.

Amphenol-RFX BNC connectors installed on the front of an attractive extruded aluminum Hammond enclosure. There are no holes or screws on the outside of the enclosure except for the stainless steel Allen-key screws attaching both face-plates. Custom designed graphics layout and durable plastic lamination of the brushed aluminum face-plates for a professional "Lab Instrument Look". Connections between LO DDS out and detector's LO INs are looped-through on the front panel for additional configuration flexibility.

The internal interconnects are done using gold-plated and stainless steel SMA connectors, semi-rigid RG-405 coax and special high-isolation (triple-shielded) Semflex mil/aerospace grade teflon / silver coax for minimal loss, phase errors, cross-talk and RF leaks, resulting in a very low noise floor. Extensive ferrite RFI filtering for all power and signal lines.
Everything is modular and interconnected using quality gold-plated connectors - front and rear panels, Main VNA board and Internal Power Supply Module - all can be easily disconnected from each other and removed if necessary. All you need to take the whole instrument apart is an allen key and a SMA wrench. All connectors are properly marked to avoid connection mistakes. The Main VNA PCB ground layers are connected to the chassis by 2 special edge mounted copper-beryllium clips - it is a solid friction mount for the PCB assembly.
Dynamic Range is between 120 dB and 130 dB as expected - on request I can provide noise floor plots for both detectors. Frequency range is the typical N2PK 0.05 to 60 MHz. Minimum voltage supply required at the rear DC jack (PS is using linear LDO regulators) is 13.4V (maximum recommended +18V).

 The Accessory connector has all extra control signals and +9V power for connecting a S-parameter Test Set with Adjustable Attenuator control, RF-IV Sensor or Transverters.
The presence of the two main power supply voltages +12V and +5V is indicated by LEDs

- External USB to Parallel  interface /w USB to Mini USB cable. The v4.3 VNA PCB has a parallel port interface and with this additional interface module it can be used with any USB enabled computer. The interface drivers are 100% compatible with myVNA software (the USB`
interface EEPROM is already programmed, only drivers need to be installed on the host computer). This converter is specifically designed for N2PK VNA by the creator of the MyVNA software. It is mounted in a separate die-cast aluminum enclosure for RFI shielding and it is allowing the user to effortlessly select Parallel Port or USB interface use.

- The standard N2PK T1-6T Reflection Bridge /w BNC connectors (Female silver-plated BNC DUT port). Mounts directly onto the VNA front panel connectors.

- N2PK VNA RF I/V Sensor. Uses only one VNA detector, feeding I and V samples from the DUT. Employs Makarov's PCB and ferrite cores for both transformers. Extensive internal RF shielding between components. Mounted in aluminum enclosure, native stainless steel SMA (f) connectors and HQ SMA-to-BNC between-series adapters already installed. Plugs directly into the VNA Accessories connector and mounts right on the front panel VNA connectors.

- Custom External Power supply - small, low-noise, regulated and filtered linear 16V power supply. Using external PS reduces internally generated heat and RF noise.

- A set of Open, Short and Load (50 ohm)  Male BNC cabliration standards ,an additional male BNC connector for use as a Test Fixture (same reference plane as the calibration standards) - just solder DUT directly. The Load standard is using special high-frequency, high-precision resistor.

- Custom, High Quality, shielded PC Parallel Port to N2PK VNA cable - extra long (12ft)

Price is set to $995 and includes insured USPS Priority shipping. Shipping to Continental USA ONLY! No international buyers please. Payment can be done by mailing a Cashier's Check or a Money Order only. Will ship in two business days of receiving the funds.

If you have any questions or you are interested in buying this unit - do not hesitate to contact me - ae1s (at)

I have built two N2PK VNAs - a smaller enclosure, BNC version with external USB converter (this is the one I am selling) and a larger Type-N connectors version with an integral USB. It seemed as a good idea at the time to build two units - one for portable / field use and another unit for my lab work-bench. As it turns out - only one unit covers completely my VNA needs and I decided to sell the extra one in order to raise funds for some future projects I would like to dive into. It just doesn't get used enough and it is sitting on my shelf, while somebody could have a good use of it.
As I stated above - no expense was spared when building this VNA - I was building it for myself and not in a hurry - I wanted to have the best, the N2PK design has to offer. I've used the highest quality components and materials I was able to put my hands on and took me months to complete it. The built process is very well documented here, on my blog - from August 31, 2009 and on. You'll find many pictures and comments regarding this unit.
I am not trying to get rich by all means with this sale, so let me be upfront - the cost of components and materials is somewhere between $700 - $800 (I have Digikey/Mouser/eBay invoices for most of the components and materials). It took me many weeks, if not months to collect all of the parts and build this instrument -  many hours of SMD soldering under magnification, painstakingly inspecting every single solder joint, a lot of  mechanical work on the face-plates, the semi-rigid coax assemblies and the PS Module, design work (CAD PCB layout for the PS, graphics design for the panels), wiring etc.
Frankly, I can not even put value on the time and labor this project so readily consumed. I think the sale price is fair and if it doesn't sale I won't be incredibly disappointed  - I have some mixed feelings about selling it anyway.

Monday, July 2, 2012

DIY Glow In The Dark Fob

After some experimentation with Glow-in-the-Dark pigment powder and creating the "fireworm", I came up with an application for it - an inexpensive but IMHO pretty cool solution for a GITD fob. This fob can be attached to any object, one might look for (or want to avoid) in the dark - flashlights, , keychains, backpacks, zipper pulls, water bottles, weapons, light switches (regular or pull-chain), cabinet handles, hand-held radios, etc - the list is endless. It is nothing fancy, but it is inexpressive, easy to make and very durable.
The bill of materials includes:
1. Fine particles Glow In The Dark powder - Europium activated Strontium Aluminate (green color is the brightest, followed by ice-blue in glow intensity). There are number of Internet sites selling it (,, etc).
Strontium Aluminate is the "good stuff" - it is VASTLY better than the old zinc sulfide pigment and after it is fully charged, it will glow for as many as 8 to 12 hours. (very bright for the first couple of hours and of course, 8 hr. later it will be dim but still visible in complete darkness). For comparison, the Zinc Sulfide GITD pigment will not be visible an hour after charge. Charging time, light intensity and spectrum are the main factors when it comes to glow duration.
GITD pigments work very much like a rechargeable "light battery" going thorough charging-discharging cycles. Light (UV emissions in particular - 200-450 nm wavelength) raises the electrons from a baseline energy level to an excited level. When the exciting radiation is gone, the electrons try to go back to their baseline energy level but get trapped in a "meta-stable" level from which they go to their baseline level after some delay.
The energy which excited them in first place is stored in the meta-stable level and then released when the electrons make the transition to their baseline energy level. This energy release is in the form of photon emission (light))
When purchasing, make sure that the pigment is manufactured as fine particles - not large particles which are then crushed, as breaking the crystals will change the glow properties.
2. Clear Vinyl Tubing - I used 1/4" OD but other sizes will work too. (hardware or home improvement stores). It must be tested beforehand for UV protection agents as I encountered tubing which contains such. (This cab be done easily by placing some of the GITD powder inside the tubing and exposing it to light)
3. Clear, LOW-ODOR Silicone sealant. Low-odor type is not very (or at all) acidic. Normally, as the silicone sealant cures, it releases acetic acid which might react with the pigment (again hardware/home improvement stores). I used the "Kitchen/bath" sealant as it is less likely to contain UV block agent but this is speculation on my part - I need to do some tests to confirm if such agent is present.
4. Small size cable tie
5. Strong, thick, braided type nylon string.

In addition, a small, shallow, colored plastic container, plastic spatula or flat tip screwdriver and a large syringe ( I got one from a pet supply store) are needed.

I mixed a few milliliters of silicone sealant with some of the glow powder. One must work quickly as the silicone will start curing once it is out of the container. I worked under a bright light, turning it off a few times, while adjusting the ratio of the mixture. The goal is to get as much glow powder as you can while still preserving some of the transparency of the mixture in a "test dab" approx 4-5 mm thick (hence the colored plastic mixing container). The idea behind this is to allow the light to "soak through" and charge the entire "glow core" of the tubing, even if it only comes from one direction. If the mixture is too "loaded" with glow powder it will become opaque and only the side, exposed to light during charging will glow (it will become also too thick to inject and not as flexible when it cures). Use plastic spatula to mix it very well (for a uniform glow) and load the mixture through the back of the syringe. I cut the vinyl tubing into 2 1/2" - 3" pieces and injected the mixture in each piece. While injecting, I stop when the mixture reaches about 1/2" from the opposite end of the tubing. Air bubbles can be avoided by first squeezing the air out of the syringe and also injecting in one smooth, continuous motion of the plunger.
It takes a couple of days for the silicone to completely cure as it is inside an almost sealed space. After that, the lower end of the tubing (where the injection was done) can be trimmed.
I made a small loop from the string with a double knot at the end. (If the string is thin, keep adding to the knot until it barely fits inside the tubing). I pushed the knot into the empty 1/2 inch portion of tubing and used a cable tie to squeeze the tubing right above the knot, trapping it. As an alternative, large-diameter wire-splice copper ferule can sliced to 3-4 mm rings and crimped - it might look better but I like the all-plastic version.

That's all! In an hour, I made over a dozen of these in green and ice-blue colors to mark different objects and devices. I like both colors but the ice-blue reminds me of Cherenkov radiation :-)
One neat thing is that because of the optical refraction properties of the 1/4" clear vinyl tubing, once filled with the glow mixture, the tubing walls are not visible anymore from the side - it appears as if the tubing wall is paper thin and the entire thing glows. In other words - the tubing wall acts as a lens, magnifying the GITD core.
I am not one these ARES freaks (on contrary - I have very little love for ARES) so I don't have an ARES go-box full of gear or the ridiculously tacky cooler turned into portable station (don't even want to discuss the ply wood versions) but these GITD fobs come pretty handy during power outages or camping.

The cool thing is that such GITD fob is VERY durable and can take a lot of abuse - it is 100% weather-resistant, soft and flexible, it will not break or tear easily and can be used for many many years. Most importantly for me - it is made entirely out of soft plastics and will not scratch the surface of  the object, which it is attached to. (metal fobs can scratch the anodizing finish of a flash light or damage powder coating, plastic surfaces like the display bezel of a HT radio and acrylic fobs get scratched themselves by metal parts)
Longer pieces can be even sewn to clothing - hats, jackets, shoes, gloves as a "tracer" and will not be affected by regular washing.
This GITD fob works best when used outdoors as it needs about 10-15 min direct sun light to fully charge (or a couple of minutes with a high-power flashlight will do the job too) - the longer, the better. In artificial lighting environment, it works better when charged with fluorescent, LED or halogen lights than the regular incandescent type.
If the object is normally always in the dark (in a box, pouch, cabinet) it is useless to have one of these - try tritium vials.

(Tip: For a neat GITD electric light switch face-plates, I used smaller OD tubing. Two holes (the size is the of the tubing) are drilled in the face-plate - approx. 3/4" apart and connected using a small file. This creates a small, elongated window. A slightly longer piece of the glow tubing is then attached on the back side with hot-melt glue.)