# VECTOR NETWORK ANALYZER IMPEDANCE

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#### fuseless

##### New Member
Do all vector network analyzers terminate the transistor under test with 50 ohms when measuring S-parameters?

#### Tony Stewart

##### Well-Known Member
you can use Impedance divider with any load but output must be 50

#### fuseless

##### New Member
Here are many application notes:
https://www.omicron-lab.com/applications/vector-network-analysis/application-notes/#

In one of the notes it shows setting the analyzer to 1meg and adding a termination resistor of your choosing.

I was just looking at a network analyzer with in input impedance of (50 or 1meg switchable).

Yes, I thought so. I have the original Motorola S-parameters for the 2N5179 RF transistor where the stated ZG and ZL=50 Ohms. I also have another set of S-parameters from Microsemi where ZG and ZL are unknown. The two sets don't nearly match. From what you've told me I think that Microsemi might have used an analyzer set at ZG and ZL=1MegOhm and used a couple of 75 Ohm shunt resistors across the input and output of the transistor.

#### SHI0701

##### New Member
Dear Gentleman, My name is Silvio Hideo, I´m looking for Vector Network Analyzer to do antena maching of Bluetooth devices.
Can some one suggest me some low cost equipament to I do this measurement?

#### dknguyen

##### Well-Known Member
Dear Gentleman, My name is Silvio Hideo, I´m looking for Vector Network Analyzer to do antena maching of Bluetooth devices.
Can some one suggest me some low cost equipament to I do this measurement?
If by low-cost you mean A couple thousand dollars or less, I don't think one exists.

##### Well-Known Member
The HP 8753E Network Analyzer, which is an excellent model and was, in its day, very popular in North America, sells used on ebay.com for around $2500 for 3GHZ and about$3500 for 6 GHz. At these prices, though, there is some risk of problems. Dealer prices are typically another $1K to$2K higher. This is relatively low cost for this quality.

For a PC attachment type of device, consider a USB box, one that uses your laptop as the user front end. Good suppliers include Keysight, Rohde & Schwarz, Copper Mountain Technologies, Pico Technology, Tektronix and others. These are still a bit expensive when new, cost about $5000 and up. If only doing antenna impedance matching, you can consider a one-port model such as Copper Mountain R54, which may be a bit cheaper. I found one model made in Germany, called PocketVNA which has a frequency range to 4 GHz and costs only US$490. I have no knowledge of this product other than what is on this website:
http://pocketvna.com/product/
This is not what I would call a high-performance model, but might be ok for your needs.

Another low cost unit, with 3GHz frequency range is the Wimo Mini-VNA Tiny antenna analyzer. It costs 428 Euros from Germany.

There are much cheaper VNAs out there sold in the Amateur radio community, but they typically have limited frequency range below 1.5 GHz and so won't be useful to someone doing work at 2.4 GHz for Bluetooth.

Other makers worth looking at include Megiq (2860 euros for 4GHz).