[hpsdr] VNA brigde

[Dick Faust]

Tony

The VNA bridge is essentially a Wheatstone Bridge.  Instead of using a 
"battery" and a DC micro ammeter it uses an AC source and an AC "meter".
For RF applications the AC source is often called a transmitter [signal 
source] and the ac meter is a receiver [detector].
For broadband RF applications there are attenuators on the signal and 
detector ports to maintain an impedance [50 ohms] for the transmission 
lines that connect to the signal source and detector.

The VNA bridge actually has 4 ports.  Signal IN, Detector Out, Reference 
Impedance, and Unknown Impedance.

Thus the [low power] transmitter is connected to the "IN" port, The 
receiver [very sensitive to high power] is connected to the "OUT" port, 
and the "Unknown Impedance" is the circuit under test.  Most often the 
"Reference Impedance" is a 50 ohm 1% [or better] resistor that is an 
interigal component of the VNA Bridge.  Some bridges have provisions to 
use an external reference circuit or component.

Use only Hermes and the VNA software with a bridge.  DO NOT use your 
Linear Amplifier !

The ARRL Handbook has more information on Wheatstone Bridges and RF 
Measurements.

Dick K9IVB
On 3/11/2014 4:20 AM, Tony Hagen wrote:
> Hi Dick,
> I just downloaded the VNA bridge gerber and schematic.
> There are 3 ports IN, OUT and ref OUT.
> Could you please describe me where exactly this will fit in. I have a 
> Hermes and a Linear Amplifier.
> 73s
> Tony