AQRP VIA, 2 Port Modification Instructions

This is actually based on the 2-port design from over 1 year ago (VIA Ver 1.9.1). You might have seen schematics on the website. When we evaluated it, there were problems maintaining 50 ohm impedances so we went to a 3rd mixer on a daughter board. After building a prototype and much testing it was determined that the 3rd mixer would work ......BUT the rework (cuts/adds) was too difficult for general implementation and would result in nothing but rework/wiring problems. A solution would be another VIA board but I don't want to do that with over 200 VIAs out there in the world. Must be able to upgrade existing units. 

Milt, W8NUE, decided to revisit the earlier design. Since the VIA circuit resistance at each end of the filter is ~120 ohms, we had to change the source impedance from the Si5351 to 86 ohms, and add 86 ohms as an additional load on the filter output. The 86 ohms in parallel with 120 ohms gives a 50 ohm source and load for filter testing. This would work, while maintaining 2-port and 1-port accuracy requirements. It's designed to be used in either a 2-port or 1-port mode/configuration.

1)	Remove R14 (20 ohm 1206 size resistor)….keep it for step #3. A spare R14 will be provided in the rework kit to cover any removal problems.  

      2) Cut trace between R15 and R11

      3) Solder R14 between ends of R11 and R16. a little tricky but doable. 
          Picture later.

      4) Make Port B connection to right most pad of old R14 and ground.
           I drilled a hole and came up from the bottom of the board with the 
          center coax. Picture later.

      5) Make Port C connection at the  junction of R11 and R14 and ground
          I drilled a hole and came up from the bottom of the board with the 
          center coax. Picture later.

      6) Change F0 attenuator to 86.8 ohms output impedance by removing 
           and adding the following: R1=64 ohms, R2=147 ohms, and R3 178.5
           ohms all 0805 resistors.  

      7) Connect a 86 ohm resistor across filter test fixture (you make that) 
           output terminals

These mods make the impedance seen at ports B and C  50 ohms.  That is, the source and load impedance of the filter will be 50 ohms.

Calibration procedure--

Connect a short between ports B and C, run the Reference Scan

Connect shorting load to both ports B and C, run the Zero Scan

Filter Scanning--

Connect the filter to be tested between ports B and C, using a test fixture that has an 86 ohm resistor across the filter output (Port C), run the Filter Scan

PARTS

I would prefer you find your own parts but can provide the above 5  SMT resistors for $2 postpaid via PayPal.