QRP-Labs filter adapter for NanoVNA

This page is work in progress and will be updated frequently.

Introduction

I had a few QRP-labs lowpass filters and bandpass filters kits laying around and because I had nothing better to do this afternoon, I fired up the soldering station and assembled them. After that they need to be tested and tuned.

Owning a NanoVNA for a few months now (and hardly use it because for antenna stuff i use my RigExpert AA-600), I decided to use the NanoVNA for tuning the filters. So from some pieces out of my junkbox (a piece of double sided pcb, 2 sma chassis and a header cut in 2) I build this simple filter holder allowing me to test and tune the filters to my requirements.

nanovna_qrplabs_01

 First I drilled 5 holes for each side of the filter (the filter has 4 pins, but I need a via to connect the top and bottom layer) using a piece of perforated PCB. And with my Proxxon mini tool I mild a small track to the edge on both sides. 

nanovna_qrplabs_02

 Soldering the bottom side, the via (by using a piece of wire), the SMA chasis parts (edge side) and the headers.  

nanovna_qrplabs_03

 Soldering the topside of the PCB (the SMA chassis parts to the ground plane).

nanovna_qrplabs_04

All done, now its time  to do some testing.

Testing 

First I tested the newly build  15m lowpass filter.

nanovna_qrplabs_01

  Close-up 

nanovna_qrplabs_01

 Result looks good. -0.33 dB on 21Mhz. 

nanovna_qrplabs_01

Next I tested a 30m bandpass filter.  

nanovna_qrplabs_05

And after some tuning : -1.37dB on 9.93 Mhz.  

nanovna_qrplabs_06

Very happy with the result. 

Thinking about it and finding the ease for tuning, IMHO every QRP-Labs filter user (with out a spectrum analyzer with TG) should have one.  

  

Calibration  (Update 2020-04-07) 

When using the NanoVNA and change cables, adapters etc, you should calibrate it (mental note to my self).  

The popper calibration procedure is : 

  1. Got to the calibration menu by pressing CAL.
  2. Reset the current calibration state by pressing RESET 
  3. Enter the calibration menu by pressing CALIBRATE
  4. Connect OPEN standard to the CH0 port and press OPEN.
  5. Connect SHORT standard to the CH0 port and press SHORT.
  6. Connect the LOAD standard to the CH0 port en press LOAD.
  7. When you have 2 LOAD standards : connect a LOAD standard to CH0 and one to CH1 and press ISOLN.
  8. When you just have one LOAD standar : connect it to CH1 (leaving CH0 unconnected) and press ISOLN.
  9. Connect cables to the CH0 and CH1 ports, and connect the cables with a hrough adapter and press THRU
  10. End calibration by pressing DONE.
  11. Save it in a desired save slot by choosing SAVE - SAVE[0..4]

Experimental calibration tool 

Use at your own risk, I'm not a expert just a OM who does hamradio for the hobby. 

When you want to calibrate as close as posible to the adapter, you can't use the calibration standards. For that I made a simple calibration tool (it's good enough for HF).

 adapter_cal_01

adapter_cal_02

Note : the 2 via's to connect the both groundplanes aren't drilled yet. 

adapter_cal_03

On the right you see the 2 100 Ohm SMD 1206 resistors.

adapter_cal_04

The bottom view.  

Using this experimental calibration tool.

Connect the Adapter with 2 short SMA jumper cables to the NanoVNA.

Got to the calibration menu by pressing CAL.
Reset the current calibration state by pressing RESET 
Enter the calibration menu by pressing CALIBRATE

Don't connect anything to the adapter. 

adapter_cals_02

In the Calibration menu press OPEN.

adapter_cals_01

Place the calibration tool on the CH0 socket with the short (the side without the resistors).

adapter_cals_05

In the Calibration menu press SHORT.

adapter_cals_03

Place the calibration tool on the CH0 (adapter IN) socket with the load (the side with the resistors).

adapter_cals_06

In the Calibration menu press LOAD.

adapter_cals_04

 Place the calibration tool on the CH1 (adapter OUT) socket with the load (the side with the resistors).

adapter_cals_07

In the Calibration menu press ISOLN.

adapter_cals_08

 Place the calibration tool on the adapter with the pass through trace on the side of the SMA edge connectors.

adapter_cals_10

In the Calibration menu press THRU.

adapter_cals_09

End calibration by pressing DONE.

adapter_cals_11

Save it in a desired save slot by choosing SAVE - SAVE[0..4]

Now is the question : did it work ? 

It did a little. When I calibrated the NanoVNA with the supplied standards, the bandpass filter measurement had a peak of -0.83 dB.

adapter_cals_14

When I used the calibrated tool on the NanoVNA  the bandpass filter measurement had a peak of -0.56 dB.

adapter_cals_13

Which would indicate that the entire adapter configuration would cause -0.17 dB gain (or 0.17 dB attenuation).

But then again I'm not a expert just a OM who does hamradio for the hobby and does a lot of experimenting to get hands on experience with this matter. 

 

 
A nice PCB (Update 2020-04-06) 

Knowing that not all people have tools to mill PCB's by hand, this morning I took time to create the schematic for the adapter in KiCad.

That way I could make a PCB design from it.

adapter_sch

adapter_pcb

The cool thing from KiCad is that is also has a 3D viewer. Unfortunatly the SMA Edge connectors aren't in the 3D shape library.

adapter_3d_layout

But it looks cool anyway. I also designed a small case which you can 3D print so you won't get shorts testing your filters.
Check out : https://www.tinkercad.com/things/8QNIUS7X40f 

 

When the PCB design was ready, I have ordered a pack of 10 prototype PCB's at https://www.pcbway.com/ with slow delivery. During the order process you get a image rendered based on you gerber files how it would look in real-life..

adapter_layout

When I receive the prototypes I will check if they are OK (a small design error is easily made) and I keep 3 (2 for my self and one for the hamradio club) and the rest will be sold a cost price with a addition of a small fee as a token of appropriation / commission to support my work. On request even completely assembled with soldered headers, edge connectors and a 3D printed case. But remember to read this page first.

PCB's are in the house  (Update 2020-05-16)  

Today I received my long awaited package from PCBWay and I just had to assemble one adapter

nanovna_qrplabs_06

Bottom

nanovna_qrplabs_06

The 3D printed holder for the adapter PCB.

nanovna_qrplabs_06

And the test.

nanovna_qrplabs_06

Can only say one thing : it looks cool :-) 

For those who want a adapter, I have 7 spare PCB's in stock for euro 2,50 each. Checkout my ForSale page. 

PCB's are all sold (Update 2020-05-20)  

All the PCB's I had on stock are sold. Thank you buyers for your interest.

When there is a large enough demand for this PCB I may start up a new batch. But to keep the price low I use the standard shipping method. Due to the Covid19 the shipping times for standard mail are very long (up to 60 days). I could switch to DHL  for transport, but that would almost double the price of the PCB to almost euro 4,50 for each PCB.  

But when your in a hurry to get these PCB's we could work something out via OSHPark, for that check out my ForSale page for options. 


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