Saturday, May 27, 2017

Measuring capacitance of variable capacitor (varicap)

This is just a short post of measuring the capacitance of the variable capacitor at maximum capacitance.. 

The first picture is the measurement taken at both the stators ( stationary plates), this is used for magnetic loop as per the diagram below.

Capacitance at both stators

Position of variable capacitor


The below picture measure the capacitance between the stator (stationary plates) rotor ( moving plates).



Wednesday, May 3, 2017

Variable Capacitor for ham radio

A short posting with pictures of variable capacitors made using a CNC machine by 9W2CEW. The CNC cut both the rotor (moving plates) and stator (stationary plates) in one go. Refer to the last picture below.

This design is usually found in loop antenna to change the capacitance value from the shaft.





Side view

Variable caps with laser cut cover

0.7 mm aluminium plates

Sunday, April 16, 2017

40m vertical balcony antenna using PAC-12 , adjustable coil and telescopic whip

Just want to share an updates on balcony antenna using the following setup :-

PAC-12, coil and whip antenna with mounting
PAC-12, coil and 5.6m telescopic whip

Adjustable coil
Equipments :-
Antenna Base : PAC-12
Coil : Adjustable coil ( max inductance is 23uH )
Antenna : 2.5m or 5.6m telescopic whip at 2.29m length
Frequency : 7.080Mhz ( near JT65 freq  )


Telescopic whip ( either 2.5m or 5.6m length) at 7 1/2 feet ( 2.29m ) and the adjustable coil at 21.31uH.

This is the reading of the antenna analyzer at JT65 frequency, complex impedance of  25 + j0, SWR of 1.26:1, therefore I do not need to use any antenna matching tuner. When I transmit at 25W, the meter reads an output power of 20-22W going out to the antenna.

The antenna analyzer is a version of SARK100 called MR100. The details at summary links below.

MR100 showing the SWR
LC100A LC meter to measure the inductance.

LC meter show the coil henry readings


The below is the result of the short 40m balcony antenna, I am able to reach both Europe and USA using it.. In my condo, I am almost surrounded with highrise buildings and not much openings.



9W2SVT JT65

Summary Links :-


Sunday, February 26, 2017

SVTrackR with new PCBs and case for the LCD

LCD mounted on windscreen


MicroModem & SVTrackR 

SVTrackR PCB

Modem PCB


Making of the acrylic casing ...

Acrylic cover for LCD

Front and back cover
Red acrylic lasercut

Red acrylic parts

Installed acrylic


Saturday, September 19, 2015

Making of Surface Mounted (SMD) DIY PCB TNC


SVTrackR SMD TNC

In my learning process of making my own DIY PCB and after ordering some common SMD components ( capacitors, LEDs &, resistors ), I decided to design a small and functional TNC that only need 4 connections to handy and a few jumper wires to Arduino.

*** This is the first time I ever successfully made a DIY PCB.

Let's start with the design on EagleCAD ..

EagleCAD SVTrackR SMD
I designed this small 28x23mm board for fun and to learn on how to solder SMD parts on DIY PCB. I made everything on a single layer. The only drawback is the two red and green LEDs are at the bottom where the copper traces are located.

Generate gerber and do a 3D view of the board. This method is easier to spot any errors.

3D Gerber view


Printed out for UV transfer to UV PCB
This is the tracing paper before the UV treatment. Thanks to Uncle Chow, 9M2CF made me a nice photo frame to hold the UV sensitive PCB and tracing circuit in place.

PCB holder / cover

UV lightbox

UV lightbox UV LED turned on

UV lightbox and photoframe cover
After like 15mins ( long duration was due to the diffused and evenly distributed UV light ), I drop the PCB into sodium hydroxide 0.7%. This is removed whatever parts exposed to the UV light and leaving the green part for second steps.

Exposed copper after Sodium Hydroxide bath
 Once the Sodium Hydroxide bath was done, I wash it and dump into the second solution - Ferric Chloride to eat away all those exposed copper.

Ferric Chloride bath
After a few shakes and turns, all the copper were wash away leaving the green portion of the copper traces.



I use thinner to clean away the green stuff and leave you with a shiny copper traces. Not bad for a first timer doing SMD PCB.

Now for the drilling and soldering part. A tip from 9M2CF, always solder before drilling as the solder will guide the drill bit into the holes to be drilled.

Drilling holes
Soldering SMD resistors
With too much solder at the pads, those SMD 1206 resistors are uneven on top ... or I was using a really fat tip.

SMD SVTrackR TNC back

SMD SVTrackR TNC front
After a while, got all the SMD and through-hole parts soldered. Need to find the SMD parts for the 100K POT. This is the one I currently have in my part inventory.

Add caption



Comparing sizes between the old MicroModem with Mini Pro and the new SMD TNC that will run from either Arduino Mini Pro or Arduino Nano.




Saturday, September 5, 2015

SVTrackR 1.62 : Dashboard speedometer & APRS Decoder

SVTrackR I2C LCD


One of my users suggested that I split the display from the APRS Tracker so that he can placed the SVTrackR together with the handy below the seat. I liked this idea and explore the unused I2C pins on the Arduino Mini Pro.

Once I found out that the I2C can goes up to 6m of length, I made a 1 meter cables and started my tests on the Eduboard I built with Serial and I2C header pins at the bottom right of the blue PCB.
I have also connected a APRS Modem to the Serial Rx,Tx pins.


SVTrackR 162 on Eduboard


Once I finalised to use the blue 16x2 I2C LCD, I search on Thingiverse for a 3D printed casing. I found this one below suitable and ask around for pricing and where to get it printed.

16x2 LCD I2C 3D casing
As I made my codes with #ifdef definations for OLED, I just added more #ifdef for 16x2LCD and format the display according to the size of the LCD, 16 characters by 2 rows. As these screen are physically bigger than the 0.96 OLED, the resolution is only 16x2 text whereas the 0.96" OLED can goesd up to 7 lines of 25+ characters.

As my main screen should be the large digital speedometer with number of satellites being tracked and heading in degrees, I will rotate to 2 other screen for other statistics like Rx, Tx packets, distance to base and altitude from the GPS receiver.

In order to displayed decoded packets, I wrote a checking to display the decoded packets for 10 seconds before switching back to the speedometer.

Below are some of the images taken from my dashboard, it fits nicely with the large number displaying the speed or other info.

SVTrackR on dashboard

SVTrackR decoded packets

16x2 I2C LCD during initial tests


I am still in the process of getting a 3D printed casing for this.



Tuesday, August 4, 2015

Tuning HF antenna with SWR Bridge and Rigol Oscilloscope

After viewing this Youtube video from W2AEW on #112: Use an Oscilloscope and Signal Generator help tune an HF Antenna, measure complex impedance, I decided to do a similar SWR bridge with a AD9850 as a signal generator.

Front of SWR bridge

Back of SWR bridge

SWR bridge with 3W 50ohm and 2x1K resistors
The actual circuit was on the above mention Youtube video.

SWR bridge mounted on Dremel Vise


Arduino + AD9850 + 8digit 7segment with VFO
I had the AD9850 on top of the Protoshield with a large 8 digit 7-segment display as the signal generator frequency with a rotary encoder as a VFO.

Sinewave of 50ohm compared to 50ohm terminator
Almost match impedance
The connection from the SWR bridge are BNC connector with a T-joint to the Rigol DS1052E with a 50ohm terminator. This ensure both ends are 50ohm terminated.

 To check the HF antenna impedance visually, turn VFO to the desired frequency and visually check the yellow (50ohm reference) and blue ( antenna ) sinewave. The above image is an almost match impedance. Once the two sinewave are close enough, turn the coax switcher to the IC-7200 and the SWR reading will be quite low.

Unmatch impedance
The above is an example of an unmatch impedance, with such big differences in the sinewave, it is almost certain the SWR reading on the IC-7200 will be very high.