Saturday, December 8, 2018


SVT MMDVM first calls

The Digital Voice ( DV ) for the ham radio have started a few years ago but to build a hotspot ( a tiny personal half duplex repeater ), you will need some pricey equipments like DVStick with AMBE-3000 vocoder and USB interface plugged into a Raspberry Pi with an Arduino Mega to drive the UHF transceiver. 

It all started around Sept 2017 when the price of DMR radio was getting below RM1,000 and a few of us purchased a TYT MD-2017, one of the more popular DMR radio at that time.

Secondly, without a DV hotspot, having a DMR radio is kinda useless unless you are within the range of a DMR repeater in your area.


Thanks to Jonathan Naylor G4KLX ( ) (and many many people people) that created the MMDVM, a software that integrated multiple hardware ( teensy, Arduino DUE, STM32F1, STM32F4 ) and Raspberry Pi running pi-star ( ).

When I saw the hardware requirements, I noticed that I actually have ALL the hardware with me, STM32F103 red-pill, Raspberry Pi and they were also using a version of Arduino called stm32duino

A few STM32 red-pill I purchased previously

The only missing piece was the UHF transceiver called RF7021SE module plus changing the TXCO to 14.7456Mhz. So I started doing my research on different board designs and immediately design a single board layer to test out my design.

MMDVM boards

MMDVM boards

Here is the first version after many iterations and because it was a single layer board, I had to place the SMD LED at the bottom of the board.



Once my designed was almost finalised, I bring it to Uncle Chow ( 9M2CF ) to convert my PCB design to a single layer PCB.

SVT MMDVM negative

SVT MMDVM etched

SVT MMDVM copper removed

After some UV exposure and chemical baths, I got the SVT MMDVM board ready to be soldered.

SVT MMDVM fully soldered

SVT MMDVM top side with red-pill

SVT MMDVM running

Fully connected to the RPI 1 and pi-star software loaded.

SVT MMDVM connected to RPI 1

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.


Summary Links :-

Sunday, February 26, 2017

SVTrackR with new PCBs and case for the LCD

LCD mounted on windscreen

MicroModem & SVTrackR 


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


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 ..

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.