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