Tuesday, 27 January 2015


The Ozqrp DDS VFO kit is a low cost direct digital synthesis (DDS) VFO capable of operating from 1MHz to 10MHz with programmable IF offsets , making it suitable for use in a variety of home brew transceivers or receivers.


1. Stable frequency
2. Simple to operate using a single rotary encoder control with press button switch.
3. Bright 16 character by 2 line LCD display.
4. Output frequency range of 1MHz to 10MHz.
5. Selectable 1KHz, 100Hz or 10Hz frequency steps.
6. Tuning lock control.
7. Displays power supply voltage.
8. Programmable IF frequency. Ensures the displayed frequency is the same as the transmitted frequency.
9. Programmable IF offsets: Minus, Plus, None.
10. Draws only 80mA at 13.8V DC (with LCD backlight).
11. Spurious outputs at least -45dB.
12. Typically 300mV pk-pk sine wave output.

I ordered the DDS VFO kit from in February 2013 - at the time the VFO was only available as a partial kit consisting of the PCB with pre-soldered DDS IC, crystal oscillator, a pre-programmed microcontroller, the rotary encoder and an LCD display. All other components needed to be sourced separately. At the time of writing (May 2013) there is now a complete kit available for AUS $65 which contains all the required components.

The kit I ordered was shipped from Australia and arrived in Ireland in less than 2 weeks.
It was well packed in proper anti-static packaging –


Unpopulated PCB showing the pre-soldered surface mount DDS device

Construction was completed in about 3 hours of work. There is only one surface mount part and this was supplied pre-soldered so the assembly was very straightforward. The PCB was of good quality with silk-screened logos and plated through holes.

It is advisable to use an anti-static work surface and a grounded wrist strap to avoid damaging the sensitive devices.

Completed PCB –

Power on -

The VFO defaults to 7.100 MHz with 1kHz steps  . Battery voltage is displayed on the LCD

Pressing on the rotary encoder changes the steps – 1KHz/100Hz/10Hz

It is possible to program an IF offset for the VFO if it is to be used in a transceiver that uses an intermediate frequency. This can be set up from a setup menu, which is accessed by holding down the encoder button while powering on the device.

I'd recommend this kit to anyone who is looking for a simple yet very stable VFO to drive a home brew transceiver or receiver.

When I built this back in 2013 it was only available as a partial kit , however it is now sold as a complete kit.  

I have since built the MST400   ( mark 1 version ) 40m 5w SSB transceiver from OzQRP and used this DDS as its VFO.  more details on this to follow . 

For more information refer to the OZQRP web site here -

Thursday, 1 January 2015

Spilsbury and Tindall SBX-11 Portable HF SSB Transceiver

A few months ago I managed to buy a Spilsbury and Tindall SBX-11 Portable HF SSB Transceiver on eBay.  This radio is a piece of Canadian history having been used for arctic and polar communications for over 40 years.

The SBX-11 is designed to provide 10w SSB on 4 crystal controlled channels in the range of 1.6 to 8 MHz.
It is self contained in a robust water resistant enclosure and is powered by 9 D cells - Alkaline or NiCAD.


The top lid of the SBX 11 covers the front panel and the hard wired microphone .

it also contains a set of brief operating instructions  -

the top lid clips on to the main body of the set to act as a stand

the bottom lid is the battery compartment which contains 3 tubes each with 3 D cells.

My set has already been converted to the amateur bands and has been crystalled for 1918 KHz, 3745 KHz and 7060 KHz on LSB.   Each channel requires 2 crystals and 2 coil packs , however there is a modification available for single crystal per channel.

Internal view showing crystal banks and RX/TX coil packs on right hand side -

As the set is crystal bound I hadn't much luck in making any contacts on it , however today was the IRTS 80m counties contest so I decided to try it out on 3.745MHz and I was able to make 4 contacts - EI2KA ( Cork) , EI9DZ ( Leitrim) EI8JN ( Galway) and EI8HL ( Waterford).

I was thinking about adding a DDS VFO to this set, however I think I will keep it in its original condition . Might try and add a 60m channel to the 4th position if I can get a suitable coil pack.

For more information on the SBX-11 see here .
VA7BC has posted an interesting video of the SVX-11 in use here.

there is also a good Yahoo group here