OZQRP DDS VFO kit

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.

  

Features:
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 http://www.ozqrp.com/shop.html 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 - http://www.ozqrp.com/index.html

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.

SBX-11

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 SBX-11 in use here.

see also SBX-11 group here  - https://groups.io/g/SpilsburySBX11/ 

Component Tester

I recently came across a low-cost component tester on eBay  - see eBay item 361094470192.

For about €20 including shipping it looked like a useful piece of equipment as it is capable of testing and measuring both Bipolar and FET transistors, Capacitors ( including ESR measurement ) , resistors , inductors and diodes.

I ordered one and it took about 3 weeks to arrive from Hong Kong.

this is not a detailed review , just a few photos of the device testing a few random components.

The tester is powered by a 9v battery and powers up to the following splash-screen -

First I plugged in a bipolar NPN transistor into the ZIF socket and pressed the 'test' button .
It identified it correctly and indicated which pins on the ZIF socket corresponded to the emitter , base and collector.  It also displayed the hFE  and forward voltage measurements for the device.

Next I tried an IRF510 MOSFET  -

A 100 uF electrolytic capacitor -

An inductor wound on a ferrite toroid core -

A 6.8k resistor -

A 10 nF capacitor  -

quite a useful device for €20 !

Clansman PRC-351 - removing the 150Hz tone

The Clansman PRC-351 is a military VHF manpack set that was manufactured for the British army in the late 1970s .  It is fully synthesized and covers 30MHz to 76MHz in 25KHz steps, so it is suitable for use on the amateur 6m and 4m bands.

Power output is about 4 watts of FM, however an optional 20w clip on amplifier is also available which increases this to 20w .

With the British Army’s move to the newer Bowman series of radios, many older Clansman series radios are becoming available on the surplus market at reasonable prices.  I picked one up for less than €50 although I then had to spend a further €20 on a 24v/1Ah battery and €15 on a clansman headset.

The complete set is shown below –

 

As the radio has a BNC socket in addition to its 1.2M whip antenna , I was able to connect it to an external 4m half wave antenna and was able to make a couple of contacts on 4m to Artur EI7GMB and Michael EI3GYB  - distances of 15KM and 40KM respectively – not bad for 4w out.

Unfortunately due to the set’s 25KHz channel spacing it does not cover the Irish 4m calling frequency of 70.2625MHz, so I needed to set up contacts on another 4m radio first then QSY to a 25KHz spaced channel to make a contact.

Both Artur and Michael commented on the loud 150Hz tone present on the transmitted audio of the PRC-351. This is due to the military tone squelch used by US and UK military radios.

  

A google search lead to the PRC-351 Yahoo group which had a note on how to disable the tone squelch.

The process is as follows –

-       Disconnect the battery, antenna and audio accessories.

-       Open the 4 Allen bolts on the side of the set containing the audio sockets

-       Carefully remove the end panel of the radio – it is connected to the main radio body by a fragile ribbon cable

-       remove the connector joining the end panel to the radio.

-        

remove the 4 Allen bolts on the control panel  and slide the radio out of its housing .

Locate R9 on module 13 – this is the preset resistor that adjusts the level of the 150Hz tone.

turn this pot fully anti-clockwise

Re-assemble the set and you are done.  Watch out for the drying agent sachets included in the case to protect it from condensation

After this simple adjustment Artur confirmed that the 150Hz tone was gone and the transmitted audio sounded much better.

More information on this interesting radio is available on the VMARS web site - here


http://www.vmarsmanuals.co.uk/newsletter_articles/prc351pt1.pdf


http://www.vmarsmanuals.co.uk/newsletter_articles/prc351pt2.pdf


MKARS 80 QRP SSB Transceiver for 80m

MKARS80

The MKARS80 is a QRP 80m SSB transceiver kit developed and produced by Steve Drury (G6ALU).  The design is derived from the BITX20 transceiver but with the added refinement of an LCD frequency display and ‘Huff and Puff’ frequency stabilization of the VFO.  The name MKARS80 is derived from the Milton Keynes Amateur Radio Society of which Steve is a member.

The MKARS80 provides the following features –

• Full 80M LSB coverage (3.5 - 3.8MHz)
• ~ 5 Watts output power
• Single conversion superhet with 4 pole crystal filter
• Frequency display with "Huff and Puff" circuit for stabilisation
• Modulation monitor - helps stop over modulation
• Volt meter - useful for battery operation
• Reverse polarity protection (fuse protected)
• Supply voltage 10 to 16v
• Current consumption – 120mA (RX) 1.2 A (TX)
• Microphone – low cost electret
• Speaker – 8 Ohm

A full kit of parts for the MKARS80 is available from http://www.radio-kits.co.uk/mkars80page.html for only £62 including an undrilled case and P&P to Ireland.  This is excellent value for money considering the quality of the kit.

The PCB is a high quality plated through hole, silk-screened fibreglass, and all components apart from speaker and microphone are included in the kit.  

Source code for the PIC microcontroller is also available to download should anyone want to customize their MKARS80 firmware.

Construction should be possible in a couple of evenings however I probably spent about 15 hours on construction over a number of weeks.  The build instructions are very well written and easy to follow. There is also an active Yahoo group for MKARS80 constructors here -   http://uk.groups.yahoo.com/group/mkars80/. Steve the designer of the kit monitors this group and is very quick to respond with advice to any constructors that run in to problems. 

I had a couple of minor problems in constructing the kit – I installed the LM7805 voltage regulator with the incorrect orientation. Luckily I measured voltages at the various test points as described in the construction manual prior to installing the PIC and the LCD , so I was able to resolve the problem before installing the sensitive devices.  Due to the plated through hole PCB I found it quite difficult to desolder the incorrectly installed voltage regulator and I ended up lifting some of the pads.  In the end I resorted to the ugly hack of installing the voltage regulator on the solder side of the PCB rather than on the component side. Not pretty, but it works.

I would recommend double checking the orientation of all semiconductors before soldering them.

The second problem I had was that I found the receiver to be very insensitive when doing some initial running around on 80m – I could barely hear a station that was booming in on my main transceiver.  This problem turned out to be due to a badly soldered joint on one of the toroids in the output low pass filter (also used on RX) . It can be difficult to get a good joint on the enamel-coated wire used for winding the toroids , even if you scrape and pre-tin them before installation.  I would recommend checking continuity of the solder joints after you install them.

Eventually I had a fully populated, tested PCB –

PCB – Component side

PCB – solder side

After completing the electronics side of things I needed to do some metal bashing as the supplied aluminium case is not pre-drilled.   There is a drilling template available for download from the radio-kits.co.uk site. Make sure you check that your printer is not scaling the template down in size when you print it  - I found that the first time I printed it out, acrobat reader was scaling it back to 95% of its original size.  Double check that the measurements are right before you start to cut.

The round holes were easy enough to drill – start with a small drill bit to make a pilot hole and then step up to a larger size.  A small needle file was used to de-burr the holes after drilling.

The rectangular slot for the LCD was more time consuming – I needed to drill a series of small holes just inside the line of the template. This was then filed down to produce a smooth edge.

After boxing it up I needed to provide a speaker and microphone.  A standard  set of  PC headphones was used for the speaker and for a microphone I used an old PMR mic from the junk box after removing the dynamic insert and replacing it with a cheap electret mic insert.

This radio performed well and allowed me to make many contacts throughout Ireland and Europe. In particular it worked well in the 2012 IRTS 80m counties contest with > 20 contacts made in an hour. 

Overall I can highly recommend this kit for anyone looking for an interesting home construction project without having to source all the components yourself.

New Galway VHF group blog

There is a new blog for the Galway VHF group here which provides some information on our upcoming projects  which include a new 70cm repeater , a 4m echolink gateway and an APRS iGate.