Designing and Building a Two-Tone Generator

I wanted to measure distortion in my 2m SSB-transmitter and PA. A two-tone test generator (see chapter 4.5 in this document) can reveal distortion in linear amplifiers so I decided to build the Elecraft 2T-gen on a piece of Veroboard. The 2T-gen user manual including a circuit diagram is found here.

There are two sine wave oscillators in the Elecraft 2T-gen. The first one is at 700 Hz, and the second one at 1900 Hz. I tested both oscillators with an analog oscilloscope. The 1900 Hz tone appeared perfect on the screen, but the 700 Hz tone showed distortion (clipping), and this is not acceptable in a test generator. Obviously, the problem was too high amplification in the circuit, and this pointed to poor AGC control.

I tried to solve the problem and eliminate the distortion. After some time, I gave up the MOSFET-based AGC and decided to implement a different method: Using a light bulb as automatic gain control. Here is the final circuit diagram:

Two-tone generator: circuit diagram.

I decided to create a new PCB for the two-tone generator. This PCB is visible in the photo below.

The generator is mounted inside an alu-box.

Front plate of generator.

A small 12V 40 mA light bulb worked just fine as AGC. The settling time (stable amplitude) is about 2 seconds. If you are looking for a similar light bulb on ebay.com, I recommend searching for "12V 40mA".

OZ1BXM Lars Petersen
Homepage: oz1bxm.dk

My experience with PCB manufacturing in China

I am working on a project which requires a printed circuit board.

First thing was to buy a software package for drawing the PCB layout. I picked Sprint-Layout. The price was fair (50 EUR), and I've had a good experience with another of their products (sPlan for drawing circuit diagrams).

I used Sprint-Layout for drawing the PCB.

    

I decided to try PCB manufacturing in China. I choose PCBgogo mainly because of the user recommendations on their website. Their prices seemed fair, and their product quality seemed just fine. Their minimum order was 5 pieces. I decided to order 10 x PCB single sided, dimensions 100 mm x 48 mm, payment by PayPal.

Logo of the PCB manufacturer.

Once the PCB layout was finished, I created Gerber files using the Sprint-Layout export function. The Gerber files were zipped and uploaded to the PCBgogo homepage. I soon received a mail from a person in the company. I had forgotten to include board outline data and drill data. I created the missing files and uploaded a new zip-file. The new file was approved, and production began.

The finished PCBs were shipped by DHL from China to my address in Denmark. The packet was delivered at my doorstep one week after file upload. That was fast!

PCB made in China.

The final price including shipping turned out to be 4.10 USD per PCB. The quality of the PCBs were excellent. I was a good experience for me letting PCBgogo produce the PCBs. I will certainly do this again when the need for other PCBs arise!

Regards from OZ1BXM Lars
Homepage: oz1bxm.dk

scQRPions: QRP Challenge Rules

scQRPions: QRP Challenge Rules: Starting January 1st 2016, and each year thereafter, we will be embarking on a challenge to work (not confirm) 100 DXCC entities in 100 days or less.

Remarks from OZ1BXM:

I discovered the QRP Challenge yesterday. You need to work 100 DXCC entities during 100 consecutive days or less. Your start-date and end-date must be within the calendar year 2016.

May-June-July is a good choice for QRP Challenge participation.

The rules of the QRP Challenge are pretty much the same as for the ARRL QRP DXCC diploma. Club membership is not necessary. QSL-cards are not needed - you simply submit a signed log. As of today, there are 13 participants, and only one from Europe. N4MM is in the lead - he worked 100 DXCC in just 8 days!

The QRP Challenge is backed up by the North Carolina DX & Contest Club (NCDXCC), South Carolina DX Association (SCDXA), and Greer Amateur Radio Club (GARC) in South Carolina. Program coordination is by Ariel Jacala NY4G.

I feel tempted to participate. As you can see in the figure above, the months of May-June-July are well suited for an European station like me as there are 4 major contests during this period.

Regards from OZ1BXM Lars Petersen
Homepage: http://oz1bxm.dk/

Writing for new hams

I have been a radio amateur for several decades. During all this time, I have collected experience in different fields. I wanted to give something back to the newcomers within this wonderful avocation. So I decided to write some articles aimed at the new ham and publish the material in the Danish national ham radio magazine "OZ". It is my hope, that new hams will be inspired and power up the soldering iron and start build electronic circuits.

My concept is KISS (Keep It Simple Stupid). The builder should be able to get the construction up and running during a weekend. I recommend building circuits without a factory produced PCB and using a Veroboard instead. Flexibility in component placement is maintained this way. 

Sourcing of components is another challenge that faces the new ham. It is an advantage if the circuit can be built using standard components, and that is my goal. A project should not halt due to lack of special parts.

One example of such a beginner's project is the 1 kHz sine oscillator (circuit diagram above). I tried different oscillator circuits before I settled with the phase-shift oscillator. I achieved a stable and clean output by adding buffers between the different filter stages. The result was a simple sine oscillator which is easy to build by new hams. 

The finished 1 kHz sine oscillator.

Regards from OZ1BXM Lars Petersen

Homepage: http://oz1bxm.dk

My VHF/UHF Antenna is up again

The task of moving my antenna support to the center of my garden is progressing nicely!

The assembly is two steel tubes. The upper tube is 38 mm diameter (1½ inch) and the lower one is 50 mm diameter (2 inch). The upper tube is attached to the lower one using two steel platforms (PLS 50 from UKW-Berichte in Germany). The upper tube is turned with my Yaesu G-600 rotor, which is mounted on the lower platform. A thrust bearing (KS065) is mounted on the upper platform and supports the upper tube.

How the components are assembled.

Even though the tube assembly is quite rigid, is is still easy to handle. I can "walk down" the assembly when I need to fit another antenna. When the tubes are down, they rest horizontally on the lawn, and the antenna is easy to access. The picture below shows the tubes resting on the lawn. Each tube is 6 m (20 feet) long.

The antenna tubes resting on the lawn.

Both antenna tubes are erected and support an 8-element yagi for 2 meters.

There is always something to explore. How are the surroundings affecting VHF antenna performance? Do trees obstruct the signal? How much noise is heard? And so on.

Regards from OZ1BXM Lars Petersen
Homepage: http://oz1bxm.dk

SDR transceiver: Genesis Radio G11

July is here, and this means time for vacation! In Denmark, it's normal to have 3 weeks vacation during the summer. I spend much time with my family. But there is also time available for radio projects. I've purchased a Genesis Radio kit G11. This is a 10 W all-mode SDR transceiver, and it covers all bands between 160 meters and 6 meters with the optional filter kit. The standard version covers 5 bands.

I bought the G11 kit from a fellow ham, who did not have time for construction. The building effort on my side is expected to be reasonable, since several hundred SMD parts are factory fitted. My job is to mount and solder about 100 through-hole components including toroids, different connectors and relays. Genesis Radio estimates about 10 hours of work on this part.

Here is a picture of my G11 PCB as of today. The RX part is almost finished, except for toroids. No components are fitted on the TX part.

Genesis Radio G11 board (TX not finished).

G11 assembly has been straight forward until now. The only difficulty was the USB interface. I could not load a G11 driver for Windows 7 (64 bit). When I replaced the 64-bit PC with another PC running 32 bit Windows, the driver installed immediately.

The G11 documentation is adequate. Several hundred people have built this SDR transceiver, and their knowledge is collected in a Yahoo group: GenesisRadio which is active and helpful.

73 de OZ1BXM Lars Petersen, homepage http://oz1bxm.dk/

SMD = Surface Mounted Device
SDR = Software Defined Radio
RX = Receiver
TX = Transmitter

WinKeyer, part 2

I wrote about the WinKeyer in a blog post last year. My WinKeyer is mounted in an alu-cabinet, which I found in my radio junkbox. USB connection, paddle connection, and the keying output is on the rear of the cabinet.

WinKeyer USB Lite.

Inside the WinKeyer cabinet.

My logging software Log4OM has a dedicated WinKeyer window, where you control the keyer, you can send CW via the keyboard, and you can run macros (10 different).

Log integration is a nice feature. When call and report are entered in the WinKeyer window, you can log the QSO by clicking the "Add QSO" button. All other data like time, frequency, and mode are already known by Log4OM. It draws this info from the computer clock and from the transceiver via the CAT interface.

Another nice feature of Log4OM is the use of macros. When a macro is executed, a script will do the hard work: sending your name, your QTH, your QSL info, and a contest exchange if in contest mode.

A am happy with my WinKeyer. It was easy to build. WinKeyer is easy to use, and with the log integration, my time with the radio has become more enjoyable!

73, OZ1BXM Lars Petersen
Homepage: oz1bxm.dk