mandag den 18. april 2016

New HF-transceiver - again??

Buying and selling radio gear is something all radio amateurs will do sooner or later. Some do it rarely - every 10 years or so - and some do it more often. Last weekend, I bought my second HF-transceiver in a year, and I am happy with it!

I found a mint looking Yaesu FT-1000MP Mark V Field on the Danish site where second-hand equipment is traded. The price was within my reach, and I was the first bidder. Long story short: The FT-1000MP Mark V Field transceiver now resides in my shack!

Yaesu FT-1000MP Mark V Field.
My reasons for buying this radio:
  • Competition-grade transceiver
  • Myriad of functions and facilities
  • Recommended by the contest team I consider joining 
I am now selling some gear to help paying for the new radio: Yaesu FT-920 transceiver, Kenwood PS-52 power supply, and a Genesis Radio G11 SDR transceiver.

Is there a catch when buying used equipment? Yes, sometimes. You may discovered that something is not working as expected. If minor flaws are discovered: Too bad, the sale is done. In case of major errors you can contact the seller for a price reduction or for cancellation of the sale. None of this happened to me - I am happy with my FT-1000MP Mark V Field!

Regards from OZ1BXM Lars Petersen

søndag den 10. april 2016

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, I recommend searching for "12V 40mA".

OZ1BXM Lars Petersen