I do not work January or February so this last winter 2010 we took on a couple of new projects. I have a ham friend Andy that wanted to build a QRP radio. I had seen an article about a 40 meter rig in QST but did not remember when. So we got out some of our old ones and found the No Excuses radio from December 2002 by Dan Metzger K8JWR. This radio did not need any special parts to build it and between Andy and myself we mostly had the parts. As always we did have to make an order to Mousers. I am not sure I really needed another radio but I always like a new project. We made a pack to get it done this year and that has not happen yet! We ordered boards from Far Circuits. They have a nice board we did have some problems with traces but were able to find all of the shorts. At the same time I had a neighbor kid wanting to get his ham radio license. He also wanted to build his own radio so I have ordered another board. If you are a ARRL member please refer to the original article.
Like I said in the first paragraph this radio requires no special parts. It uses Bobbins from sewing machines to wind all of the coils and garden variety transistors. The hardest part was finding 4 MHz crystals for the xtal filter and we found some used.
Here is a picture of the Transmitter and Receiver circuit.
I got into more projects just from some of the discussions in this article. One was understanding the parameters of the Field Effect Transistors used in this project. He indicated that any N-Channel FET could be used for Q7 Q8 and Q11 if the Drain Current dropped to zero when the Gate voltage was -2 volts or less. So I started to think how I could test multiple FET's so Andy and I would have a good ideal on what to use. Here is a circuit that Dan recommend.
I built this circuit and I will get a picture in here to show you what it looks like. The circuit shows that my FET's turn off a -3 volts so I take that as a good number! So you say how did you get your circuit to turn off if your bias voltage is only 1.5 volts? I could never get my FET's to turn off at that -1.5 volts. I changed the bia's and put a 9 volt battery in the gate circuit to turn the FET's off. This is something that I might talk to Dan about and send him a e-mail. I will get back on this.
The next project was testing Crystals. The three xtals should all be the same type and from the same manufacture and the same lot or they will not work well in the circuit. Andy had given me xtals that were used and I wanted a way to test them. This got into a long search of articles from some discussion boards. The major contributor's was Wes Hayward, Chris Task, David Gordon-Smith G3UUR and the EMFRED group. Here is the circuit of the test setup:
This was an introduction to xtal testing. As anyone who has done serious design of crystal filters can tell you, testing crystals for motional parameters (LM, CM, and RM) can be a real chore. These parameters are not measurable by way of commonly available LCR meters, but instead require a dedicated test set. Commercial test equipment such as that made by Hewlett-Packard (now Agilent) and Saunders Associates provides superb accuracy and convenience, but is financially out of reach for most hobbyists. By using a simple, and fairly common test procedure, an inexpensive test set with accuracy suitable for all but the most demanding applications can be made by those having good technical skills. Here is a link to the PDF document: http://jvgavila.com/other/Crystal_Test_Set.pdf
I will add more pictures here soon. Hope you enjoy: