My "Junk Box" 200mW 30m TX with BFY50 final. QRSS3/10 Keyed by PIC microprocessor. The green LED indicates the on/off state of the morse code. The LED voltage is used to modulate the oscilator 'FSK 5Hz' using the classic red LED junk box varicap. The LED's were donated by a Philips 2000 vdeo recorder as were most of the R's and C's. See they are useful for something. RIP Video 2000 "They're Flippable".
Up to the minute reports from distant stations can be seen at http://members.lycos.co.uk/qrss
Winding Down the Power.
I have never liked the thought of calling a 100W transmitter with the power turned down or padded or backed off by the ALC, 'QRP'. If the rig rig you do this to is an ICOM IC706 then it is 'pulling' 3 Amps on standby, that is a good 36 Watts of wasted power.
Having received reports from the 200mWatter MEPT Beacon TX from Australia and New Zealand, I decided to try lower power. The other Classic design from the WWWeb uses a 74HC2400 run with 7 to 8 Volts supply. I decided to use just 4 of the inverters for the 'PA' and lower voltage to give 80mW output.
Many stations go for Xtal ovens to achieve better frequency stability, I found my stability to be quite satisfactory using the polyurethane foam cube that I cut to enclose the crystal. It can be seen in the photo above at the top right, behind the variable capacitor. This time I have taken the cube a little further and housed the crstal in a cube of foam which is sealed inside its own enclosure made of copper PCB which has a thermal break between it and the main PCB.
It's not an oven it's a cool box. The biggest thing on the board the crystal enclosure gives a large degree of isolation from short term temperature fluctuations. I have used NaTUC, 'Neat and Tidy Ugly Construction' again.
It is fun to build like this, completely confusing and merging the ront panel, back panel, PCB, housing, feet etc. The result is not quite as slim as I hoped due to the use of Silvered Mica capacitors in the LPF. I originally used Ceramic types here but found that due to the tight coupling of the oscilator and 'PA' the major cause of frquency drift was from the capacitors in the LPF. (Even after adding a spare buffer stage). The chip temperature soon stabilises after enabling the 'PA' and a rapid frequency drift of the oscilator can be observed after it is disabled, as the chip cools. The perils of a single chip TX.
Those SM capacitors are all of 40 years old it was time they were put to good use again. Bringing one of the LFP coils to the other side of the board prevents any coupling between stages.
The Keyer is tested and added to the main board.
Yes truly ugly construction.
Two MEPT's 'one strong one weak' on test on the same frequency, they beat with eachother and produce sideband responses. They have been in sync. for many hours with no shift in frequency of either. They stay perfectly straight. The drift is from $3000 worth of commercial transceiver which has not been switched on for long.
This is the frequency I use for 10MHz beacons 10.140.073 +-1 Hz. The readout is from on my home brew frequency counter, prior to mounting in an enclosure. The design is from EI9GQ VISIT HIS SITE
MORE ZJO HOME BREW
I eagerly await reports on the 80mW NaTUC MEPT. They will be posted here. http://members.lycos.co.uk/qrss
NaTUC Construction is dedicated to my XYL. She may be Ugly but at least she is Neat and Tidy, and VERY tollerant. and a great Artist. I am getting her recent work on the WEB.http://portraits-landscapes.blogspot.com There is some earlier work on http://homepages.tesco.net/~wbsuuk Phew! that should have saved my bacon. That site is a better way of viewing my QSL.net site in Europe, it also has extra other hobby content.
(c) G3ZJO 2006 All material is the intelectual property of the author,all opinions are solely personal,true and accurate to the knowledge experience and observations of the writer