|Updated March 10, 2014|
QRP-Tech Group Projects: .. .. 8640Jr Signal Generator
(4 digit # refers to QRP-Tech group message)(Click on a project below to go to my Project-nnn page)
Project-000 = Simple EMRFD DC Receiver 4960
Test Equip used here: Tek DSO scope TDS2012C, Hatachi scope V-422 (very old but still works), HP Sig Generator 8640B, B&K Freq counter, B&K DVM, HP3400A RMS volt meter (good past 10MHz, 3 each HP lab power supplies, Simpson 260 VOM, AADE LC meter, Veleman DVM, Step Attenuator ARRL design.Building a couple of 50ohm loads, a return-loss bridge, a couple of AD8307 power meters, and a couple of scalar network analyzers.
Collecting Parts - Found a 365pf air variable with 8:1 gear reduction. Will use it without a fine tune capacitor but I'll leave room to mount a fine tune capacitor if I decide to add it later. Didn't have a 3 position rotary switch so I ordered one from Mouser. In an effort to eliminate the fine tune capacitor I've chosen a 3" diameter knob to go along with the 8:1 tuning ratio. I had to pick out a larger than necessary enclosure to accommodate the 3" knob. Oh well, that'll mean I have room in the back section of the enclosure to build a nice power supply. BTW, the tuning knob is from a Collins 75A-4.
Well, changed my mind. That box was too big. I found a nice tuning knob that's just a little smaller which will enable me to use an enclosure that's not quite so large. This knob will be nice because it's a spinner which will work nicely with the 8:1 drive of the tuning capacitor.
I won't get my 3 position rotary switch from Mouser until Monday (this is Friday) so I'll begin construction of the board today. I'm going to try to make this look nice enough to earn a place on the bench as a nice looking piece of test equipment. The tuning capacitors, switches and connectors will be mounted on the enclosure. I'll start out with battery power just so I have confidense that it's "clean". Later I might build a power supply for it that includes common mode chokes and lots of other filtering to make it "clean".
When I choose the location of the tuning capacitor and rotary switch on the front panel I'll leave enough room to add in the upper left corder a LCD display so I can have an accurate readout without having to use my freq counter. Since I'm right handed I'll put the LCD display on the left so my hand won't be in the way. The knob on the right will be the "FINE TUNE" knob. Then in the bottom left corner I'll add an ON/OFF toggle.
To save time I'm gonna use NA5N's layout to go by. Since I don't have my new HP laserjet yet and can't do muppet construction this will be another manhattan board.
Here's a piece of pcb material to use. Shown here is the pcb in the bottom of the enclosure with a small 12VDC power supply that I had laying around. It just fits perfectly. The PS is a small switcher so I'll probably add an line filter on the AC input and a small common mode filter on the output.
Collected parts for the oscillator section. Will get it goin' 1st and that add the buffers,dividers and amps.
Adding components - BTW, I was trying to use up some old wire-wrap wire on the toroids but I don't like it. It seems to kink easily and I can't seem to wrap it as tightly as I'd like to. I'll rewind the toroid in the pix with #22 enameled wire.
Oscillator section is wired and is working nicely from 13MHz to 32MHz. Looks like a relatively clean signal of about 0.5Volts P-P.