Our hobby can only move forward if there is a cadre of hams who are filling the well. Early on the allure of ham radio was the pure adventure of advancing the technology. A One Tube transmitter soon advanced to multi-band, multi-stage radios where something more than QRP was putting fire in the wires.
But today the technology is being advanced by corporations, not hams and the hams have given way to knowing nothing. (Thank You, ARRL.) But they do spend huge sums on radios they know nothing about let alone how to operate them properly.
Challenge yourself to build something and here is a small one and done project that has many uses. Cheap computer crystals work well in this circuit. This is not an original design but something I think I lifted from W7ZOI. Caveat -- likely good for most crystals in the HF range but might not work in the 2200 Meter band nor on 430 MHz.
The genesis of this transistor test oscillator was in connection with the fabrication of a 40M high performance CW transceiver. I needed a test circuit early in the build to supply the BFO input, to align the IF, to set the BPF on 40M CW and as a general weak signal source once the whole rig was built. As things usually happen the 1st thought was to build a better receiver (something more than a regen). But as time went on and I saw how well the receiver worked -- the project got bigger. A line from the link that details the project.
What started as a receiver project has ended up a small sized feature packed transceiver.
The 5.185 MHz was the IF and the 7.030 MHz was for testing the Mixer, BPF and overall gain. As a weak signal source, I placed this unit in the back yard operating with a 9VDC battery and was able to peak the rig to hear the signal.
The link has the build details of this 40M CW Transceiver.
As I now look at this design and the project, it is really sophisticated with the NE555 TR Switch (SSDRA), the FET audio muting and the integration of 4 MMIC devices into the rig. The VTO (VFO) running at 2 MHz made for a stable signal. The offset was done with a separate Crystal Mixing scheme in the transmitter. What I didn't think of at the time was a two-band rig as the shifting the VTO down in frequency and a new BPF and LPF gives 80M CW. Today this project would be ripe for an Arduino and Si5351.
This project is a simple one transistor Colpitts Oscillator with output taken from the Emitter. I used this device for the following purposes:
- Weak signal source for determining if a receiver is working.
- Aligning Band Pass Filters.
- Code Practice Oscillator.
- Signal Injector for testing various modules in a receiver.
- With a reconfiguration and adding a Low Pass Filter -- a QRP transmitter
- BFO for a receiver
- CIO (Carrier Insertion Oscillator) for a Balanced Modulator.
- In connection with an SDR to measure crystal frequencies for selection of devices as being close enough for a Crystal Filter
These are but a few and you can add your own to the list.
The cost is low and with a bit of reconfiguration even its PNP brother could do the job (2N3906).
BTW Mouser and Digi-Key sell crystals that can be used as BFO/Carrier Oscillator devices for a 9 MHz Crystal Filter. (8998500 and 9001500). The switch can select USB or LSB.
Show your stuff and build this jewel.
In a subsequent posting I will show how to build an RF Probe that can be used with a VOM to sense and relatively measure RF output. By this I mean you can see A is much bigger than B, but the actual value is not precise. In most cases hams want MORE, and this will tell you if what you changed is MORE!
73's
Pete N6QW