There are a couple of areas that has sparked my interest lately, I’m burning out with software projects.
- Really simple radios such as the Pulga and the Gnat
- Parametric amplifiers, mixers, and oscillators.
- Tunnel diodes used as amplifiers and oscillators, this one is a time critical issue since supplies of available parts are all but gone. May be a moot issue if item #4 works out.
- Experiment with Lambda diodes as substitutes to Tunnel diodes in new designs.
- Anti-Parallel diode sub-harmonic mixers.
- Regenerative Receivers
- Use some of these older devices and techniques with Software Defined Radios.
- Linear RF Power Amplifiers
I became interested in Parametric devices and tunnel diodes after visiting the site of Michael Rainey AA1TJ. You should visit his site he has some very interesting projects there, clearly a out of the box thinker.
One project that I will try to do is creating a replacement for the the SoftRock radio using parametric mixers instead of FET commutating switches, the advantage besides simplicity is the frequency range possible with a parametric mixer which can be into the Microwave range.
Another area to be explored is using anti-parallel diodes as the mixers of a SDR receiver. Towards that end I have acquired a large NOS supply of Agilent (HP) dual matched diodes that are very fast on eBay. I have also located some matched anti-parallel diodes at Mouser that cost about $1 but are good for use at up to a little beyond 5GHz
Another area to explore is using FET switches to implement an equivalent to the anti-parallel diodes, the advantages are that the clock circuitry can remain digital while the clocking speed is 1/2 the normal clocking speed
Due to the scarcity of Tunnel Diodes and quality Varactors ( with leads ) at present I’m concentration on acquiring supplies of the devices and literature on them. It seems that peak usage of tunnel diodes was in the 60’s and 70’s and most devices have not been manufactured for at least 30 years.
I have bought a good supply of 27pf, 45pf, 90pf, and 420pf high Q Varactors in lead packages which should be useful at HF, VHF, and UHF frequencies but I’m looking for an inexpensive source of higher capacity units( 220 pF ) for use at HF frequencies. One source that looks promising is Power Schoktty Diodes, I have about a dozen different devices that I need to test in an actual radio, they range in value from 80pF to 700pf at 1V bias while having 10,000V dv/dt capability so they “should“ work great in the HF bands.
Recently I also purchased a supply of 1N3714 (2.2ma) tunnel diodes on eBay, at over $3.50 a device they are expensive components but since they are all but gone from supply sources I consider it a worthwhile investment. I also have a small quantity of 1N3716 (4.6ma) diodes. At present I’m trying to find some larger current (10ma) devices in small quantities.
Other items that I have acquired lately in anticipation of having additional time and room available are several RF Power Transistors that I was able to buy in large quantities and are available in my store for less than $1 in quantity 1.