Tunnel diodes

Back in the 1960s these were all the rage.  I remember making a simple tunnel diode oscillator at university in about 1969.

I am not sure if you can buy them still. They are 2 pin negative resistance diodes that work by quantum mechanical tunnelling. 

Very simple uW TXs are possible and there was one published that was copied about 200km away in New Zealand on 80m.

See https://en.wikipedia.org/wiki/Tunnel_diode .

See https://www.rfwireless-world.com/Vendors/Tunnel-diode-manufacturers.html .

Para-saki all diode QRP transceiver

This looks like a design by Michael Rainey AA1TJ, but this one was on a German blog site of Peter DL3PB. I was very annoyed by the Facebook pop-up that kept appearing. I kept closing the pop-up but it is really annoying. Website owner - PLEASE get rid of it!

See http://streampowers.blogspot.co.uk/2013/08/para-saki-qrp-transceiver-fact-diodes.html .

The design makes extensive use of tunnel diodes, a Michael Rainey favourite.

Remarkable "all diode" transceiver QSO

DL3PB's "all diode" transceiver

Today I got this most interesting email from Peter DL3PB. Peter must be congratulated on this excellent achievement.

Hi folks,

I'd like to share with you a long-cherished dream, that recently came true, fourty years after I came to read about hams using tunneldiodes to make QSOs when I was aged twelve or so:

Finally I managed a first skywave QSO with my PARASAKI-transceiver, an 'all diode' rig:  Christophe/F8DZY replied to my very first call on 20m band in REF-contest last weekend. I was running 2mW into a temporary vertical dipole on my balcony. Distance between us is  918km - obviously OM Christophe has excellent ears.

Those interested in the cruel details of my circuit, please find attached a schematic and a photo of the pretty ugly setup. The circuit is designed straight-forward with exception of the parametric VXO, derived from Mike/AA1TJ's famous Paraceiver design. (see  http://fhs-consulting.com/aa1tj/paraceiver.html)

The low impedance of the high peak-current tunneldiodes make it very difficult to built a really crystal controlled oscillatorrather than an LC-oscillator, synchronized by the crystal more or less, at least on the higher SW-bands. The Parametric VXO provides a crystal-stable, chirp-free signal on expense of an output power of two milliwatts only instead of ten, but with an amazing spectral purity, no need for a low pass filter or such. Of course it sounds pretty cool making a QSO with a 'bunch of diodes' and a parametrically excited crystal, but believe me or not, I'd preferred to bring that full ten milliwatt into the air - on the other hand that approach allowed  to tune the rig a bit ( ~ 5kHz/per xtal ), which turned out to be much more valuable than a few milliwatts more while being 'rock-bound'.

The receiver in its 'gain-less' version works fine for strong signals - while listening to QRP(p) stations, the moderate gain of the audio amplifier helps a lot. A comfortable frequency shift between receive and transmit is realized by the 5µH inductor at the LO-port of the mixer, with little effect on sensitivity.

Thanks for the bandwidth, OMs, won't bother again you with such mails, unless I make a cross-pond QSO with that rig ( not that likely ) or any skywave QSO with homemade semiconductors ( probably impossible )...

72!

Peter/DL3PB"

Lambda diode circuits

Mike Rainey AA1TJ has some good tunnel diode ideas on his pages but these devices are hard to find these days. Instead one can create a negative resistance device called a Lambda diode with a couple of FETs or an FET and a transistor. See for example the pages of Ramon Vargas Patron at http://www.zen22142.zen.co.uk/Theory/neg_resistance/negres.htm where he has examples of oscillators and regenerative receivers using Lambda diodes.

Tunnel Diodes rigs

Way back in the 1960s I recall making a simple tunnel diode oscillator as part of a lab project and being excited to see such a circuit used to span 160 miles on 80m by a ZL station despite the power being microwatts only. These days tunnel diodes are almost unheard of.

Recently I spotted a similar tunnel diode TX and RX on AA1TJ's excellent webpages on which you can find more data and links to off-air records made at DX distances.