1 Volt/2 Volt Transceivers

Transceivers with a power supply of 1 and 2 Volts, how much can one achieve with that? Well, actually quite a lot according to DL2AVH, Helmut, who together with DL4ALJ, Gero, wrote two articles about that in the German QRP-Report in 2011. I am impressed by the output power, up to 200 mW with one battery cell (1.5 Volts) and 0.5 Watts with two cells.

I wrote about this in April last year where I also mentioned that the 1 Volt design from 2000 later had been corrected. Those corrections can be found in the article in QRP-Report 3/2011: "Niederspannungs-Schaltungstechnik - der 1-V- und der 2-V-transceiver" (Low voltage circuit technology - the 1 Volt and the 2 Volt transceivers). The improvements are concerned with better input filtering at 14 MHz with a quartz crystal in the front-end filter and better efficiency in the mixer and removal of an audio stage in the direct conversion receiver. This design only uses bipolar transistors and no ICs.

Whatever happened to the 1 Volt QRP Transceivers?

Output stage of the 1 Volt DL2AVH transmitter
(from http://www.lichtnetzwerk.de/1volttxvr_dkumentation.pdf)

I am intrigued by minimalist transceiver designs like the Pixie 2 which I built some years ago. Therefore the "1 VOLT Challenge" from Dayton 2000 is also something I wish I knew more about. It had these winners:

1. Duncan Walters, G4DFV - The HAMEOBA - A 100 mW Single Cell CW Transceiver (30m)
2. (tied) Helmut Siefert, DL2AVH - A 30m 1V QRP transceiver
2. (tied) Charles Fletcher, G3DXZ - An 80m CW QSK Transceiver
4. Jim Roberts, NC9H - A 20m 1.5V Transceiver

Now, what happened to these designs? I'll try to figure it out from sources on the web.

A regenerative receiver for the 40 m band

I've had a lot of fun with the modified WBR (Wheatstone Bridge Regenerative) receiver which I built Manhattan-style some years ago. The design builds on the receiver described by Daniel Wissell, N1BYT in QST August 2001. Although it doesn't match a good superheterodyne, you get more performance per component than in any other receiver!

QRPp: Ultra low power operation with the Pixie 2

QRPp is radio amateur jargon for communication using a transmitter with less than 1 Watt power output. That’s less than a handheld GSM mobile phone (max wireless range ~35 km) or a flash light. My Pixie 2 transceiver has so far contacted 15 different countries on 3.5 MHz CW. The first version from 2002 was made in an Altoids tin (picture later), but in 2010 I repacked it in one of the nice clear top tins from the 4SQRP (picture below).

My repackaged Pixie 2

How to make a very cheap VHF receiver

What is the cheapest receiver you can make for VHF? Here is a candidate where all you need to do to modify a small FM headphone receiver is to desolder one end of two capacitors, and connect a short cable with an antenna connector. 

One 22 pF capacitor lifted on the right-hand side near the headphone 

 connector for connection to the external antenna, and another one lifted on 

the left-hand side, above the volume control for increasing the tuning range 

(The receiver IC is on the foil side of the board).

Unleashing the LM386

From Wikipedia Commons, author 'Samba pa ti'

The LM386 must be one of the most popular audio output amplifiers among radio amateurs, despite having been around for a long time. It's an IC which even has its own Wikipedia page. The LM386 can be obtained in both dual-in-line and surface-mount packages and outputs 325 mW in the standard version that runs from 4-12 Volts supply voltage.

Its voltage gain of 46 dB is in many cases too little, especially in direct conversion receivers. When I built the Pixie 2 with the LM386 audio stage, it struck me how the sensitivity of the receiver was limited by the audio gain. I asked myself if it would be possible to increase the gain and add some filtering in a simple way. The result is a gain of more than 70 dB and an audio bandwidth of a few hundred Hz by only adding 5 passive components to the standard circuit: 3 resistors, 1 capacitor and an inductor.