The 4069

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The '4069', a low power QRPp Tx/Rx

for 160,80, and 40 metre operation

            This project was originally conceived as a way of carrying out Morse practice sessions in the workplace at lunchtimes. This was to enable two of my colleagues to upgrade their B licences to the full GØ callsign by passing the 12wpm Morse test. We found that we had to operate in a side room to avoid annoying the other Department members with the CW, so the idea of a low power transceiver to enable silent operation between desks was born. In fact the prototype rig used a regenerative receiver, and an 1834 KHz xtal on transmit, but this wasn’t completed by the time the two had passed their morse tests and received their licences – so the project lapsed. This gives an indication of the project timescales as the new MØ callsigns came into force in 1996!

Required Rig specification was that:- 

a)                  The rig had to be simple, CW Tx/Rx.

b)                  Low power as required for inter-desk communications.

c)                  Cost had to be low.

d)                  It had to be tuneable over a reasonable frequency range.

e)                  Full QSK keying was required.

f)                   Transmit side tone was needed.

g)                  Receive frequency offset required.

h)                  Self contained, battery operated.

i)                   Small so it could be moved and stored easily.

j)                   Earphone output for quiet listening.

    Initial work has produced a small rig which could be built to operate on 160m or 80m, and work is proceeding on a 40m version after consultation with the RSGB. The Xtal has been replaced by a ceramic resonator, and the receiver is now direct conversion.

    When the rig is described as 'small', I am hoping to be able to fit a model into a standard size match box - complete with battery and possibly a flip out micro switch Morse key, where the earphone lead acts as a local antenna.

    The normal model is laid out on a PC board about 1.5" square, and is single band, but I am looking at making the frequency dependent parts capable of being plugged in as an alternative to building them directly on the board for the single band version.

    The rig is based on just one CMOS IC, a 4069 Hex inverter, with no other active devices, and the output power on 160/80m is in the order of 1mW. I have had a contact over 13km on 160m when using my 70ft vertical antenna with the prototype, signal report being S8.

    Envisaged enhancements include an 'add on' audio output stage driving a small loudspeaker, and perhaps a transistor power amplifier to boost the rig output.

    Investigation on the use of a doubler with the 3.5MHz ceramic resonator to provide 7MHz coverage continues, but still retaining a single IC as the active device. 7MHz resonators have now been sourced, and when they arrive the work will resume.

    The main reason for the 'matchbox' format was that when I was quite young my father made me a crystal set in a match box.....

The work continues as time becomes available!

G3TVU

© Copyright G3TVU

5th January 2015