04/14/2015 23:13


My friend, Mr Hartley, after long experience with single tube transmitters, has been bitten by the SPY BUG. I'm responsible for this ... Here below his spy set, half made with tubes and half with solid state components.


Now a brief description of this jewel.

Transmitter : single tube 'EL86' Clapp oscillator, crystals driven. Covers from about 4.0 up to more than 9.0 MHz, 8W output. The antenna impedance matching network is a parallel LC plus tuned link, like in the well known 'PARASET'. The plate voltage is derived by a modern 12VDC to 220VAC inverter, as big as a cigarettes packet: rectified and filetered, provides 300 VDC to EL86 plate, that are more than enough. The tuning is accomplshed by a few leds spread over the circuit, to get to know when the maximum RF current flows to the antenna.

Receiver : regenerative solid state (... only 40 $), with some improvement like audio filter and antenna preamplifier.

The changeover is fully manual: a lever switch selects the Transmitter or the Receiver connection and on side turns on/off the solid state inverter.

This wireless set is totally fitted into a hand suitcase, Lead-Acid batteries included for a few quarters of an hour operations. The Operator just has to open it, throw a few meters of wire to the closest support, put the headsed on, plug the key and ... here we go!

It has been named 'PARADOX' (to make some fun of the well known historic 'PARASET') in the sense it merges some very old technologies and concepts with some very new. A valve power oscillator fed by a modern inverter. A solid state ... regenerative receiver.

A few tests are being done on frequencies between 4.0 and 8.2 MHz, during night time and day time. At the moment the antenna is a 30 mt doublet, but tests are being planned to use a 2 mt whip and a few meter wire. QSOs have been performed with solid signals QSA/QRK 5 // RST 599 + on 150 miles QRB.

That's a very good, interesting, funny and instructive way to communicate on the Shortwaves. No matter what frequency. Yes ... no matter. Short contacts are at hand at very low cost, and one might experiment what real spies might have done in the past, someway.

A single tube transmitter plus a regenerative receiver. A few money to get all the pieces and some hours to put everything together. And you are on the air with 100% reliable radio contacts over distances. Do you still think that some expensive Yaesu, Icom or whatever transceiver, are really needed to stay in touch on the Shortwaves ? Don't you think that Mr Hartley's way is much more fun ? I do, and we will continue testing this 'Wireless Set' over the Shortwaves ...

Radioman, April 2015

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