Pantry Transmitter with only one valve

[billjarvis]

A “Pantry” transmitter typlically is a very low power Medium Wave transmitter which is ready to be audio modulated by any audio source of your choice.

The purpose is to serve all medium wave receivers around your home, whether vintage or modern.

It ought not to be detectable beyond your own premises of course!

Any frequency changer valve of the triode-hexode or triode-heptode variety can be used.

The circuit contains no critical parts, so this makes a good “junk box” project which might well cost nothing.

The triode provides audio amplification. The voltage at its anode amplitude modulates a Hartley oscillator, which feeds a short random length wire aerial.

A very little antiphase modulation occurs because of the internally connected grids, but it is of no consequence.

Power requirements: Heater supply, typically 6.3 V 0.3 A; and about 200 V HT at about 20 mA.

Setting up: Connect your choice of input oudio source. Turn the pot right down for no modulation.

Tune to a quiet frequency in the Medium Waveband and place the receiver near the transmitter.
Adjust the tuning capacitor until you are transmitting on your chosen frequency. Now turn up the audio pot until you are getting good modulation without audible distortion.

Connect a random length of insulated single flex as aerial, and move it around for best results in different parts of the house. At the same time try to avoid being detectable by neighbours, or beyond your own environs.

It might be interesting to try running an insulated wire right round the outside of a house. This might form a loop or frame aerial with most of the radiation concentrated inside the loop.

[G8HQP Dave]

Also see https://www.vintage-radio.net/forum/...ad.php?t=48384