Another Pantry Transmitter

[PJC58-Hythe]

Hello everyone,

I finally decided to get around to making a pantry transmitter for the radio collection in the house. I looked at a lot of different designs but in the end decided to design one myself. The attached PDF is the final circuit and with a couple of feet of wire attached covers the whole house from inside a front room cupboard.

The frequency of operation is set by C5/L5 and adjusted a small amount by C9, I chose around 1MHz as the operating frequency as there are no broadcast signals on this frequency where I live. An audio input of 280mV will 100% modulate the carrier which is around 14V RMS at the output. R5 is shown as 10K which will work fine in most cases but may need to be adjusted while monitoring the output with a scope at the 'RF Out' to make sure the carrier is linearly modulated and doesn't 'flat top'. A simple 12V AC supply from a transformer is all that is need to power the unit.

If you do decide to have a go at building it make sure the values of L1, L2, L3, L4 and C8, C10, C11, C12 are adhered to. If you have a higher level audio input then use a potentiometer on the AF input.

All the best

[paulsherwin]

Nice simple circuit. Do you get much frequency drift?

You probably already know this, but 1MHz isn't a valid AM channel in Europe, not that it matters in this case.

I don't know, a pantry transmitter in a cupboard? Whatever next? I have a real pantry but my "transmitter" er. "modulator" is in the kitchen, I guess the RF doesn't mind at all.
Good job, nice and simple as said.

[PJC58-Hythe]

Hi Paul,

Yes I did realise that but as you said it doesn't matter in this case. it's absolutely rock solid where it is but as I haven't tried heating or cooling it I don't know what the drift would be like.

[G6Tanuki]

Originally Posted by paulsherwin

You probably already know this, but 1MHz isn't a valid AM channel in Europe, not that it matters in this case.

Some would say that this is a benefit - less likely to cause low-frequency heterodynes with existing band-occupants.

My xtal-controlled pantry-transmitter stealthily fits in between two 'official' channels, neither of which are currently used by any broadcaster within 500Km.

"Hide in the gaps"!

[Graham G3ZVT]

I used to send music round the house on 300 Meters using the 1MHz position of my Class D Wavemeter. I think I just applied low level mod to the grid (TC) of the oscillator valve.