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Mikey405 · 19th Aug 2019, 6:00 pm

Hi all.

I wonder whether this has already come up or not and whether I'm asking a years-old question. Anyway, here goes...

I recently purchased a Spitfire MK2 AM transmitter from eBay but I'm having terrible problems with hum on reception. I say "hum" although most of the time it's actually a loud "buzz" (louder than the input). The problem occurs using all inputs I've tried - but I'm currently using a standalone (battery operated) MP3 player.

I've tried different and various PSUs but none seem to make much difference (even the bench variable PSU does the same).

I've tried earthing the device to various radiator or sink pipes, earthing to the "earth" pin of the mains and not earthing at all - and still the same. Not earthing at all means that the buzzing is so loud that you can barely hear the music at all.

I've tried using an isolating transformer, earthed and not earthed and still no (or very little) difference.

Even if I use 15V worth of batteries and a battery operated MP3 player and no earth, there is still a loud hum all the time the aerial is inside the building.

I've tried different frequencies from one end to the other, and used the ATU to "tune" the loading but barely any difference.

The only way I've managed to get the setup working without any hum or buzz is by running the whole thing outside - the modulator running with 15v worth of batteries, using a battery operated MP3 player and hanging the aerial in a tree. If I run a PSU to either the MP3 player or the Spitfire device from an outside socket then the hum is back with a vengeance.

Any help would be much appreciated.

Thanks everyone.

Kind regards.

From Mike.

19th Aug 2019, 6:00 pm	#1
Mikey405 Octode Join Date: Jul 2006 Location: Solihull, West Midlands and Beaford, Devon Posts: 1,626	Spitfire AM Transmitter Hum (Buzz) Hi all. I wonder whether this has already come up or not and whether I'm asking a years-old question. Anyway, here goes... I recently purchased a Spitfire MK2 AM transmitter from eBay but I'm having terrible problems with hum on reception. I say "hum" although most of the time it's actually a loud "buzz" (louder than the input). The problem occurs using all inputs I've tried - but I'm currently using a standalone (battery operated) MP3 player. I've tried different and various PSUs but none seem to make much difference (even the bench variable PSU does the same). I've tried earthing the device to various radiator or sink pipes, earthing to the "earth" pin of the mains and not earthing at all - and still the same. Not earthing at all means that the buzzing is so loud that you can barely hear the music at all. I've tried using an isolating transformer, earthed and not earthed and still no (or very little) difference. Even if I use 15V worth of batteries and a battery operated MP3 player and no earth, there is still a loud hum all the time the aerial is inside the building. I've tried different frequencies from one end to the other, and used the ATU to "tune" the loading but barely any difference. The only way I've managed to get the setup working without any hum or buzz is by running the whole thing outside - the modulator running with 15v worth of batteries, using a battery operated MP3 player and hanging the aerial in a tree. If I run a PSU to either the MP3 player or the Spitfire device from an outside socket then the hum is back with a vengeance. Any help would be much appreciated. Thanks everyone. Kind regards. From Mike. __________________ G7TRF Last edited by Mikey405; 19th Aug 2019 at 6:09 pm.