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Registered Member #103
Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845
I cannot fathom this out at all.
I have an FM transmitter running about 145Mhz and 1 watt. Fairly good SWR reading into an external aerial. When I power this thing up, the speakers of my hi-fi system on the other side of the room put out mains hum at 50Hz, as if a high impedence input had been left dangling
I can't figure out how this can happen. The TX is running from a sealed lead acid battery. Any ideas? It doesn't usually hum! I know how I could prevent it, I just can't understand why it happens in the first place!
Registered Member #16
Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554
Ok, long time since this was posted, but I'll see if I can help.
Its not at all uncommon for this to happen with cheap or poorly shielded speakers. My blackberry makes my car speakers go absolutely apesh*t.
Ferrite on the power lead of the speakers (if they have one), and constructing a small grounded metal enclosure for them will almost certainly fix the problem.
When I was growing up, a ham up the road from me, WW3S had a 1kw HF CW station transmitting through an enormous yagi on a 50' tower. When he was beaming within 45 degrees of my house, I could hear CW on my computer speakers. He was more than a quarter of a mile away!
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Mains hum when TXing?
