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Registered Member #1412
Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278
I'm experimenting with base feed vacuum tube plasma tweeter.But I worried that it might transmit a lot of RF power and cause interference.I'm thinking that if i tune my (radio)scanner/receiver to it's frequency,can I receive the audio(in AM mode)?If I tried this,is there any risk of damaging my scanner or receiver?And how can I measure the working frequency of my plasma tweeter?Can I use a frequency counter?(my scanner scan very slow)
this is the schematic I use(I use 6DQ5 instead of PL519 and get about 1cm spark)
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Yes, it is an AM modulated radio transmitter, you just have to hope that the "antenna" is ineffective, and no radio hams with pitchforks live nearby.
When building a device like this, it's nice to aim for one of the ISM bands and/or enclose it in a Faraday cage.
The RF output may well be high enough to damage your scanner if it was brought too close. A frequency counter should work, but again I wouldn't bring it too close.
Registered Member #1412
Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278
I test it with a frequency counter.It easily detected the signal several meters away.The frequency is about 8.5MHz. But my scanner cannot pick up the audio.
I'm worried that causing this kind of interference might be illegal.Will the signal travel very far?If I use a faraday cage,how can I know if my faraday cage work?
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
In your circuit there is nothing to limit high frequency components of your audio input from modulating the screen of the power oscillator. You are not going going to hear anything in the supersonic range, except subharmonic distortion. Also keep audio level to a point where your scope shows no clipping of the modulation.
Roll the top frequencies off at 6 dB/octave starting at 15 kHz. This way splatters of radio interference are less likely to get into nearby receivers.
A resistor R in series with C9 and a capacitor C from the base of T1 to ground will do this.
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Is a vacuum tube plasma tweeter also a transmitter?
