[R-390] image

[Bob Camp]

Hi

The neon bulb is not real effective when the transmitter fires up and  
you are still on the antenna .... There are a bunch of R-390's out  
there with black charcoal where one of the front end coils used to  
be. Could have been lightning, probably was a transmitter.

Here's one way to look at it: The bulb will fire at about 20 watts of  
RF. It's rated below a watt. It's not going to do very much  
protection before it vanishes. It will glow a really neat bright  
purple color before it goes though. Don't ask how I know that ....

If you ever have had an antenna party when maybe you should have been  
indoors, it's amazing how fast you pick up charge on even a fairly  
modest antenna. One might even call the experience shocking. Again,  
don't ask ...

Without a DC path to ground the charge on the antenna will just build  
up. Something has to give. There's not a lot of energy, so the neon  
bulb does just fine.

Bob


On Oct 22, 2007, at 10:38 PM, Bill Hawkins wrote:

> Static electricity? I thought the bulb was there for the transmitter
> in your, or an adjacent, comm trailer. Dunno why people would remove
> the bulb. It does nothing, nonlinear or otherwise, until it strikes
> at around 90 volts.
>
> Isn't shared ignorance wonderful?
>
> Bill Hawkins
>
>
> -----Original Message-----
> From: r-390-bounces at mailman.qth.net
> [mailto:r-390-bounces at mailman.qth.net] On Behalf Of Bob Camp
> Sent: Monday, October 22, 2007 5:52 PM
> To: Jim M.
> Cc: R-390 List
> Subject: Re: [R-390] image
>
> Hi
>
> If the neon bulb is glowing you have over 70 volts on the antenna
> terminals. If that's the case, the radio is a bit overloaded ...
>
> The neon bulb is mostly there to protect the input capacitors against
> static induced voltages on a whip antenna.
>
> Bob
>
>
> On Oct 22, 2007, at 6:37 PM, Jim M. wrote:
>
>> Both of my 390as have had that neon lamp removed by someone before I
>> got them.  It would be interesting to look at the lamp to see if  
>> it is
>
>> glowing from the big BCST signal down the road.
>>
>
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