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  Antenna problem on handheld VHF radio

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Author Topic:   Antenna problem on handheld VHF radio
Frank O posted 11-29-2008 03:32 PM ET (US)   Profile for Frank O   Send Email to Frank O  
Recently I noticed getting a loud hiss on all channels of my Standard-Horizon HX500S handheld VHF radio, even with the squelch set at maximum. After some playing around I found that this was dependent on the positioning of the flexible antenna. It's possible that the antenna got bent at too great an angle and is damaged.

Could an antenna defect cause the symptoms I'm seeing (hiss on all channels)? If I unscrew and remove the antenna completely, there is no hiss (but of course also no received signals). I'm therefore wondering what the scenario is that would cause the hiss. I gather that the problem is not that the radio is finding no antenna at all, but rather a partial antenna that is causing the symptoms?

Are antennas of this type manufacturer- and model-specific, or is this more of a generic item that I'd be likely to find at a marine shop?

fishgutz posted 11-29-2008 05:12 PM ET (US)     Profile for fishgutz  Send Email to fishgutz     
I had the exact same problem with a West Marine radio that had a damaged antenna. Seems the only antenna that would fit was in fact a West Marine antenna. Replaced the antenna for $9 and all was good. I'll bet the antenna for your radio is a specific Standard-Horizon antenna.
fishgutz posted 11-29-2008 05:27 PM ET (US)     Profile for fishgutz  Send Email to fishgutz     
$15 replacement
http://dogbytecomputer.com/standard-horizon-cat460-rubber-duck-antenna. html
Frank O posted 11-30-2008 12:27 AM ET (US)     Profile for Frank O  Send Email to Frank O     
Thanks. I found the antenna a little cheaper (once shipping was factored in) at Sailnet, and ordered one.

jimh posted 11-30-2008 10:28 AM ET (US)     Profile for jimh  Send Email to jimh     
Consider for a moment what a radio receiver does: it has an electro-magnetic pick-up (antenna) which detects fantastically small changes in voltage, then amplifies those signals from a level of less than one-millionth of a volt to several volts, a voltage gain of perhaps 5,000,000-times, and extracts the intelligence or modulation on those signals and applies it to a loudspeaker. To do this properly it must process the signals in such a way that it adds as little electronic noise of its own creation to the signals. Given that situation it is not surprising that some sort of malfunction at the very lowest signal level (the antenna) might disrupt the system.

But all that said, it is odd that the antenna is creating noise, as usually the antenna is a passive device and does not generate any sort of electrical voltage itself. I'd expect that the antenna was either connected or disconnected, and there is not much in between those two states.

Perhaps the description of the noise is really just a manifestation of the very poor reception that takes place with the broken antenna. The signals being received are so weak they never produce a suitable signal to noise ratio in the output, and buried in that noise output is a very weak signal. When the antenna is removed, no reception takes place, and thus the receiver output is quiet. However, generally it is possible with full squelch to silence the receiver output even with a weak signal present.

I doubt the antenna is making noise, but it does sound like it is broken and should be replaced.

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