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Old 08-18-2011, 9:41 PM
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Default VHF sounds Good UHF hums

VHF sounds Good UHF hums

while listening on my Black berry both sound good however when useing a PC the fire on my feed (Lawrence Fire Department 154-45500 PL 100.0
) sounds crisp but the PD ( Lawrence Police Department 482-56250 PL 146.2) speak and I get that HUMMMMM what, why, where, and how do I fix this

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Old 08-18-2011, 11:46 PM
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Whatever you are hearing wasn't evident on a PC here....I listened to your feed for about an hour (just out of curiosity) PD traffic sounded fine. Only humm I heard was from one of the dispatch positions, sounded like a fan running in the background, but it was low.

I just moved to a desktop PC with a good set of speakers.. I can hear it - I believe it's their CTSS tone (146.2) that you hear. Need to roll off the bass in your audio coming from the scanner? It does not sound like 60 hum or 120 cycle buzz from the AC, the pitch is higher.

Edit - It is their CTSS tone - I ran this tone generator at the same time with the level set at the same as your audio. D below middle C is 146.83 - when both were on at the same time you could hear the slow beat frequency.
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Last edited by old_CJDC_ops; 08-19-2011 at 12:41 AM.. Reason: Delete ref to intermod
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Old 08-19-2011, 10:59 AM
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Ahhh wow that's pretty wild way above my pay grade so is there any thing I can do about it or is it what it is and thanks for your very technical assistance
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Old 08-19-2011, 11:35 AM
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First off I missed a "C" .. it's CTCSS. It's also known as "PL" and other vendor specific nicknames. You can read about it here or here. I've never noticed the problem here because a) It hasn't been in use on the systems I listened to or b) The receiver audio rolls off the frequency response above these "subaudible" tones with a high pass filter.
Have you tried substituting one of the other scanners? I'm sure that this is a common issue and someone with more experience than I have will fill in the blanks. Here is one RR thread on a DIY notch filter, but it's designed for one of the lower tones .I apologize for not being more help.
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Old 08-19-2011, 11:57 AM
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All PL tones are lower than 300 Hz, and most decent scanners are designed to either strip off or degrade frequencies below that point, so you don't hear the PL tone. But it doesn't always work out so you may hear PL tones, depending on their audio level on the transmitted signal. The tone is also used to transmit a short burst immediately after the transmitter is unkeyed and this is used in a way that eliminates the squelch tail on the other system receivers. It's called "reverse burst" and you can actually hear it on any system that uses it.
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Old 08-19-2011, 12:12 PM
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IIRC, the Bearcat 210 actually had a cap and resistor or two on the speaker audio... Probably in most cases the speaker in the radio just doesn't respond to anything lower than about 300 hz. whereas the line output (if the mfr. hasn't put in a highpass filter) puts it all out.. Could dig up a flea market graphic audio equalizer to put in the feed chain...the more bands on it the better. Also, there is graphic EQ software, but I'm not sure if it could be inserted into the chain in the computer used for streaming..
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