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Question about HARMONICS
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RadioMan
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Joined: 03 Nov 2003
Posts: 48

Post Question about HARMONICS Reply with quote
I am operating @ 93.9mhz. On a "police" scanner I have found a harmonic (5th or 6th) @ 469.5Mhz. It is only audible however, when a song is FADING OUT(the carrier is at low modulation). When I am at nearly full modulation it can't be heard at all.

Can anyone explain why?

I have the scanner about 40 feet from the antenna. Later this week I will take a handheld and walk the neighborhood to see if this has something to do with the location of the scanner.

Also, at the lower harmonics, such as 187.8Mhz or 281.7Mhz I don't hear a thing.

Any ideas would be appreciated. Thanks!
RadioMan
Tue Mar 02, 2004 8:14 pm View user's profile Send private message
pcs
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Joined: 18 Jan 2002
Posts: 3063
Location: Radio Land

Post Reply with quote
Receivers, especially wideband scanners and other miniature
cheap radio equipment are basically prone to all kinds of
interference. In short, they respond not only to received
signal but to mirror frequeny and a number of other signals.

For example, if you have two very strong signals at the antenna
at, say 400MHz and 600MHz you're likely to hear a signal at
200MHz (difference between the two). Its just a crude example.

Why you only hear it at low modulation is because broadcast
FM radio is wideband and your scanner is narrowband (10KHz).
When you increase modulation you modulate at 75KHz and you only
hear noise on your scanner.

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Marko - PCS Electronics
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Turn your PC into a FM radio station!
http://www.pcs-electronics.com
fax +386 4 2316 128
Tue Jul 20, 2004 9:48 am View user's profile Send private message Visit poster's website
RadioMan
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Joined: 03 Nov 2003
Posts: 48

Post harmonic & (update) Reply with quote
thanks marco...good answer..it makes sense now.

For an update on me, I have moved my freq from 93.9 to 107.1. There were some bozo's in this market that went on @ 93.9 with 150Watts and blew me off while gaining attention of the FCC. They busted these guys twice, so I deceided to move my 5 or 6 watts somewhere else. With my low power, either the commish doesn't care that I'm on or they haven't found me yet (probably the latter). I am carful not to cause any interference and keep my programming as professional sounding as I can. I am in a major metro area in the USA. I have been on-air now for 4 months straight with no problems with gear. I am getting out about 2 miles with good coverage. Have not as yet tuned the antenna to new frequency but will do that in a month. My coverage is slightly less @ 107.1 than it was @ 93.9. I assume it is because of the antenna not being in resonance.

One question...with output power being equal- does the frequency affect the coverage on FM the way it does on AM? (Example: 1,000 watts gets out further at 600 khz than it would at 1600 khz? ).

Thanks for your help on this site by the way.

RadioMan
Mon Feb 28, 2005 7:56 pm View user's profile Send private message
pcs
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Joined: 18 Jan 2002
Posts: 3063
Location: Radio Land

Post Reply with quote
I don't think there's a significant difference between 88 and 108MHz
as far as range is concerned. You probably just need to tune antenna.

_________________
Best regards,
Marko - PCS Electronics
--------------------------------------------------------
Turn your PC into a FM radio station!
http://www.pcs-electronics.com
fax +386 4 2316 128
Mon Feb 28, 2005 8:02 pm View user's profile Send private message Visit poster's website
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