RF distortion - Electronic Circuits Projects Diagrams Free

bioborg · 21st June 2006, 05:48 PM

Just wondering...
I am here at work and occasionally I have to move my antenna for my frequency modulated (FM) radio station that I like to listen to. It's only about 2 miles away, and all is stationary (both antennas). So why do I have to occasionally move my antenna to regain my good reception. I think it's perhaps something to do with the air and how it changes after warming up ? Or perhaps it's something else, I don't know?

JimB · 21st June 2006, 07:41 PM

VHF radio signals are affected by changes in air temperature/humidity/pressure. But over a range of two miles, I dont think that is the problem in this case.

More likely you are suffering from signal changes due to reflections from nearby objects. You do not state where you work, but I assume that things are moved around in your building and adjacent buildings. This will change the pattern of peaks and nulls in signal strength, so you have to move your radio around to find a peak.

My best guess.

JimB

philba · 21st June 2006, 08:18 PM

I'd bet this is a multipath problem. are you near a parking lot? trucks and cars make for nice reflections...

bioborg · 21st June 2006, 09:15 PM

Well, I am in Connecticut, USA. Yes, there is a parking lot with alot of cars parked outside, and yes there are alot of things moving around inside the building. So is it safe to say that it's a combination of the air characteristics, and the succeptability of the signal to reflective objects that interfere with reception ? This makes sense now that I consider that RF is essentially photons at a particular frequency (just like visible light, gamma, x-ray, or any other frequency in the electro magnetic spectrum...

audioguru · 21st June 2006, 10:22 PM

A high quality FM receiver has a high "capture ratio" which allows it to lock on to the main signal and ignore the changing reflected signals. A cheap FM receiver has a poor capture ratio.

Stage singers use an FM wireless microphone and the receiver has "diversity" which is two antennas and a circuit to select the antenna with the best signal. Some car radios also have two antennas with diversity to avoid multipath interference.

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21st June 2006, 05:48 PM	(permalink)
bioborg	RF distortion Just wondering... I am here at work and occasionally I have to move my antenna for my frequency modulated (FM) radio station that I like to listen to. It's only about 2 miles away, and all is stationary (both antennas). So why do I have to occasionally move my antenna to regain my good reception. I think it's perhaps something to do with the air and how it changes after warming up ? Or perhaps it's something else, I don't know?

21st June 2006, 07:41 PM	(permalink)
JimB	VHF radio signals are affected by changes in air temperature/humidity/pressure. But over a range of two miles, I dont think that is the problem in this case. More likely you are suffering from signal changes due to reflections from nearby objects. You do not state where you work, but I assume that things are moved around in your building and adjacent buildings. This will change the pattern of peaks and nulls in signal strength, so you have to move your radio around to find a peak. My best guess. JimB __________________ Experience is directly proportional to the value of the equipment ruined.

21st June 2006, 08:18 PM	(permalink)
philba	I'd bet this is a multipath problem. are you near a parking lot? trucks and cars make for nice reflections...

21st June 2006, 09:15 PM	(permalink)
bioborg	Well, I am in Connecticut, USA. Yes, there is a parking lot with alot of cars parked outside, and yes there are alot of things moving around inside the building. So is it safe to say that it's a combination of the air characteristics, and the succeptability of the signal to reflective objects that interfere with reception ? This makes sense now that I consider that RF is essentially photons at a particular frequency (just like visible light, gamma, x-ray, or any other frequency in the electro magnetic spectrum...

21st June 2006, 10:22 PM	(permalink)
audioguru	A high quality FM receiver has a high "capture ratio" which allows it to lock on to the main signal and ignore the changing reflected signals. A cheap FM receiver has a poor capture ratio. Stage singers use an FM wireless microphone and the receiver has "diversity" which is two antennas and a circuit to select the antenna with the best signal. Some car radios also have two antennas with diversity to avoid multipath interference. __________________ Uncle $crooge