Why do I lose my FM reception when I roll up to a stoplight intersection?
Nothing but static.
It could be a bunch of things.
It might be something physically blocking the radio signals like a nearby building or a truck at the intersection. The signal might be reflecting off of a nearby car or truck as well, leading to interference that causes you to lose the station.
It might be that the signal uses an RF traffic detector (cheaper and more reliable in the long term than a buried loop inductive detector). The radio from the RF traffic detector isn’t on the same frequency, but you are close enough to it that the radio waves might basically be swamping your FM radio’s input.
It might be that a nearby car has noisy spark plugs (electrically noisy) which are generating enough radio static to swamp your FM receiver if you are close enough to them. Usually this won’t just be static, though. You’ll hear a putt-putt-putt-putt static pattern that corresponds to the speed of their engine.
It might be some sort of local communication system used by emergency and non-emergency services. They’ll often mount antennas on traffic lights and lamp posts since the structure is already there and under their control.
It might also be a communication system used by the traffic lights themselves. Traffic lights these days are often synchronized so that they can better control the traffic over larger areas.
Some of the newer LED lights put out a lot of radio frequency noise, which can swamp your radio’s receiver.
Nearby power lines might also be putting out enough RF noise to cause you to lose reception.
If the signal is weak, you might also be experiencing an issue often referred to as “picket fencing”. Basically, if you drive by a picket fence fast enough, you can see well enough between the slats to see what is behind it. But if you stop, your view is much more severely blocked. The same thing happens with radio waves. As you are moving, you get enough of a signal peeking through the trees and between buildings and such that you get good enough reception to hear, but if you happen to stop where the signal isn’t so good, your reception goes to crap. Sometimes if you inch forward a bit at the light you can reach a point where the signal strength improves.
There are probably some others, but that’s what I could think of off the top of my head.
One intersection in particular or any intersection in town?
damn, my fM and Am reception went all to hell last year. I suspect & IANAE it’s in the “antenna” connection. Can’t get AM at all I miss the David packham show and RUsh and all my heartburn fiends. The FM is wonky, have to dial, +1, -1 to tune in. Google has not solved this problem.
VW tig 2012
My kitchen clock radio goes static when I plug in the mixer same outlet.
If it’s any intersection it may be something going wrong with your car at idle that is causing interference.
I was thinking about this, too. One explanation is that the idle voltage is too low for the radio. (If there’s an amp involved, this is much more likely.)
Places like AutoZone often have a free battery/charging test service to determine if there’s a problem in this department.
I think **e_c_g’s **answer covered all possibilities, so I hope I can piggyback on this question with a similar phenomenon:
I live in a mountainous region and my car radio is always tuned to the same FM station of which I normally have good coverage in at least a 50 km radius around here. But every time I pass a certain point of a street I often drive by, the signal shortly (about 2 seconds) switches to another station. There’s no static in between the switches, just a short clear signal from the different station, and then the clear signal of the correct station again. I think it has to do with the fact that this point is shortly after a local peak in the landscape.
AF switching. More common in Europe, I have not encountered it in North America.
I knew about AF switching, and yes my radio has RDS. But in my case it must be a malfunctioning of AF, cause it switches to a different station, mustn’t it?
FM is Frequency Modulation. It encodes the signal by changing the frequency up and down. An FM receiver typically works by locking onto the signal and tracking the frequency as it changes up and down (I can go into detail about the various methods of FM decoding if you want but it’s not important for this discussion - the only important thing here is the concept that the receiver locks onto and tracks the changing frequency).
If you have two stations on the same frequency, the FM receiver will tend to lock onto the strongest signal. If you reach a point where the landscape blocks or at least reduces one of the signals, then the FM receiver will end up latching onto the other signal since it is now the strongest.
I live close to the PA/MD border, and this happens on one particular radio frequency near me. There is a small ridge line near the state border, so on the north side of that line my FM receiver will latch onto the PA station, and on the south side of that line the receiver will latch onto the Baltimore station.
I strongly suspect that the local peak that EinsteinsHund describes is responsible for blocking one of the signals, allowing the radio to latch onto the other signal.
In my case, the switch from one station to the other is abrupt and there’s no static or flutter between the two stations. I have been in some areas though where the signals from the two stations are both equally strong (or equally weak, depending on how you want to look at it), and minor variations in signal strength caused by the local landscape can make it difficult for the FM receiver to accurately track either signal. You can end up with this really annoying fluttering as the receiver switches back and forth between the two signals that it is tracking.
Here’s a short summary of the capture effect. (Two stations on same frequency.)
There’s also an odd effect for AM stations (of all freq. ranges) but I don’t think it applies to FM.
If two stations (on different frequencies) are in a direct line to you (hence you need to be on that line) then the closer station’s antenna can modulate the signal of the farther station and you end up hearing the farther station on the nearer station’s frequency. This requires the relative powers and distances to favor receiving the farther ones signal.
All sorts of odd effects like these out there.
Various ones.
The closer to the intersection, the worse it gets.
No, this has happened with two different cars, of different models & years.
oh, in that case, yeah there’s something amiss. perhaps incorrect AF info coming in over RDS?