I have reached a point of extreme frustration with the inability to receive a clear signal from any radio station except 102.9 WIQB and 107.1 WQKL without extensive manipulation and modification of the antenna of my bookshelf style stereo unit. I would like to lodge a formal complaint with the FCC, but I would like to know how widespread this problem is first. I live on South First, in central Ann Arbor, and I cannot listen to stations on frequencies 88.7, 91.7, 93.9, 94.7, 95.5, 96.3, etc. due to interference from the signal broadcast at 107.1. I live in a second floor apartment (i.e. above ground). As a side note, does anyone know of a simple and/or effective way to filter out the signal on the 107.1 carrier? This is driving me bonkers.37 responses total.
You could get what it called a notch filter, which dampens the signal at 107.100 MHz but lets other frequencies through. It will dampen stations right around there, too to 107.3 and 106.9 (if there are any there) are likely to be washed out too. However, that may not work at all for you. I believe the transmitter is located ontop of Tower Plazza, and if so, you may be right in the "lobe" of the transmitted signal, and your little radio may simply be overloaded with signal, such that the 107.1 RF is strong enough to crawl right into your radio. Welcome to urban RF problems. *sigh* Have you tried other radios?
On the brief occasions I've been driving near your apartment, I've gotten radio signals fine, Eric. My radio receiver at home, which is connected to the large stereo system (we don't use it much) gets lousy reception too. Except, we dont' have too many houses around.
ironic isn't it that 107.1 WQKL and 102.9 WIQB are both owned by the same company (as is 1050 am WTKA)
I suspect that the problem may be with your receiver. Try something with a decent front end like a GE Super Radio or Cambridge Soundworks Model 88. I'm sure there are many others but I also know there are several radios with very poorly designed tuners that are very very susceptible to RFI and can barely tune a station in the best of conditions.
... have a friend drop by with their radio before you buy, of course...
What Klaus says is right. Most radios being sold are not very well designed. The "front end" of a radio is that part which should be able to differenciate signals. Unforunately, most don't do such a good job.
Have you contacted the stations? They may be able to help you. They would certainly want to do that before fielding a complaint from the FCC.
I remember, when I lived on Ellsworth Road across from the "Old Meijer" store, picking up WAAM (AM 1600) on my telephone/answering machine. Fortunately, someone from Ameritech (them Michigan Bell--An Ameritech Company) placed a filter on the line so I could not pick up any radio signals.
I phoned WUOM to ask if they had received any comments about it, and I was
put in touch with the chief engineer, whom I know through another
connection, and he suggested a filter of the type described above. I have
a JVC portable unit. I am not considering buying another radio. Here is
what the WUOM engineer had to say:
Regarding your call from this morning in which you stated that WUOM is wiped
out by WQKL on your radio:
It sounds like your experienceing "blanketing interference", which is what
can happen when a strong signal such as from a nearby transmitter
overpowers your receiver.
Though we have never been happy with the idea of WQKL (formerly WAMX)
having their transmitting antenna operating from the top of Tower Plaza, I
don't have any reason to think that they are operating outside of their
legal parameters.
Here's what the FCC Interference Handbook has to say about blanketing:
The second problem is called "blanketing." It occurs when electrical
or electronic devices are very close to the transmitter and where
the FM signal is very strong. Operators of new FM stations are
required to respond to all reasonable interference complaints in the
immediate vicinity of the station. If the station is more than a
year old or you live outside of the protected area, installation of
an FM broadcast band rejection filter at your TV and/or stereo
receiver antenna input leads, as well as use of a highly directional
antenna may reduce your problem. You may also wish to reposition the
location of your equipment to attempt to minimize or eliminate the
problem(s).
See
http://www.fcc.gov/Bureaus/Compliance/WWW/tvibook.html
for more about interference.
Because WQKL has been broadcasting from Tower Plaza for more than a year
they are no longer under any obligation to take care of listener complaints.
However they may wish to do so, if you give them a call.
What kind of radio do you have? Is there an external antenna? If so the
best bet is probably to install a tunable filter to reduce the strength of
the WQKL signal. Otherwise, if you have a
built-in telescoping whip antenna it might improve matters to shorten it.
While I was living in College Station, and was desparate to get anything other than the local boring radio stations, I bought an "antenna amplifier" thing for my stereo. It plugs into the wall and has a little knob you can twiddle to improve the reception of any particular station. Moving it around sometimes helps too. I'm not completely convinced that this thing is doing anything wonderful, and have no idea if such a device would help Eric, but thought I would mention it.
i've seen versions of such an item in catalogs, usually a knob that fits in the end of an antenna to boost signal reception indiscriminately.
Most likely a preamp is *not* what you want in this situation. The problem here is simply too much RF that is invading the front end of the radio.
When I lived in the Flowerpot neighborhood in East Lansing, I could hear WKAR-AM very clearly on my telephone. Eventually, I called up WKAR to let them know about it, and they were effusively grateful that I had called. Nevertheless, they were no help. They told me that I should get rid of my cheap phone and get an AT&T phone -- this was in the days when the pre-breakup phones were so much heavier and better made than the flimsy ones available in stores). I said: "This *is* an AT&T phone." That silenced them, and they had nothing else to say.
I haven't had this problem on my radio. I have found WQKL leaking through on my TV on various channels. I like in a rather different part of town from Eric, and when I've had that problem lately I've usually been able to turn the antenna a bit and make it go away. A year ago, living in yet another different part of town, I used to find WQKL coming in strongly enough on my TV when I was watching channel 67 that it was hard to hear the sound from channel 67 over it, and there didn't seem to be a way to make it go away. That was really annoying.
Perhaps a better way to go would be to call up a competing radio station (one you'd like to listen to) and say "I love your station, but the signal is pushed out by that darn oldies station. Any suggestions?". That is, try to get info/help from someone who has something to gain, rather than ask for help from someone who only stands to lose.
So THAT'S why both of my last 2 cars had trouble keeping WDET in tune when driving downtown. The only other place I had anything like that happen was on I-696 around Greenfield, in the tower forest. This is a fairly common problem. An excessive signal going into the receiver front end will force it into a non-linear region of operation. This causes what is called "intermodulation distortion", where different signals mix together. Generally, it means that anything but the strongest signal is probably screwed up. A notch filter isn't a bad idea, but there's another route to try: an attenuator. Sometimes knocking all the signals down a ways will get the receiver back into the linear operating region, and the remaining signal at the desired frequency is still strong enough to come in clearly. That's all you care about anyway. Lowering the antenna, or pointing it directly toward or away from the source of the blanketing signal, is another cheap technique. Problem is, reflected signals get you from all angles. A notch filter isn't that hard to make. There are two kinds of notch filter, parallel-resonant and series-resonant. A parallel-resonant filter looks like an open circuit at the notch frequency, and it's put in series with the signal lead. A series-resonant filter looks like a short circuit at the notch frequency, and it's put between the signal lead and ground. You can probably fit a notch filter inside your JVC box without much hassle. It is amazing how much empty space there is inside radios. The impedance of your whip antenna is probably 30 ohms or less, so anything above about 10 ohms between the antenna and ground, or less than 100 ohms in series, probably won't be very noticable. For a series resonant trap, you might try something like a 1-5 pF trimmer capacitor in series with a small coil, connected between the antenna and ground. At 107.1 MHz, a 3 pF cap has an impedance of about 500 ohms. Put it in series with an inductor of about 1 microhenry and you should be able to tune it onto the offender pretty easily. You connect this between the antenna connection (inside your radio) and the ground plane nearby on the circuit board. You tune it to 107.1 MHz, and the impedance of the capacitor and inductor are equal and (in the ideal case) opposite; they cancel, making a short. At 106 MHz, the impedance of the capacitor has increased by about 5 ohms, and the impedance of the inductor has gone about 5 ohms in the opposite direction. This gives you about 10 ohms from antenna to ground instead of a dead short, and your signals should start coming in. STeve, you've probably got ARRL handbooks handier than I do right now; how many turns of 16 gauge wire at 1/4" diameter do you need to get something between 0.7 and 1 microhenry? Does Rat Shack sell trimmers?
They should sell trimmer pots.
i believe i've seen trimmer pots there. i'm not sure i'm sufficiently skilled at electronics to translate the above into a solution, although i do understand most of the language. what i'm lacking is the solid understanding of the theory behind the list of components... ...and the time to do this...
I love it when people talk about technology that I don't understand. It sounds both profound and focused at the same time... Don't mind me, I need to go to sleep.
I like the idea of trying an attenuator before attempting to build a filter. There much simpler, consisting of a couple of resistors. What kind of antenna are you using, Eric?
(( Winter Agora #182 <---> Music #182 ))
What, waiting to time it just right so the item numbers match up?
No, I messed up, the winter Agora number is wrong, sorry.
Re #17: A tripper POT isn't useful for making a tuned circuit. You need a trimmer capacitor, which is a rather different beast. Re #18: You may not be, but the hams in this bunch probably are. I can usually get things to work halfway if not better. If you're willing to risk working on your radio, someone will probably volunteer to calculate the numbers and do the soldering. I've already got some numbers above. This doesn't require much theory, it's strictly cookbook. You probably need one capacitor, some wire formed around a bolt, some solder to connect it and a bit of hot glue to hold everything down. Cost should be a buck or so. Time I can't help you with. Re #20: A 20 dB attenuator should be easy. I'd try a 270 ohm resistor between the antenna and the radio's (internal) antenna connection, and a 27 ohm resistor from the antenna connection to ground. Both ought to be off-the-shelf at Rat Shack. Something that might be useful for experimentation: put the antenna down, and try placing a sheet of something metallic (a cookie sheet or aluminum foil) close to the radio to shield it. If you can get the interference to go away while you still have the desired signal strong enough to listen, an attenuator may be workable. If not, you need something that's frequency-selective. That means a notch filter.
What about a 1/4 wave open stub tuned to the overpowering station? Seriously, You may have to go to extremes to solve this problem. Like wrapping the radio tightly in aluminum foil with only an outlet for the antenna wire and a filter in the antenna wire to knock down the strong signal. Ferrite beads would have to be put around any other wires going to the radio. If you have ever opened up a radio like the one in question, you will see that it is noting more than a plastic box with electronics screwed to the inside of it. The enclosure provides NO shielding at all. Sometimes you will find a little shielding around the RF section, soldered to the PC board, but generally not. The standards for FR susceptibly for consumer electronics are practically nonexistent so many of the radios sold are very susceptible. The front end of most receivers are also exercises in minimalism with poor selectivity, sensitivity and rejection figures. Tower Plaza glows in the dark from all of the RF on the rooftop. You just don't see it because it never gets dark in downtown Ann Arbor ;-) However, the equipment up there has to meet pretty stringent regulations for spectral purity and most stations are pretty particular about making sure that their signals are clean. I've talked to the technical person at WIQB too. Several years ago one of their old remote transmitters was getting into the ARROW's 440 repeater and we were listening to Art Fair news in the 70 cm amateur band. They were very responsive and I've not heard them since.
Re #25: A 1/4 wave open stub is just another twist on the series-resonant trap. The disadvantage is that it's much harder to adjust; once you've cut it too short, you need to make another one. It's also quite a bit larger physically, and I wouldn't bet on being able to coil one up inside the case of a small radio. I keep thinking about traps which could be built with hardware-store parts and tuned with something like a 6-32 screw, but I am having trouble thinking of materials which would be suitable. Copper pipe suggests itself. The mechanical complexity would go way up, as would the cost. You'd have a tough time building anything more rugged, though! I wouldn't worry about shielding the entire radio. This would only be necessary if the signal was coming in by the speaker leads or something, and you'd know if that was the problem because the volume control wouldn't reduce the interfering signal. Blanketing has to hit before the mixer (the device which converts the 88-108 MHz input signal to the intermediate frequency of [typically] 10.7 MHz), and the best way to get a signal to it is via the antenna. Worse comes to worst, you'd need ferrite beads over the speaker leads and power cord to block RF from coming in over them. Oh, I checked Rat Shack for trimmer capacitors. They have nothing of the sort. I had no time to look at Purchase Radio.
Actually, I believe that it is possible to have RF coming in through the speaker wires, and not have the volume control have any effect on such RF. My boom box has a very quite hum which is constant regardless of the volume setting; it can be obnoixiously loud sometimes when the volume is turned down and I'm using headphones. (The hum continues to be just as audible when the volume is turned all the way down to silence.)
That's not RF. That's 60 Hz AC hum. I'd guess the hum is on the DC power, which is why it's not affected by the volume control.
Actually - probably 120 Hz...bad cap in the power supply?
Re #27: You can probably get rid of the hum by adding more power supply filtering. If you're interested, enter something in the Science conference.
Get rid of the hum by unplugging the radio and running it on batteries. It is not uncommon for hum to be caused by magnetic coupling instead of ripple on the DC.
Then one would have the hum in the radio when it was new (and operating properly). Did it?
I recognize that the hum is a power supply related issue, not an RF issue. However, the point I'm trying to make is that you don't have audio source <--> amp <--> volume control <--> speakers you have audio soucre <--> volume control <--> amp <--> speakers And indeed, if RF is leaking in through the speaker wires, the volume control won't affect it, if you have this sort of design.
I have never seen audio source <--> amp <--> volume control <--> speakers except when a pad is used to balance two or more speakers of an audio output. RF doesn't care about connections. RF cares about resonance and / or proximity.
Usually one has audio <-> preamp <-> volume and tone controlls <-> amp <-> speaker (for whatever relevance that has.....).
I've seen amp -> volume control -> speaker, but only for low power (under 1 watt) in things like cheap TVs.
Re #33: Interference coming in through the speaker leads is very different from "blanketing" interference, which is what other has. A CB can come in over the the speakers, without affecting the audio coming from the desired station at all.
You have several choices: