FM Reception is like Day and Night

[Murf]

I have recently ditched my old all-in-one bookshelf system for a Harmon/Kardon amp with Klipsch KG 4.2 speakers and Harmon/Kardon TU-211 tuner. The problem is my FM reception is lousy during the day, especially for low frequencies, but around midnight the signal comes in loud and clear.

The amp is fine because the sound is fantastic for CDs and digital audio input. I have eliminated the possibility of interference by trial and error. I have tried plugging the tuner into the accessory terminals with no improvement. I am using a wire dipole wall mounted antenna. I get a strong signal that pegs the LED lights, in fact the stronger the signal the worse the distortion. Unfortunately, moving the unit to another location is not an option. The bookshelf radio never had this problem.

I have talked to local so-called experts and they have no explanation. Does anybody have any experience with this problem and any suggestions on how to correct it?

Many thanks - this is a great forum!

MURF

[WMcD]

I have an issue with too much signal strength at the office in downtown Chicago. The office is a block from Sears and two miles from Hancock.

People would tell me it is a matter of being inside a building with a lot of steel, which can act as a shield. The solution in one case was to short out the antenna terminal with a paperclip. It was overload issue.

Home is about four miles north of the transmitters, up the lakefront . The problem seems to be mulitpath reflections. That is the same thing which causes ghosts on TV reception.

I'm pretty convinced it really is multipath. There are quite a few buildings in the way. Also, I've found the same distortion while listening to a Walkperson FM and riding the bus. When we get into my neighboorhood, reception gets fuzzy.

One suggested solution to multipath is a circularly polarized antenna which can be homemade. In theory the reflected signal gets flipped in polarization. The antenna is not sensitive to the flipped signal coming from the 180 degree direction. I've not built one yet because I wonder if it will work in the apartment where the signal may have so many reflections that polarization is random. I'll let you know.

The night and day thing is hard to explain. FM tuners have adjacent channel issues. A strong signal on nearby channels can overload the front end of the receiver. It maybe that signal strenght changes at night because of different propagation qualities.

For the record, this hit home one day when a power failure put many local transmitters out of action. Distant ones were, then, receivable.

Try the paperclip. The next easy solution is to construct a dipole (the T shaped thing made out of 300 ohm twin lead) with a longer lead and move it around the room. You might find a spot without multipath for your favorite station.

Gil

[Murf]

Thanks Gil.

I will try the paperclip and let you know if it helps. I have already tried moving the antenna around the room but it didn't work and my wife made it obvious that I was crazy if I thought I was going to put that ugly antenna anywhere that it could be seen.

I hadn't thought of multipath but now that you mention it I have noticed that the tuner is landing one decimal over from the actual station in seek mode.

I appreciate your suggestions. This thing is driving me crazy!

Murf

[WMcD]

I don't know if it will help in the short run. But tell us all here about your situation. It might be worth it in the long run.

I see you're in Austin. Are you close to the transmitters. Is this a matter of a favorite station, or all. Is it close or far.

Do you have a clear shot at the transmitter.

Best,

Gil

[Jay481985]

I remember it has to due with the atmosphere, sunlight, temperature. I am not a engineer nor scientist but I remember once reading something about radio frequencies working better at night since the atmosphere is cooler something contracts (ionosphere) to make the signal enhanced. Plus the fact that the cosmic rays and electromagnetic interference is not present since the sun is on the other side of the earth. I guess I will google to re-educate myself.

Edit

http://www.newton.dep.anl.gov/askasci/eng99/eng99322.htm gives some desciption why.

[Murf]

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On 8/11/2005 11:42:55 PM William F. Gil McDermott wrote:

I don't know if it will help in the short run. But tell us all here about your situation. It might be worth it in the long run.

I see you're in Austin. Are you close to the transmitters. Is this a matter of a favorite station, or all. Is it close or far.

Do you have a clear shot at the transmitter.

Best,

Gil

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I am about 12 miles NNE from the transmitter towers for most of the stations that I listen to. I am probably below the ekevation of the towers but I can't see them from my location. I am in a valley and there is a watershed divide or ridge between me and the towers that probably would block andy attempt at a straight shot. I would probably have to go 100' high to have any chance of that.

I tried the paperclip idea but alas no improvement. I am listening to my favorite station as we speak. It is slightly fuzzy but strong. This station actually broadcast from Bastrop which is about 30 miles to the east, but I can't hear any real difference between this station and the others that are transmitting about 12 miles NNE of here. My music preferences are eclectic so I tend to skip around the dial.

Thanks for your feedback.

Murf

[Murf]

This is a most excellent description of the problem. I guess that this new tuner receiver is both more sensitive and more amplified than the small low wattage system that I have been listening to for the past few years. That may explain the fact that I hear the distortion more now than before.

It is looking more and more like I need to put an antenna on the roof if I am to solve this problem, or just stop listening to radio during the day!

[scriven]

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On 8/11/2005 10:02:14 PM William F. Gil McDermott wrote:

...

The night and day thing is hard to explain. FM tuners have adjacent channel issues. A strong signal on nearby channels can overload the front end of the receiver. It maybe that signal strenght changes at night because of different propagation qualities.

...

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Another, all be it remote, possibility is that there is a station that is interfering that only has a daytime license. I know in the past the FCC used to issue licenses with time restrictions. It might be worth finding out if any stations in the area only operate during daylight hours.

[JJkizak]

From what you say I believe your signal strength is not strong. FM travels in straight lines and your in a hole. If the transmitting antenna is 1000 ft high you can usually pick it up ok from 46 miles away as long as you are not in a hole. (curvature of the earth). There are other factors, (ducting) and Ralieghe's distribution (spelling). I would put up a gigunda antenna. Also the noise figure of your receiver comes into question. Should be at least 3 to 4 db. When you hear the noise background you are running about 10 db quieting on the receiver. (not enough signal). You can duplicate this with precision test equipment and see what I mean. You need at least 20 db quieting to get rid of the noise. It might be cheaper to go satellite rather than put up a huge antenna and a $4000 receiver and cut a Panama Canal through your mountain. If you can round up an old military Parametric Amplifier (noise figure 1.8 db, 20 db quieting at -100 dbm) that would really help but unfortunately they cost about 100K new.

JJK

[boom3]

For the VHF frequencies of 88-108 MHz, where American FM is broadcast, the ionosphere is normally a non-issue. The portion of transmitted power that strikes it goes right through into space, as do TV signals. There is a sweet spot of frequencies, about 9-12 MHz, that the ionopshere reflects reliably at night. During periods of intense sunspot activity, portions of the ionsphere may get dense enough to temporarily reflect VHF signals.

I tend to agree that you may have overload and/or multi-path issues. Another possibility is ducting. When the atmosphere has layered weather systems, like fog, ducts are created which allow distant signals VHF to sound strong.

[dbflash]

Murf,

My guess is you will not have this problem in the fall,winter and spring.

2 things could be causing this: leaves on trees and hot summer time temperatures. that is why it sounds better at night, lower humidity and temperatures.

The attached may also answer some of your questions.

http://www.fanfare.com/rfms-bk.html

Danny

[Murf]

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On 8/12/2005 4:54:36 PM dbflash wrote:

Murf,

My guess is you will not have this problem in the fall,winter and spring.

2 things could be causing this: leaves on trees and hot summer time temperatures. that is why it sounds better at night, lower humidity and temperatures.

The attached may also answer some of your questions.

http://www.fanfare.com/rfms-bk.html

Danny

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Great site Danny!

I appreciate all of the advice and information from everybody.

One last thing that I plan to do is have a local stero shop take a look at the tuner. He says that it is possible that a circuit my be faulty. This seems like something I should do before I invest in a serious antenna.

Just for grins I attached long wires attached to a dipole antenna to the FM antenna connectors and listened while I walked around the room trying different locations. I also took the antenna out into the yard. Neiter improved the signal clarity and there was not one sweet spot. This was true and consistent for different channels. So It is possible that the tuner is faulty.

Murf

[Murf]

I took the tuner in today and it did reproduce the problem in the shop. The tuner is faulty and will likely need a new circuit that controls the gain. The signal was evidnetly being driven wide open causing the distortion. There is no explanantion for the day and night problem. I will let you guys know if we solve that issue.

Being a novice at all this, I am incredibly impressed with the expertise provided by this forum. You guys are great and if nothing else you have completely educated me on antenna issues and FM reception problems.

Thanks...

Murf

[WMcD]

I had a bear of a problem in my sister's garage in Dallas. The problem is that it is down in a hollow. I improvised a mast up 10 feet and that was not up to rooftop level of surrounding houses.

My guess is that I and you might have a problem resulting from the propagation path. We are getting some signal from diffraction from the land mass and buildings in between. That is similar to multipath.

- - -

There is also an issue in FM reeiver design. I'll have to look it up.

There is one type of detector which works well but requires a pre set level. Therefore there must be several "limiters" in the circuit in from of it. Picking numbers out of the air, each limiter might adjust for 10 dB. So you need four to act as automatic gain control over 40 dB. Obviously this leads to cost issues.

The other is more simplistic and does not need limiters. But it does not function as well. It finds its way into some designs. I don't know how well it responds to difficult reception conditions.

I'm very curious how this works out for you. Plus I'd love to hear from others with better understandings.

Gil

[jbsl]

Hey Murf nice to see a fellow Austin Klipsch owner on the forum!! I've noticed more of us on the forum. May have to see if we can set up a Austin KLipsch get together.

Whenever I drive down to San Antonio just after I leave San marcos I start losing reception to KLBj during the day. But at night I have made it all the way to SA and then started to lose it. So I don't understand the science but at night radio stations are stronger and better sounding. Sometimes at night I tune in to a rock station and get a country station for a moment.

Enjoy your Klipsch but be careful the next thing you know you will have a bigger pair of Klipsch, and then a bigger, and then you have to upgrade your whole stereo. It's a vicious cycle so be careful I know from personal experience!!

Xman

[reznil]

Here is some info on radio waves...

Radio waves naturally travel in straight lines, so you would naturally expect (because of the curvature of the earth) that no radio station would transmit farther than 30 or 40 miles. And that is exactly the case for ground-based (as opposed to satellite) TV transmissions. The curvature of the earth prevents ground-based TV transmissions from going much further than 40 miles (64 km). Certain radio stations, however, especially in the short-wave and AM bands, can travel much farther. Short-wave can circle the globe, and AM stations transmit hundreds of miles at night.

This extended transmission is possible is because of the ionosphere -- one of the layers of the atmosphere. It is called the ionosphere because when the sun's rays hit this layer, many of the atoms there lose electrons and turn into ions.

As it turns out, the ionosphere reflects certain frequencies of radio waves. So the waves bounce between the ground and the ionosphere and make their way around the planet. The composition of the ionosphere at night is different than during the day because of the presence or absence of the sun. You can pick up some radio stations better at night because the reflection characteristics of the ionoshphere are better at night.

[jbsl]

Hey Murf I have a Terk powered FM antenea that I don't even use. If you still have problems after getting it back from the shop you can have this Terk antenea and see if it helps any.

I live in Austin also, well just outside it and have some Klipsch La Scalas and just posted on your radio post. Nice to have another Austin Klipsch owner on the forum.

Xman/James

[Murf]

Thanks for the offer Xman. I will let you know if I need the antenna after I get the tuner back in a week or so.

I can't believe what a difference it makes to listen to music on these Klipsch speakers. The great thing is that you can pick up this top of the line equipment for nothing right now because everyone is converting to home theater units. I piced up these Klipsch KG-4.2 speakers. Harmon/Kardon KH 6600 amplifier (pre-Korea 90 watts/channel) with a tuner and a Sony CD player for $325 off of Craigslist. Easily over $2,000 worth of equipment if bought new. Are these people crazy? Looks like I will have another $75 into it with the tuner repair, but still a total steal.

Ain't Austin great!

Murf