FM interference

[Mr. RF62]

Hi All,

I have a problem with some radio interference and its driving me nuts. I have a Yamaha receiver and the signal is coming in loud and strong, but so is this high pitched ringing. Somewhere around the 16kHz - 20kHz range. I'd like to eliminate it if possible. Does someone have an idea.

Help would be appreciated.

THX.

[WMcD]

More information is needed.

Are you saying that an FM station is being received?

Are you saying it is everywhere on the dial?

Is this an AM station which is being picked up while the input selector is set to Aux or Phono or something else?

Is this a new installation? When did the problem start.

Have you found the physical location of the radio station which being picked up?

Gil

[Mr. RF62]

FM station is being revceived. It is everywhere on the dial, no AM station, new installation of new 5.1 receiver.

The problem started asap, and the FM station is within 3 miles of me.

RF62.

[WMcD]

Okay, we're getting closer. It seems like the local transmitter is swamping the front end of the receiver. I'm a bit surprised that three miles is close enough to do it.

Does the manual (read the ___ manual) say anything about local and distant (DX) setting for the receiver? The local setting reduces the sensitivity. BTW, what is the model number of the receiver; maybe we cann all look at an on line manual.

What are you using for an FM antenna? I had a table top Panasonic which had an input for a 300 ohm twin lead antenna, which is two screw down connections. I had to short out the terminals with a paperclip to get good reception downtown. Maybe you have an F connector.

Let us know.

Gil

[Mr. RF62]

I don't see anywhere where it says (DX) local/distant settings. I am using a FM dipole antenna(300 ohm)with 2 screw connectors and does have an F connector, and Model # RVX-361 Yamaha.

[WMcD]

I see you're a technician in your background info. Sorry if my inquiries did not assume more technical knowledge. BTW, where is Kingston?

I looked at the manual and agee there is nothing in there about adjusting sensitivity. RX-V361. Since you are a technician I'm sure you've run into people who have problems which are in some ways addressed by the manual. Smile.

It is a shame that the manual, like many others, seems to assume that reception problems are due to lack of signal strenght. I think, again, that the local station is overloading the front end or at least the discriminator.

I see the unit only has a 75 ohm co-ax connection. Therefore you must be feeding from the 600 ohm dipole through a matching transformer. Which is normal procedure of course.

My first experiment would be to rig up a poor antenna. You might bring out the coax connector with a lenght of coax and then just clip on an allegator test lead to the center conductor. Or just stick the bare end of a 6 inch (or more or less) piece of wire into the center of the F connector on the back of the receiver.

There is a classic problem overall, perhaps. That is when there is a very near strong station and you want to receive a distant and therefore weaker station. A poor antenna will cut down the strong station but then put the weak station in the noise. The trick may be to cut down the effectiveness of the antenna to reduce the strong signal without reducing the weak too much.

A directional antenna on the roof can help if the stong and weak are coming from different directions. I've never gotten involved in this personally.

One very clever scheme of diversity antennae deserve mention. Imagine two antenna (need not be directional) mounted on a bar. They are fed with equal lenght coax to a splitter which becomes a mixer, which feeds the receiver. Of course signals which are received in phase add. But signals which are received out of phase, add to zero. (This part of wave mechanics always impresses me. You can add to get 3 dB gain with in phase, but out of phase gives a very deep null.)

So imagine the good station is north and the bad station is east. The bar is placed east-west and the signal from the north adds.

Consider what happens to a signal coming from the "bad" stong station to the east. We can adjust the spacing of the antennae on the bar so that they are half a wavelenght along the bar, and thus the station to the east gets nulled out.

Actually, the bad station does not have to be 90 degrees away, as long as it is not on the same compass heading as the good one, of 180 behind. At some spacing there will be a null.

This was from an article by a famous McIntosh receiver designer. I may be able to find it in my disorganized technical collection.

But back to simple solutions. I do think that a poor antenna is what you need overall.

Let us know.

Best,

Gil

[boom3]

Does this receiver have switchable de-empahsis? If it is set to the Euro standard (25 usec, IIRC) it will have increased treble over the American standard (75 usec) IIRC

[Mr. RF62]

The receiver does not have a switchable de-emphasis. As for the coax with an alligator clip, it works better believe it or not, but not accross the entire FM band, mostly in the centre 100MHz.

Thanks for the help.

[Islander]

Have you thought of calling the station? Maybe other listeners are having the same problem.

[Mr. RF62]

I'll give that a shot, Islander. Thanks

[pocket.change]

With the 3 mile distance and coupled as you mentioned, try NO antenna and see what happens.  Do you have any wall warts, clocks, tooth brush charger etc.. in your immediate area?  

Stations typically monitor their signal full time but you never know...

[MatrixDweller]

What gauge speaker wire are you using? Too thin and it can be influenced by RFI.

Could this be a ground loop of some kind? Try unplugging any other amps, like your sub. Run an extension cord to your Yammy from an outlet on another circuit.

[Mr. RF62]

I am using 14ga. wire. I have 12ga. will be trying that but don't expect an improvement. The tin foil didn't help either. I have unplugged everything else that would be on this circuit even, and still no difference.

Thanks for the tips, keep em coming.

[]

[MatrixDweller]

14 gauge should be ok.

Is the feedback coming out of just one speaker? If so possible defect in the crossover...

If money wasn't an issue I'd say get a new receiver. Or first borrow one and see if it goes away. A lot of the big box stores have a 30 day no-questions-asked return policy. You could borrow one for a week so-to-speak and if the problem goes away it's the receiver.

[pauln]

Do you have a cathode ray tube TV nearby? The flyback operates in the frequency range you mentioned.

[Mr. RF62]

No, it is both speakers.

I have thought about trying another source for the tuner, and that is a good idea. Only thing is, it doesn't happen on every frequency band. Mostly the upper ones.