RADIO INTERFERENCE

[shyamwestwind]

This is something really intriguing and I hope someone can explain this.
Our Duo had a programme last might at the terrace on the eigth floor and we used two dB Opera 415 speakers (powered) and the moment we connected the system, an FM radio station came on through the speakers !!!!! We tried everything to get rid of the interference, and even disconnected the audio cables but of no avail - THE FM station kept coming on strong and clear at a constant volume. We had no option except to play our music louder to drown the "intruder"
After a half hour of playing this way, we decided to bring in our dB Basic 400 speakers (powered) which we occassionally use as monitors. Very surprisingly the Fm radio station, though still present, was so inaudible, we had no problem playing our music as we usually do.
The Radio station Tower, I must mention here, was visible from the terrace and must have been about two furlongs, as the crow flies.
Can some friend explain this phenomenon to me and suggest a remedy ? I am truly intrigued .
With warm regards
Shyam

[mark]

Hi Shyam
Years ago my friend and I used to get the odd Taxi firm anouncements come through the PA.
We upgraded all the cables and it seem to eliminate this problem.Only an idea.
Regards
Mark

[FoothillsSound]

Hi Shyam

FM transmitters broadcast in a 'line of sight' or direct beam pattern. The closer you are to the center of this beam, the stronger the signal.

FM, AM, CB, VHF, cordless phones and other transmitter's signals can be rec'd by PA gear. Manufacturers attempt (usually) to 'shield' particularly sensitive areas in equipment. In your case, depending on the wattage output of the station and your postion relative to it's signal path, 'reasonable' sheilding may not have been possible.

As Mark stated, your cables themselves could have acted as a very good antenna. Lower quality cables tend to have less sheilding around their core. Also look for frays at terminal connections. Worn or frayed areas allow interference f/ many sources including FM signals.

However, since you noted that switching f/ your Operas to your Basics seemed to diminish the problem, I tend to think you were receiving the FM signal thru the amp or other circuitry in the cabinet itself. As I mentioned earlier, this could have been due to less shielding in the Operas. But, as both cabinets are f/ the same company, I tend to think it was due to a stronger preamp in the Operas. If I had to guess, I'd say you typically are able to set your gain lower in the Operas than the Basics for that reason.

Hope this helps,
Alan

[shyamwestwind]

Hi Mark
I wish it were that simple, but as I said, we removed the audio cables completely and the only cable to the speakers were the power cables. The speakers are powered and I guess its something to do with the amplifier circuitry.

[shyamwestwind]

Hi Alan
You will find it interesting to note we turned the volume controls on the Operas to zero but the FM transmission came through irespective !! The transmission had a constant volume with our without the audio cables andwith the gain controls turned to zero.
Is there any way the amplifier in the Opera an be shielded ?
I appreciate your inputs.

[FoothillsSound]

shyamwestwind said:

Hi Alan
You will find it interesting to note we turned the volume controls on the Operas to zero but the FM transmission came through irespective !! The transmission had a constant volume with our without the audio cables andwith the gain controls turned to zero.
Is there any way the amplifier in the Opera an be shielded ?
I appreciate your inputs.

Shyam,

This actually makes sense. If your cabs were in the transmitters direct beam, it's output wattage strength at your proximity could very well drive your speaker baskets with no assistance f/ the cab's intenal amp & it's signal would remain constant.

The odds of the circumstances you had in this venue duplicating themselves elsewhere are slim. However, adding adhesive backed aluminum shielding foil to the inner walls of the cabinet around it's preamp/amp/crossover circuitry might create a barrier against unwanted transmission reception in the future.

You may want to contact Db directly, explain your situation and see what they suggest. Their contact info can be found here.

Have a good one,
Alan

[midimart]

I know I'm off the subject a little here, but wouldn't it be funny - If it was the other way around.

The FM station could pick you up.... You'd be playing to millions of listeners and maybe end up with a lucrative contract....

From the FM station "And tonight we have a concert from Shyamwestwind, so sit back listeners and enjoy this uninterrupted live coverage from the Terrace arena".

I'd make a good Radio DJ...... lol

[FoothillsSound]

Glenn,

This actually happens!

You have 'legitimate' simulcasts such as the one Pat was on a while back and "Pirate" radio operators, who sometimes piggyback a licensed operators broadcast. At least until they're caught.

[shyamwestwind]

Hi Alan
Thanks for your advice. The aluminum shielding is definitely a good thing to do, but the speaker cabinet is pretty inaccessible so I'll have one helluva time fixing that. I have got a prompt response from the dB guys and I'm waiting for their analysis.
Thank you once again for your advice .
With warm regards
Shyam

[shyamwestwind]

Hi Glenn
That sounded good but I dont think I'd want a LIVE coverage ....... it'll pick up all the off stage "masala" we musicians are prone to !!

[FoothillsSound]

Shyam,

You're quite welcome.

Please keep us updated. I'm curious as to what Db will have to say.

Cheers,
Alan

[shyamwestwind]

Hi Alan
No news from dB as yet . I hope I get some response from them - they were pretty prompt in their initial response. I'll definitely keep you informed

[shyamwestwind]

Hi Alan
The dB guys got back to me saying they checked with their Operas anbd found no offending FM intrusions. They wanted more info about the proximity to the FM transmitters etc, which I furnished to them
I explained that it wasnt a case of FM broadcasts coming in always, but when the dB Basics behaved well there was obviously some problem with the Operas. I gave them your opinion on the matter and the possibility of low shielding at the preamp placements
The dB person phoned me to say they would look into the matter and if a technical remedy was found they'd fix my speakers too.
Well, I guess I'll need to be satisfied with that response. Till the remedy can be found I'll steer clear of FM broadcasting neighbourhoods.
Thanks for your opinion and advice, Alan

[FoothillsSound]

Shyam,

You're quite welcome.

Thanx for the update. If they contact you further, please keep me abreast.

Regards,
Alan

[shyamwestwind]

Dear Alan
Heres the exerpt from the mail I recd. from dB.

Thanks for your valueable feedback. We really appreciate your keen interest & concerned in our range of products.

Don't worry, we are not treating this as "complaint",
on the contarary customer's feedback is very important for us & our factory works seriously on the
each & every feedback that we get from our customers.
.
We are working on your feedback & shall get back to as early as possible. I will be in touch with you & as soon as we have a solution, your units will be modified free of cost.

Its heartening to know that they do value our feedback, dont you think Alan ? By the way, I played at a Club here this afternoon and was surprised to see two Opers 215s rigged up and ready. I thought they had another group in for the day but was told they were the Clubs hired out equipment. Surprisingly these Operas 215s also picked upt the FM radio statio ! This is a club quite close to the Radio Station and we had such FM interference earlier in our Operas 415s.
I'm eager to know what modifications are going to be made to remedy this

[levi2]

Simple solution all you need is a bazooka fire it straight at the mast to bring it down problem solved

[shyamwestwind]

HI levi2
Believe it or not but I actually did think of that !!! he he he

[shyamwestwind]

Hi Alan
No further responses from dB. I guess thats the end of it !! Well, atleast they were polite !! I'm staying clear of those sensitive areas and making certain the frequencies dont frequent me !!

[thingyy]

Get RF filters installed.

[shyamwestwind]

Hi thingyy
Please give me more details on this,