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Re: Low frequency hum with musical accompanyment

Subject: Re: Low frequency hum with musical accompanyment
From: Dudley Edmondson <>
Date: Mon, 17 Mar 2003 13:56:33 -0600
On 3/16/03 11:35 AM, "Walter Knapp" <> wrote:

> Dudley Edmondson wrote:
>>     In recent months I have experience a strange thing with my HHB portadsic
>> recorder and parabolic stereo DAT mic.
>> 
>> When I am recording bird audio near a resident or near city limits  I can
>> hear a low frequency hum or buzz with music or voices in the background.
>> What I am picking up is no doubt a local radio station.  In fact once I
>> heard the station say it call letters.....OLDIES 107 FM.......  It is not
>> super loud or anything it just at a sound level that gets picked up in any
>> recording you make BUT not loud enough to overshadow the subject source.
>> But Just loud enough to be heard during moments of silence during a
>> recording
>> 
>> What the heck would make my recording set pick up radio stations??  Has
>> anyone else had this problem. This sounds crazy to me and NO there are no
>> voices in my head........
> 
> I had a hydrophone that would always do this when used in shallow
> freshwater, anywhere, even many miles from towns or radio towers. I
> tried all kinds of shielding, chokes etc to no avail and finally gave up
> and bought a new hydrophone, which never does that. So, strange things
> do happen.
> 
> The combo of the HHb Portadisc and the Telinga Pro V with Stereo DAT mic
> has never done this to me. And I have recorded right next to radio
> towers for some pretty high powered stations. I can get some 60 cycle
> hum if recording under high voltage electrical lines. But, then, under
> those conditions I'm usually also picking up the discharge crackle from
> the wires, which is real audio.
> 
> What model Telinga are you using, Stereo Miniplug or XLR? If using the
> miniplug version did you interconnect signal cold to shield ground in
> your adapter? Whichever way you have try it opposite. I do not intertie
> signal cold and shield currently, but have done so in the past with
> little problem. Of course it's important to make sure all connectors are
> working properly, maybe try some contact cleaner on them to make sure.
> Damage to the cable shielding or conductors can do this sort of thing too.
> 
> Of course changing to a different mic negates the advantages of the DAT
> Stereo Telinga, but have you tried other mics to see if you can
> reproduce the problem? If it reproduces with other mics then the suspect
> has to be a problem with the Portadisc. But the reverse probably does
> not prove the Telinga defective. Most likely culpret is the connection
> between the two.
> 
> As Klas has noted, the circuit board inside the handle is not shielded,
> the handle is plastic. So it can pick up interference in strong enough
> electrical fields. If this is just occurring in a limited area that's
> probably the explanation. Though you seem to be saying it's more
> widespread. Maybe you are picking up the cable TV system in the town
> that was not properly installed? Those usually carry FM stations as
> well. If that's the case, the FCC will be interested. Those cable
> systems are not supposed to be radiating like that.
> 
> Walt
> 
> 
> 
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> 

I just had two sets of custom made unbalanced XLR's plugs made and my HHB
portadisc recorder was just in for a tune up service so I  don't think they
are the problem.......

I think  the problem may have something to do with my connection between the
the stereo miniplug and my unbalanced XLR's plugs.  Usually when this radio
problem occurs I also get some sort of discharge feedback sound that ruins
my recordings.  I jiggle or hold the  miniplug/XLR connection to ground it
but to no avail.  






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