BCD536HP: 536HP Audio Problems

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mule1075

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I recently purchased a used 536hp set everything up and have a horrible audio squeal on channels set as NFM. I switch them to FM and everything works correctly I have tried known good sd cards from a 436hp and tried a brand nrew card with the same result. If this has come up before on the forums i am sorry i missed it just getting back in the scanning game after a unexpected hiatus.
 

buddrousa

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Welcome Back have not ever heard that before could they be FM and not NFM?
 

Ubbe

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In the scanner there are different filters used for NFM and FM. It sounds as if the one for NFM have gone bad. They are usually made of crystal and can be fragile. Drop a scanner and often the first thing that goes bad are one of the crystals used for filtering or frequency stability.

You probably need to have a signal generator to tell if it's busted. Slowly sweep the frequency over the bandwidth of the filter and the demodulated signal sounds distorted and has an overlaid sound that could be said to sound like a squeal.

/Ubbe
 

mule1075

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Welcome Back have not ever heard that before could they be FM and not NFM?
No it is a definite scanner issue. I will live with it and change the modulation on all channels to FM a pain but i am do not have the extra cash right now to send it in for repair. I just have to remember if you can switch the modulation on p25 systems i have only been out of scanning for 3-4 months and it is amazing how much I cannot remember. It is coming back to me though slowly but surely.
 

tvengr

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When you switch to NFM, you probably have additional audio gain to make up for the loss of bandwidth. The additional gain could cause the radio to break into oscillation if you have poor power supply regulation. Does it make a difference if you raise and lower the volume. Try substituting another power supply if you have one. If you don't have another supply, try it on a cigarette lighter adapter in your vehicle.
 
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mule1075

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When you switch to NFM, you probably have additional audio gain to make up for the loss of bandwidth. The additional gain could cause the radio to break into oscillation if you have batteries with high internal resistance. Does it do the same thing on an external power supply and does raising and lowering the volume make a difference?
What do batteries have to do with a 536hp? And it does it on multiple power supplies and no difference on adjusting the volume.
 

tvengr

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If it were a power supply regulation problem, changing the volume level would change the frequency of and the amount of oscillation. It's beginning to look like a hardware problem in the scanner. To eliminate the possibility of software corruption, I would try reloading or updating the firmware.
 

mule1075

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If it were a power supply regulation problem, changing the volume level would change the frequency of and the amount of oscillation. It's beginning to look like a hardware problem in the scanner. To eliminate the possibility of software corruption, I would try reloading or updating the firmware.
Did all that previously to posting no change. As I said earlier it indeed looks like a scanner issue just started the thread to find out if anyone had the same problems.
 

fxdscon

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Did all that previously to posting no change. As I said earlier it indeed looks like a scanner issue just started the thread to find out if anyone had the same problems.
Can you post a clip of the audio?

.
 

RFI-EMI-GUY

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Forgot I recorded one when I received it.
That's nasty! Not microphonic, but it sounds like something in the PLL filtering. But if switching to NFM makes it happen, I wonder if there is a short on the board creating a situation where both filter paths are engaged and the tone is phase differential of the two IF streams. Try pushing the IFX button to see if that changes anything. It also could be a bad firmware, or a bad setting.

Not something I would live with...
 

bob550

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Forgot I recorded one when I received it.
At first, I couldn't hear any squeal at all and wondered if my hearing was going bad. But after making some adjustments to my computer audio, I heard it very clearly. The point to this is that you could pipe the audio through a computer and utilize the internal audio adjustments, depending on their sophistication, to null out the squeal. Of course this is only a workaround until you either determine the source of the squeal, or have it repaired.
 

mule1075

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That's nasty! Not microphonic, but it sounds like something in the PLL filtering. But if switching to NFM makes it happen, I wonder if there is a short on the board creating a situation where both filter paths are engaged and the tone is phase differential of the two IF streams. Try pushing the IFX button to see if that changes anything. It also could be a bad firmware, or a bad setting.

Not something I would live with...
Not bad firmware or a bad setting most definitely a hardware issue. Switching the mode to FM from NFM cures the problem for now. When I get some extra cash I might send it in or sell it for parts.
 
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