Re: TDA2822 Audio problem #ubitx #tda2822

Jerry Gaffke
 

Here's an old thread on it:
    https://groups.io/g/BITX20/message/40038

Here's a summary:

The uBitx 11.9965mhz BFO can have harmonics that can beat with harmonics of the 16mhz oscillator
on the Raduino.  There's also a 12mhz oscillator on the Raduino for the USB port to the host that
may be causing trouble.  Those with this issue have found that swapping to a new Nano seemed to cure it.
In your case, you could instead add a low pass audio filter in there somewhere.

The Nano's use a resonator, not a quartz crystal, something like this:
    https://www.mouser.com/ds/2/281/p16e-522700.pdf
Can be some variation between Nano's.

Ideally, we would either move the 12mhz IF to some other frequency,
or build a custom Nano/Raduino that does not have 16mhz and 12mhz oscillators.

The work-around for now is to keep the BFO below the 12mhz filter,
swapping sidebands by moving the second local oscillator (clk1) between
high side and low side.  This works fine on most rigs.

Jerry
 

On Tue, Mar 13, 2018 at 10:31 am, Jason Schlager wrote:
Assembled my ubitx last week and after a demonstration last night in front of some boy scouts one of the parents complained of a loud tone coming from the speaker.  So I busted out my cell phone and fired up the Spectroid app mentioned in another post.  There is definitely a 9khz tone coming out of the speaker.  Its does change intensity when changing volume but it is a good 3 times the volume of all other audio coming out of the speaker. I have the MX TDA2822 chip. I rerouted the wires going to the volume control pot and to speaker without any positive changes. Any suggestions on how to clear this up or just swap the chip or build an alternate audio amp circuit or filter it out?  Just looking for some recommendations on how to attack this problem.

Jason Schlager
KM6AUS

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