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Is this just diode noise?

Started by amdx February 1, 2016
Hi all,
I'm working on a circuit to test LC ferrite antennas.
I found the amp output very noisy with the rectifying
diode in the circuit. I can hear the noise and measure
it on my meter. Very little noise without the diode.
  See the link below for a block drawing of the circuit with
and without the diode.
> http://theradioboard.com/rb/download/file.php?id=4374
Is it simply the diode noise, or something else? Thanks, Mikek PS, while receiving a local station, with a tuned LC driving the input, I can get 2v on the meter, although it is over driving the LM386.
On 1.2.16 16:43, amdx wrote:
> Hi all, > I'm working on a circuit to test LC ferrite antennas. > I found the amp output very noisy with the rectifying > diode in the circuit. I can hear the noise and measure > it on my meter. Very little noise without the diode. > See the link below for a block drawing of the circuit with > and without the diode. >> http://theradioboard.com/rb/download/file.php?id=4374 > > Is it simply the diode noise, or something else? > > Thanks, Mikek > > PS, while receiving a local station, with a tuned LC driving the input, > I can get 2v on the meter, although it is over driving the LM386.
Do you have a DC path to ground at both ends of the diode? You may be running the amplifier chain effectively from an open circuit. -- -TV
On 2/1/2016 9:32 AM, Tauno Voipio wrote:
> On 1.2.16 16:43, amdx wrote: >> Hi all, >> I'm working on a circuit to test LC ferrite antennas. >> I found the amp output very noisy with the rectifying >> diode in the circuit. I can hear the noise and measure >> it on my meter. Very little noise without the diode. >> See the link below for a block drawing of the circuit with >> and without the diode. >>> http://theradioboard.com/rb/download/file.php?id=4374 >> >> Is it simply the diode noise, or something else? >> >> Thanks, Mikek >> >> PS, while receiving a local station, with a tuned LC driving the input, >> I can get 2v on the meter, although it is over driving the LM386. > > Do you have a DC path to ground at both ends of the diode? > > You may be running the amplifier chain effectively from > an open circuit. >
I don't. I'll try a resistive load. I suggest there is some type of impedance on the input because when it's open the output hits the positive rail. There is no reason I can't load the diode, I have a high input impedance 50 ohm output amp that is between the LC and the diode. Thanks, Mikek
On 2/1/2016 9:45 AM, amdx wrote:
> On 2/1/2016 9:32 AM, Tauno Voipio wrote: >> On 1.2.16 16:43, amdx wrote: >>> Hi all, >>> I'm working on a circuit to test LC ferrite antennas. >>> I found the amp output very noisy with the rectifying >>> diode in the circuit. I can hear the noise and measure >>> it on my meter. Very little noise without the diode. >>> See the link below for a block drawing of the circuit with >>> and without the diode. >>>> http://theradioboard.com/rb/download/file.php?id=4374 >>> >>> Is it simply the diode noise, or something else? >>> >>> Thanks, Mikek >>> >>> PS, while receiving a local station, with a tuned LC driving the input, >>> I can get 2v on the meter, although it is over driving the LM386. >> >> Do you have a DC path to ground at both ends of the diode? >> >> You may be running the amplifier chain effectively from >> an open circuit. >> > I don't. I'll try a resistive load. > I suggest there is some type of impedance on the input because > when it's open the output hits the positive rail. > There is no reason I can't load the diode, I have a high input impedance > 50 ohm output amp that is between the LC and the diode. > > Thanks, Mikek
I put a 100k resistor from the diode cathode to ground, it dropped the noise measurement from 330mv to 102mv. Probably will even get better when I tighten things up. Thanks, Mikek