EMRFD Message Archive 2382
Message Date From Subject 2382 2008-11-11 08:33:40 la3pna Microprocessor noise in receiver IF
processor.
This is done in an clasic way, with 10.7MHz If and an crystal filter
that is switched between receive and transmit.
The transceiver is working as it should except I have a loud noise
from the PIC proscessor is getting in to the receive chain.
The If board is not enclosed in an box at the moment. I would like to
remove the noise from the proscessor in addition to screening the
receiver. I have been trying capacitors (0.1µf) on the 5V supply.
Do i need to put the whole control board in an box and complete screen
it, using feed thru capacitors? or is there an more easy way to remove
the noise?
I would prefear to have the control board open, there is a lot of
wires going to display, encoder and keyboard.
Best 73's de Thomas LA3PNA.2383 2008-11-11 08:39:49 Hari G Re: Microprocessor noise in receiver IF
I have a Atmega 32 running at high speed 16Mhz , for that iam using
2200mfd in the controller board and no screening just placed as far as
possible in the box.
73
Hari
On 11/11/08, la3pna <la3pna@gmail.com> wrote:
>
> I have build an transceiver for 2M with an DDS controlled by an PIC
> processor.
> This is done in an clasic way, with 10.7MHz If and an crystal filter
> that is switched between receive and transmit.
> The transceiver is working as it should except I have a loud noise
> from the PIC proscessor is getting in to the receive chain.
> The If board is not enclosed in an box at the moment. I would like to
> remove the noise from the proscessor in addition to screening the
> receiver. I have been trying capacitors (0.1µf) on the 5V supply.
> Do i need to put the whole control board in an box and complete screen
> it, using feed thru capacitors? or is there an more easy way to remove
> the noise?
>
> I would prefear to have the control board open, there is a lot of
> wires going to display, encoder and keyboard.
>
> Best 73's de Thomas LA3PNA.
>
>
>
--
De Hari
VU2GHB
[Non-text portions of this message have been removed]2384 2008-11-11 08:46:56 leon Heller Re: Microprocessor noise in receiver IF
2388 2008-11-11 20:56:17 wimmie262000 Re: Microprocessor noise in receiver IF 2392 2008-11-11 21:29:59 Nick Kennedy Re: Microprocessor noise in receiver IF
>
>
>
the PIC to go to sleep after each action? It might be a pain though if you
have a lot of lines used as inputs -- you'd want any line to wake the PIC
up.
73--Nick, WA5BDU
[Non-text portions of this message have been removed]2393 2008-11-12 02:49:34 Thomas S. Knutsen Re: Microprocessor noise in receiver IF
The display is an LCD with backligth. I should try an other LCD
At this moment I'm condidering decoupling all pins of the PIC with
decoupling capacitors. This way I migth get rid of some of the noise.
73 de Thomas LA3PNA
2008/11/12 Nick Kennedy <kennnick@gmail.com>
> >[Non-text portions of this message have been removed]
> >
> >
> >
> Not a direct response to your question, but I wonder if you could program
> the PIC to go to sleep after each action? It might be a pain though if you
> have a lot of lines used as inputs -- you'd want any line to wake the PIC
> up.
>
> 73--Nick, WA5BDU
>
>
> [Non-text portions of this message have been removed]
>
>
>
2396 2008-11-12 08:39:19 Johan H. Bodin Re: Microprocessor noise in receiver IF
since the clock oscillator will stop when the PIC is in sleep mode, the PIC
cannot be blamed for the noise. Well, if you have the WDT enabled, there is a
small low frequency RC oscillator running on-chip but it radiates almost nothing
at all. I would suspect the LCD, there is a lot of square waves on the LCD board
for multiplexing all the segments. If the backlighter is of EL type, then the
DC/AC converter feeding it may be a problem too. Try disconnecting the LCD to
see what happens to the noise.
By the way, if you want to put lowpass filters on PIC output pins that are
rattling often, do not connect capacitors directly from the PIC pins to ground
because the PIC have "strong pins" with fast rise times and the resulting high
current spikes may give you strange surprises. It is better to use R + C. If you
are using a standard alphanumeric LCD (Hitachi HD44780 controller or similar),
the E signal must have a fast rise time, less than a microsecond, otherwise the
LCD will not work. RC filtering is not appropriate here unless you put a schmitt
trigger close to the LCD to square the signal up.
73
Johan SM6LKM
Thomas S. Knutsen wrote:
> I did try programming it to go to sleep, but the noise is still there,
> The display is an LCD with backligth. I should try an other LCD
> At this moment I'm condidering decoupling all pins of the PIC with
> decoupling capacitors. This way I migth get rid of some of the noise.
>
> 73 de Thomas LA3PNA2420 2008-11-18 14:42:53 timshoppa Re: Microprocessor noise in receiver IF 2424 2008-11-18 21:33:03 Thomas S. Knutsen Re: Microprocessor noise in receiver IF
changed to an regular LCD display without backligt the noise did dissapear.
So good for now.
Best 73's de Thomas LA3PNA.
2008/11/18 timshoppa <timshoppa@yahoo.com>
>