Re: RF out with RF OFF: Clock feed through


Have you tried opening the Rset pin on the AD9850?  The resistance between this pin and ground sets the DAC full scale output current with the relationship Iout = 32(1.148 V/Rset)  Doesn’t say what  “V” but with Rset = infinity (open circuit) the current should be zero and no output.  Rset is nominally 3.9K ohms for a max current of 10 mA.  Don’t know what version of the AD9850 board you’re using but if it’s the one with three rows of seven pins you can just remove J3.  If it’s the one with two rows of ten pins there is no jumper, just a 3.9K SMD resistor soldered to ground.




From: PHSNA@... [mailto:PHSNA@...]
Sent: Monday, July 10, 2017 6:44 PM
To: PHSNA@...
Subject: Re: [PHSNA] Re: RF out with RF OFF: Clock feed through



Yes, I think I looked at that while trying to produce the RF ON/OFF function, but IIRC there's a way to tell it to sleep, but once done you can't wake it back up quickly without going through the normal startup routines, possibly even powering off and back on.




Nick, WA5BDU



On Mon, Jul 10, 2017 at 3:28 PM, wb4jfi1@... [PHSNA] <PHSNA@...> wrote:


Perhaps a better way to turn OFF the RF would be to put the DDS chip in sleep mode, NOT to just program it to 0Hz.  IIRC, putting it to sleep also powers down the internal clock multiplier (AD9851).

73, Terry, N4TLF



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