On 07/06/17 10:31, Clifford Heath wrote:
> On 06/06/17 00:01, John Larkin wrote:
>> We use the AD9850 and a couple of other ADI dds parts, and a couple of
>> ADI dacs in home-brew DDS applications, and we've never seen anything
>> like that kind of rolloff. Usually we get a bit of filter rolloff and
>> the usual sinc thing. You should be maybe a dB down at Fclk/3.
>
> I don't think I understand the sinc thing. What should I expect
> to see from it?

Never mind, I found an explanation here:
<https://ez.analog.com/thread/3364>
It doesn't explain my problem, but that's ok.

Jan Panteltje wrote on 6/6/2017 4:44 AM:
> On a sunny day (Tue, 6 Jun 2017 04:32:41 -0400) it happened rickman
> <gnuarm@gmail.com> wrote in <oh5p4j$uro$2@dont-email.me>:
>
>> Jan Panteltje wrote on 6/6/2017 4:00 AM:
>>> On a sunny day (Tue, 6 Jun 2017 07:19:11 +1000) it happened Clifford Heath
>>> <no.spam@please.net> wrote in <NpkZA.37030$J83.33061@fx39.iad>:
>>>
>>>>> The 3dB down point varies with load impedance. With a
>>>>> 50ohm load my output is ~500mVpp and the 3dB point is
>>>>> a little under 50MHz. At higher resistance, the 3dB
>>>>> point can be significantly lower.
>>>>
>>>> That must be what's happening. It looks like a buffer is
>>>> needed after the DAC load resistors, before the filter,
>>>> though a buffer afterwards would help. Shame that AD
>>>> didn't show that on their data sheets and eval boards.
>>>
>>> It is just that YOU do not understand the datsheet, as I stated in my fists reply the intention
>>> is not that point as output, but they use a comparator (in the same chip did you notice!!)
>>> to make the varying filter amplitude into two SQUARE WAVE 50 Ohm outputs.
>>> Its a freaking CLOCK generator, not a VFO.
>>> you got the WRONG SHIELD :-) :-) :-) :-)
>>>
>>> loop_the_loop:
>>> hehe
>>> LOL
>>> LMAF
>>>
>>> funny funny funny
>>> bra loop_the_loop
>>>
>>> stack overflow, cosmic ray, FLASH corruption, loop break, Russian hacker succeeded
>>>
>>>
>>> :-)
>>>
>>> LOL
>>>
>>> hahahaha
>>
>> You are in one strange mood.  You also write a *lot* worse than he does.
>> Your sentences often make no sense... if you even use actual sentences.
>
> Apart from the sense-wire for humor you also need in depth No Ledge of the subject to make sense of what I write.
> Else the humor will not even escape you, it won't even ave been be with you,
> as your typing exorcism shows.

Sir, you are one weird dude!

-- 

Rick C

Jan Panteltje wrote on 6/6/2017 4:40 AM:
> On a sunny day (Tue, 6 Jun 2017 04:29:31 -0400) it happened rickman
> <gnuarm@gmail.com> wrote in <oh5ove$uro$1@dont-email.me>:
>
>> Jan Panteltje wrote on 6/6/2017 3:42 AM:
>>> On a sunny day (Tue, 6 Jun 2017 07:14:38 +1000) it happened Clifford Heath
>>> <no.spam@please.net> wrote in <wlkZA.60881$zj3.3944@fx15.iad>:
>>>
>>>>>>> I just looked up that AD9851 datasheet.
>>>>>>> You would not happen to be looking at that DAC output?
>>>>>>> It has a 120k or so Rout,
>>>>>> You expected a current source to have a small Rout?
>>>>> I did not expect anyting, do not even have a duino, nevrr used one either AFAIK.
>>>>
>>>> The AVR has nothing to do with the AD9851.
>>>
>>> So why did you blabber about it?
>>
>> The only one blabbering about is you.  He simply described his setup.
>
> No he did not,. no circyuit diagram,, nothing,
> just 'shields' and duinos
>
> Maybe even Dinos come to think of it.
>
> You have no sense wire for humor.

Actually I have a pretty keen sense of humor... when I see it.  Besides, you 
criticized him for his grammar and yours is *always* atrocious, not to 
mention your spelling.

-- 

Rick C

On a sunny day (Tue, 6 Jun 2017 04:32:41 -0400) it happened rickman
<gnuarm@gmail.com> wrote in <oh5p4j$uro$2@dont-email.me>:

>Jan Panteltje wrote on 6/6/2017 4:00 AM:
>> On a sunny day (Tue, 6 Jun 2017 07:19:11 +1000) it happened Clifford Heath
>> <no.spam@please.net> wrote in <NpkZA.37030$J83.33061@fx39.iad>:
>>
>>>> The 3dB down point varies with load impedance. With a
>>>> 50ohm load my output is ~500mVpp and the 3dB point is
>>>> a little under 50MHz. At higher resistance, the 3dB
>>>> point can be significantly lower.
>>>
>>> That must be what's happening. It looks like a buffer is
>>> needed after the DAC load resistors, before the filter,
>>> though a buffer afterwards would help. Shame that AD
>>> didn't show that on their data sheets and eval boards.
>>
>> It is just that YOU do not understand the datsheet, as I stated in my fists reply the intention
>> is not that point as output, but they use a comparator (in the same chip did you notice!!)
>> to make the varying filter amplitude into two SQUARE WAVE 50 Ohm outputs.
>> Its a freaking CLOCK generator, not a VFO.
>> you got the WRONG SHIELD :-) :-) :-) :-)
>>
>> loop_the_loop:
>> hehe
>> LOL
>> LMAF
>>
>> funny funny funny
>> bra loop_the_loop
>>
>> stack overflow, cosmic ray, FLASH corruption, loop break, Russian hacker succeeded
>>
>>
>> :-)
>>
>> LOL
>>
>> hahahaha
>
>You are in one strange mood.  You also write a *lot* worse than he does. 
>Your sentences often make no sense... if you even use actual sentences.

Apart from the sense-wire for humor you also need in depth No Ledge of the subject to make sense of what I write.
Else the humor will not even escape you, it won't even ave been be with you,
as your typing exorcism shows.

On a sunny day (Tue, 6 Jun 2017 04:29:31 -0400) it happened rickman
<gnuarm@gmail.com> wrote in <oh5ove$uro$1@dont-email.me>:

>Jan Panteltje wrote on 6/6/2017 3:42 AM:
>> On a sunny day (Tue, 6 Jun 2017 07:14:38 +1000) it happened Clifford Heath
>> <no.spam@please.net> wrote in <wlkZA.60881$zj3.3944@fx15.iad>:
>>
>>>>>> I just looked up that AD9851 datasheet.
>>>>>> You would not happen to be looking at that DAC output?
>>>>>> It has a 120k or so Rout,
>>>>> You expected a current source to have a small Rout?
>>>> I did not expect anyting, do not even have a duino, nevrr used one either AFAIK.
>>>
>>> The AVR has nothing to do with the AD9851.
>>
>> So why did you blabber about it?
>
>The only one blabbering about is you.  He simply described his setup.

No he did not,. no circyuit diagram,, nothing,
just 'shields' and duinos

Maybe even Dinos come to think of it.

You have no sense wire for humor.

Jan Panteltje wrote on 6/6/2017 4:00 AM:
> On a sunny day (Tue, 6 Jun 2017 07:19:11 +1000) it happened Clifford Heath
> <no.spam@please.net> wrote in <NpkZA.37030$J83.33061@fx39.iad>:
>
>>> The 3dB down point varies with load impedance. With a
>>> 50ohm load my output is ~500mVpp and the 3dB point is
>>> a little under 50MHz. At higher resistance, the 3dB
>>> point can be significantly lower.
>>
>> That must be what's happening. It looks like a buffer is
>> needed after the DAC load resistors, before the filter,
>> though a buffer afterwards would help. Shame that AD
>> didn't show that on their data sheets and eval boards.
>
> It is just that YOU do not understand the datsheet, as I stated in my fists reply the intention
> is not that point as output, but they use a comparator (in the same chip did you notice!!)
> to make the varying filter amplitude into two SQUARE WAVE 50 Ohm outputs.
> Its a freaking CLOCK generator, not a VFO.
> you got the WRONG SHIELD :-) :-) :-) :-)
>
> loop_the_loop:
> hehe
> LOL
> LMAF
>
> funny funny funny
> bra loop_the_loop
>
> stack overflow, cosmic ray, FLASH corruption, loop break, Russian hacker succeeded
>
>
> :-)
>
> LOL
>
> hahahaha

You are in one strange mood.  You also write a *lot* worse than he does. 
Your sentences often make no sense... if you even use actual sentences.

-- 

Rick C

Jan Panteltje wrote on 6/6/2017 3:42 AM:
> On a sunny day (Tue, 6 Jun 2017 07:14:38 +1000) it happened Clifford Heath
> <no.spam@please.net> wrote in <wlkZA.60881$zj3.3944@fx15.iad>:
>
>>>>> I just looked up that AD9851 datasheet.
>>>>> You would not happen to be looking at that DAC output?
>>>>> It has a 120k or so Rout,
>>>> You expected a current source to have a small Rout?
>>> I did not expect anyting, do not even have a duino, nevrr used one either AFAIK.
>>
>> The AVR has nothing to do with the AD9851.
>
> So why did you blabber about it?

The only one blabbering about is you.  He simply described his setup.  Here 
you complain about him giving info, later you complain he *doesn't* give 
enough info.  Jeeze, what is up with you?


>>>>> The slightest capacitance on the 20mA (if it is that much) into a 2k2 load,
>>
>> It's not a 2k2 load. 2k2 just programs the current sources
>> fro the DAC.
>>
>>>>> Datasheet seems to use a 1:1 transformer to 50 Ohm.
>>>> That's to derive output from both polarities of the DAC
>>> No, it is to short any output capacitance.
>>
>> That's not what the data sheet and app-notes say.
>
> Well it actually does.
>
>
>
>
>>> I dunno what you use for scope, mine is just after Fred Flinstone,
>>> but my probes are 1/10 of 30 pF on X10, so say 3 pF.
>>
>> 20MHz Hung Chang 2502. You're right to point out that I
>> don't know much about my probes though.
>>
>>> But you were driving 2k2, for 3 pF probe and 2k2 your 3 dB cutoff is already 24 MHz low pass.
>>> Now ads peeseebee and wire capacirance, and whatever any filter you use adds.
>>
>> I think you're right, it just doesn't want to drive a load.
>> I'll add a buffer.
>
> Oh help
> ;-)
>
>
> Maybe, just to stop the silly shit, publish a circuit diagram of your whatever it is you talk about?
>
>> Probably for the same reason you couldn't spot that the 2k2
>> is not the R in question.
>
> From your text '2k2' and your lack of a circuit diagram, your writing skills are sub-standard ;-)
> No wonder it does not work 4 u

Pot, meet kettle.

-- 

Rick C

On a sunny day (Tue, 6 Jun 2017 07:19:11 +1000) it happened Clifford Heath
<no.spam@please.net> wrote in <NpkZA.37030$J83.33061@fx39.iad>:

>> The 3dB down point varies with load impedance. With a
>> 50ohm load my output is ~500mVpp and the 3dB point is
>> a little under 50MHz. At higher resistance, the 3dB
>> point can be significantly lower.
>
>That must be what's happening. It looks like a buffer is
>needed after the DAC load resistors, before the filter,
>though a buffer afterwards would help. Shame that AD
>didn't show that on their data sheets and eval boards.

It is just that YOU do not understand the datsheet, as I stated in my fists reply the intention
is not that point as output, but they use a comparator (in the same chip did you notice!!)
to make the varying filter amplitude into two SQUARE WAVE 50 Ohm outputs.
Its a freaking CLOCK generator, not a VFO.
you got the WRONG SHIELD :-) :-) :-) :-)

loop_the_loop:
hehe
LOL
LMAF

funny funny funny
bra loop_the_loop

stack overflow, cosmic ray, FLASH corruption, loop break, Russian hacker succeeded 


:-)

LOL

hahahaha

On a sunny day (Mon, 5 Jun 2017 16:46:23 -0700 (PDT)) it happened George
Herold <gherold@teachspin.com> wrote in
<f252e421-4702-4d21-a69e-fdee368cb9d7@googlegroups.com>:

>Oh I was going to say, I always have issues with my probes,
>and forgetting what their load is.   
>Sometimes I'll look at a signal with a x10 'scope probe in series 
>with a 1 pf cap. (or just a turn or two of insulated wire) 
>
>George H. 

Sometimes I watch teefee,
yesterday I watched a recorded movie the das_turbogeile_gummiboot_1984_german.ts
Was original US I think, German voice over, very well done.
It reminded me of this discussion.
:-)
 https://en.wikipedia.org/wiki/Up_the_Creek_%281984_film%29
 https://www.youtube.com/watch?v=K6S3KuZvxxQ

On a sunny day (Tue, 6 Jun 2017 07:14:38 +1000) it happened Clifford Heath
<no.spam@please.net> wrote in <wlkZA.60881$zj3.3944@fx15.iad>:

>>>> I just looked up that AD9851 datasheet.
>>>> You would not happen to be looking at that DAC output?
>>>> It has a 120k or so Rout,
>>> You expected a current source to have a small Rout?
>> I did not expect anyting, do not even have a duino, nevrr used one either AFAIK.
>
>The AVR has nothing to do with the AD9851.

So why did you blabber about it?


>>>> The slightest capacitance on the 20mA (if it is that much) into a 2k2 load,
>
>It's not a 2k2 load. 2k2 just programs the current sources
>fro the DAC.
>
>>>> Datasheet seems to use a 1:1 transformer to 50 Ohm.
>>> That's to derive output from both polarities of the DAC
>> No, it is to short any output capacitance.
>
>That's not what the data sheet and app-notes say.

Well it actually does.




>> I dunno what you use for scope, mine is just after Fred Flinstone,
>> but my probes are 1/10 of 30 pF on X10, so say 3 pF.
>
>20MHz Hung Chang 2502. You're right to point out that I
>don't know much about my probes though.
>
>> But you were driving 2k2, for 3 pF probe and 2k2 your 3 dB cutoff is already 24 MHz low pass.
>> Now ads peeseebee and wire capacirance, and whatever any filter you use adds.
>
>I think you're right, it just doesn't want to drive a load.
>I'll add a buffer.

Oh help
;-)


Maybe, just to stop the silly shit, publish a circuit diagram of your whatever it is you talk about?

>Probably for the same reason you couldn't spot that the 2k2
>is not the R in question.

From your text '2k2' and your lack of a circuit diagram, your writing skills are sub-standard ;-)
No wonder it does not work 4 u


>Clifford HeathKitten