Real output circuit from AD9850 /HC_SR08 module wnated

Hi Vaclav,
I found some advice on interfacing the module here.
"Second mod is to bring the current output pins directly, without load resistors connected to them, out of the board so that they can be hooked to to transformer as shown in application note. The output filter on IOUT output (pin 21) also needs to be eliminated. I simply removed all filter components and load resistors from the board, the list of removed parts is R4, R9, C1, L1, C2, C3, L2, C4, C5, L3, C6, C7, R5. Then to connect the IOUT to ZOUT2 pin of the module you simply solder a wire from a pad closer to board edge of R4 resistor to pad of R5 resistor, also closer to the board edge." the author says. He then uses a RF transformer with symmetrical primary (center tap grounded) to interface the IC to a 50 ohm loading resistor and a one-transistor output amplifier.

Maybe this is of some use for you.
VBR from Ivan

Nazdar, Václave,
konečně jsem se dostal k prostudování dokumentace, na kterou odkazuješ.
The doc of the module is rather confusing. The pictures show two sinewave outputs ZOUT1 and ZOUT2, According to the table on page 7, they are complementary. BUT they are nowhere in the chematic! Outputs IOUT and IOUTB are displyed instead. IOUT is filtered by a LC filter, while IOUTB is connected via a resistor to the ground. I see no symmetry in this arrangement! Oscillograms of the output are displayed too. They show a sinewave 1 V p-p (354 mV eff) - unclear, whether at Vcc = 3.3 V or 5 V, whether between ZOUT1 and ZOUT2, ZOUTx against GND, IOUT1 against something etc.
Measure the RF output voltage between ZOUT1 and ZOUT2 on high impedance if you can. It may be DC biased! Then load the output pair with a decent resistor and measure the RF again - it will be smaller, as the module of the output impedance with the resistor form a voltage divider. You can calculate the module of the impedance from these values.
The LC filter probably ends with 200 ohm and 1000 ohms in parralel, so cca 167 ohm impedance can be expected. The IC perhaps is unable to deliver power to a fully matched load and it may overheat. It may expect a resistive load several times bigger than 167 ohm. Moreover, if the LC filter is designed for a 167 ohm load, its frequency response will be ruined by loading it too much.

Experiment and have fun!
VBR from Ivan OK1SIP

Nazdar nebo ahoj Ivane,
Well the problem still remains
I have ZOUT1 and ZOUT2 output from the module and per schematic they do no appear to be directly connected to the chip DAC.
If they  are same output and it should be connected as you suggested that can be verified on scope, no issue.
However, how do I determine the impedance to match ?
What is really puzzling - most "tutorials" concentrate on programing and there is not a single one
actually running AD9850 as a signal source , with  schematic and actual connections.
There is an app note but it runs directly from the chip , the HC_SR08 module is different.
I just cannot believe there is no ham ever used the module as local oscillator - but there
are plenty of "toy computer" applications sporting the fancy display - been there done that.

The link to the docs of the module is here.

Hi Vaclav,
if you disconnect the primary of the input transformer from the amplifier ground and attach both ends of the winding to the DDS module terminals, you do not need bother whether it is balanced (differential) or unbalanced. You can match the input impedance of the amplifier to the module by tweaking the number of turns of the primary.

VBR from Ivan

OK, I have new , stupid , request.
I am looking for a schematic  so I can connect AD9850 DDS to this push-pull amp.
All I am seeing is how to program the AD9850 module. I have an HC_SR08 module and it looks as if it has only ONE DAC output.
That  is fine , but I need the output impedance so I can properly interface it to my amp.
I am not sure if the output is in reference to ground or differential.
Any reference / links would be appreciated.
I have AD9850 spec , but the HC_SR08 module contains additional components, I have that too but it is pretty fuzzy ,
and the output spec is pretty vague.
So instead of muddling thru HC_SR08 spec a real circuit connected to the  module would be great.
So far no luck.

And I am sorry to be such bother, I am getting nowhere with other "amateur radio" groups.