Thanks and DDS filter query


David
 

I've only just started building the PHSNA but already the UNO and Ad9850 with the Arduino and Windows software has allowed me to generate test sigs proving one of the band pass filters in my G3TSO multiband txrx is way out (I stared building this in 1999 and never finished it properly!) I will wait now until the PHSNA is built before doing more work on my switchable filters but wanted to say thanks to everyone involved in the project - maybe if I'd had one back in 1999 I'd have finished the original radio back then.


Also could someone please point me at some background info ref the changes needed to the DDS filter, I've seen the details on what needs to be done to improve it,  but wondered what the issue is with the built-in filter on the board......wondering really if I can get away with amplifying this to get some signal to the detector initially before doing it properly as components etc become available.


Thanks,


David - G4ZDT


N5IB
 

Hi David,

On the DDS filters...

The biggest issue is that the filter on the DDS module, regardless of whether a 9850 or a 9851 DDS is being used, is designed for a roll off at about 70 MHz. While this might be OK for a 9851, it is much too high for a 9850. That filter should roll off at a bit above 30 MHz.

Also, the L and C components used in the on-board filter are not of particularly high quality.

Finally, if you are using the "Type-2" DDS with the corresponding PHSNA or Experimenter boards, the circuit is designed to take the output from both of the available sinewave output pins and combine them with a transformer is a push-pull fashion, which helps to suppress even harmonics. The filter on the DDS module is applied to only one of the outputs, which would upset the symmetry.

You can certainly go "as is" for the time being and apply signal to the detector. It won't hurt anything. You probably just won't get quite as clean a signal as otherwise

The "Type-1" DDS and PHSNA board would be much more suitable if you wished not to remove the filter from the DDS. A filter of the appropriate roll off is included on the PHSNA board.

Jim, N5IB


David
 

Hi Jim,
It's a type 2 board and I'm planning to build it to the exact spec detailed in the relevant folder on here with the filter change etc but it will be useful to get it working as is for now pending the correct components, pcb etc.

Thanks for the extra info, much appreciated.

David


Alfredo Mendiola Loyola
 

Hello,

Try this guide to make Harmonic Filter.

I made the filter for the 10Mhz and works perfect.

 
Regards
Alfredo Mendiola Loyola