Adjust the capacitor and directional coupling turns for best RL/phase response.

Connect a good quality -20dB attenuator between DUT and DET. This capacitor will be adjusted for best RL and flat response between 0-180MHz. The directional coupler is compensated with a small capacitor, in order to increase the return loss (RL). Here is possible to see my spectrum analyzer connected at VNA output: ~ 30MHz and 160MHz. Phase noise performances of the DDS are not very good due usage of internal PLL multiplier (like miniVNA). The coils of filter can be hand made when SMD coils are not available. LPF must to be recalculated if maximum frequency >180MHz.

At the begin, LPF is possible to be bypassed. My VNA was limited to 180MHz by using a Cauer LPF 180MHz/-3dB. Software calibration of the output frequency is done at 30MHz. Internal PLL multiplier (x20) is used for 500MHz clocking, using 25MHz external crystal. The DDS oscillator is capable to generate signals up to 250MHz. Bellow i will speak only about AD9951 version.įor more details: Link to IZ1PMX web site. IZ1PMX VNA is capable to use two DDS chips: AD9850 (50MHz) or AD9951 (180MHz). PC Software supported: IZ1PMX - IT_VNA VNAJ IG miniVNA PC connection: RS232, USB FT232 or Bluetooth HC-06. Return loss of directional coupler: -25dB.-34dB. Recommanded upper limit of frequency: 180MHz (AD9951, 500MHz clock).ĭynamical range in detection mode: 70dB (AD8307) Thank you Alfredo for help and for your ham spirit! If an 'miniVNA' is too expensive or if you like to build an useful RF instrument, IZ1PMX vectorial network analyser will be a good choice.

Minivna