aliahmedrauf
Newbie level 5
![Newbie level 5](/styles/images/ranks/blevel2.gif)
Hi. I'm working on my RF transmitter. I'm creating RF signal using VCO which is attached to gain block and then fed to moduler Power Amplifier. When i tested this chain in lab on spectrum analyzer using coupler and 50 ohm load my whole chain works fine. But issue arise when i attached antenna at the output. I usually provide bias to my PA first which takes current about 0.3A with no RF in normal condition. But when i attached antenna at the output and attached my VCO board at the input at the PA. I turned on bias for PA (bias for VCO still off so no RF input fed) the amplifier load itself and draws current up to 4A even there is no RF input. I tried to investigate further i removed my VCO board and attached a 50 ohm termination at the input then this issue disappear. Then i removed termination and attached my VCO again but i have attached 20 dB external attenuation between VCO and PA. This issue doesn't appear but it can significantly reduce my desired power. Any one know why this problem is appearing and how can i solve it??