I am modifying a DX Engineering RPA-1 preamp to put dc power on the antenna 'input' coax for an upstream active antenna.
I am having difficulty finding a good RF coupling/ DC blocking capacitor for my modification.
For a starting point I examined the components of the DC power injector that came with the preamp. The capacitor in it is a generic .1uF ceramic disc.
By calculation the Z of the cap is 5 ohm at 300KHz. I tested it on a HP LCR meter up to 1MHz and was shocked to see how how poorly it responded. Its Q wasnt too bad at 300KHz but it went down to Q=3 at 1MHz. That tells me it is very lossy. Therefore I want to reduce the losses with a higher value and/or different type cap.
I did some research on RF caps and found MLCC COG, and X7R materials to be recommended. Unfortunately COG caps are .1uF max. I purchased some 1uF X7R caps to test and was disappointed with the results...not much better than the original disc cap. I had some .1uF COG caps on hand which I tested with much better results @ 1MHz the Z= .1 ohm and the Q>20. Paralleling 10 caps for 1uF is a real pain.
Can anyone recommend some other type of cap that isnt lossy from 300KHz to 35MHz?
I am having difficulty finding a good RF coupling/ DC blocking capacitor for my modification.
For a starting point I examined the components of the DC power injector that came with the preamp. The capacitor in it is a generic .1uF ceramic disc.
By calculation the Z of the cap is 5 ohm at 300KHz. I tested it on a HP LCR meter up to 1MHz and was shocked to see how how poorly it responded. Its Q wasnt too bad at 300KHz but it went down to Q=3 at 1MHz. That tells me it is very lossy. Therefore I want to reduce the losses with a higher value and/or different type cap.
I did some research on RF caps and found MLCC COG, and X7R materials to be recommended. Unfortunately COG caps are .1uF max. I purchased some 1uF X7R caps to test and was disappointed with the results...not much better than the original disc cap. I had some .1uF COG caps on hand which I tested with much better results @ 1MHz the Z= .1 ohm and the Q>20. Paralleling 10 caps for 1uF is a real pain.
Can anyone recommend some other type of cap that isnt lossy from 300KHz to 35MHz?