RF choke inductor for 500 MHz
It is basically to block the RF signal to the DC voltage source for varactor control. I am wondering whether 10uH is good enough? What type of RF choke should I use, SMT or hole-through axia?
Any other considering I should count for the selection of RF choke?
Thanks.
Exact value, like 10uH doesn't really help at high freq. You should choose SMT, with parallel resonance at 500MHz. You may also look for broadband RF chokes from Epcos:
SMD-HF-Drosseln Simid 1210-100 Typ Epcos B82422-A, Ausführung mit Tr?germaterial Ferrit Typ B82422-A1, value from 1,8 μH to 10 μH. We have been using 2u2 and 3u3 as broadband chokes up to 5GHz and it is great!
hi, rfmw. Thanks for your reply. I am a little curious about the self-resonant frequency (SRF) of the rf choke. Should it be higher than the operation frequency, or just the same as the operation frequency?
And for the broadband RF choke, is it still a inductance, or utilizing other technique? Are there any good articles about that?
Thanks.
SRF shall be higher than the operating frequency. Above SRF the inductor becomes capacitive.
There are some application notes here: http://www.coilcraft.com/appnotes.cfm
If you are operating at 500 MHz, the SRF should be at least 600 MHz. When it resonates, it COULD resonate as a short circuit--ie no rf attenuation!
Thanks your guys information. So where can I find a suitable RF choke inductor for UHF applications? Since I looked up a few datasheet, the SRF of most of them are lower than 500 MHz.
Hi winglj,
you can look at Murata.
It has good ferrite beads for high frequencies.
I'm posting you the datasheet catalog.