RF choke vs inductor - Page 1
Forum section: electronics / rf-microwave

author: DMartens
author_rank: Contributor
timestamp: August 04, 2024, 05:45:37 pm
content: Silicon Chip Australia magazine featured a 12-digit 2.5 GHz frequency meter in their December 2012 issue. The parts list calls for two "47uH RF chokes, axial type" used in the power supply rails of the ECL input channel / prescaler. Are these any different from "regular" inductors with a traditional THT resistor form factor? Attachment shows the component layout.

author: radiolistener
author_rank: Super Contributor
timestamp: August 04, 2024, 08:09:44 pm
content: Usually inductor has high Q (low loss), because they are used in LC circuits whenre energy loss is critical. While RF choke for DC filter may have low Q, because their goal is just to block RF, if part of blocked RF power will be dissipated into heat this is not an issue for RF choke, at least if amount of heat is not too high to destroy the RF choke...

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: August 06, 2024, 07:43:49 am
content: These are just plain ordinary wire ended RF chokes. eBay or your regular low cost supplier?SJ

author: A.Z.
author_rank: Super Contributor
timestamp: August 06, 2024, 09:10:32 am
content: just search for axial inductors and you'll find them, an examplehttps://www2.mouser.com/c/passive-components/inductors-chokes-coils/?termination%20style=Axial&_gl=1%2Aafcan9%2A_ga%2AdW5kZWZpbmVk%2A_ga_15W4STQT4T%2AdW5kZWZpbmVk%2A_ga_1KQLCYKRX3%2AdW5kZWZpbmVk

author: vk4ffab
author_rank: Frequent Contributor
timestamp: August 06, 2024, 10:36:15 pm
content: Quote from: DMartens on August 04, 2024, 05:45:37 pmProbably not. About the only thing to consider is if your replacement part has the same current handling as what was speced.

author: mag_therm
author_rank: Frequent Contributor
timestamp: August 07, 2024, 12:23:51 am
content: Check the actual impedance of those chokes and their decoupling capacitors at 2.5 GHz.I am just designing my first L1 band (1.57GHz) project with a bias Tee.My L section dc chokes are very different. I selected : AVX Air Core AL series 0.68 nH with self resonance pole at 1.50 GHz, DC rating 2.5 AmpDecoupling Capacitors were selected usinghttps://spicat.kyocera-avx.com/product/:npo 33pF 50 V self resonance zero at 1.24 GHz, 1.24 Ohm atL1 band (1.57GHz)And Lam/4 at 2.5GHz is 30mm, do a smith.

author: ftg
author_rank: Frequent Contributor
timestamp: August 07, 2024, 09:55:35 am
content: The 47µH chokes seem to be used for DC supply filtering and general EMC mitigation, not on the RF path.So how good they are on 2.5GHz is less of an issue.Based on the picture in the first post, the design is THT anyway.

author: mag_therm
author_rank: Frequent Contributor
timestamp: August 07, 2024, 06:51:32 pm
content: I purchased the Silicon Chip Australia Dec 2012 issue with part 1 of the project.The 47 uH RFCs were +5V rail filters along with 10nF and 100nF capacitors for Motorola MC12095 Monolithic ECL /4 phase lock loop,taking up to 2.5GHz.Further upstream, there was a special bias choke , Mini Circuits 10GHZ ADC80A, from that +5V, for input amplifier MMIC ERA-2sm+It would be necessary to purchase the following monthly issues to next part of the project containing the BOM showing part numbers of those RFC and decoupling capacitors.

author: DMartens
author_rank: Contributor
timestamp: August 12, 2024, 03:01:27 pm
content: Thanks. I have PDF-copies of all relevant SC articles for this design (including errata, improvements and expansions that appeared years later).You are correct that for the Mini Circuits part number is provided. But not so for the "47uH RF choke, axial type", so I was wondering if I can just cut two from the ribbons in my "200-in-a-box-of-various-values" that I got from AliExpress (the ones that look like ribbons of resistors).

author: mag_therm
author_rank: Frequent Contributor
timestamp: August 13, 2024, 11:30:22 am
content: It seems to be a long lived project which is a basis to just build it using generic components.It could be that the ECL does not draw high switching transient currents from the power rail.I would user the Kyocera SpiCat to select and solder 0805 or 1206 mlcc across the pins of the 100nF.Select capacitors that have srf above the highest used frequency, even if they are low pF values.

author: igor78
author_rank: Contributor
timestamp: August 20, 2024, 06:03:52 pm
content: I hope someone with high freq experience will chime in.How did they calculate these low pass filters between the freq dividers?The input freq is 100Mhz-2.5GHz.MC12095 have current pulsating on the power pin at 25-600MHz rateThe other divider have current pulsating on the power pin at 2k-5MHz rateWay before freq crosses 600Mhz, all these capacitors will turn into inductors and inductors turn into capacitors, so the pi-filter network should stop working.If one causally solder in an 47uH choke from ebay - it would just give some unpredictable oscillations with parasitics. These chokes are meant for audio freq and below.