[solved] Ceramic cap marked 6_? - Page 1
Forum section: electronics / beginners

author: kalel
author_rank: Frequent Contributor
timestamp: August 15, 2017, 06:45:47 pm
content: I'm not sure about this cap value.I have a few of 6_ capacitors that don't seem to give any value in the multimeter or little multi-component tester for China.There's no 3 number code.Looks a bit like this quick drawing:If you could point me to the right coding system for these, would be great.

author: jpanhalt
author_rank: Super Contributor
timestamp: August 15, 2017, 06:48:36 pm
content: I have some like that. The meaning is 6 pF.What is its actual size? Mine are quite small (ca. 6 mm).

author: kalel
author_rank: Frequent Contributor
timestamp: August 15, 2017, 06:51:24 pm
content: Quote from: jpanhalt on August 15, 2017, 06:48:36 pmThanks, might be too small to be measured. Yes, it's a small thing. I don't know the exact size atm, as a rough measure, width is slightly less than 3 pins of a dip 8 socket.

author: Yansi
author_rank: Super Contributor
timestamp: August 15, 2017, 06:57:54 pm
content: A generic 6 puff cap.

author: tautech
author_rank: Super Contributor
timestamp: August 15, 2017, 08:40:56 pm
content: Quote from: Yansi on August 15, 2017, 06:57:54 pm+1I repaired a garage door remote recently with a couple of these in the RF output. They're quite small ~5mm dia and they were used for output resonance paralleled with a tiny variable cap. The RF output had drifted slightly off frequency but having a 3.2 GHz demo SA it was easy to get in band again at which it worked better than ever before.

author: jpanhalt
author_rank: Super Contributor
timestamp: August 15, 2017, 08:57:51 pm
content: Quote from: tautech on August 15, 2017, 08:40:56 pmI am jealous. Was that a Rigol?

author: tautech
author_rank: Super Contributor
timestamp: August 15, 2017, 09:06:24 pm
content: Quote from: jpanhalt on August 15, 2017, 08:57:51 pmYou know it wasn't.

author: kalel
author_rank: Frequent Contributor
timestamp: August 15, 2017, 09:56:50 pm
content: Quote from: tautech on August 15, 2017, 08:40:56 pmWhat would be the process if you didn't have one of those? Just curious, I'm not working with any remotes (was just trying to identify the cap, and thanks to everyone, it's done).

author: tautech
author_rank: Super Contributor
timestamp: August 15, 2017, 10:30:13 pm
content: Quote from: kalel on August 15, 2017, 09:56:50 pmI first thought the remote's 339 MHz would make it possible to get some measurement from my 300 MHz DSO and go from there but with the additional info on the carrier there was no useful info gained from just a BNC/coax sniffer loop. I couldn't get accurate frequency measurements. I might have tried the scope's FFT but didn't instead just grabbing a SA.RF is black magic and not a strong point of mine so just working with what I have.........and a frequency counter might have done the job......a SA will show the peak fundamental frequency and I was able to trim it onto the band with the tiny variable cap added for just this purpose. Same BNC/coax sniffer loop used.As what is the normal/standard procedure......well it must be transmitting *near* the middle of the intended frequency and it wasn't which this explained this remotes poor performance for some years.......nudging closer and closer to the garage door in order to get within range and then having to roll backwards to give the tilting door room to open.Now it works from 20+ meters.Lately it was so bad that you'd have to hold the remote close to the passenger seat upright to get the steel mesh inside to act as a RF reflective backplane to direct the RF better towards the receiver.Luckily I had another *working* remote (wife's) so could see that signal amplitude was comparable between them so it had to be an off band issue.Others with more experience will have better ideas.

author: tautech
author_rank: Super Contributor
timestamp: August 15, 2017, 10:37:16 pm
content: Quote from: kalel on August 15, 2017, 06:45:47 pmBTW, under 100 pF the value is actual value.......no code.

author: kalel
author_rank: Frequent Contributor
timestamp: August 15, 2017, 11:34:44 pm
content: Quote from: tautech on August 15, 2017, 10:37:16 pmThanks. I definitely won't be experimenting with circuits that need this value any time soon as a beginner. I'm happy with anything that oscillates at a few Hz, and possibly up to a few kHz for making some sounds.

author: Yansi
author_rank: Super Contributor
timestamp: August 16, 2017, 08:27:03 pm
content: That actually is a wrong assumption. Many many circuits, even the audio frequency ones, sometimes needs a little tweak here or there, with a cap of a pF range.

author: Zero999
author_rank: Super Contributor
timestamp: August 17, 2017, 12:38:58 pm
content: Quote from: Yansi on August 16, 2017, 08:27:03 pmYes, small capacitors are often used for frequency compensation in amplifiers. There's one in every frequency compensated op-amp IC.The value is usually under 20pF, as they take up a large amount of die area.