Nice job for freehand. I spent a lifetime in Aerospace tooling though I am retired now. When you have a lot of identical parts to make, if you can join the individual parts into a larger block you accuracy and speed go way up. If you want to make another tuning condenser after you cut your plates but before trimming to final shape or drilling any holes, you can use double sided tape (very thin) to join all your parts into a block. Now final sanding to shape will go much quicker and the parts will be all the same. When drilling your holes, all the holes will also be the same. If you have even a small hand drill press, that will keep your drill square to your work and a belt sander or disc sander will make final shaping a snap. With better accuracy you can then reduce the gap between the stator and rotor too. Again, very nice job for free hand work!
@mike-M0MSN3 жыл бұрын
Great tip many thanks 😊
@orangmakan Жыл бұрын
He needs that big of a gap because there might be up to 5000Volts between them when used for trimming a loop antenna.
@MrPanetela3 жыл бұрын
hopefully i an keep this story short. way back in the day, my Dad called a repair man to look at his TV and radio. The repair man first looked at the radio. I as a baby boy thought wow! there's a city in there! The gang capacitor was like a gothic cathedral. Then the repair man giggled and say to my Dad, here's the problem, and proceeded to pull a tiny deceased mouse that had nibbled it's way into the radio for its new home. And of course shorted out the tube while scurrying around in there. Thanks, your presentation evoked a lot of great memories. Wish you the very best, you and your family. This generation will never realize how wonderfully great those days were before everything changed.
@mike-M0MSN3 жыл бұрын
Beautiful story, thank you for sharing. best wishes Mike-M0MSN
@philandmia2 жыл бұрын
Thank you for the inspiration. I have now built 2 for my antenna tuner. Not as hard as I had imagined.😁
@paulperano9236 Жыл бұрын
Love the idea and great execution too Mike. You could design the plates on a PCB system and get them made through the like of PCBWay, 10m boards for a few pound, then use std brass washers to space them. With double sided PCBs and plated holes it could be very interesting.
@jbgreer3 жыл бұрын
I feel certain you've explained how effective the scroll saw is at cutting sandwiches. Very effective. Great work, Mike.
@mike-M0MSN3 жыл бұрын
Thanks 👍 almost as good at cutting fingers...
@jeffreydove20363 жыл бұрын
Hi, nice capacitor you made. Though you need to round all the corners or you will leak out at high voltage. I have built some of them also, and yes it is a lot of time. But you have something you built yourself and can now build even better. Great job there. Jeff
@mike-M0MSN3 жыл бұрын
Thanks for the tips!
@stevenlstout3 жыл бұрын
It is important to deburr the edges to reduce arcover. I used to make similar parts on a CNC Punch machine. I would check with local sheet metal shops for a bid. They can make complete parts that are drilled and deburred very quickly.
@mike-M0MSN3 жыл бұрын
De-bur very important.. and yes next time CNC it maybe££
@lc79tourer26 Жыл бұрын
Ahh, I see you beat me to sharp edges bit already, sorry to have made the point again. Something to be said for reading comments first before shooting my mouth off.
@maurasmith-mitsky7622 жыл бұрын
Excellent video. Lots of work involved. May your new variable capacitor serve you well.
@mike-M0MSN2 жыл бұрын
Many thanks!
@andrewskater8813 Жыл бұрын
Impressive dedication! I bought an old radio to get the tuning capacitor and germanium diodes and after destroying some of the polystyrene capacitors realised it did not have germanium diodes and was using tube diodes as detectors..............so months later I am slowly getting the radio to work as a restoration project
@americaswayout44893 жыл бұрын
I think the word you Brits use to describe something fantastic is BRILLANT, so we can go with that. Years ago Crushcraft sold a vertical called an R3 it had some traps for 10,15,20 but also used a capacitor like you just built with a motor and outside box plus it had a control box for inside. I acquired the control box, have a 24-28 volt motor and should have other parts to try to make something work. I also have the driven element from an av4 beam that is about the same as the r3. You make everything seem so easy, but every time I try a project, some hard to find or use tool gets in the way. Trying to build some spreaders for a version of DX Commander the key whole size was not available. You really have a lot of talents !! If you get bored or would like a challenge, I would send you the control box and other parts if you would like to tackle building the outside box, etc to remote tune the antenna. The control box has the voltages etc? Also, the same inside control might be stable with other capacitor tuned antenna like those loops you have built recently?
@mike-M0MSN3 жыл бұрын
Maybe one day, but for now I have too much to do... thank you for your nice comments
@BoB4jjjjs3 жыл бұрын
You should be proud of that one Mike! Excellent, I would not have thought to try it. I threw a box of these out when I got married, never thought I would ever have a use for them :-(( the daft things one does when moving house in a hurry!
@mike-M0MSN3 жыл бұрын
Yes I think I did the same, we live and learn.. :)
@hydromakers Жыл бұрын
absolutely the finest capacitor that i have ever seen.
@hyperionsixzeroeight5064 Жыл бұрын
I seem to remember kits being available to construct variable caps. Hamfest flea markets another good source. Surplus military gear (old stuff) another source for us scroungers.
@thehulkster27073 жыл бұрын
Very helpful and an inspiration because the price of variable air caps are through the roof..ty
@mike-M0MSN3 жыл бұрын
Glad it was helpful!
@stephennelson-smith33122 жыл бұрын
Super job - it came out really well! I must say I did chuckle when you baulked at the price of a VC on ebay, and then spent twice as much on just the saw, let alone the parts, but inspiring all the same.
@ConsertandoTudo3 жыл бұрын
To people looking for a way to make it, and does not have access to all tools, that could be made using raw printed circuit board and a rotatory (?) sand papper. Prefer fenolite (?) pcb over fiber glass. Great job.
@AGeekNamedRoss Жыл бұрын
Next time, for that semi-circle notch on the stator plates, try this: Drill the holes first, then cut them out. That small diameter semi-circle is hard to get right with a scroll saw. Also, this project would warrant the purchase of a small drill-press.
@joewoodchuck3824 Жыл бұрын
Nicely done! There's a design I have in mind that's much easier to make. I'll just cut out squares. Drill a hole in one corner for shafts so the square is used as a diamond shape, and nip off the opposite corner to clear the next shaft. I know it's a little unconventional and won't look as cool as semi circles but I'll save a lot of time. Accumulating hardware as I go along.
@michelemarchitiello18682 жыл бұрын
Complimenti. È bellissimo questo condensarore variabile, costruito con le tue mani.
@problemwithauthority3 жыл бұрын
I remember the sound of using a scroll saw on metal...makes a heck of a racket.
@mike-M0MSN3 жыл бұрын
yep, next time, ear plugs.
@quebirt10 ай бұрын
Very cool. I assumed special materials and exact spacing would be required. I may actually give this a go. I have a very nice variable capacitor that came out of an old ham radio but it's lost in my "collection."
@Joe-KN4IFI3 жыл бұрын
Great work Mike. Doing plate after plate can get a wee bit tedious. 73 Joe
@mike-M0MSN3 жыл бұрын
yep two days of work one cap... :(
@DavidALovingMPF1026 ай бұрын
Nice. the variable caps I use for my homebuilt A.M. radios have gone from $15 to $36. 10 pf to 360 pf. I too am looking into making my own. Thanks!
@southernexposure1233 жыл бұрын
Real nice job on the cap. A few years before I bought a commercially made antenna tuner I red necked a tuner together from junk box parts. My coil was the spring which was still in a 5 subject school notebook and the variable cap was from a defunct 9 volt transistor radio. I switched the number of turns on the coil using Rat Shack test jumper wires. You remember those. They had spring loaded alligator clips on each end. Oh, and the 5 subject notebook served as my log book. lol I used it with a 200 watt Swan 400 tube rig and it never arced. My key was a Rat Sheck roller switch - hand held. ((-: Long live CW.
@mike-M0MSN3 жыл бұрын
Oh I remember them, great times. Cheers
@g0fvt3 жыл бұрын
An interesting project, well done, I may make similar but using double sided PCB for the plates with brass hardware. Watching the test I got the impression your minimum capacitance would be lower if the lower pates were a simple rectangle below the spindle. Not being critical but would make construction a little easier. I do see some companies offer water jet cutting..... might be worth looking into?
@mike-M0MSN3 жыл бұрын
Great idea
@sheilamoore62552 жыл бұрын
Yes, all you need is a 300 dollar table jigsaw, some high-dollar aluminum plate material, etc., etc., to make your very own variable capacitor!!! Great!
@mike-M0MSN2 жыл бұрын
😂😂😂💋
@philippejoigny59283 жыл бұрын
Congratulations Mike for this wonderful achievement! 73, Philippe (F1PBT)
@mike-M0MSN3 жыл бұрын
Merci beaucoup pour vos commentaires
@PE3FS3 жыл бұрын
nice prototype and a lot of work . I hope you don't forget to peel of the plastic from the alu. The value is a bit different then. But I am sure you know. looking forward to the next video
@mike-M0MSN3 жыл бұрын
Thanks, will do!
@chuckmaddison29249 ай бұрын
Impressive, I tried a couple of years back, and it was a glorious failure . After seeing this might have another attempt.
@SuburbanDXing3 жыл бұрын
All I can think of here is that if I tried half of the stuff you do, they'd call me "Lefty" (with the local hospital getting plenty of my gear money). Fun to watch your craft, Mike...good stuff. 73! de WX0V
@mike-M0MSN3 жыл бұрын
Thank goodness for the NHS
@SuburbanDXing3 жыл бұрын
@@mike-M0MSN Indeed...hopefully I will not be in use of their services...keep up the great work here...73!
@lc79tourer26 Жыл бұрын
Very nicely done, My only thought would be to try and get rid of any sharp edges that might help avoid arching, other than that, a good effort.
@warrenkeillor9034 Жыл бұрын
That is inspiring! I too have always wished to get a big air gap capacitor. That is a nice simple design. I wonder how large of range one can possibly get with this concept, going big?
@Timtron432 Жыл бұрын
Hi Warren, A friend of mine that has a cnc water jet cut all my parts for a very very very big air variable cap lol 900 pf minimum to 1.8 uf max that i put inside a plastic sealed clear box. I use it to tune and find the peak's when i tune the coils of ( Not A BiTT or A BiTT ) The variable 1.5 uf cap is used with other ac caps to get in range and find the peak output of the BiTT or Not A BiTT.. Cheers!!!
@Stelios.Posantzis3 жыл бұрын
You could have stacked the plates together and secured them in a vice, with some support blocks judiciously placed, before filing them. That way you could get uniformity. Achieving uniformity with the spacers is more critical to making a precision part and also harder to achieve but still doable. It would be best to cut them using an alignment jig though in order to minimize the filing work needed afterwards in order to get them all to be square cut and of the same length.
@mike-M0MSN3 жыл бұрын
Yes, a vice is the next purchase.
@TEGEscalator3 жыл бұрын
73 Mike, great achievement, but you have to be patient. I was just talking about it this morning with my friend but it will be a 500pf. ps: do not forget to remove the blue plastic which protects the aluminum.
@mike-M0MSN3 жыл бұрын
Blue plastic, oh yes
@michealbell50423 жыл бұрын
Keep up good work I would love to see this with a mag loop🤔👍😀
@mike-M0MSN3 жыл бұрын
Maybe???
@MrMrsteve012 жыл бұрын
Those flux capacitors are crazy. Total banana bibulation and scheming. Been thinking about doing it in a full stasis pizza loadout.
@sagorreza11411 ай бұрын
Wonderful built! Impressive.
@mike-M0MSN11 ай бұрын
Thank you! Cheers!
@whamni3 жыл бұрын
Brilliant Mike, soon as I saw you using the file I knew lol
@mike-M0MSN3 жыл бұрын
;)
@MiscDotGeek3 жыл бұрын
FB OM! I built one this week too, but I used PCB's and switches. It actually went to about 400pf, but I don't think it would handle the higher voltages that yours would. My channel has it if anybody wants to see. But I like yours a lot- very properly built and as good as any much more expensive one, if not better :)
@mike-M0MSN3 жыл бұрын
many thanks I have a visit. :)
@johng.37408 ай бұрын
Good job building the capacitor! I'm wondering if you could cut the individual capacitor plates from plastic or wood, then cover them with a layer or layers of aluminum foil.
@mike-M0MSN8 ай бұрын
Yes you can!
@josephleister91983 жыл бұрын
Excellent work...thank you for sharing.
@mike-M0MSN3 жыл бұрын
Thank you! Cheers!
@waynedavies31852 жыл бұрын
Excellent video.... well made.
@thefallenone79883 жыл бұрын
Good job because they get an arm and a leg for them these days if you can find them. Although some can be had at a decent price if you look hard enough. 😎👍
@mike-M0MSN3 жыл бұрын
To true 😀
@Dr._Spamy Жыл бұрын
One trick to drill holes from even distance is to drill a clamped stack of roughly cut sheet metal peaces all at once. The final shaping could be done after the drilling then.
@jeanlouisberthault76033 жыл бұрын
Very nice job, have a nice day, JB from FRANCE
@mike-M0MSN3 жыл бұрын
Thanks, you too!
@KenPaisley3 жыл бұрын
Nice job. A belt sander and a drill press might make that a lot easier. Why did you leave the plastic film on the plates? Wondering if it changes the capacitance. I would think it does.
@flapjack9495 Жыл бұрын
I was wondering that, too. There's no good reason to leave that film on there. It shouldn't change the capacitance too much but it might increase the dieletric losses.
@radioman32298 ай бұрын
Mike-M0MSN, ty for your videos, how can we know what size variable capacitor we need. I am building a loop for 100 watts for 20 meters?
@mike-M0MSN7 ай бұрын
the reality is you make the capacitor form 10pF to the best you can get (maybe 200pF) and then play the the size of loop....
@radioman32297 ай бұрын
@@mike-M0MSN ok, ty NS9T
@jmd628003 жыл бұрын
Fantastique job !! You are in crédible , you transform idéal in real !!! ( not,so easy) congrats 👍👍👍
@spuddyspud81783 жыл бұрын
I might have a go at building one.but will see if I can get the plate's laser cut.what is the best plate size to use
@tvdylan Жыл бұрын
so how do we make capacitors with more pico farrads ? just add more plates ? do we increase or decrease the distance between plates ? nice work !
@M4CHINE693 ай бұрын
yes add more plates or make the plate distance closer
@johnnydunphy63962 жыл бұрын
Top class ..well done .. SIR
@mike-M0MSN2 жыл бұрын
Many thanks
@ahmedisml Жыл бұрын
Wonderful job
@antonioroccuzzo421411 ай бұрын
Nice job 👍👍👍👍👍
@mike-M0MSN11 ай бұрын
Thanks 👍
@ianide24808 ай бұрын
apply contact adhesive to the printed parts and stick aluminum foil to those?
@omsingharjit2 жыл бұрын
you can make it's rang more better and flexible by connecting each stationery plate with jumpers connectors or 7 step rotary switch found in Stepped fan regulators and sure you have to seperate all plate electrically .
@MichaelEdelman19543 жыл бұрын
Saw this and immediately subscribed. Very nice.
@mike-M0MSN3 жыл бұрын
Awesome, thank you!
@andyquattro3 жыл бұрын
Fantastic work Mike ! I've subscribed so I don't miss the roller coaster inductor video ;-) 73 Andrew G1PPZ
@mike-M0MSN3 жыл бұрын
Welcome aboard! and that's a great Idea too.
@markjhonthan9123 Жыл бұрын
WoooooW Good job I like . I was want to make one like this but I want made A small variable capasiter
@jeremycole30082 жыл бұрын
very nice build. i like it
@TechTed1 Жыл бұрын
Great job there
@francisauspert5133 жыл бұрын
Thanks Mike (Belgium)
@pierre53259 ай бұрын
Mike, most excellent job Mate!
@AdamosDad3 жыл бұрын
This is real HAM Radio!
@mike-M0MSN3 жыл бұрын
Many Thanks 🤩
@ben2e0omr3 жыл бұрын
Excellent build Mike. I shall put my order in now please.
@mike-M0MSN3 жыл бұрын
ha ha,, :)
@kariolavi3 жыл бұрын
Looks great Mike! I´ve used a cheap nibbler attachment on my drill. The thickness of the aluminium plate was 1,5 mm and it works fine. Some filing is still needed of course. 73 de Kari OH2BCY
@mike-M0MSN3 жыл бұрын
Great idea.
@ianxfs3 жыл бұрын
I’m very pleased too Mike 👍🏻
@mike-M0MSN3 жыл бұрын
Cheers Ian
@attilarivera2 жыл бұрын
👏👏👏👏👏👏 Thank You!!! ✌😊👍 💚💛💙 🇧🇷🇧🇷🇧🇷
@jean-marcparatte55643 жыл бұрын
Fine work.
@mike-M0MSN3 жыл бұрын
Many thanks!
@iestynwyn43113 жыл бұрын
good job mike. you should have been in the A team tidy
@mike-M0MSN3 жыл бұрын
Merdoc, or Face-man
@husabyrr64962 жыл бұрын
Très bonne vidéo. Je me lance pour en faire une.thank you.
@vanpenguin226 ай бұрын
Just curious, but, Would it have changed its performance in either direction if the bottom plates were also semicircles?
@mike-M0MSN5 ай бұрын
Not really, maybe a little less capacity...
@vanpenguin225 ай бұрын
@@mike-M0MSN Thank you for answering 👍
@harryszwergstatt2879 Жыл бұрын
Really great job!👍
@chazrw2chz2903 жыл бұрын
Nice build. 👍👍 Although I'd likely be lazy and outsource the cutting to a friend that has a plasma cutter. 😉
@mike-M0MSN3 жыл бұрын
A friend yes, but a company!!! way to expensive..
@chazrw2chz2903 жыл бұрын
@@mike-M0MSN Without a doubt. Really liked your video, gives me all sorts of ideas.
@M7XCB3 жыл бұрын
Excellent work love making my own things bet your miss not happy about chest freezer lol
@mike-M0MSN3 жыл бұрын
You got that right!, but you should see the kitchen......
@M7XCB3 жыл бұрын
@@mike-M0MSN haha bad as me I had yaesu 767 Gtl DX on the kitchen table apart for over 1 week yer it took me to fix it my wife was very supportive at least she knows where I am lol
@crazycrab85782 жыл бұрын
need this for me crystal radio , nicely done
@kellypaws3 жыл бұрын
It’s a talented piece of work, and VCs are expensive. But, and it’s a big but, looking at the tools you have to own, and the time it takes, not to mention the skill, obviously the skill, I was rather thinking there’s a reason they’re dear.
@RssutharJaisalmer3 жыл бұрын
Wow 😯👌👆🙏
@RobR3863 ай бұрын
I’m going to build one for my mag loop antenna 🙂
@Nathan1975Liggy3 жыл бұрын
I would like a go at doing this one day but is there any special calculations that need to be done to determing the spacing of each plate for the power used on the radio? I do know that the larger the gap the lower the capacitance will be.
@mike-M0MSN3 жыл бұрын
yes but the more power it will handle.
@luckydubeinrc51653 жыл бұрын
1mm spacing= 1kv safely.
@Nathan1975Liggy3 жыл бұрын
@@luckydubeinrc5165 WOW as small as that, many thanks for the reply.
@DedyBlackLaBeneamata Жыл бұрын
incredible idea
@mike-M0MSN Жыл бұрын
Thank you! Cheers!
@michealbell50423 жыл бұрын
You have inspired me to build one it's over halfway done. It's very time consuming I don't know if I will do it again😅
@mike-M0MSN3 жыл бұрын
Yep, two days of cutting and filing and drilling and printing and.....
@Tump20103 жыл бұрын
need to get the foot to sit on the work to keep it from jittering. :-) You need to add a disc or belt sander to your tool list to help with the shapes and edges.
@mike-M0MSN3 жыл бұрын
Good call!
@GeorgeWMays3 жыл бұрын
That is very cool. Thank you for a truly interesting video. It is much appreciated.
@mike-M0MSN3 жыл бұрын
Glad you enjoyed it!
@boxingday113 жыл бұрын
Thanks Mike 👍🇬🇧
@garyjohnson4608 Жыл бұрын
How did you know what sizes to make the plates ? Or was it just all guess work ?
@mike-M0MSN Жыл бұрын
Its all guess work, If you do not have enough capacity just add more plates......
@wfwtheradioguy34143 жыл бұрын
Nicely done.
@mike-M0MSN3 жыл бұрын
Thanks! :)
@andylinton27983 жыл бұрын
Nice work! But I wouldn't have had the patience to cut out that ally, I'd have got some metalwork place to CNC cut it!
@mike-M0MSN3 жыл бұрын
Next time!
@Melw443 жыл бұрын
Nice job!
@mike-M0MSN3 жыл бұрын
Thanks!
@Ind4213 жыл бұрын
To use in a superhet you have make two of them on ganged configuration.Does it make it bigger?
@mike-M0MSN3 жыл бұрын
Not sure I understand your question sorry. :(
@JoseSilveira-newhandleforYT3 жыл бұрын
Looks good! I wonder, with all the work and expense, if it would not have been more effective to have them cut (water jet or laser) professionally - you obviously have the means to draw the CAD files required. That would also benefit from tighter specifications, allowing for smaller plate gap and smaller size for the same range of capacity (unless you are going for an high voltage application).
@mike-M0MSN3 жыл бұрын
Yes Jose, Laser or water cut is the next level, I wanted to do it all myself first, that way I know it can be done.
@JoseSilveira-newhandleforYT3 жыл бұрын
@@mike-M0MSN Absolutely! And as you got the prototype running very smoothly, it can only get better :-)
@kathrynwhitby97993 жыл бұрын
does the size of the gap make any different to the workings?
@g0fvt3 жыл бұрын
A large gap between plates reduces the capacitance but increases the working voltage.
@peterdemey10832 жыл бұрын
Hi Mike, Do you have the measurements for the alu parts ? didnt vind any in the comment or i overlooked.
@johnpeterson72643 жыл бұрын
Marvelous !
@stevek54163 жыл бұрын
The protective covering on the "al-you-min-ee-um" as you say, is going to give you a little capacitive bump due to the dielectric effects. Don't know how much (or if it will even be noticeable). I would say that you did an excellent job of achieving your goal for a very high Q cap at a very low cost. What cap value were you shooting for?
@mike-M0MSN3 жыл бұрын
Yes will be removed before use.. :) and 200pf so one or two more fins.. :)
@stevek54163 жыл бұрын
@@mike-M0MSN - Depending on the voltage that it will carry (power), you could also use shorter spacers between fins.
@peasant8246 Жыл бұрын
@@stevek5416 I was about to comment the same thing: 3,5mm spacing between fins is a lot. I would've tried to limit it to ~1mm.
@kirklindstedt20183 жыл бұрын
Did you find any calculations on how large plate, distance between, etc? or did you just gustimate?
@nevellgreenough4043 жыл бұрын
See any copy of the ARRL or RSGB Radio Amateur's Handbook in the first 50 pages or so. These were made your way in the 1920s. Nice build! --N2GX
@kirklindstedt20183 жыл бұрын
@@nevellgreenough404 Thank you. I found another youtube video that covered the formulas as well (after I posted this question) I also checked my ARRL Handbook 2013, and it was covered in 2.7.2.
@mike-M0MSN3 жыл бұрын
Looks like you have answered you own question, but I guesstimated.....
@markg6jvy1353 жыл бұрын
Nice build Mike 👍👏👏
@mike-M0MSN3 жыл бұрын
Thanks 👍
@Stelios.Posantzis3 жыл бұрын
Good call. Ebay prices on these things are astronomical. I guess most of those items have long been scrapped or are simply rotting away in sheds or labs.
@mike-M0MSN3 жыл бұрын
yep!
@NHaq-e7d8 ай бұрын
Would Tin Foil from kitchen not work .. Can you please explain why you choose Aluminum ? I understand you may have current requirements , but for a ham radio it should not need that much current.
@mike-M0MSN7 ай бұрын
Foil will burn or pit but it can be used with low power, I used Aluminium because it is malmble and less expensive than Cooper and can withstand high voltages, and when using power of over 50Watts many kV are present.
@peterpauldonoghue70243 жыл бұрын
Hi Mick Did you look into a price of getting them alluminium profiles laser or water cut ? Definitely easier on the ears !!
@mike-M0MSN3 жыл бұрын
Yes, way to expensive for the quantities I want..☹️
@ADVRydrBloke3 жыл бұрын
What filament material are you using in the 3D printer for outdoors / UV. Cheers.
@mike-M0MSN3 жыл бұрын
Standard PETG, I am not too concerned about it breaking down over time.
@ADVRydrBloke3 жыл бұрын
@@mike-M0MSN thanks mate. I just ordered a 3d printer and intend on making a heap of bits and pieces for various HAM antenna builds.
@mike-M0MSN3 жыл бұрын
@@ADVRydrBloke I would start with PLA, it is a lot better to use than PETG, I am finding that the PETG is stringing and needs a lot more work than PLA.... just thought I would let you know