Howard you and Johnny are right. It is not rocket science but it is thermodynamics. There are many nuances... conduction, radiation, and convection. Often optimizing for one may diminish another characteristics. There are many trade-offs. Copper is a better conductor of heat flux than aluminum but it adds more weight. Black bodies radiate heat faster than than bare metal but they also absorb heat from sunlight faster so do you optimize for dark or sunlight?
I think the good news take away is this an easy area to do your own experiments and homebrew. You don't even need a thermometer. It's already there. Thank you Elecraft. 73 Fred, AE6QL (The other Fred) -----Original Message----- >From: Howard Hoyt <[email protected]> >Sent: Aug 13, 2014 10:55 AM >To: [email protected] >Subject: [Elecraft] Some "Cool" heat sink info. > >Hi all, > >Johnny, VR2XMC wrote: > >>>It should not?be any rocket science, all you need is a piece of thick metal >>>plate >>>to suck the heat from the PA transistors and with fins to facilitate air >>>circulation. > > >You are right: a thick piece of metal will sink the heat from the PA >transistors. But how thick? Too thin and there is little benefit. Too >thick and the stored heat in the metal mass actually inhibits recovery >time after a heating event. > >How many fins? How tall? How far apart? And what combination of all of >these gives the most benefit at a targeted small size? > >You are right: it is not rocket science, but a dismissive attitude >towards the importance of learning the interaction between the variables >leads to some of the poorly-performing (not to mention ugly) designs I >have seen hung off of several KX3s. I also happen to agree with >Elecraft's design criteria which is the same as just about all >amateur-radio gear made: 100% power on CW and SSB, 50% power on digital >modes. To upgrade this to commercial broadcast equipment performance of >100% duty cycle in all modes would greatly increase the price and size. >If someone wants more power and xmit time in digital they can always buy >a heatsink, and the cost of doing so is not added to the KX3 for 90% of >the purchasers who do not need it. > >More info on my website www.proaudioeng.com if you are interested, > >Howie - WA4PSC > >______________________________________________________________ >Elecraft mailing list >Home: http://mailman.qth.net/mailman/listinfo/elecraft >Help: http://mailman.qth.net/mmfaq.htm >Post: mailto:[email protected] > >This list hosted by: http://www.qsl.net >Please help support this email list: http://www.qsl.net/donate.html >Message delivered to [email protected] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
