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John, I'm not sure that's correct. The 5 W out is not the issue, it's the 3.3 W not produced as RF due to the 40% (or maybe a bit less) inefficiency as class D. The 5 W out is only an issue when or if

Thanks Hans, and everyone else, for your replies. I guess I was tempted by a less complex build.? The reality is that this is my biggest project to date, and you have all helped me to realise, to

So Daniel, as an example. If we produce 5W RF, and 0.56W is reflected (2:1 VSWR), we have 5.56W RF to deal with, in addition to the DC dissipation. Let's say we DO dissipate 3.3W across all four

Congratulations, you will have a lot of fun, just be patient. Terry? ?w6leo

And with four probably un-matched transistors (I don't know if Hans has that performed or performs it), there's probably uneven dissipation too. So from the over-voltage perspective, seems to be, keep

Or if you decide to try five, be pragmatic and consider hedging your bets by leaving room for an extra QRP Labs filter board. It will cost you nothing but space and a few extra chassis holes for now.

You might want to consider the Hermes Lite N2ADR filter board. Has built-in SWR bridge. $52.70 at Makerfabs. It's only rated for 5 watts however. -Steve K1RF

Hello Daimon As others have said, the answer depends a lot on your performance objectives. Assuming that you want to meet license regulations regarding spectral purity (harmonic levels) then you need

Back in the good old days when the world needed home grown RF Engineers, your employer or educational establishment would end up sending you on a day or weekend course on using measurement equipment,

My QDX smoked with SWR of 8 on the 60 m band.? I forgot my antenna was not resonant on 60m.? I've ordered the 4SQRP 4S tuner that has a VSWR resistive bridge so the QDX will never see >2:1 mismatch

John, If the QDX is about 60+% efficient, at 5 W RF out, you are putting nearly 8.3 W DC into the finals. That 3.3 W mostly goes into heat in the finals. If this is correct, then each BS170 is

Whence why we refer to power dissipation as well as the voltage seen across usually the Drain + Source of the FET's (we assume at this point that we're not using a common gate configuration). Of

Hi all, With a mismatch, it is not only high voltage that could kill the finals but also high current, or am I wrong? 73 John M0JBA

Spot on. The reflected power has to be added to the total device dissipation (which depends upon amplifier class, device rating and de-rating for temperature (the latter can be the most harsh) and of

No, not the antenna switch, the rig switch ! The antenna switch - an import having three positions - currently switches between the PAR Electronics OA-50 Omniangle and the 160m EFHW antennas.

Thanks guys. -- 73, Dan? NM3A

OHIM, probably means "Oh Hell It's Monday"? Roy WA0YMH [email protected]> wrote:

Alan is 100% correct. That's how I have my own groups set up. Text remains forever, but old attachments fall away when space is exceeded. -- - 73 de Andy -

Can't find OHIM, that's a new one for me ;-) TGIF is of course familiar (Thank God It's Friday, same as POETS days mentioned by my learned friend M0PWX). Trivia lesson coming up.. A play on this was a

Dan Quite possibly they have gone forever. I suspect that this group is setup to delete old attachments so data storage is not exceeded. The way to do it is to save anything you think is useful. Easy