Re: Current Draw & Power Output Question

Russ Hines

Lurk mode: OFF

You did.
"On 40m it looked like my power was about 5w."

Let me preface the rest of my reply with this - every once in a while, I do something foolish.  Like make a post.  You open yourself up for more BS than need be.  Who needs that?  But since I'm seeing the same voices here most of the time, I thought I'd add a different one.  Mine.  Not concerned about the song, just hoping I'm in the same hymnal. ;-)

A stock Bird 43 displays average power but not PEP which is what you're kind of interested in for SSB.  Being that as it may, let's make some assumptions and take your 12v source voltage and multiply it by what you indicate your currents are:

12v x 166 mA is just under 2 watts.  From what I gather from your post, this is the DC power your radio uses during receive.

12v x 540 mA is about 6-1/2 watts.  This is the DC power consumption on transmit with no RF output.  THIS is actually what we call idle current.  We can set the operating point of the IRF510's looking at this current.

12v x 1.02 A is about 12 watts.  This is total DC power consumption during transmit.  With RF output. 

Okay so far?  Good deal.  From what I read on this forum, and based on measurements of my own uBitX, the 2 x  IRF510 final amp isn't terribly efficient at 12v, this drive and output power level, but again let's assume we're as efficient as we need be.  For SSB, class A/B finals are somewhere in the 50-55% range efficiency.  You're pipping your Bird wattmeter at 5 watts, so your DC-to-RF efficiency is around 42%.  In reality, it's probably worse, but you'll likely not pop the FET's at this level.

IMHO, not great, but not terrible.  Lots of assumptions.  But it's better than what I see on my rig right now (I'm still hacking on it, installed several of Allison's suggestions, more to go).

Wait, it gets better.  A Bird 43 isn't frequency selective and this radio has spurs/harmonics issues.  Some of that output is not on frequency, or maybe even on 40m.  How much?  Beats me, you'll have to measure it.  My radio's what I call reasonable, around -40 dBc according to my Rigol SA.  That's 40 dB down from carrier.  Not technically legal as far as "spurious radiation" is concerned.  But it gets much worse on 20m and higher, and at higher than 3 watts or so output.  Make another assumption and say several milliwatts.  You can read or let others here tell you about the gory details... and hem and haw about -43 dBc no doubt. ;-)

Better news is, you're making contacts with the rig and, it's hoped, having fun.  Could be worse, you could be an "appliance operator."  But you obviously chose a different path.  Good for you.

So, unless you want to improve what you have, get your hands dirty, and suffer slings and arrows from forum denizens, my suggestion is stay on 40m, stay at 5 watts or less, and sin no more.  Otherwise, jump in with more questions, heat up the soldering iron, and dive into your uBitX.

BTW, the short answer to your original question is, currents sound about right to me for a few (more than 2) watts RF out or so on this radio. YMMV.

Ain't radio fun?

Lurk mode: ON


Join to automatically receive all group messages.