[Amps] High SWR

[Pete Smith]

Jeff, there's a huge difference between being conservative - a good 
thing, usually - and forgoing significant benefit because of a 
misconception.  I love my SB-220 too, and I try very hard not to do 
dumb things like operating it into no load, but SWR, per se, is not 
something to worry yourself about, so long as the amplifier can match the load.

73, Pete N4ZR

At 05:21 PM 4/22/2009, Jeff Carter wrote:
>I have had others tell me I can get away with it, too.  At the center
>of the issue, the problem isn't engineering, it's cowardice.
>
>See, I built this amp from the metal up, and it's probably the coolest
>ham-related thing I ever built.  I regularly build things for work,
>and I can even do surface mount component work if I have to do so, but
>this old SB-220 is special to me.
>
>If the cost of keeping well within the lines of operation is missed
>contacts, then I guess I'm just going to miss them.  I don't really
>care about talking to anybody anyway, but I do care about this
>amplifier.
>
>It's probably a little bit psychotic, but I was really, really proud
>of this thing when I got it finished, and unless the coming Global
>Depression forces me to sell it for food money, I'll still have it
>when I die.
>
>Then my kids can sell it for $5 on eBay, not understanding that their
>Dad built it by hand, piece-by-piece, or even understanding for sure
>what it is.
>
>Jeff/KD4RBG
>
>
>---- Original message ----
> >Date: Wed, 22 Apr 2009 16:54:53 -0400
> >From: Pete Smith <n4zr at contesting.com>
> >Subject: Re: [Amps] High SWR was SB-1000 tuning question
> >To: amps at contesting.com
> >
> >You are missing out on a lot by limiting yourself this way, because
> >the SB-220 is a great active antenna tuner.  I routinely use mine on
> >antennas cut for the low end of 80M up in what used to be called the
> >DX window at 3790-3800 KHz.  The indicated SWR is over 3 to 1 but so
> >long as the amplifier finds an output peak somewhere in the Load
> >capacitor range I just go with it.  My best antenna is 1:1 at one
> >point in 15 meters, but everything else ranges from a low of 1.2 to a
> >low of 1.5, depending on band - as for the high end of the range on
> >those bands .... don't even ask.
> >
> >I think your math only tells part of the story.  According to TLW,
> >the ARRL's transmission line calculator, for 100 feet of RG-213 into
> >a 100 ohm resistive load at 3.5 MHz, SWR at the transmitter end is
> >1.88 (less than 2 because of line loss), the total loss is .43 dB,
> >and the additional loss due to SWR is .066 dB.  Losses are higher at
> >higher frequencies, of course, but still in roughly the same proportions.
> >
> >The idea about large amounts of reflected power coming back down from
> >a high SWR and causing problems was debunked here years
> >ago.  Open-wire transmission lines are routinely run at very high
> >SWRs.  So long as they can be matched to your transmitter, that is
> >not a problem.
> >
> >73, Pete N4ZR
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