[Amps] High SWR

[Jeff Carter]

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