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
At 04:06 PM 4/22/2009, Jeff Carter wrote:
>I feel this way, too. I have a SB-220, but I only run it on 80m
>because that's the only place I have a 1:1 SWR.
>
>I have other antennas, but none of them give me a good enough match
>for me to feel confident running power into them. If I remember the
>math correctly, a 2:1 mismatch at 900 watts means 90 watts is coming
>back down the line at you, and I just can't imagine that ever being a
>good thing.
>
>So, I run barefoot on the other bands. The good news is I mostly work
>digital modes and PSK31 is wildly efficient for the contacts I expect
>to be able to make.
>
>Jeff/KD4RBG
>
>---- Original message ----
> >Date: Wed, 22 Apr 2009 14:43:02 -0500
> >From: "KB0NLY" <kb0nly@mchsi.com>
> >Subject: Re: [Amps] SB-1000 tuning question
> >To: <amps@contesting.com>
> >
> >5:1? Why even bother running an amp if your SWR is that high. That's a lot
> >of reflected power back into the shack and on your feedline.
> >
> >I know a guy that runs an amp with a huge antenna mismatch and guys that
> >hear me at 100w with a properly tuned antenna can't hear him for crap. He
> >isn't making efficient use of his power. Run all the power you want, but
> >there is no substitute for a good antenna to connect to it.
> >
> >Scott
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