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Author Topic: Americtron 811 & SWR  (Read 1464 times)
KI4KQQ
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Posts: 5




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« on: March 18, 2006, 05:39:11 AM »

Just purchased a new Ameritron 811 and put it inline with my Icom  718 and dipole. The dipole is resonate with a 1.1 SWR when hooked directly to the 718 or to my 259b analyzer.  When I put the Ameritron in line, the radio shows about 1.25:1 when in standby mode. As soon as I switch to operate mode the SWR at the radio jumps to 2:1.

I can get full output from the amp and stay within manufacturers specs using approx 65 watts from the exciter.

My question is:

1. Should I worry about the SWR the radio is seeing.

2. Can the Input Tuning slugs be adjusted to reduce the swr, and if so, what kind of tool is needed to make this adjustment.

Thanks in advance,

73
Terry / KI4KQQ
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K0BG
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« Reply #1 on: March 18, 2006, 05:57:38 AM »

I don't own an 811, so I don't know if the input can be adjusted. However....


Is 2:1 excessive. No. That said, if you're relying on the 718 to provide you with a good SWR reading, you're kidding yourself. What you need is a known good directional wattmeter to put between the 718 and the amp. Fact is, the 1.5:1 the radio sees may be off too.

Another aspect of this, even if the input was 2:1, I wouldn't worry too much. The drive needed is about 60 watts, and even with a 3:1, the 718 could easily handle the extra heat load.

Alan, KØBG
www.k0bg.com
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KI4KQQ
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« Reply #2 on: March 19, 2006, 08:18:33 PM »

Alan, thanks for your response. I did'nt think that the 2:1 was all that bad, but wanted to be sure.  I made the adjustment to the input tuner and the swr is now 1:1.

Thanks again,

Terry
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WB2WIK
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« Reply #3 on: March 20, 2006, 08:22:15 AM »

Of course you can tune the input of the AL-811.  You need an insulated (non-conductive, plastic) .100" hex alignmnent tool.

You didn't say what band you were using.  *All* amplifiers, including the AL-811 and all other ones having a tuned input and not a big dummy load wired across their inputs (as some amps might), cannot possibly achieve a great input match across the entire spectrum.  Especially on "wide" bands like 160m, 80m and probably 10m, if you tune the input to achieve a perfect match on one end of the band, it will be a lot less than perfect on the other end.

Presumably, the factory sets these about midway between the high and low end of the bands, but you can surely touch up the input tuning.  It's easy and takes only a few seconds, and any change is reversible.

WB2WIK/6

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W7MJM
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« Reply #4 on: April 12, 2006, 11:10:33 AM »

Where can one obtain an insulated (non-conductive, plastic) .100" hex alignmnent tool? I checked at RadioShack but they didn't carry them.
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