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Re: [WriteLog] Help with FT-990 & WL setup

To: writelog@contesting.com
Subject: Re: [WriteLog] Help with FT-990 & WL setup
From: "Ian White, G3SEK" <G3SEK@ifwtech.co.uk>
Reply-to: "Ian White, G3SEK" <g3sek@ifwtech.co.uk>
Date: Thu, 8 Jul 2004 10:01:18 +0100
List-post: <mailto:writelog@contesting.com>
Wolf wrote:
Does the interface has an optocoupler for the PTT-Line. Then it will not work for FT-1000MP and may be for the FT-990 also.

I made some experiments with my FT-1000MP with the result that the voltage over the closed PTT-switch must be lower than 0.5 Volt, so that the tcvr goes to transmit. And normal optocouplers has a voltage of 0.7 Volt and more.

The FT-1000 series does seem to require very low "ground" voltage levels to make the PTT, keying and FSK operate reliably. A lot of the original 1000D circuitry was re-used in the FT-990, so the same may be true of the 990 also.

But the "plain vanilla" optocoupler interface works just fine for all of these inputs. If the switching transistor in the optocoupler is fully turned on, the collector voltage will be well below 0.5V.

I've had consistent good results with the PTT/FSK interface detailed in the WL Help files (Help - Index tab - Keyword=WinRTTY - scroll down the page).

The most common problems are when people try to do something different or "clever" (not). For example:

* Using low-gain optocouplers (<100% Current Transfer Ratio)

* Using too high a resistor value on the input side, so the switching transistor is not turned fully on (the recommended 2k or 2.2k works fine)

* Using a series "isolating" diode - the worst problem of all. The diode increases the on-state voltage of the opto-interface by about 0.6V, which is almost *guaranteed* make the switching levels marginal! You don't need that diode anyway... so don't use it.

73 from Ian G3SEK
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