[RTTY] DESREVER

[Richard Ferch]

At 09:35 AM 16/10/2004, FireBrick wrote:
>hmmmm, that's not been my experience at all Richard.
>I use a FT1000MP which has a menu bug. You have to set the menu to 
>'reverse' for it to send FSK right side up.
>Now I do use MMTTY, both stand alone and as the decoder in Writelog.
>The only way I can see for it to get out of whack is if you accidentally 
>(or intentionally) click on the Reverse Button.
>
>Please correct me but I've thought that MMTTY reverse button changes BOTH 
>transmit and recieve.
>At least when I'd had to use it to connect with someone who was inverted, 
>I THOUGHT it did.

Hi Bill,

If you are using AFSK, when you press the "Rev" button in MMTTY it changes 
both TX and RX, so your TX and RX do indeed stay in sync with each other. 
However, if you are using TxD to key FSK with MMTTY, the "Rev" button only 
changes the RX.

Here is a direct quote from the MMTTY Help file: "With FSK, the Rev button 
on the main menu has no effect on the shift of TxD. You can receive someone 
who is using reverse-shift, but you cannot transmit reverse-shift." To be 
precise, the last phrase should really read "..., but if the hardware is 
properly adjusted to send normal shift you cannot transmit reverse-shift." 
If the hardware is improperly adjusted you cannot transmit normal shift!

I wouldn't call the situation with your FT1000MP menu a bug, exactly. The 
designers had to pick one of MARK and SPACE for the tone to send when the 
keying input is shorted (and of course, the other one is sent when it is 
open). As it happens, the Yaesu and Kenwood designers (TenTec too??) picked 
closed = SPACE and open = MARK as their default convention.

The COM port hardware (UART) output from TxD is fixed; it is current on = 
MARK and current off = SPACE. If you use an inverting keying circuit like 
the one-transistor circuit in the Help file, current on = closed, which is 
the opposite polarity from the one the Yaesu and Kenwood radio designers 
designed for. You can fix this either by using a non-inverting keying 
circuit (e.g. a common-base switch instead of the usual common-emitter 
circuit), or by using the radio's menu item to switch the radio's keying 
polarity.

There is yet another option with MMTTY: you can use the EXTFSK dll instead 
of the COM port's UART to control the keying line (as an added bonus, with 
EXTFSK, you can key from any of TxD, DTR and RTS either from a real COM 
port or from a USB serial adapter). With EXTFSK the software has complete 
control over the polarity of the output, so you can adjust the polarity 
switching in software. However, you cannot change the transmit polarity in 
software if it's a UART that is controlling the TxD keying signal. Clear as 
mud?

73,
Rich VE3IAY