To: | RTTY Reflector <rtty@contesting.com> |
---|---|
Subject: | Re: [RTTY] DESREVER |
From: | Kok Chen <chen@mac.com> |
Date: | Sat, 16 Oct 2004 10:31:56 -0700 |
List-post: | <mailto:rtty@contesting.com> |
On Oct 16, 2004, at 6:20 AM, Richard Ferch wrote:
In particular, I believe recent Kenwood and Yaesu radios assume the opposite polarity to the one assumed by JE3HHT in MMTTY, so on these radios you have to change one of the radio's menu items. Ah yes, Yaesu and their nutty interface :-) The FT-1000MP is reversed, but not wrong per se, since it is actually documented exactly in the FT-1000MP manual. In the "RTTY Polarity" section of the Operation chapter of the FT-1000MP Operating Manual, they state "Normally a Mark tone (2125 Hz by default) is transmitted during keydown in LSB RTTY operation. With reverse polarity, a Space tone (2295 Hz) would be generated instead." The rub is that the normal "standard" calls for the Space tone to be transmitted on an assertion of the keying signal, not the mark tone. My understanding is that the RTTY standard calls for the teletypewriter to be latched to the idle position outside of a character where a mark tone is transmitted. A start bit (22 ms of space tone) releases the latch and the stop bit again relatches the mechanical system. I.e., a space tone should be produced by the keydown position since the mark tone is supposed to be transmitted when you are not sending a character (you can hear that mark idle tone from stations that don't use diddle). The FT-1000MP (ditto FT-990) defines the factory default keydown to be the Mark tone. Hence the need to reverse it for us who practices RTTY for a living :-). It actually depends on what you deem an "assertion" to be. To most of us, a keydown is a state where maximum current flows through the keying circuit (this way, an open circuit on the keying line is a deassertion). Yaesu engineers might be thinking that it is more logical to think that a higher voltage at the keying signal is the assertion position. I think it was Andrew Tenenbaum who said "The nice thing about standards is that you have so many to choose from." He might have been quoting some sage before him. 73 Chen, W7AY _______________________________________________ RTTY mailing list RTTY@contesting.com http://lists.contesting.com/mailman/listinfo/rtty |
<Prev in Thread] | Current Thread | [Next in Thread> |
---|---|---|
|
Previous by Date: | Re: [RTTY] DESREVER, Richard Ferch |
---|---|
Next by Date: | [RTTY] Thanks, Sid Ashen-Brenner |
Previous by Thread: | Re: [RTTY] DESREVER, Richard Ferch |
Next by Thread: | [RTTY] Thanks, Sid Ashen-Brenner |
Indexes: | [Date] [Thread] [Top] [All Lists] |