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Re: [RTTY] FSK vs AFSK

To: RTTY Reflector <RTTY@contesting.com>
Subject: Re: [RTTY] FSK vs AFSK
From: Kok Chen <chen@mac.com>
Date: Fri, 10 Dec 2004 13:30:19 -0800
List-post: <mailto:rtty@contesting.com>

On Dec 10, 2004, at 1:02 PM, Reid Hill wrote:
But FSK has a BIG advantage over AFSK for one reason
in my mind, FILTERS.

I have no problem at all with using narrow filters on my FT-1000MP in AFSK (what Yaesu calls "packet" mode).


Ditto the dial offset (someone else mentioned that as an advantage of FSK, but it is not true: it depends on your rig. My 4 year old rig can do it. I think the MP is much older than 4 years, but that was about how long I have had mine.).

With my FT-1000MP, I am in fact running a dial offset of 1615 Hz with one of the selectable Packet tone pairs. The reason for such an odd frequency is because Packet tone pairs are 200 Hz apart, referenced to the center frequency whereas the "standard" RTTY is 170 Hz, referenced to the Mark (unmodulated, un-diddled) carrier. By choosing this offset, I can use very narrow filters and still have the signal right smack in the middle of a narrow IF passband.

I had previously used the high tone pair, but W1ZT convinced me that the lower tones are more pleasing to the ears (I think as you age :-).

I have set my (software) modem to center the Mark tone on the crossed banana at 1615 Hz, and centered the DSP filters of the modem appropriately. With both a KAM Plus and an ST-8000, you can also arbitrarily set their mark and space tones, so it is not just with software modems that you can do this to.

I use the exact same mode/offset setting when I operate PSK31. In my case, my waterfall display's frequency scale is calibrated to show the offset of a line in the waterfall from the rig's dial (given the known 1615 Hz offset on the rig).

I use AFSK and FSK interchangeably. When I transmit through the KAM, I use FSK, for example. When I finally get the software modem working with the microKEYER, it will be yet one more box that works with FSK.

73
Chen, W7AY
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