[OZAPRS] 80m on thursday night

[Hamish Moffatt]

On Mon, Oct 04, 2004 at 02:28:20PM +1200, G T & C A Beagley wrote:
> OK Hamish, you are quite correct. But if you are netting to the same 
> signal using upper sideband instead of lower sideband then the tx tones 
> are still in the same place. If the mark and space designated 
> frequencies are in band then it doesn't matter if you use USB or LSB. 

Agreed. But that does not change anything.

You have 2100 Hz and 2300 Hz tones from your modem, but they are not 
single point frequencies (of infinitely small width). When you switch
between them at 300 bps to convey information, there are sidebands
created around each tone, proportional to the switching frequency.

You can expect the sidebands to be at least the baud rate around each
tone, ie 300 Hz. That means +/- 150 Hz from the tone frequency. Thus
the 2300 Hz tone extends up to 2450 Hz. 

For an upper limit of 3.625 MHz, you can afford your dial frequency to be 
no higher than 3.62745 MHz (3625 + 2.45 kHz). If higher, you are out of
band.

Hamish
-- 
Hamish Moffatt VK3SB <hamish at debian.org> <hamish at cloud.net.au>
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