[RTTY] BARTG 75 Sprint

[Kok Chen]

On Jun 14, 2010, at 6/14    4:39 AM, Stephen/Marilyn Haines wrote:

> The difference between 45 and 75
> baud pushes me from "yes it's hard but I enjoy it" to "It's impossible
> -- why bother." Is there anyone else on the list with a truly weak  
> signal that had the same reaction?


Steve,

Since you mentioned the power that you are using, I assume the  
diffculty is because you are not heard by others, and not because you  
can't copy the others, correct?  Do you get a lot of AGN, AGN when you  
call them?

One does lose a couple of dB in SNR when demodulating 75 baud versus  
45.45 baud.  Most big guns that are heard in a contest are way, way  
over the threshold of decodability however (perhaps not from ZP,  
though), so losing a couple of dB usually means that a previously  
decodable big gun signal is still perfectly decodable at 75 baud.

Copy should only become difficult for the marginal signals -- ones  
that are just barely over the noise floor of the receiving system  
before.  I.e., people who used to throw an error or two at 45.45 baud  
would now, at 75 baud be fully garbled.

If others can no longer copy you at 75 baud, your signal might be  
right at the edge of copy for most people even when you were using  
45.45 baud.

One experiment you can perform is by lowering your RF power from 40  
watts to between 24 and 25 watts during the next contest and then try  
to work people at 45.45 baud.  Do you have the same difficulty as  
using 40 watts at 75 baud?  If you do have the same problem being  
heard, then yes, short of raising your RF output or adding some gain  
to your antenna system, it is a problem that is going to be hard to  
fix (other people would need better modems or their antennas need to  
point your way, etc).

Now, on the other hand, if the problem is due to your not being able  
to copy the other folks cleanly, it is probably some setup thing (for  
example, using I.F. filters that are too narrow for 75 baud) that can  
be fixed.

73
Chen, W7AY