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[aprssig] Looking for 9600 Baud equipment.

R.M. King krm1012 at qwest.net
Sun Sep 28 23:05:14 UTC 2008



> 9600 bps G3RUH is not your choice for mobile APRS. It does not cope well
> with multipath phase rotation and flutter.


My experience with 440MHz 9600 Baud operations does not support the above 
comment.

There are several people using 9600 Baud 440.875MHz APRS equipment in the 
Puget Sound area of Washington State.  Mobile operation using Kenwood 
D700's, D710's, D7's and a variety of other equipment manufacturers for base 
station operations has been outstandingly successful.  Puget Sound is 
surrounded by mountains.  The Cascade range and the Olympic range are almost 
always in site and there are many 200 ft. to 600 + ft hills in this area. 
We have had no problems operating at 9600 Baud in this area. This has been 
going on for over 4 years now.

As a matter of fact, many of us will tell you that they have BETTER success 
using 9600 Baud than 1200 Baud.

You can check us out on find-u.  Most of our digi's use an alias of Uxxxxx 
.  ie: UCAPK, UNCMNO, USAM, UQA and UVCMP etc..  There are a few using 
normal convention such as K7OFT-10 and WSV.

With the TXD overhead, 9600 Baud packets are about 1/3 the length of 1200 
Baud packets.  This is a huge advantage.  They are shorter and so there is 
much less time for man-made and normal operational phenomenon to affect and 
corrupt the packet. Throughput is higher and the BER is lower.

It is true that at 440MHz there is a 9.7Db propagation loss when compared to 
144MHz.  But the I.F. gain of modern transceivers and the higher antenna 
gain of most 440 base station and mobile antennas helps to make up for this 
loss.  The net result is BETTER performance using 9600 Baud vs. 1200 Baud.

The one real caveat is one must use a good service monitor to set the 
deviation at 9600 Baud.  You can NOT guess by listening to the recovered 
audio. It just doesn't work.

Our APRS 9k6 Baud APRS network is growing here in the Puget Sound area.  I 
would encourage anybody to try 9600 Baud APRS.  On two meters (NOT 
144.390MHZ) or on 440.875MHz.

 Bob King K7OFT

krm1012 at qwest.net






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