[aprssig] Re: motorcycle mobile tracker

[Stephen H. Smith]

apratt at bestbits.org wrote:
> I have been trying to set up a tracker on my motorcycle. I have a 25W
> Yaesu radio and a 1/2 wave antenna. The range is great, but it only
> works when I'm moving under 55 miles an hour. The antenna's not stiff
> enough - it flexes and my outgoing signal drops. I'm in the market for
> a new antenna or some way to stabilize the one I've got.
>
>   

1)    Bear in mind that ALL of a data packet MUST be received ABSOLUTELY 
PERFECTLY for ANY  data to be recovered.   A pop of noise or a momentary 
fade or flutter that is negligible on voice will fatal to a data 
packet.  You MUST have a noise-free solid hard-quieted signal at the 
receiver for reliable data operation.   APRS is even worse than standard 
packet in this respect, since it doesn't use any kind of ACK/NAK 
handshaking protocol to retransmit missing or defective packets.   


2)   You need enough signal margin so that even with 10-15 dBs of mobile 
flutter (typical variation for a mobile), the signal will remain fully 
quieted.     [ The instruction manual for the Kenwood D700 essentially 
confirms this fact by stating you can't expect reliable data operation 
until signals deflect the S-meter bar full-scale. ]


3)   As a result of these facts, roughly speaking, for a given transmit 
power and antenna, you can expect about *ONE-HALF* to *ONE-THIRD* the 
reliable range on packet data that you get on voice. 


4)   The transmit power of the pocket tracker is about the same as an 
unlicensed FRS walkie-talkie. I.E the Pocket Track can be expected to 
have about ONE-THIRD the range of an unlicensed FRS radio on voice!!


5)    Further, the 1/4-watt Pocket Tracker simply can't compete with 
normal handhelds, let alone full-sized mobiles. It's tiny signal doesn't 
stand a chance on a busy channel where even handhelds are transmitting 
with *10-20* times the power and many mobiles are using *200 TIMES* the 
power (50W) of a PT !!!!  Bear in mind that even through the channel may 
sound empty to you on the ground, a digipeater in a high location is 
constantly hearing many many signals you don't hear.  Your puny signal 
has to cut through all this stuff to be heard and repeated.