[OZAPRS] RE: Ozaprs Digest, Vol 5, Issue 20

[Darryl Smith]

It is called 'Energy per bit' or 'Eb/n0'.

Basically, the performance of a radio system for a given bit error rate is
proportional to the Energy per Bit. Therefore if you are transmitting 1200W
at 1200 bps, you are transmitting 1W per bit. If you go to 9600, you are
transmitting 0.125W per bit. 

The reliability of transmission depends on the amount of energy per bit. The
more energy you transmit per bit, the more reliable it is. 

Think about it this way - how much more reliable is 5 WPM Morse over 25 WPM
Morse. Same idea

Darryl

P.S. My calculations were wrong earlier. 24W Vs. 8W was wrong. It should
have been 24W Vs. 3W


-----Original Message-----
From: ozaprs-bounces at aprs.net.au [mailto:ozaprs-bounces at aprs.net.au] On
Behalf Of Ian Mills
Sent: Friday, 23 May 2008 12:58 PM
To: 'ozaprs at aprs.net.au'
Subject: [OZAPRS] RE: Ozaprs Digest, Vol 5, Issue 20

Darryl,

I'm having a hard time comprehending your statement 
" .. since you are transmitting at 8 times the speed, and so this is the
equivalent of only transmitting 1/8th the power"

Is there any theory I could google to understand it better, I'm not sure
where to start my search?

Thanks
Ian vk2him

------------------------------

Message: 3
Date: Fri, 23 May 2008 09:26:29 +1000
From: "Darryl Smith" <Darryl at radio-active.net.au>
Subject: RE: [OZAPRS] 70cm APRS
To: "'Australian APRS Users'" <ozaprs at aprs.net.au>
Message-ID: <049f01c8bc63$42ff4930$c8fddb90$@net.au>
Content-Type: text/plain;	charset="US-ASCII"

I think a 9600 bps UHF APRS frequency is not a great idea.

The reason is that each APRS transmission at 1200 bps takes about 1 second.
Most of this is the TxDelay. The TxDelay on UHF is commonly the same, so you
might go from 1000 mSec to 600 mSec. This is not much of an improvement.

But since you are transmitting at 8 times the speed, and so this is the
equivalent of only transmitting 1/8th the power. Your 9600 bps 24 Watt radio
becomes a 8 Watt 1200 bps radio.

Darryl

-----Original Message-----
From: ozaprs-bounces at aprs.net.au [mailto:ozaprs-bounces at aprs.net.au] On
Behalf Of Peter Schrader
Sent: Thursday, 22 May 2008 10:59 PM
To: VK / ZL APRS Users
Subject: [OZAPRS] 70cm APRS

Hello all,
What does everybody think about having a dedicated frequency for 9k6 APRS on
UHF?

Next question, could we all agree on a nationwide frequency?

Regards,
Peter Schrader,
VK4TGV/9V1PS
Redcliffe and Districts Radio Club
Singapore Amateur Radio Transmitting Society WIA Assessor 4-055

APRS - VK4TGV-12, VK4TGV-7, VK4TGV-2 and 9V1PS ALE HFN Pilot Station -
http://hflink.com

AWA Limited

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