[OZAPRS] 434 MHz tracking

Norm VK3XCI vk3xci at aanet.com.au
Mon Aug 6 11:49:39 EST 2007

But wait, there's more!

Most of our packet "stuff" is based on equipment designed for two-way FM
voice communication, complete with pre/de-emphasis and as Darryl points
out, slow PLLs and even slower TRX relays. Using this gear, 9600 is
pretty well acheivable with minimal modification, in fact some gear
already comes with the capability.

However... above 9600, the delay required to ensure the pll is locked
and the relay closed before transmitting, becomes an appreciable part of
the packet time! Similarly at the end of the tx period, the rx pll has
to lock and the relay again change over.

Add to this the "lowest common denominator" (read plug-and-play) effect
and it looks like the proletariat will be stuck with 1200 for some time

Perhaps it may be time to formulate a new "standard" towards which we
can all work? Sending high speed data bursts to an open receiver on UHF
is a relatively simple task, doing so half or full duplex is a fish of a
completely different colour.


Darryl Smith wrote:
> We can use these technologies, but they are not as easy as you think to
> as reliably.
> The problem is that a 50W transmitter on 144 MHz takes commonly about
> to 500mSec to become stable and up to full power, if they are frequency
> agile. It takes less time if you don't care about having two PLL's and
> increase in power consumption and cost.
> The data rate of 19,200 means that the data is significantly more
> susceptible to noise. Close to 20 times more susceptible, since the
> per bit is so much less. The performance of 10 mW at 19200 is similar to
> mW at 2M. I am just wondering how many people are using this little
power on
> APRS :-)
> One of the ways to get people to use these new technologies, even with
> issues, is to write a paper for the TAPR DCC, or the TAPR PSR
> Darryl
> -----Original Message-----
> From: ozaprs-bounces at aprs.net.au [mailto:ozaprs-bounces at aprs.net.au] On
> Behalf Of Andrew Rich
> Sent: Monday, 6 August 2007 9:49 AM
> To: Aprssig
> Cc: ozaprs
> Subject: [OZAPRS] 434 MHz tracking
> You know its a pity that we hams could not use the technology of easy
> on the ham bands.
> I see that a 1200 baud packet takes a seconds to send.
> On the weekend I was sening 20ms databursts @ 19k2 on 434 MHz at 10mW
> I wonder if we are ever going to break the shackles of 1200 baud ?
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Norm, VK3XCI,
Mildura, The Wintersun City

Victoria, Australia.

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