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'Serial directly to Ming xmitter.'
1999\02\08@194428 by Matthew Ballinger

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       I've been reading postings every once in a while stating that PIClisters
have
connected RF transmitter directly to serial outputs to send data. I have been
using the Holtek series encoder/decoders to send data via a Ming transmitter
and this works fine, but I have tried everything to get good data be sent
using normal async serial data sent at 1200 baud. Looking at the data out from
the receiver with a logic probe it looks like I'm getting too much other
noise. How is this noise filtered and not the data? Or is this just a bad
selection for an RF transmitter/receiver pair? Thanks too all.
Matt

1999\02\08@194858 by dave vanhorn

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At 07:33 PM 2/8/99 -0500, Matthew Ballinger wrote:
>        I've been reading postings every once in a while stating that
>PIClisters have
>connected RF transmitter directly to serial outputs to send data. I have been
>using the Holtek series encoder/decoders to send data via a Ming transmitter
>and this works fine, but I have tried everything to get good data be sent
>using normal async serial data sent at 1200 baud. Looking at the data out from
>the receiver with a logic probe it looks like I'm getting too much other
>noise. How is this noise filtered and not the data? Or is this just a bad
>selection for an RF transmitter/receiver pair? Thanks too all.
>Matt


These simple transcievers usually want data that's got a 50% duty cycle, to
keep it's bit-slicer balanced. You could try F/2F or some other encoding to
help.

1999\02\09@075841 by Thomas McGahee

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Matthew,
Is the serial data you are applying to the transmitter of the
proper level, or are you directly applying RS232 level signals?
If so, first convert the RS232 levels to 0-5v level signals.

That might be the source of your problem.

Fr. Tom McGahee

----------
> From: Matthew Ballinger <spam_OUTMattBeckTakeThisOuTspamAOL.COM>
> To: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
> Subject: Serial directly to Ming xmitter.
> Date: Monday, February 08, 1999 7:33 PM
>
>         I've been reading postings every once in a while stating that PICliste
rs have
> connected RF transmitter directly to serial outputs to send data. I have been
> using the Holtek series encoder/decoders to send data via a Ming transmitter
> and this works fine, but I have tried everything to get good data be sent
> using normal async serial data sent at 1200 baud. Looking at the data out from
> the receiver with a logic probe it looks like I'm getting too much other
> noise. How is this noise filtered and not the data? Or is this just a bad
> selection for an RF transmitter/receiver pair? Thanks too all.
> Matt

1999\02\09@081339 by Nigel Orr

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At 07:39 09/02/99 -0500, you wrote:
>         I've been reading postings every once in a while stating that
PIClisters have
> connected RF transmitter directly to serial outputs to send data. I have
been
> using the Holtek series encoder/decoders to send data via a Ming transmitter
> and this works fine, but I have tried everything to get good data be sent
> using normal async serial data sent at 1200 baud. Looking at the data out
from
> the receiver with a logic probe it looks like I'm getting too much other

Have a look at your grounds- make sure they are all good short connections,
to one common (star) point.  And try to ground the 'scope or probe near the
receiver ground- all that significantly reduced the amount of spurious
noise that I saw on my system.

Nigel
--
Nigel Orr                  Research Associate   O   ______
       Underwater Acoustics Group,              o / o    \_/(
Dept of Electrical and Electronic Engineering     (_   <   _ (
    University of Newcastle Upon Tyne             \______/ \(

1999\02\09@090335 by Anderson, Roger

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What  is a Ming transmitter?

Roger

Roger H. Anderson
Bioengineering
The University of Iowa
54 Medical Research Facility
Iowa City, IA  52242-1183
(319) 335-8644



>     I've been reading postings every once in a while stating that
>PIClisters have
> connected RF transmitter directly to serial outputs to send data. I have
>been
> using the Holtek series encoder/decoders to send data via a Ming
transmitter

1999\02\09@135454 by John Payson

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>        I've been reading postings every once in a while stating that
>PIClisters have
>connected RF transmitter directly to serial outputs to send data. I have been
>using the Holtek series encoder/decoders to send data via a Ming transmitter
>and this works fine, but I have tried everything to get good data be sent
>using normal async serial data sent at 1200 baud. Looking at the data out from
>the receiver with a logic probe it looks like I'm getting too much other
>noise. How is this noise filtered and not the data? Or is this just a bad
>selection for an RF transmitter/receiver pair? Thanks too all.

The problem you are having stems from that fact that there is
always going to be some noise at any frequency and the receiver
has no idea how strong a signal to expect.  If the signal strength
at 310MHz is much higher than the recent norm, it knows that it
should output a "1" and if it's much lower it should output a "0".
It cannot, however, distinguish between a steady signal received
from a distant transmitter and a non-signal received in the pres-
ence of a lot of noise.

The remedy to this problem is to ensure that anything you want to
be detected as a "1" is stronger than the recent average signal
level and anything you want to be a "0" is weaker.  This is done
by ensuring that the average signal level is about half of peak,
i.e. that the transmitter is on about half the time.

One simple approach to doing this is to start each transmission
with a clearly recognizable pattern; I'd suggest starting with
about 8 bit-times of "1", followed by something like "00110110",
and then write out each bit of data using two bits: "01" for a
"0" bit and "10" for a "1" bit.

One other caveat I've noticed with the Mings is that they seem
to cause the "1" bit time to be a bit shorter than it should be
[i.e. a square wave will come out as a somewhat narrow pulse
wave].  It may be helpful to compensate for this in the trans-
mitter by "stretching" any "1"'s that are send.

1999\02\09@145409 by andy

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-----Original Message-----
From: John Payson <supercatspamKILLspamCIRCAD.COM>
To: .....PICLISTKILLspamspam.....MITVMA.MIT.EDU <EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU>
Date: 09 February 1999 18:54
Subject: Re: Serial directly to Ming xmitter.


>>        I've been reading postings every once in a while stating that
>>PIClisters have
>>connected RF transmitter directly to serial outputs to send data. I have
been
>>using the Holtek series encoder/decoders to send data via a Ming
transmitter
>>and this works fine, but I have tried everything to get good data be sent
>>using normal async serial data sent at 1200 baud. Looking at the data out
from
{Quote hidden}

Try this place-- http://www.lprs.co.uk some good tx rx stuff desighned for data
transmition
Andy

1999\02\10@043757 by Mark Willis

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Ming makes RF-based transmitters and receivers, http://www.mpja.com among
others sell these.

 Mark

Anderson, Roger wrote:
{Quote hidden}

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