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DPRG: BOUNCE dprglist@dprg.org: Admin request of type /\buns\w*b/i at line 4

Subject: DPRG: BOUNCE dprglist@dprg.org: Admin request of type /\buns\w*b/i at line 4
From: Jim Brown brownjim at airmail.net
Date: Sun Aug 15 21:58:36 CDT 1999

>Date: Sun, 15 Aug 1999 20:30:08 -0500
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>Message-ID: <DBAFA48A776AD111AF25006008925D5F3A4DC3 at pegasus.centtech.com>
>From: Dan Miner <miner at centtech.com>
>To: "'dprglist at dprg.org'" <dprglist at dprg.org>
>Cc: "'aaron at bottle-rocket.org'" <aaron at bottle-rocket.org>
>Subject: RE: DPRG: Ming Transmitters/Receivers
>Date: Sun, 15 Aug 1999 20:36:47 -0500
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>
>I just hooked up the first pair of my group buy Ming modules.
>I'm having trouble too.  Low of 1.4V, high of 5.0V.  *BUT*
>the "high" signal (detecting carrier) is *VERY* erratic and
>unstable.  Where the signal should be high for 1msec (as an 
>example), instead I get hash (high frequency noise) in the
>range of 1kHz to 1Mhz that is not periodic - just noise.
>
>Adding antennas on Tx and/or Rx doesn't seem to matter.
>By moving my hands around the modules, I can sometimes get a
>good signal but then I loose it.
>
>It seems the Rx is the culprit but I can't verify because I
>don't have a good general purpose receiver or spectrum analyzer.
>I can also get a little bit of response out of the Rx when the 
>Tx is totally disconnected!  Maybe this means I've got a source
>of interference?  My robot's microprocessor?  ...could be...
>
>Anyone have any ideas?  Anyone want some Ming modules cheap?  :-)
>
>				- Dan
>
>PS - More comments mixed w/ Mike's comments below...
>
>PPS - Late breaking news...  I just discovered by accident that
>if I touch the Rx's inductor L1 (coil) near the variable cap (the 
>coil that is furthest away from the antenna connection), then 
>release it, the signal is good for ~1 second then slowly fades 
>back to noise.  Maybe the Tx / Rx aren't tuned correctly???
>
>Anyone who knows RF design have any ideas?
>
>More news - a second module I just tried is even worse.
>Same symptoms when I touch the coil but not as good of a result.
>I also noticed that BOTH of these modules have C8 removed
>from underneath the coil.  I can tell it WAS there but has
>been taken off.
>
>Maybe Digikey gets the modules that WORK and we got the others?  :-)
>
>
>> From: MIKE MCCARTY -- 93789 [mailto:JMCCARTY at DEVEL.USA.ALCATEL.COM]
>> Sent: Thursday, August 05, 1999 3:30 PM
>> 
>> I obtained some Ming transmitter/receiver pairs, and did some
>> experimenting with them last weekend. (I found a source at $5.95 per
>> transmitter, $6.95 per receiver.) I was somewhat disappointed, given
>> the other reports I had heard.
>> 
>> First, the output of the receiver was +3 VDC with no carrier present,
>> and the same with carrier present. When the transition from carrier to
>> no carrier, or no carrier to carrier was made, a pulse up to +6VDC was
>> observed. So DC levels cannot be transmitted. Secondly, when pulses
>> were being transmitted, the output still was a 2-3V P-P square wave,
>> riding on a 3VDC offset, never dropping below 3V.
>
>[...snip...]
>
>> A 'scope on the receiver output showed that when the signal was
>> received well, it was a nice clean square wave. When the reception
>> became bad, I saw a square wave as the envelope of noise. It looked
>> like a child had colored in a drawing with a pencil, leaving lots of
>> vertical marks.
>
>Me too!  But for me, I get the hash at 6 inches and can not get a
>reliable signal at all.  Also (as mentioned above) my Rx module drives
>from 1.4V to 5.0V.  (I edited the picture below to match mine:)
>
>> Clean signal 
> **VERY RARE and ELUSIVE**  -DM
>
>> Noisy Signal
>> 
>> +5      +-------+       +-------+       +-------+       +
>>         |||||||||       |||||||||       |||||||||       |
>>         |||||||||       |||||||||       |||||||||       |
>>         |||||||||       |||||||||       |||||||||       |
>>         |||||||||       |||||||||       |||||||||       |
>> +1.4    +|||||||+-------+|||||||+-------+|||||||+-------+
>> 
>> This is the output at the receiver terminal, not at the input to the
>> serial port.
>> 
>> This shows me that the problem was not with my simple level 
>> translator, but rather with reception.
>> 
>> I purchased these hoping to use them at distances up to 50 feet or so.
>> It appears that I cannot use them beyond about 10 feet, which means
>> they are basically useless to me.
>
>Me too.  :-(  
>
>				- Dan
>
>
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