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[wxsig] T238+ modem problem update and a question

Ted11 tedlists at hullar.com
Fri Aug 13 05:57:14 UTC 2010


Yup, it was the capacitor!  Weather station is on the air as KE6ROS-2.
Thanks for a really fun kit and a great feeling of accomplishment.  And
thanks, Mark, for identifying the solution.  

I would be more than happy to make revisions to the documentation, if you
would like someone else to take that on.  If you have a word document, I
could do it using "track changes" so you can see what I've done.  Just a
thought. 

Now it's time for mission creep - figure I need a humidity sensor,
barometric pressure, and I remember reading something about snow depth...

Ted

-----Original Message-----
From: wxsig-bounces at tapr.org [mailto:wxsig-bounces at tapr.org] On Behalf Of
William Beals
Sent: Thursday, August 12, 2010 9:44 PM
To: 'TAPR Weather Station SIG Mailing List'
Subject: Re: [wxsig] T238+ modem problem update and a question

Ted:

Hopefully the capacitor issue will fix things.  I *thought* I had fixed that
a while back, it looks like not.  I will go back and look.

Mark, thanks for looking that up!

On recommending software downloads.  Very good suggestion!

I did get lucky on the header beside the RJ11 connector.  That was insurance
for no known purpose at the time.

Hopefully you will be able to get on the air shortly.  Let us know when you
do.  If you are covered by one of the APRS servers, one thing I can do is
look at some of the diagnostic data I append to packets and maybe get an
idea of what the errors are.  For the TAI-603 some of the errors are
unavoidable.  The way the weather head works is the micro inside the weather
head just "steals" the 1-wire bus without asking first.

I didn't get home until late this evening, but will look at the voltage
issue tomorrow evening.

will


-----Original Message-----
From: wxsig-bounces at tapr.org [mailto:wxsig-bounces at tapr.org] On Behalf Of
Ted11
Sent: Thursday, August 12, 2010 8:22 PM
To: 'TAPR Weather Station SIG Mailing List'
Subject: Re: [wxsig] T238+ modem problem update and a question

I haven't implemented the fix yet, but thanks for the information!  I found
the posts you referenced by looking through the email archives, and there it
was.  For reference to anyone else:  February 2006 was the (first)
discussion, and the relevant information:

"Change R101 to 4.7 K and the output coupling capacitor from 100 pf to a .1
uf. "

Thanks again for the quick reply, I appreciate it.  

Ted

-----Original Message-----
From: wxsig-bounces at tapr.org [mailto:wxsig-bounces at tapr.org] On Behalf Of
Mark Patton
Sent: Thursday, August 12, 2010 5:53 PM
To: TAPR Weather Station SIG Mailing List
Subject: Re: [wxsig] T238+ modem problem update and a question


  Ted,

You were on the right track with the cap idea.  C111 is a DC blocking 
cap on the output side. Yo work with a 100pf it needs to drive a high 
impedance input on the radio.  Most radios are not high impedance 
enough.  I don't have my notes in front of me but try sticking in a .1uf 
(or even larger)  in it's place.  I think you will find this will solve 
your audio problem.

This issue has been covered a few times on the forum so you may want to 
do a search for "low audio" and see what that turns up.  i think the 
resistor issue has also been covered.

Good luck getting it working!  Mine has been working non-stop for at 
least 4 years!

Mark

On 8/12/2010 6:03 PM, Ted11 wrote:
> Okay, I think I'm getting this figured out.  This is my first packet
attempt
> and my first kit in a long time, so it's been a slow but very interesting
> process.
>
> First, some typos in the T238 modem assembly manual (Rev 8, March 2006).
> Top of page 6, the table listing voltage checks:  "C8" should be "C108".
> Second, and more importantly, the values for R100 and R101 are switched in
> the assembly instructions relative to the schematic.  R100 in the
schematic
> is 100K, in the parts list and construction section is 10K.  Similarly,
R101
> is 10K in the schematic, and 100K in the instructions.  I think the
> schematic is correct, as it matches the resistor values in another similar
> MX614 project I found on the web.
>
> Since my problem was no signal out of pin 8 of the DB9 connector, I had
high
> hopes reducing the resistance from 100K to 10K would fix everything.
> Unfortunately, no.  But, when I turned the trimpot down all the way, I got
a
> very faint sound when monitoring my output signal.  So, I bypassed R101
and
> used only the trimpot for resistance control.  I slowly turned down the
> resistance, and the signal kept getting louder, until finally I was at 0
> ohms.  However, even with no resistance between pin 7 of the MX614 and pin
8
> of the DB9, my signal was still considerably fainter than others I
> monitored.  Encouragingly, I've seen some packets make it to the internet
> (http://aprs.fi/?call=KE6ROS-2), but not as many as I would like.
>
> Which leads me to another thought:  I'm running the output of modem into
the
> rear panel DB9 input of my Alinco DR-135.  According to the manual, it
wants
> 100mV/600 ohms in.  I'm guessing the modem was designed to hook up to a
> microphone input, which I would think would be a lower input.  Does this
> theory make sense?  Anybody hook their T238 modem up to this radio, or a
> similar one with a DB9 jack?  I suppose I can hook the T238 using the
> microphone and rear speaker jacks, but was hoping to use the DB9 for a
> tidier install.
>
> Thanks for any help!
>
> Ted
> KE6ROS
>
>
> _______________________________________________
> wxsig mailing list
> wxsig at tapr.org
> https://www.tapr.org/cgi-bin/mailman/listinfo/wxsig
>
>


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