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[wxsig] Radio Interference Question

John Koster w9ddd at tapr.org
Tue May 15 14:01:00 UTC 2007

The cable looks OK to me.

Do you ever see the PTT LED on the modem light?  (I don't remember how
fast you can set the TX rate, but setting it faster than 5 min if possible
will help for trouble shooting).  Does the radio TX light ever come on?

What is the PTT requirement of the radio?  Ground to TX or pulled high to 
TX.  The T238+ is set for ground to TX and would require an external 
inverter if you need to pull up to TX.

Is the voltage measurement being taken with the radio disconnected?  

On Tue, 15 May 2007, Leon Bruner wrote:

> Hello,
> I'm hoping someone can help me determine the correct final set-up for my 
> just completed T-238+ and modem.  The problem is that after hooking up 
> the system to the radio I do not appear to be able to transmit wx data.
> Information relevant to the situation I can think of is as follows:
> After assembly all the voltage checks are OK except for one:   between 
> pin 4 of U101 and P100 pin 6 the voltage is 3.42 V instead of the 
> specified 5 V.  I have rechecked the R109, D101, and Q100 and they are 
> oriented correctly and appear to have good solder joints.  Except for 
> this out of specification all else seems to work OK as far as I can tell.
> I have also updated to the latest version of the firmware.
> The radio I want to use is an ICOM 27H (a radio I purchased about 20 yrs 
> ago).  I have wired an interface cable to connect between P100 on the 
> modem board and the mic and speaker inputs to the radio.  I have 
> connected as follows:
> Pin on P100                    Radio  Connection
>      6                           Microphone Pin 5 , PTT
>      7                           Speaker  in
>      8                           Microphone Pin 1, mic in
>      3                           Microphone Pin 6, gnd
>      4                           Speaker ground
> I used this radio for packet back in the late 80s-early 90s and am 
> reasonably sure I've wired the interface cable the same as was used in 
> the packet system once upon a time...  Also, the amber rx LED lights 
> when the squelch is turned down or when a transmission is received.
> I have watched for transmissions from the T-238+ Modem and radio.  So 
> far I've seen none, nor have transmissions been heard (checked on 
> findu.com, using call sign NT8B-3). 
> I am heard using another radio and same antenna under call sign NT8B-1.
> The UART setting I'm using is 5-min avg (modem).
> Does anyone have any suggestions for what might be wrong?  Is there a 
> way to force a transmit to help facilitiate testing?  The help is much 
> appreciated-
> Regards,
> Leon
> NT8B
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John, W9DDD

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