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[wxsig] Radio Interference Question

Leon Bruner leon at ljjf.net
Wed May 16 02:16:45 UTC 2007


I see the PPT LED light when I first plug the modem in, but have not 
observed it subsequently, nor have I seen the TX light-up on the radio.  
I've also cycled through the menus and have been unable to find a 
setting that allows me to change the tx interval- It's very possible 
that I've missed transmissions given the 5 min interval.  If anyone 
knows how to force transmissions for testing purposes I'd appreciate 
knowing how to do it.

With regard to the PTT requirements for the radio, the only information 
I have on this is a schematic showing wiring for microphones that can be 
used for the radio.  I'm a biologist by training and self taught in 
electronics and reading schematics- so we need to take the following 
interpretation with caution...  The schematic shows the PTT switch has 2 
connections.  It looks like to me that when the PTT is pushed it 
connects Microphone pin 5 to pin 6 ground.  Could I test this by 
shorting microphone pins 5 and 6 (hoping it won't somehow blow the radio)?

The voltage measurements were all made without the transmitter connected.


John Koster wrote:

>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:
>>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 
>>wxsig mailing list
>>wxsig at lists.tapr.org

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