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[wxsig] Radio Interference Question

John Koster w9ddd at tapr.org
Wed May 16 04:21:09 UTC 2007

I don't see any choices for TX frequency.  So I guess we're stuck with 5 
minutes.  Need a clever way to 'capture' the event.  

At this time we really don't know whether its' a PTT problem or an audio 
problem.  If you have a receiver and audio recorder perhaps you could 
record the audio on the frequency over a period of time and see what you 
might hear.  I assume you've checked the radio with  microphone to be sure 
it's not developed a problem over the years.  You'd want the monitoring 
receiver to have a poor or no antenna so you don't pick up other signals.

I am a little puzzled by the low voltage reading.  If I didn't read the 
schematic wrong the reading is from collector to ground of the PTT 
transistor.  It should be 5 unless you have a real low impedance 
voltmeter.  Of course that also depends on you having a solid +5 VDC rail.

I'm leaving in the morning for Hamvention, so I'll probably not be reading 
my email very frequently.

On Tue, 15 May 2007, Leon Bruner wrote:

> John-
> 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.
> Leon
> 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:
> >
> >  
> >
> >>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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> >>wxsig at lists.tapr.org
> >>https://lists.tapr.org/cgi-bin/mailman/listinfo/wxsig
> >>
> >>    
> >>
> >
> >  
> >
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John, W9DDD

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