[wxsig] Radio Interference Question

[Mark Patton]

Leon,

I dug out my marked up schematics and I ended up using a 2.7uf cap in 
place of th 100pf cap at C111.  I chose that because that's what I had 
in my junk box. I think something a lot smaller (ie even a .1uf  as you 
suggest will work much better).  If you use an electrolytic like I did, 
hook the + side to the mic_aud signal (ie to the right on the 
schematic).  I also used a 20K resistor between the mic_aud signal and 
the mic_ptt signal to key the radio.   The mic_aud pin and ground were 
the only two signals I needed to key and send the audio to the radio.  I 
don't know if I changed R101 or not - I don't have it marked on my 
schematic if I did. I'm using an old Icom W21AT.

For setting the audio level, I hooked up another radio to the soundcard 
input of my laptop and used an audio program (like Audacity) to capture 
the audio off the air and compare it with other signals that I heard.  I 
adjusted the level to be about 70% of what some of the others (like a 
local digi) were because I didn't want to over deviate.

73's & Good luck!

Mark, K0YG

leon at ljjf.net wrote:
> Mark,
>
> Thanks for the suggestion.  I borrowed a scope from work, hooked the
> ground lead of the probe to pin 4 of U101 and looked for a signal on pin 7
> of U100.  When the TX LED lights there the scope shows a trace.  So,
> assuming my hookup is correct, it looks like tones are being generated. 
> I've also tried adjusting pot R114 but still don't hear audio during
> transmission.
>
> I've looked in the archives and found a chain of messages about low audio.
>  The suggested correction seems to be to change  R101 to 4.7K and C111  to
> .1uf.  Does the group agree this is my next step?  To be honest I simply
> don't have enough knowlege to be able to answer this question...  My radio
> is an ICOM 27 H if that helps.
>
> Thanks again to all for the suggestions.  Because of your help I think I'm
> making progress.
>
> Regards,
>
> Leon
>
>
>
>
>
>
>   
>> The problem I had was just the opposite - the audio level was to low.  I
>>  needed to make some changes to resistors and caps in the audio path in
>> order to get the audio level up.  I think this was due to a low
>> impedance input to the radio.  Check the email archive.  Several others
>> have had this same low audio problem.
>>
>> If you have a scope, check the output of the modem chip to see if you
>> are getting tones generated.  That will give you a big clue as to where
>> the problem is.
>>
>> 73's
>> Mark, K0YG
>>
>> John Bennett wrote:
>>     
>>> Be sure you are not over-deviating. If severe enough, it will cause
>>> the problem you described.
>>>
>>> GL es 73,
>>>
>>> John, N4XI
>>>
>>> On Wed, 2007-05-16 at 20:47 -0400, Leon Bruner wrote:
>>>
>>>       
>>>> John,,
>>>>
>>>> Tonight I sat down with a glass of my favorite and a handleld radio
>>>> and  kept an eye on the unit for a reasonable period of time.  I have
>>>>  verified that the red PTT LED goes on approx every 5 minutes and it
>>>> keys  the transmitter.  The signal from the keyed transmitter is
>>>> received on  the handheld.  However, there does not appear to be any
>>>> audio output  associated with the transmission.  Said another way,
>>>> the radio is keyed,  a signal is transmitted but there appears to be
>>>> no information going  out.  The transmission is very short- only a
>>>> second or so...  So it  appears that I have an audio problem...  I'll
>>>> have a look through the  manuals tonight to see if I can identify a
>>>> solution.  In the meantime, I  thank you for the help and hope you're
>>>> having a great time in Dayton.
>>>>
>>>> Leon
>>>>
>>>>
>>>> John Koster wrote:
>>>>
>>>>
>>>>         
>>>>> 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:
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>           
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>>>>
>>>>         
>>
>>
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