[LakelandARC] WX4AMS test on the repeater

[Don Jeerings]

Bill,   Some schooling......


It looks like your method to measured the frequency was by using the 
time interval between peaks and calculating the reciprocal of  8 
milliseconds. = 125 cycles.


Isn't the repeater CTCSS frequency at 127.5 cycles  ? (which would be 
7.9921 Milliseconds)


You measured 8 milliseconds, you could easily have had a possible 
measuring error of 8 *micro*seconds ?


I generally teach that Measuring time intervals on a scope by time 
between peaks is not good practice because the rate of change of the 
sine wave at the peaks is very small. (actually you are looking for a 
time period where there is no change (Zero) and I don't think 
mathematically you can do that.)


Normal procedure would be to expand the scope time base out to display a 
single cycle and */measure the time between zero crossings/*, where the 
rate of change is at maximum and better defined.


Just a logical question..
'
Don  Ki4EFL




On 12/03/2014 05:06 AM, 'Bill' billkodak at verizon.net [LakelandARC] wrote:
>
> Got your call, but it was too late. Things were a bit hectic last 
> evening.
> I am still trying to make sense out of the repeater project.
>
>  1. That hum is not related to the wallwart. It is still there after I
>     replaced it with batteries.
>  2. I discovered another oddity. If I transmit near the recording
>     radio using another HT, my voice gets blanked out. However, if I
>     move to another room, my voice gets recorded.
>  3. I measure the hum at 125 HZ. This is probably measurement error,
>     with the real frequency being 120 Hz.
>
> See below, Audacity output. Period is 8 milliseconds.
>
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