[App_rpt-users] Simulcasting with RTCM/voter

[Joe Leikhim]

"The DAC problem is related to audio phase not launch delay. So the 
audio will sound bad even with the proper launch delay."

I am just shooting from the hip on this, but would it be possible to 
insert a preamble into the simulcast stream that the DAC's would each 
reproduce and some additional circuitry or code could monitor and use to 
correct the audio phase at each RTCM?

I am sure I am oversimplifying, but, thoughts?

Joe


On 3/14/2017 10:33 AM, Tim Sawyer wrote:
> The delta should be less than 83uS for voice is what I read. Digital 
> (i.e. P25) needs to be even less, not that that's what your dealing 
> with here. Of course the signal strength comes into play as well. The 
> overlap areas are defined as areas where the signal is within 10dB.
>
> The Radio Mobile program can accept these figures and plot the 
> simulcast interference. It takes some doing to figure out but well 
> worth the effort. I've found it amazingly accurate. I might have an 
> example plot to share if anyone is interested.
>
> The DAC problem is related to audio phase not launch delay. So the 
> audio will sound bad even with the proper launch delay.
>
>
> On Mon, Mar 13, 2017 at 8:10 PM, Hayden Honeywood 
> <haydenph91 at gmail.com <mailto:haydenph91 at gmail.com>> wrote:
>
>     Thanks for your thoughts Jesse and Tim.
>
>     Ah, perhaps that was my issue, I was setting the delay, doing a 99
>     to save to EEPROM but not rebooting. Perhaps I need to try this
>     next. Basically the test you have described Jesse is what I am
>     doing at home.
>
>     I believe from what I have read and understand from Joe's
>     messages, Tim that some error in the launch delay is OK at voice.
>     I read somewhere over 110uS it starts to become a problem.
>
>     I certainly can get away with no PL encoding on the transmitter, I
>     was merely using it as a means of double checking my audio
>     phasing. Voice sounds OK, depending on my frequency offset. It
>     does have a level of distortion however - again maybe due to the
>     launch delay not being set correctly. I suppose a semi bonus is
>     that at 6 metres, normal propagation effects cause noise,
>     crackles, phase cancellations etc so it may just all sound natural
>     anyway. Sporadic E openings will be interesting though :).
>
>     Currently my main site has a significant overlap of my planned
>     secondary site. I may need to reconsider this to reduce the overlap.
>
>     73
>     Hayden
>
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> -- 
> --
> Tim
>
>
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-- 
Joe Leikhim


Leikhim and Associates

Communications Consultants

Oviedo, Florida

JLeikhim at Leikhim.com

407-982-0446

WWW.LEIKHIM.COM

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