Eric,
Thanks for the excellent response. The information in your response was just
what I was looking for. I'm evaluating an MX828 decoder chip for a project
and the reference to TIA-603-B will be especially useful.
Steve
WA6ZFT.
On Sunday 10 October 2004 15:46, Eric Lemmon wrote:
Steve,
The industry standard for Land Mobile Radio is TIA-603-B. This standard
states that the maximum response time for CTCSS frequencies 100 Hz and
above shall be 250 ms. Below 100 Hz, the maximum response time in
milliseconds is found by dividing 25,000 by the CTCSS frequency in Hz.
Therefore, a CTCSS frequency of 67 Hz must be decoded within 373 ms.
Note that this standard is based upon a CTCSS deviation of 500 Hz.
Modern receivers use digital signal processing, which may respond much
faster than either PLL or reed based schemes. Personally, I like radios
to unmute for CTCSS in 150 ms or less, but I'm not going to choose a
brand or a model to achieve the quickest response time. I ignore the
specsmanship game played by some decoder manufacturers; they know what
TIA-603-B requires, and they might state better than or maximum or
typical response times. Who knows? Most of them seem to work okay...
It is true that higher CTCSS tones decode quicker, but some some radios-
Amateur rigs in particular- have little or no high-pass filtering to
keep the tones out of the speaker audio, and the higher frequency tones
are more likely to make it through the receive audio chain and cause an
annoying buzz to be heard. This effect can be minimized by keeping the
tone deviation within the 500-700 Hz range.
73, Eric Lemmon WB6FLY
Steve Rodgers wrote:
What is considered a high performance number for CTCSS/PL ackquisition
time? According to what I see posted on the web (which may or may not be
real) The Comspec TS-32 is 250msec, and the TS-64 is 150msec. The actual
decode time should get worse as you go lower in frequency, so what would
you think are high performance numbers for at say, 67 hz?
Steve
WA6ZFT
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