Subject: [NEXTEL-1] RE: CTCSS or DCS Signaling?

From: [email-masked]
Date: Wed, 2 Jul 2003 15:10:16 -0400

Thanks to the several of those who responded to my question directly (as
well as some posted in other lists).  Interestingly, most of the
respondents pointed me in the same direction, by far, based on my two
specific concerns.  Still others brought up other concerns in such a
decision, in case I hadn't considered those, either.  (And indeed there
was one aspect that I had not thought of.)
This has been a great help.  -Alan

--------- Original Message ----------
From: [email-masked]
To: [email-masked]
Date: Tue, 1 Jul 2003 16:06:31 -0400
Subject: CTCSS or DCS Signaling?

Okay, stupid question time.  I need to hear from folks with specific,
real-world field experience in this.  I already have all the textbooks. 
For an FM UHF system I am designing, I need to know whether CTCSS or DCS
signaling would be the better choice.  My main interest is the robustness
of the signaling.  Specifically, I have two operational concerns:
1)  For fringe area (low RSSI) reception of the transmitted signal, which
method, if either, is more likely to keep the squelch open?
2)  For errant "doubled" (simultaneous) transmissions by two mobile
units, aside from FM capture effect (assume equal RSSI at receiving
station), is either signaling method more or less likely to open the
receiving station's squelch (assume both transmitting stations to be
using the *same* signaling method, of course)?  Okay, I admit I am
grabbing at straws on this second concern.

This system will be operating on a shared channel that is very lightly
loaded, and will have a very small number of subscribers (I am planning
on six).  Are there any other considerations of which I may not be aware,
please??  DCS inversion should not be a factor as this is a simple
base-mobile system, not operating a repeater.

Many thanks to all,
Alan Dixon

[Please copy replies to: [email-masked] <wpuc720[a]juno.com>]

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From: [email-masked]
Date: Wed, 02 Jul 2003 23:31:22 -0400

-------- Original Message --------
   From: [email-masked]
Subject: Re:CTCSS or DCS Signaling?

> grabbing at straws on this second concern.

In regard to:

1) Life general features more grey-area than back and white and this is likely to
be yet another example. My personal real-world experience indicates that CTCSS
will decode further into noise than DCS/IDCS however, you asked which format is
more likely to keep the squelch open. Since the ability to remain open during
instances of signal dropout has more to do with the design parameters of the
decoder which are usually fixed. I would still tend to favor CTCSS since it would
be more likely to decode even momentarily thus resetting the decoder's dropout
delay more frequently.

2) If both signals arrive at the receiver simultaneously and at equal levels one
would expect to have so much phase distortion or cancellation that probably
neither would decode with any reliability but here again, I find the less complex
CTCSS signal more likely to decode than the octal based DCS word.

In short, the KISS principal appears to be applicable here.

Bob Fay, Systems Engineer
SmartLink Radio Networks