Threaded...
Eric Lemmon wrote:
>
> Joe,
>
> The fact that you have never, ever heard of this problem is interesting,
> because it is very common. In fact, the County of Santa Barbara had to make
> some major changes in their vast radio system to preclude the problems I
> mentioned.
>
> The most common situation resulting in the unwanted turn-off code action is
> when a mobile in the coverage area of Repeater A is talking through distant
> Repeater B, while a portable (or weaker mobile) is using repeater A. Each
> time the mobile transmits, it captures Repeater A- blocking the portable-
> and then mutes Repeater A when it unkeys.
That's capture effect if I'm understanding what you are saying. If so,
it has nothing to do with any CTCSS/CDCSS used (or not used).
Even if it mutes repeater A, that repeater should immediately unmute
when it sees the valid code from the portable after the mobile unkeys.
If not, it is a controller problem.
> Needless to say, this can be very
> frustrating to the portable user, especially when he cannot hear any voice
> from the other station.
Yes it would. I've heard capture effect, too, as well as repeater
blocking (which happens when a strong signal has capture effect over
another user). Of course it results in muting of the repeater and the
inability to use it unless you can crank out a signal strong enough to
capture the signal that is capturing yours, but again, this has nothing
to do with CTCSS/CDCSS other than it would appear the repeater is
'down'.
> The same radio system also had a problem at one of the really dense sites,
> where every channel on both VHF and UHF used the same CTCSS tone, because
> the County made it their "standard." Due to various mixing and intermod
> products, many repeaters were being keyed without any valid input.
Sounds like poor RF management or poor TX/site design.
> Once the
> various repeaters were given different PL tones, the problems went away.
I bet it didn't go away. Changing the tones simply masked the problem
the same as adding CTCSS to a repeater receiver will not let you HEAR a
signal on the input. But the interfering signal is still there causing
interference to any users.
It is a proven myth that CTCSS/CDCSS will eliminate interference.
> As you pointed out, PL tones that are close to 134.4 Hz can cause
> inadvertent turnoff of CDCSS-equipped receivers.
>
> 73, Eric Lemmon WB6FLY
That's not what I said. I said the TOC would be interpreted as an
'invalid' CTCSS tone on a repeater that uses... say 162.2 Hz. But, what
causes the muting is capture effect of the signal which results in the
inability of the decoder to see the valid CTCSS/CDCSS through the
stronger signal with a different CTCSS/CDCSS or even no CTCSS/CDCSS. It
has nothing to do with any turn off codes. It has everything to do with
capture effect.
Joe M.
> -Original Message-
> From: Repeater-Builder@yahoogroups.com
> [mailto:[EMAIL PROTECTED] On Behalf Of MCH
> Sent: Tuesday, August 28, 2007 6:58 PM
> To: Repeater-Builder@yahoogroups.com
> Subject: Re: [Repeater-Builder] Re: Subaudible Tones (Was subaudibe tones..)
>
> Fortunately, all are still using FM, so capture effect will not allow
> the repeater to see the TOC of the other weak user.
>
> I have never - ever - heard a false mute of a signal from the TOC of
> 'other users'. Before that happens, the repeater will lose the CDCSS
> code and will mute due to loss of code rahter than see a TOC. And even
> when that happens, the signal will come right back when it can see the
> valid CDCSS code.
>
> Aside from the above, what is the difference of what you described vs a
> repeater using CTCSS seeing the TOC as another CTCSS tone? It seems that
> should happen too if it can happen at all.
>
> Joe M.
