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Just do me and the group a favor and don't waste
any more of
our time with your ignorance on this subject!
Mick - W7CAT
Mike Morris wrote:
At 08:33 PM 04/22/06, you wrote:
Okay, you know it all! I
only
have been using this for a year and a half without any
problems, and I know others who also use this.
OK, that proves you have a working system.
Of course you can run
without
the PL, just minimizes a chance of getting into the receiver.
Pray tell, how does it do that? Is PL a receiver
preamplifier?
Remember, PL is modulation, and your receiver has to hear the modulated
signal before PL does any good. Any grunge on the input is something
that
your
users signal has to overcome in order for the modulation to be
heard. Yes, you
can configure your receiver so that carrier OR the PL signal opens the
squelch
but that's pretty rare... users tend to not like the extended squelch
tails that setup
causes so most systems are set up so that the receiver unmutes when it
hears
both carrier AND the PL tone.
If you have any grunge or energy on the receive frequency it is going
to
reduce the
effective sensitivity of your receiver, which will make it harder for
your users to get
into the receiver.
You have measured the effective sensitivity of your system, right?
Because
test bench sensitivity only matters when comparing receiver A vs
receiver
B when
ON THE BENCH.
In the real world your receiver is going to be hit with everything that
your antenna
hears and manages to get through your duplexer and pass cavities -
which
is a
very different environment than the single signal generator on the
bench.
Look at
<
http://www.repeater-builder.com/tech-info/effectivesens.html> -
a
writeup
from Chris Boone WB5ITT, who
happens
to be a pretty sharp guy.
Back to your environment:
My transmitter and
receiver use
the same PL, so pretty much the same as carrier
squelch.
How does that work? If you have a active PL decoder then it's not
carrier
squelch.
The definition of carrier squelch is that the receiver squelch opens up
(and thereby
keys the transmitter) whenever the receiver quiets enough (from a
carrier
signal)
to drop the channel noise below a threshold set by the squelch
pot.
So how does your receiver and transmitter using the same tone make it
pretty much
the same as carrier squelch. Your system either requires the user
to send a tone
or it doesn't.
By the way, using the same tone just makes your receiver MORE
susceptible
to hearing grunge and intermod, as your own transmitter now has the
correct
tone to open the squelch or to keep it open.
Maybe you need to turn
off your
CD player and open your mind!
If you will re-read my posting it wasn't my CD player.
I was trying to make an example of the fact that when you are chasing
desense, grunge or crud you will never hear the interfering signal if
you
are hiding behind a PL decoder.
Yes, PL is a good thing, but when you are trying to optimize a system
(which in many cases means eliminating interference) you will find it
much harder to identify the interference if there is a PL decoder
preventing
you from hearing it.
My comment of:
>If you want good performance, you need to leave it in carrier
squelch
>mode and FIX IT.
still stands - you can't fix a problem by ignoring it or turning on a
PL
decoder so you don't hear it, and let you pretend it's not there.
Now the circumstances change once you know what the grunge is...
then you enable the PL decoder and get some peace and quiet while...
a) if it's your problem you get the tools, test gear and other
stuff together
for a hill trip, or
b) you figure out how to tell the guys in the next rack over that they
need
to install a circulator.
Mick - W7CAT
Mike
Mike Morris wrote:
At 09:54 AM 04/22/06, you wrote:
Hello Randy,
With only 25 watts, the other option is to use two antennas with
some separation. And it is also helpful to add a filter to the
transmit line and another to the receiver. At least add one to the
transmit side. Adding a filter to the transmit side would help
eliminate the high power interference, and no loss for the receiver.
And of course PL on your receiver would help too.
NO IT WON'T.
PL only hides a problem. It's like a lady down the block that had
a
squealing left front brake shoe (it was dragging) so she kept her
window closed and turned up the volume on the CD player.
If you want good performance, you need to leave it in carrier squelch
mode and FIX IT.
Mike WA6ILQ
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