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Kevin, with regard to your DTMF "Falsing"....what
decoder chip is being used?
If it is a Mitel 8870, you need to change the
"Guard Time" to add more delay before decoding.
40 ms is the normal setting but that is often too
fast for regular voice.
There is an 8870 C and an 8870 D
chip. The "C" version will accept up to 6 db of positive
or negative twist and the "D" version is good up to
8 db of twist.
Also check the level that you are sending to the
chip, it will work from - 29 to +1 dbm.
-10 dbm is a good setting to use. Too much level
will cause falsing as well. Several years ago
we had one lady in our area that could "talk" the
repeater off....we were using a three
digit on - off code at the time. If she
talked in a normal soft voice there was no problem
but as soon as she got excited, and raised her
voice, the repeater would have problems.
Another approach is to use a separate CTCSS tone to
access the DTMF decoder and that way it
will remain "Silent" until the proper CTCSS tone is
used as part of the access code.
73 John VE3AMZ
----- Original Message -----
Sent: Monday, December 13, 2004 10:59
PM
Subject: Re: [Repeater-Builder] 600 - 10k
ohm Interface
Thanks everyone, I think I have a number of ideas to try.
The unit has a transformer inside, 600/600ohm, the output is floating, so
live and ground should be able to be connected across the output. The TX has
the same transformer 600/600ohm, but the controller to the TX is a 600ohm line
anyway, so it should be fine (by my understanding)
For those interested the units are Tait Repeater modules.
The reason for the request, was the matching, and also I have one
receiver that has bag DTMF twist, falsing. Unable to use DMTF blanking, as it
does it so much with voices. Have setup the radio/controller as required, and
tested. Thought a impedance mis-match.
Regards
Kevin.
----- Original Message -----
Sent: Monday, December 13, 2004 2:30
PM
Subject: Re: [Repeater-Builder] 600 -
10k ohm Interface
Kevin, I just built one here for our
Church for a DVD player, "Stereo" to an 10 K input
on a "Mono" amp.
You can use half of what I
did......
From the 600 ohm OP put a 4.7K resistor to the
top of a 5 K trim pot.
The bottom of the trim pot goes to
ground.
From the centre of the trim pot put a 4.7 K
resistor to the 10 K input.
Adjust the pot for the desired level going in
to the 10 K input and it works very well.
Since you are using resistors there is no freq.
roll off. A 600 to 10K transformer
would also do but they are expensive these days
for anything that is quality....
73 John VE3AMZ
----- Original Message -----
Sent: Sunday, December 12, 2004 6:14
PM
Subject: [Repeater-Builder] 600 - 10k
ohm Interface
Hi All,
I need a simple interface for a 600 ohm output radio to a controller
which accepts 10k ohm.
This is a RX not TX.
I don't want to make a circuit board if I don't need to.
Any ideas?
Regards
Kevin.
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