Hi. We have a stereo (two channel) Marti STL-10 system.

A few weeks ago we started noticing noise, and we traced it to the STL link.
One of our two STL transmitters was showing a low +13.5 voltage. We
discovered this voltage was +13.5 when not transmitting and dropped to +9v
when transmitting. We pulled the unit and swapped out the power supply and
the symptoms disappeared.

BUT - while that unit was out we ran with our supposed good unit (normal
meter readings). All of a sudden we started hearing significant noise on
that channel.

Anyone have experience with noisy Marti units? Where should I search first?
Transmitter or receiver? Noise sounds like HF clipping - all kind of
distorted in the high end, almost like an echo on a long distance line.
Unit is using 75usec pre emphasis and driven below 100% modulation.

-Andrew

Andrew Dickens wrote:
Hi. We have a stereo (two channel) Marti STL-10 system.

A few weeks ago we started noticing noise, and we traced it to the STL link.
One of our two STL transmitters was showing a low +13.5 voltage. We
discovered this voltage was +13.5 when not transmitting and dropped to +9v
when transmitting. We pulled the unit and swapped out the power supply and
the symptoms disappeared.

So, you checked the positive regulator?

BUT - while that unit was out we ran with our supposed good unit (normal
meter readings). All of a sudden we started hearing significant noise on
that channel.

What sort of noise? Crackling? Hissing? Humming?

Is there ripple on the power supply output? If you swapped it with a power
supply that has been sitting on the shelf for years, I could see why a cap
might fail and produce a lot of hum.

Anyone have experience with noisy Marti units? Where should I search first?
Transmitter or receiver? Noise sounds like HF clipping - all kind of
distorted in the high end, almost like an echo on a long distance line.
Unit is using 75usec pre emphasis and driven below 100% modulation.

HF clipping doesn't sound like noise. Are you talking about a noise problem
or a distortion problem?

A line echo does not sound like either noise or distortion.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Scott:

Thanks for your help. The regulator was good. We swapped it with a brand
new one and it did not fix the voltage drop (13.5 down to 9). Replacing the
power supply fixed it. The power supply that failed was the factory
original. The replacement unit was pulled from our other STL transmitter.

The second unit - the one that exhibits noise has a constant white noise
that can be heard during both quiet and loud periods. It also has a raspy
high frequency distortion that you can hear, particularly when someone is
talking.

It is not a line echo. But the sound is similar to a bad long distance
connection, where you say something and hear a distorted version summed with
it.

-A


"Scott Dorsey" wrote in message
...
Andrew Dickens wrote:
Hi. We have a stereo (two channel) Marti STL-10 system.

A few weeks ago we started noticing noise, and we traced it to the STL
link.
One of our two STL transmitters was showing a low +13.5 voltage. We
discovered this voltage was +13.5 when not transmitting and dropped to
+9v
when transmitting. We pulled the unit and swapped out the power supply
and
the symptoms disappeared.

So, you checked the positive regulator?

BUT - while that unit was out we ran with our supposed good unit (normal
meter readings). All of a sudden we started hearing significant noise on
that channel.

What sort of noise? Crackling? Hissing? Humming?

Is there ripple on the power supply output? If you swapped it with a
power
supply that has been sitting on the shelf for years, I could see why a cap
might fail and produce a lot of hum.

Anyone have experience with noisy Marti units? Where should I search
first?
Transmitter or receiver? Noise sounds like HF clipping - all kind of
distorted in the high end, almost like an echo on a long distance line.
Unit is using 75usec pre emphasis and driven below 100% modulation.

HF clipping doesn't sound like noise. Are you talking about a noise
problem
or a distortion problem?

A line echo does not sound like either noise or distortion.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Andrew Dickens wrote:

Thanks for your help. The regulator was good. We swapped it with a brand
new one and it did not fix the voltage drop (13.5 down to 9). Replacing the
power supply fixed it. The power supply that failed was the factory
original. The replacement unit was pulled from our other STL transmitter.

Right, but what was wrong with the power supply? Knowing what was wrong
with the power supply might tell you a lot about what is going on.

The second unit - the one that exhibits noise has a constant white noise
that can be heard during both quiet and loud periods. It also has a raspy
high frequency distortion that you can hear, particularly when someone is
talking.

If you return the new power supply to the other transmitter, does the problem
follow the new supply?

Is the received signal strength on the receiver good? If you listen to
the signal with a scanner right in front of the transmitter, do you hear
the distortion on that as well?

If you're hearing a higher noise floor AND distortion, that makes me suspect
that the signal strength isn't high enough to get full quieting on the
receiver.

If you put a wattmeter on the transmitter output, are you seeing good
deflection? What if you use a dummy load?

Your first goal is to isolate the problem and make sure it really is the
transmitter and not the receiver. Your next goal is to make sure you are
getting full power output from the transmitter. If so, it's probably a
modulation issue.

It is not a line echo. But the sound is similar to a bad long distance
connection, where you say something and hear a distorted version summed with
it.

Does it sound like fringe FM reception?
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."