to Andy Wade

Andy,

Justin at ATV Hillsboro asks, "Why do masthead amps have a lower noise
figure than distribution amps?"

Bill Wright asks, "What's the difference between the Proception Mk I power
supply unit and the Mk II version?"

Bill

"Bill Wright" wrote in message
...
Andy,

Justin at ATV Hillsboro asks, "Why do masthead amps have a lower noise
figure than distribution amps?"

Bill Wright asks, "What's the difference between the Proception Mk I power
supply unit and the Mk II version?"

Bill


For ****ing spam.

"tudor" wrote in message ...
"Bill Wright" wrote in message
...
Andy,

Justin at ATV Hillsboro asks, "Why do masthead amps have a lower noise
figure than distribution amps?"

Bill Wright asks, "What's the difference between the Proception Mk I
power supply unit and the Mk II version?"

Bill


For ****ing spam.

Probably more satisfying than eating it.

In message ,
Doctor D Proclaimed from the tallest tower:

"tudor" wrote in message ...
"Bill Wright" wrote in message
...
Andy,

Justin at ATV Hillsboro asks, "Why do masthead amps have a lower
noise figure than distribution amps?"

Bill Wright asks, "What's the difference between the Proception Mk I
power supply unit and the Mk II version?"

Bill


For ****ing spam.

Probably more satisfying than eating it.

Watch out for any sharp edges on the tin though!!

--
Regards,
Chris.
(Remove Elvis's shoes to email me)

"Bill Wright" wrote in message
...
Andy,

Justin at ATV Hillsboro asks, "Why do masthead amps have a lower noise
figure than distribution amps?"

Bill Wright asks, "What's the difference between the Proception Mk I power
supply unit and the Mk II version?"

Bill


I'm probably way off the mark, but is it because the quoted noise figure for
a masthead amp is for the "amp" only and doesn't include the noise created
by the power supply?

Bill Wright wrote:
Andy,

Who, what, me?

Justin at ATV Hillsboro asks, "Why do masthead amps have a lower noise
figure than distribution amps?"

Because they're designed to. Masthead preamps _need_ a low noise figure
to make the most of a weak signal; distribution amps in general don't.
By compromising the noise figure a little the input stage of a
distribution amp can provide a better input return loss (better
impedance match) and better signal handling.

Bill Wright asks, "What's the difference between the Proception Mk I power
supply unit and the Mk II version?"

This is for the proPSU11F, and LF cut-off frequency of the RF passband
is the answer. The Mk 1 passes frequencies down to 47 MHz (lower end of
Band I) and cuts off fairly sharply below that. The Mk 2 will pass down
to 5 MHz, i.e. it will pass Sky-eye type remote control signals and you
can use it where the 50 or 75 mA available from the RF-2 o/p of a Sky
box isn't quite enough. Also the non-powered side of the Mk 1 is s/c
to ground whereas on the Mk 2 it's o/c (a fact not usually of
consequence, but it is a difference).

HTH...
--
Andy

"Andy Wade" wrote in message
...
Bill Wright wrote:
Andy,

Who, what, me?

Justin at ATV Hillsboro asks, "Why do masthead amps have a lower noise
figure than distribution amps?"

Because they're designed to. Masthead preamps _need_ a low noise figure
to make the most of a weak signal; distribution amps in general don't. By
compromising the noise figure a little the input stage of a distribution
amp can provide a better input return loss (better impedance match) and
better signal handling.

I'll pass this on to Justin. Or are you lurking you bugger?


Bill Wright asks, "What's the difference between the Proception Mk I
power supply unit and the Mk II version?"

This is for the proPSU11F, and LF cut-off frequency of the RF passband is
the answer. The Mk 1 passes frequencies down to 47 MHz (lower end of Band
I) and cuts off fairly sharply below that. The Mk 2 will pass down to 5
MHz, i.e. it will pass Sky-eye type remote control signals and you can use
it where the 50 or 75 mA available from the RF-2 o/p of a Sky box isn't
quite enough. Also the non-powered side of the Mk 1 is s/c to ground
whereas on the Mk 2 it's o/c (a fact not usually of consequence, but it is
a difference).

Thanks Andy. That's useful to know, especially the fact that it can be used
to replace the power from a Sky box RF2 output. I'll pass it on to a few
people.

Now, on a related matter, I went to a job just after the heavy rain where I
found that the green light on the PSU had turned red. Measuring the power
consumption of everything up the downlead (using a different PSU) I found
that it was hovering about between 80 and 136mA. The actual load should have
been 40mA (A Maxview 2 stage amp). The cause of the trouble was a very tiny
bit of damp inside the four way splitter on the masthead. Now the thing is,
what current does it take to trip the proPSU11F? It must be about 100mA
judging from this experience. Just a suggestion, but wouldn't it be better
if the PSU didn't trip until the overload was a bit more than that? False
trips in wet weather are not what we want! I could actually see some
installers avoiding the product after one such incident.

Bill

On Fri, 25 Jan 2008 01:16:24 -0000, "Bill Wright"
wrote:


Now, on a related matter, I went to a job just after the heavy rain where I
found that the green light on the PSU had turned red. Measuring the power
consumption of everything up the downlead (using a different PSU) I found
that it was hovering about between 80 and 136mA. The actual load should have
been 40mA (A Maxview 2 stage amp). The cause of the trouble was a very tiny
bit of damp inside the four way splitter on the masthead. Now the thing is,
what current does it take to trip the proPSU11F? It must be about 100mA
judging from this experience. Just a suggestion, but wouldn't it be better
if the PSU didn't trip until the overload was a bit more than that? False
trips in wet weather are not what we want! I could actually see some
installers avoiding the product after one such incident.


Can you count it as a false trip though? If there was enough water in
there to pass 96mA, wouldn't that cause big problems signal-wise?
Also, if you have that much current flowing through water for any
length of time, I'd have thought you'd get some horrendous
electrolysis, with black gunk building up everywhere.

Colin.

Bill Wright wrote:

Thanks Andy. That's useful to know, especially the fact that it can be used
to replace the power from a Sky box RF2 output. I'll pass it on to a few
people.

It's 12 V output of course, though, not 9 V. Our dual-mode masthead
(the 'MHD14R) will take 9 - 12 V OK, as I think will the Global F-series
products. In fact I think there is or was one Sky box around
(Panasonic?) that put out 12 V on RF-2, not the 9 V that Sky had specified.


Now the thing is, what current does it take to trip the proPSU11F? It
must be about 100mA judging from this experience. Just a suggestion,
but wouldn't it be better if the PSU didn't trip until the overload
was a bit more than that?

No, it's not a precision overload trip at all, it's a short-circuit
indicator. The circuit uses a PTC 'polyfuse' type device with a nominal
current rating of 200 mA, so it should need well over 200 mA to trip it.
It should be very tolerant of short-term overloads, and even brief
dead shorts (up to 100s of milliseconds). Once tripped though it's
effectively latching if there's any load connected at all, since it then
only needs a few mA to keep the PTC device on the hot side of its
tripping temperature.

False trips in wet weather are not what we want!

They certainly aren't, but I've not heard of any before. In this case
I'd say that either (a) something really was drawing 200 mA, or (b)
the PTC devices in the PSU is faulty, or (c) the PSU is running very hot
for some other reason, combined with the moderate overload.

Equally, you don't want liquid water getting anywhere near DC-carrying
parts of equipment, even in wet weather. Electrolytic corrosion will
rot things pretty quickly if it does.

--
Andy

"Andy Wade" wrote in message
...
Bill Wright wrote:

Thanks Andy. That's useful to know, especially the fact that it can be
used to replace the power from a Sky box RF2 output. I'll pass it on to a
few people.

It's 12 V output of course, though, not 9 V.

The Global f280 16 way amp sends 11.5V to the remote eyes and it doesn't
cause problems.

Our dual-mode masthead
(the 'MHD14R) will take 9 - 12 V OK, as I think will the Global F-series
products. In fact I think there is or was one Sky box around (Panasonic?)
that put out 12 V on RF-2, not the 9 V that Sky had specified.

Yes I think I remember that.



Now the thing is, what current does it take to trip the proPSU11F? It
must be about 100mA judging from this experience. Just a suggestion,
but wouldn't it be better if the PSU didn't trip until the overload
was a bit more than that?

No, it's not a precision overload trip at all, it's a short-circuit
indicator. The circuit uses a PTC 'polyfuse' type device with a nominal
current rating of 200 mA, so it should need well over 200 mA to trip it.
It should be very tolerant of short-term overloads, and even brief dead
shorts (up to 100s of milliseconds). Once tripped though it's effectively
latching if there's any load connected at all, since it then only needs a
few mA to keep the PTC device on the hot side of its tripping temperature.

False trips in wet weather are not what we want!

They certainly aren't, but I've not heard of any before. In this case I'd
say that either (a) something really was drawing 200 mA, or (b) the PTC
devices in the PSU is faulty, or (c) the PSU is running very hot for some
other reason, combined with the moderate overload.

I'll dig that PSU out and have a mess about with it.

Bill