Amplified Splitters vs Pre-Amps?

[(PeteCresswell)]

I'm trying to parse this summary from
http://tinyurl.com/c6qgenw

"Antennas Direct recommends using a pre-Amplifier for outdoor
installations or cable runs over 100 ft. A distribution amplifier
should be used to make up for loss due to splitting but is not
recommended to compensate for long cable runs, or weak signal due
to distance from the towers."

Reading elsewhere, I come away thinking that

- A pre-amp goes on or as near as possible to the
antenna.

- A pre-amp increases the signal by a much higher factor
than a distribution amp does. As in 26 db vs 4 db
So much so, in fact, that overloading the TV receiver(s)
becomes a possibility.

- A distribution amplifier goes as close to the antenna
as possible, but on the TV side of any pre-amplifier.

- By implication, a pre-amplifier and a distribution amplifier
can coexist. OTOH, I've seen several statements to the
effect that they cannot bc the second amp will amplify the
increased noise out of the first as well as the "good" signal.

- If the signal to any one TV is adequate, then a pre-amp
is not required.


Seems like two broad approaches are possible:

- Put a pre-amplifier on at the antenna, amplifying
the signal by 20+ db, and then splitting the heck
out of it (four ways, and then four ways again on
one of the first split's outputs) using un-amplified
splitters

- Ditch the preamp, and just put a 4-way distribution
amplifier behind the 4 tuners.

Since I've got 2 TVs hanging on that first 4-way split and
they're not having any problems I'd say the pre-amp is not
only moot, but might even risk over-loading those TVs and,
therefore, it comes down to a distribution amp behind the 4
tuners.

Am I on the right track here?
--
Pete Cresswell

[Jim Wilkins]

"(PeteCresswell)" <x...@y.Invalid> wrote in message
news:cq4m08dsoq39fgit0...@4ax.com...

The 15-321 I have fits that description, with two outputs:
http://www.radioshack.com/product/index.jsp?productId=3770519

Despite what the RS reps told Ant it has a preamp meant to go at the
antenna and a variable-gain distribution amp on the TV end. I'm about
as far from the transmitter as reviewer KG4YUU and can echo his
remarks, including how to adjust it and reception off the side of the
Yagi.

I used splitters to temporarily attenuate the tuner inputs when I was
setting up and testing the installation. The signal was still strong
enough. YMMV.

jsw

[J G Miller]

On Saturday, July 21st, 2012, at 17:36:17h -0400, Peter Cresswell wrote:

> - A pre-amp goes on or as near as possible to the
> antenna.

A better term is masthead amplifier. The masthead amplifier
unit does indeed go as near to the antenna on the support mast
but with some it is recommended to have it place an appropriate
distance below the antenna to avoid degrading the antenna performance
and/or creating modulation problems. Some antennas have the
option of having the masthead amplifier actually being incorporated
into the unit where the balun attaches to the active dipole element
eg Televes DAT-43 and DAT-75

The masthead amplified is powered by a unit which is often located
near the TV set and plugged into a power outlet. This feeds an
appropriate DC voltage 12 V or sometime 18 V up the cable to the
antenna. Obviously there must be no splits in the cable between
the power unit and the masthead amplifier.

The purpose of the masthead amplifier is to amplify weak signals
and the biggest problem is the introduction of noise which with
analog signals means grain on the picture -- at least better than
the snowstorm of a weaker signal. With digital TV, noise is
not so critical and neither is the signal level -- the signal
level needs to be above a certain level and above that having
more signal makes no difference. With regard signal quality
that is also very important because a strong signal with
very poor quality is just as useless as a too weak signal
with good quality.

The purpose of a distribution amplifier (amplified splitter)
is not to amplify the signal from the antennas per se,
but to ensure that the signal level is maintained either
over a very long run of cable (more than 100 m say) or
to split into many different feeds. Obviously this can be
placed anywhere along the length of cable that is practical
for the different feeds to different rooms eg some people
have them in the loft or attic.

For analog signals, placing a low quality amplifier after
a masthead amplified download often degraded the picture
quality rather than improving it.

If your signal strength is adequate from your antenna,
you do not need a masthead amplifier. If you want to
split the feed to many receivers you will want to
use a distribution amplifier suitably placed.

If you did need to use a masthead amplifier, then you
could probably use a passive splitter (two way) after
the power unit for the masthead amplifier.

One nice feature of the Televes masthead amplifier for
their antennas is that there are two outputs from the
power unit box making it ideal for a situation where
there is a TV and a PVR and no loop through via the PVR
is necessary.

> - By implication, a pre-amplifier and a distribution amplifier
> can coexist.

They can but this needs to be done in a very precise arrangement
with good quality equipment -- just consider a MATV system
where it is necessary to use a masthead amplifier for some
distant stations, but it is still necessary to use a distribution
amplifier for all the feeds to N rooms / appartments.

> - Ditch the preamp, and just put a 4-way distribution
> amplifier behind the 4 tuners.

Keep it as simple as possible and that will almost always
be the best arrangement, so that suggestion sounds the best.

Multiple splitting is always a bad idea eg where some people
have ridiculous schemes like, because it is "convenient"
just add another amplified box or passive splitter
and then they wonder why they get problems (see other
thread for somebody who has moved to such an arrangement).

ANTENNA ------- one splitter ----- another splitter
|
|
another splitter --- maybe yet another

Cable companies can do it because they keep all their
signal levels and noise levels within tolerance using
professional equipment installed in the correct sequence
and they have the professional meters to measure that
the outputs are what they need to be.

A DIY single home installer has neither the need nor budget.

> Am I on the right track here?

Just so long as there is not a train coming the other way ;)

[(PeteCresswell)]

Per J G Miller:

>A better term is masthead amplifier....

>The purpose of the masthead amplifier...

>The purpose of a distribution amplifier...


That one made it to my "Keepers" file.

Thanks!!!!!!!
--
Pete Cresswell