sci.electronics.repair - 25 new messages in 8 topics - digest

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TOPIC: Calculating Power Factor
http://groups.google.com/group/sci.electronics.repair/t/b2d11ce5d56ec333?hl=en
==============================================================================

== 1 of 16 ==
Date: Sun, Nov 14 2010 5:15 pm
From: Jamie

Steve Kraus wrote:

> I'm trying to figure power factor for a large transformer-type DC power
> supply. This is pretty much just for my own amusement (so I can figure
> power draw from current and voltage readings) so there's nothing critical
> here.
>
> This device runs on 208V 3-phase (as in each leg is 120V from neutral but
> there's no neutral connection). The 3 transformer primaries are wye
> connected but there's no other connection to the wye point. It draws about
> 18A per leg.
>
> I decided to compare current and voltage waveforms using a dual trace
> scope.
>
> To look at current, rather than put a small resistance shunt in one line I
> decided to take advantage of the small voltage drop that occurs between the
> breaker panel and the cutoff switch for the device. So I had one channel
> of the scope looking at the voltage difference between one leg at the
> cutoff switch and the "hot" side of a 120V outlet on the same leg.
>
> For voltage I just looked at one leg vs. neutral.
>
> I'll skip over boring details about having to float the common side of the
> scope in order to do this without creating a short circuit. Anyway, it
> seemed to work. Emphasis on "seemed."
>
> What I saw looked like voltage vs. current was out of phase by about 90°.
> Is that what one would reasonably expect going into a transformer? Seems
> kind of extreme so I wonder if my entire setup was bogus in some way.
>
> Part of the reason for the question is that in retrospect I should have
> probably been looking at voltage as measured from one input leg to the wye
> point, not neutral since that's what a transformer primary sees. But I
> would think the wye would be similar to neutral.
what you're seeing in the xformer is normal. the xformer is returning
the current phase from the current applied source which comes back out
of phase with it, thus, the current you see is lagging behind from which
it was created from the voltage you now see going the other way...

Power Factor (F) is the difference between True power (resistive) and
Apparent power (reactive)...

== 2 of 16 ==
Date: Sun, Nov 14 2010 5:17 pm
From: "Phil Allison"

"Steve Kraus"

>
> To look at current, rather than put a small resistance shunt in one line I
> decided to take advantage of the small voltage drop that occurs between
> the
> breaker panel and the cutoff switch for the device. So I had one channel
> of the scope looking at the voltage difference between one leg at the
> cutoff switch and the "hot" side of a 120V outlet on the same leg.
>
> For voltage I just looked at one leg vs. neutral.
>
> I'll skip over boring details about having to float the common side of the
> scope in order to do this without creating a short circuit. Anyway, it
> seemed to work. Emphasis on "seemed."

** Pure insanity.

The scope common ( or ground) is at the same voltage as one phase.

For god's sake monitor the neutral current ( using a current clamp probe)
and one phase.

..... Phil

== 3 of 16 ==
Date: Sun, Nov 14 2010 5:58 pm
From: Steve Kraus

> For god's sake monitor the neutral current ( using a current clamp
> probe)

There is no neutral connection so no neutral current.

But assuming you misspoke, what's the difference between sensing current on
one of the legs using a current clamp probe and wiring a shunt into that
line and looking at voltage across it? In effect that's what I've done
except I'm taking advantage of the small voltage drop that already exists.

== 4 of 16 ==
Date: Sun, Nov 14 2010 6:15 pm
From: Steve Kraus

Jamie wrote:
> what you're seeing in the xformer is normal. the xformer is
> returning
> the current phase from the current applied source which comes back out
> of phase with it, thus, the current you see is lagging behind from
> which it was created from the voltage you now see going the other
> way...
>
> Power Factor (F) is the difference between True power (resistive)
> and Apparent power (reactive)...

My aim here is to estimate real power draw. I've got a switch mode supply
putting out about the same output and it draws about 8A per leg. (I don't
know anything about PF or reactive power on that one). This transformer
type rectifier is drawing 18A per leg. I know from asking around that this
particular brand is known to have inefficiently wound transformers. So
that accounts for part of it. But there's also the matter of taking into
account reactive power & power factor.

BTW, output in both cases is about 62A at about 22V.

== 5 of 16 ==
Date: Sun, Nov 14 2010 6:20 pm
From: "Phil Allison"

"Steve Kraus"
>
>> For god's sake monitor the neutral current ( using a current clamp
>> probe)
>
> There is no neutral connection so no neutral current.

** Then monitor one of the phases and the voltage of that same phase.

>
> But assuming you misspoke, what's the difference between sensing current
> on
> one of the legs using a current clamp probe and wiring a shunt into that
> line and looking at voltage across it?

** The common connection is LIVE in your case - IDIOT !!

> In effect that's what I've done
> except I'm taking advantage of the small voltage drop that already exists.

** You are so dangerously * STUPID * you have no clue as to what PF even
is.

Hint:

In the example you are discussing, phase angle barely comes into it.

.... Phil

== 6 of 16 ==
Date: Sun, Nov 14 2010 6:47 pm
From: Jamie

Steve Kraus wrote:

> Jamie wrote:
>
>> what you're seeing in the xformer is normal. the xformer is
>> returning
>>the current phase from the current applied source which comes back out
>>of phase with it, thus, the current you see is lagging behind from
>>which it was created from the voltage you now see going the other
>>way...
>>
>> Power Factor (F) is the difference between True power (resistive)
>> and Apparent power (reactive)...
>
>
>
> My aim here is to estimate real power draw. I've got a switch mode supply
> putting out about the same output and it draws about 8A per leg. (I don't
> know anything about PF or reactive power on that one). This transformer
> type rectifier is drawing 18A per leg. I know from asking around that this
> particular brand is known to have inefficiently wound transformers. So
> that accounts for part of it. But there's also the matter of taking into
> account reactive power & power factor.
>
> BTW, output in both cases is about 62A at about 22V.
It's possible it has a saturated core transformer. What this does is
causes the input side to exert the rated operating current at all times
but this type of design is best at keeping the transformer at a safe
operating Q to help prevent unwanted harmonics and oscillations in the
circuit that can take place where capacitors are in the coil design.
You see this in microwave ovens due to the cap in the hV circuit..
with out the saturated transformer it can hit a resonance that can
become destructive.

This isn't a problem if you plan on using the supply to it's fullest,
as far as efficiency goes..

I think what you're looking for his is efficiency measurements, not
PF..
Just load the supply to its max and measure the input side and compare
the wattage to the output side.
You will see that more energy is going to be used on the input side..

== 7 of 16 ==
Date: Sun, Nov 14 2010 6:55 pm
From: Steve Kraus

Phil Allison wrote:

> ** The common connection is LIVE in your case - IDIOT !!

I'm aware of that and dealt with it carefully and appropriately. It's not
particularly difficult not to contact anything live for the few seconds I
was looking at the traces. Scope front? Plastic. Scope knobs? Plastic.
It's not rocket science. You've never worked around something live? Well
good for you. I'm sure I don't have to point out that the voltage, while
certainly dangerous, is less than in other parts of the world.

But by all means please continue with your name calling.

== 8 of 16 ==
Date: Sun, Nov 14 2010 7:02 pm
From: "Phil Allison"

"Steve Kraus is a Krackpot "

> Phil Allison wrote:
>
>> ** The common connection is LIVE in your case - IDIOT !!
>
> I'm aware of that and dealt with it carefully and appropriately.

** Like hell you did !!!!

Only a COMPLETE IDIOT does what you did.

> But by all means please continue with your name calling.

** Listen here pal -

you are one fucking arrogant, pig ignorant, snipping, trolling pile of vile
autistic dung.

And them are all your GOOD points.

... Phil

== 9 of 16 ==
Date: Sun, Nov 14 2010 7:18 pm
From: Steve Kraus

Jamie wrote:
> This isn't a problem if you plan on using the supply to it's
> fullest, as far as efficiency goes..

No, it won't need to go much more than it is now. These are xenon arc
projection lamp supplies. We have sufficient light output at 55A but as
the bulbs age it's necessary to raise the current to keep the arc from
wandering on the electrode tips. If I have to go much over 65A (70A is max
on these bulbs) it will be time to replace the bulbs but that time is
coming very soon on the basis of hours alone. Fortunately for me the bulbs
last years.

I was just kind of curious what the difference in power draw was and
realized simple current & voltage measurements that I would take might be
meaningless when going into a transformer. I do know the difference is
real since the conduit going to the transformer type supply gets slightly
warm after many hours but the one going into the switch-mode supply doesn't
seem to rise detectably above ambient so I tend to believe the 8A figure on
that one.

If I'd known the transformer type of this particular brand was so
inefficent I would not have bought it 3 years ago. The original 20 year
old equipment (two of that same brand) failed about 6 months apart in 2007.
The first I replaced with a new one of the same make though of larger
capacity. When the 2nd old one gave up the ghost I decided to go with the
switch-mode supply.

Electricity is a tiny part of operating costs but still, just on
principle...8A vs. 18A* for the same output? It seems rather amazing.

*not counting reactive power issues

Oh, in case anyone cares, I'm measuring current with a Fluke / LEM LH2015
true RMS AC/DC clamp meter.

== 10 of 16 ==
Date: Sun, Nov 14 2010 7:22 pm
From: Jeffrey Angus

On 11/14/2010 9:02 PM, Phil Allison wrote:
> Only a COMPLETE IDIOT does what you did.

Along with several idiots at Xerox.

While i was working on a switching power supply, we had reason
to measure the input (live) AC line. Tectronix to the rescue.
Apparently they knew there were a few insane people that would
want to float a scope for live AC line measurements and they had
a special isolation box that the scope plugged into for just that
occasion.

Of course, some fool removed it while we were at lunch.

Ya know, it's amazing the fwipzzzt noise the ground lead on an
expensive scope probe makes when it goes up in flames when you
turn the power on.

Jeff

== 11 of 16 ==
Date: Sun, Nov 14 2010 7:24 pm
From: "Phil Allison"

"Steve Kraus = IMBECILE "

>
> Electricity is a tiny part of operating costs but still, just on
> principle...8A vs. 18A* for the same output? It seems rather amazing.

** No one tiny bit - if you have a clue about PSUs.

> *not counting reactive power issues

** Already told ya - there IS no reactive power issue.

> Oh, in case anyone cares, I'm measuring current with a Fluke / LEM LH2015
> true RMS AC/DC clamp meter.

** Then you already know the VA figure.

But to find true power in this example - you need a wattmeter.

No if or buts.

.... Phil

== 12 of 16 ==
Date: Sun, Nov 14 2010 7:25 pm
From: "Phil Allison"

"Jeffrey Angus"
Phil Allison wrote:
>
>> Only a COMPLETE IDIOT does what you did.
>
> Along with several idiots at Xerox.
>
> While i was working on a switching power supply, we had reason
> to measure the input (live) AC line. Tectronix to the rescue.
> Apparently they knew there were a few insane people that would
> want to float a scope for live AC line measurements and they had
> a special isolation box that the scope plugged into for just that
> occasion.
>
> Of course, some fool removed it while we were at lunch.
>
> Ya know, it's amazing the fwipzzzt noise the ground lead on an
> expensive scope probe makes when it goes up in flames when you
> turn the power on.
>

** ROTFL

..... Phil

== 13 of 16 ==
Date: Sun, Nov 14 2010 8:40 pm
From: Jeff Liebermann

On Sun, 14 Nov 2010 21:22:33 -0600, Jeffrey Angus
<jangus@suddenlink.net> wrote:

>On 11/14/2010 9:02 PM, Phil Allison wrote:
>> Only a COMPLETE IDIOT does what you did.
>
>Along with several idiots at Xerox.
>
>While i was working on a switching power supply, we had reason
>to measure the input (live) AC line. Tectronix to the rescue.
>Apparently they knew there were a few insane people that would
>want to float a scope for live AC line measurements and they had
>a special isolation box that the scope plugged into for just that
>occasion.
>
>Of course, some fool removed it while we were at lunch.
>
>Ya know, it's amazing the fwipzzzt noise the ground lead on an
>expensive scope probe makes when it goes up in flames when you
>turn the power on.
>
>Jeff

Nicely done. I usually had a sign hanging on the test mess during
lunch. Something like "Touch anything and you'll die". However,
ty-wrapping the power cords to both the instrument and the power strip
worked somewhat better. I also placed mouse traps in strategic
locations until my boss demanded that I stop (after one got him).

So, why didn't you use two probes, with the scope set to differential?
To get the phase, you would need a 4 trace scope, but those are common
enough. I believe that differential is also the recommended method as
it keeps the scope case at ground level and takes care of the common
mode noise on the line. The isolation xformer method puts one side of
the power line on the case of the instrument, which is not pleasant if
you touch both the instrument case and a nearby ground.

Remember.... you have but one life to give to your profession.

Incidentally, I always kept my old broken scope probes. The
intermittent probes were especially prized. I would destroy one about
every 2 months. I would mark them with a tiny red nail polish dot,
and leave them connected in a conspicuous location, while I hid my
working scope probes. When they would predictably disappear, I would
just smile. I also had a #2 Phillips screwdriver with a self
stripping plastic handle. I think it was borrowed (stolen) at least 3
times, and then returned. I still have it somewhere.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

== 14 of 16 ==
Date: Sun, Nov 14 2010 9:00 pm
From: Jeff Liebermann

On Sun, 14 Nov 2010 18:44:27 -0600, Steve Kraus
<screen@SPAMBLOCKfilmteknik.com> wrote:

If all you want are the results, the common Kill-A-Watt power meter
has a PF measurement feature. $25-$40 everywhere.
<http://www.p3international.com/products/special/P4400/P4400-CE.html>
I have 4 of these (various models).

If you want to do it safely with a scope, it really requires a 4
channel scope (or 2 channels with two differential inputs per
channel). Put a small value non-inductive resistor in series with the
power line. One pair of diffential input probes go across the
resistor for the current waveform. The other pair of probes go across
the line for the voltage waveform.

With a switcher, you're going to have a non-sinusodial current
waveform. Therefore, you can't just use the phase angle as the power
factor and will need to measure the Apparent Power and the RMS powers.
<http://www.pge.com/includes/docs/pdfs/mybusiness/customerservice/energystatus/powerquality/nonsinusoidal_power.pdf>

There's also quite a bit of work done on power factor correction these
days which probably includes some measurement techniques.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

== 15 of 16 ==
Date: Sun, Nov 14 2010 9:24 pm
From: "Phil Allison"

"Jeff Liebermann"

>
> With a switcher, you're going to have a non-sinusodial current
> waveform.

** Same for a transformer based PSU too.

> Therefore, you can't just use the phase angle as the power
> factor and will need to measure the Apparent Power and the RMS powers.

** PF = true power / VA

No phase angles in sight ......

.... Phil

== 16 of 16 ==
Date: Sun, Nov 14 2010 11:48 pm
From: Jeff Liebermann

On Mon, 15 Nov 2010 16:24:55 +1100, "Phil Allison" <phil_a@tpg.com.au>
wrote:

>> With a switcher, you're going to have a non-sinusodial current
>> waveform.
>
>** Same for a transformer based PSU too.

True. Once you get away from a pure sine wave current waveform, the
phase angle method doesn't work. See the PG&E article I cited.

>> Therefore, you can't just use the phase angle as the power
>> factor and will need to measure the Apparent Power and the RMS powers.

>** PF = true power / VA
> No phase angles in sight ......

True. I just hate to agree with you, but I'll make an exception this
one time. But don't worry... it probably won't happen again.

Handy buzzword translator:
RMS power = True power
Apparent power = VA power.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

==============================================================================
TOPIC: Another reason ...
http://groups.google.com/group/sci.electronics.repair/t/a9a63c157742e708?hl=en
==============================================================================

== 1 of 1 ==
Date: Sun, Nov 14 2010 5:50 pm
From: "Arfa Daily"

"LSMFT" <boleyn7@aol.com> wrote in message
news:znVDo.15923$Ou2.6814@newsfe20.iad...
> Arfa Daily wrote:
>> Remember my post a few weeks back "Another Reason to Hate CFLs" ? Well,
>> here's yet another. That one that I put in my bench light, that started
>> it all, has now become so dim, that it is worse than useless. It has
>> been getting worse and worse over the last week. There are signs of the
>> ballast enclosure running hot, so I guess that any electros in there,
>> have just cooked dry, due to the fact that it is predominantly hanging
>> down, in a semi-enclosed 'shade', much like a lot of household room and
>> decorative lighting does. They are fundamentally a crap technology that
>> has been forced on a largely unwanting public, by supposedly green
>> issues with a dubious foundation in fact.
>>
>> I know a lot of people on here seem to like the dreadful things, and
>> swear by them, but my continuing experience, judged from when they first
>> appeared, right up until now, just makes me want to swear *at* them ...
>>
>> I have now found an internet site selling all varieties of
>> incandescents, including 60 watt pearl, so I shall be stocking up post
>> haste. I have also just started trying out the halogen versions of
>> traditional light bulbs, which still seem to make it into the eco-bollox
>> "book of energy savers", even though they only consume a few watts less
>> than their equivalent light-output 'traditional' tungsten cousins. Thus
>> far, I am impressed. I now have a 70 watt actual, 100 watt equivalent,
>> fitted to my hallway main light fixture. It is very bright, very easy
>> (for me anyway) to see by, and has a good colour spectrum, not in the
>> slightest way offensive to my eyes, unlike the CFLs, which no matter how
>> much anyone says that *they* can't tell the difference with, *I* can ...
>> d :-\
>>
>> Arfa
>
> One bad bulb condemns the entire line. Good thinking.
> I use them everywhere and they work great. There are different brands,
> some made in the US, some in China or other places. Some have a short warm
> up cycle others have longer ones.
> I will never go back to incandescent heater bulbs.
> If anything I will move onto to LEDs. Do you have stone wheels on your
> car?
>
>
>
> --
> LSMFT
>
> Simple job, assist the assistant of the physicist.

And where did I ever say "one bad bulb" ? I actually said, if you took the
trouble to read the post properly, " - but my continuing experience, judged
from when they first
appeared, right up until now - "

Does that perhaps suggest to you that I have been trying different types
from all manner of manufacturers in all sorts of countries, for the last 15
years or more ? Yes, some do have a 'short warm up period' but that is still
massively long compared to an incandescent, which reaches its maximum light
output in a few mS - for all intents and purposes, instantly. There are some
places where CFLs have their uses, but for me, not many of them are inside
the house. If you like them, and want to fill your house with them, that's
fine. I however, don't.

But more than anything, I object to self-obsessed greenie politicians,
trying to force me to use them, based largely on a misconceived notion that
the things are 'eco-friendly'. If countries embraced nuclear power
generation in the way that France for instance, has, then there would not be
any need to mandate this nonsense, nor to cover the countryside and
coastline with stupid ugly and noisy windmills, and now to carpet the rest
of the countryside, in ridiculously inefficient photovoltaic panels ...

Arfa

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TOPIC: EXTORADINARY HOT PHOTOS & videos
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== 1 of 1 ==
Date: Sun, Nov 14 2010 10:11 pm
From: SAILAJA LOVES U

==============================================================================
TOPIC: Why the same price with and withtout an antenna amp?
http://groups.google.com/group/sci.electronics.repair/t/9162c2bb89bfe618?hl=en
==============================================================================

== 1 of 3 ==
Date: Sun, Nov 14 2010 10:15 pm
From: mm

Not a repair question, so maybe this is OT, but...

Why do you suppose at solidstate.com, the Winegard MS 1000 antenna,
which doesn't include an amplifier, costs the same as the Winegard MS
2000 which does have a built-in amplifier 60 dollars. This is a
round omnidirectional antenna that looks like a flying saucer.

FWIW, the 2000 even includes 50 feet of cable that the one without the
amp doesn't include.

Does that mean the amp in the one with an amp is really cheap?

Does that in turn mean that one of the amps they sell for 50 or 60
dollars without an antenna is many times better?

Does that mean one should buy the one without the amp and then get a
separate amp if necessary?

Thanks.

I'm not asking you to look at the webpages, but I always get
criticized if I don't include links.
http://www.solidsignal.com/pview.asp?mc=03&p=MS-1000&d=Winegard-MS-1000-Metrostar-Omnidirectional-NonAmplified-TV-Antenna-%28MS1000%29&c=TV%20Antennas&sku=
http://www.solidsignal.com/pview.asp?mc=03&p=MS-2000&d=Winegard-MS2000-Metrostar-Omnidirectional-Amplified-TV-Antenna-%28MS2000%29&c=TV%20Antennas&sku=615798301705

== 2 of 3 ==
Date: Sun, Nov 14 2010 11:35 pm
From: "Wild_Bill"

I dunno about the quality of the various amps, but a simple RF amp can just
be 2-3 transistor circuit with a few other complimentary components added.

What I can recommend, would be that an RF amp be placed as close to the
actual antenna element(s) as practical, and not at the end of a long feed
line.
This type of setup requires power-thru-coax delivery of the voltage needed
by the amp, whether built-in, or near the antenna. This eliminates the need
for additional wires to be added for powering the amp. Most mast-mount amps
have this type of power adapter included.

However, there are some coax cable types that have two power leads attached
to the coax cable in a siamese fashion (cross-section looks like a figure
8), so using a variety of amps could be practical if everything is enclosed
in a weatherproof and UV resistant enclosure.

--
Cheers,
WB
.............

"mm" <NOPSAMmm2005@bigfoot.com> wrote in message
news:khj1e6dq6va55j4iglsrvpb1f28rbcli85@4ax.com...
> Not a repair question, so maybe this is OT, but...
>
> Why do you suppose at solidstate.com, the Winegard MS 1000 antenna,
> which doesn't include an amplifier, costs the same as the Winegard MS
> 2000 which does have a built-in amplifier 60 dollars. This is a
> round omnidirectional antenna that looks like a flying saucer.
>
> FWIW, the 2000 even includes 50 feet of cable that the one without the
> amp doesn't include.
>
> Does that mean the amp in the one with an amp is really cheap?
>
> Does that in turn mean that one of the amps they sell for 50 or 60
> dollars without an antenna is many times better?
>
> Does that mean one should buy the one without the amp and then get a
> separate amp if necessary?
>
> Thanks.
>
>
> I'm not asking you to look at the webpages, but I always get
> criticized if I don't include links.
> http://www.solidsignal.com/pview.asp?mc=03&p=MS-1000&d=Winegard-MS-1000-Metrostar-Omnidirectional-NonAmplified-TV-Antenna-%28MS1000%29&c=TV%20Antennas&sku=
> http://www.solidsignal.com/pview.asp?mc=03&p=MS-2000&d=Winegard-MS2000-Metrostar-Omnidirectional-Amplified-TV-Antenna-%28MS2000%29&c=TV%20Antennas&sku=615798301705
>
>

== 3 of 3 ==
Date: Mon, Nov 15 2010 12:02 am
From: Jeff Liebermann

On Mon, 15 Nov 2010 01:15:06 -0500, mm <NOPSAMmm2005@bigfoot.com>
wrote:

>Not a repair question, so maybe this is OT, but...

Close to the bitter edge of off topic, but not quite.

>Why do you suppose at solidstate.com, the Winegard MS 1000 antenna,
>which doesn't include an amplifier, costs the same as the Winegard MS
>2000 which does have a built-in amplifier 60 dollars. This is a
>round omnidirectional antenna that looks like a flying saucer.
>
>FWIW, the 2000 even includes 50 feet of cable that the one without the
>amp doesn't include.
>
>Does that mean the amp in the one with an amp is really cheap?

Yes.

>Does that in turn mean that one of the amps they sell for 50 or 60
>dollars without an antenna is many times better?

No.

>Does that mean one should buy the one without the amp and then get a
>separate amp if necessary?

No.

>Thanks.

You're welcome.

>I'm not asking you to look at the webpages, but I always get
>criticized if I don't include links.
>http://www.solidsignal.com/pview.asp?mc=03&p=MS-1000&d=Winegard-MS-1000-Metrostar-Omnidirectional-NonAmplified-TV-Antenna-%28MS1000%29&c=TV%20Antennas&sku=
>http://www.solidsignal.com/pview.asp?mc=03&p=MS-2000&d=Winegard-MS2000-Metrostar-Omnidirectional-Amplified-TV-Antenna-%28MS2000%29&c=TV%20Antennas&sku=615798301705

The explanation is easy enough. The pancake antenna is nothing but a
big circuit board inside. The difference between the amplified
version and the non-amplified version is one MMIC amplifier (probably
a Mini-Circuit Labs MAR-6) two caps, one resistor, and maybe a choke.
Total added costs, in large quantities, is about $0.50. Because the
boards are identical, and the cost differences are minimal, the
selling prices are the same.

There's a reason why two models are offered. The amplifier is useful
in weak signal areas, but a disaster in very strong signal areas,
where overload and intermod from nearby TV xmitters are a very real
problem. Two versions gives the customer a choice.

The antenna amplifier is also useful for compensating for the losses
of the coax cable between the antenna and the receiver. If the cable
is fairly short (i.e. less than 15ft), then the antenna amplifier
isn't going to do much good. However, if there is 50 or 100ft of
RG-6a/u attached, the antenna amplifier is very necessary to preserve
the receiver sensitivity.

External versus internal amplifiers is a religious issue. There are
merits to both approaches. I can't offer an opinion without knowning
how the antenna is to be used, the location relative to the desired TV
stations, length of coax, and receiver model (so I can check the
sensitivity specs). For what it's worth, I don't like such pancake
omnidirectional antennas (with or without amplifier) as an omni
antenna has very little gain. The name "Metro" might offer a clue
that it has to be used in a metropolitan area, where strong signals
are usually present.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

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