Chip with simple program for Toy

[Eric Jacobsen]

On Thu, 27 Sep 2007 09:09:11 -0400, Jerry Avins <jya@ieee.org> wrote:

Jeff Liebermann wrote:

...

Do the math. The cable companies are not going to allow themselves to
lose revenue. Their total receipts (gross income) is going to remain
the same or they go out of business. So, ala carte programming allows
you to pay for fewer channels. Fine, but with penetration bordering
on saturation in most metro areas, the number of customers isn't going
to change much. So, the price of each channel goes up to compensate,
and your monthly bill remains the same.

Or buy an antenna and forgo the cable junk.

Jerry

I was just telling somebody recently that I've been disturbed by the
media and gov't officials acting like OTA no longer exists. The cute
blonde on CNBC was doing a piece on how consumers are confused about
buying HDTVs, since they won't really get HD unless they subscribe to
an HD option with a cable or satellite provider. GAH! How about
just paying $10 for a set of rabbit ears and watch the HD that the
gov't has forced the broadcasters to spend millions to provide?

Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.ericjacobsen.org

 

[Jerry Avins]

Eric Jacobsen wrote:

On Thu, 27 Sep 2007 09:09:11 -0400, Jerry Avins <jya@ieee.org> wrote:

Jeff Liebermann wrote:

...

Do the math. The cable companies are not going to allow themselves to
lose revenue. Their total receipts (gross income) is going to remain
the same or they go out of business. So, ala carte programming allows
you to pay for fewer channels. Fine, but with penetration bordering
on saturation in most metro areas, the number of customers isn't going
to change much. So, the price of each channel goes up to compensate,
and your monthly bill remains the same.
Or buy an antenna and forgo the cable junk.

Jerry


I was just telling somebody recently that I've been disturbed by the
media and gov't officials acting like OTA no longer exists. The cute
blonde on CNBC was doing a piece on how consumers are confused about
buying HDTVs, since they won't really get HD unless they subscribe to
an HD option with a cable or satellite provider. GAH! How about
just paying $10 for a set of rabbit ears and watch the HD that the
gov't has forced the broadcasters to spend millions to provide?

I'm about 50 miles from most stations I might watch, so rabbit ears
won't work for me. Does anyone yet have knowledgeable antenna
suggestions? I guess digital TV has some DSP connection, but I recognize
that this is OT the OT.

Jerry
--
Engineering is the art of making what you want from things you can get.
ÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻ

 

[Randy Yates]

Jerry Avins <jya@ieee.org> writes:

Does anyone yet have knowledgeable antenna suggestions?

Jerry, try the folks (or scan the archives) over at alt.tv.tech.hdtv -
this question has been asked a lot over there.
--
% Randy Yates % "Though you ride on the wheels of tomorrow,
%% Fuquay-Varina, NC % you still wander the fields of your
%%% 919-577-9882 % sorrow."
%%%% <yates@ieee.org> % '21st Century Man', *Time*, ELO
http://www.digitalsignallabs.com

 

[Jerry Avins]

Randy Yates wrote:

Jerry Avins <jya@ieee.org> writes:
[...]
Does anyone yet have knowledgeable antenna suggestions?

Jerry, try the folks (or scan the archives) over at alt.tv.tech.hdtv -
this question has been asked a lot over there.

Thanks, I will. I have nothing to view it on yet, but something has to
come first.

Jerry
--
Engineering is the art of making what you want from things you can get.
ÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻ

 

[robb]

<tonym924@gmail.com> wrote in message
news:1194462545.578813.284170@z9g2000hsf.googlegroups.com...

On Nov 7, 12:57 pm, "robb" <s...@where.on.net> wrote:
tonym...@gmail.com> wrote in message



What resistance do you get on the other rails?

TM

the 30V rail to 0V is 1.28 MegOhms

robb

 

[Jerry Avins]

JosephKK wrote:

Allen allen@nothere.net posted to sci.electronics.design:

Jerry Avins wrote:
Gene E. Bloch wrote:

...

Oh - Thunderbird. I use it for e-mail. Its spell checker is very
bizarre, IMHO

Luckily I also use the organic spell checker after a pass or three
of
Thunderbird's. When I remember to do it, that is...

I use a bunch of spell checkers (not by choice - each program
seems to have a checker of its own), and they *all* are bizarre -
it's just that what one screws up the next does fine, etc
A spell checker ought to be an OS service. That way, any additions
such as frequently encountered names become universal.

Jerry
I really have to disagree, Jerry. I think that operating systems
should be as universal as possible. By putting a spell check in at
that level would mean, for instance, a US operating system couldn't
be used in England. Now a stand-alone checker that any application
could access would be quite desirable. I wish that we could come up
with a checker that is context-sensitive, but I'm afraid that would
be asking too much. Allen

In the *nix world there is a program called ispell, one interface,
works for any application, has multiple dictionaries and languages,
is fully internationalized, learns new words on the fly, and has
dictionary editing. Does that sound like what your asking for?

I've used it. It was my model. Another example of Windows ans Apple )I
think) lagging behind.

Jerry
--
Engineering is the art of making what you want from things you can get.
ÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻÂŻ

 

[Green Xenon [Radium]]

Richard Dobson wrote:

wrote:

Richard Dobson wrote:

The trick therefore is to learn enough about the technology to
engineer your own version,



Oh and just how the !$!#%$ do I learn about this technology when
Creative-Technology -- being the sick f**k it is -- is keeping the
technical info of Creative Music Synth a secret???!!!

You've probably succeeded in putting them off from any help they might
have been able to give.

The only reason I've ever been rude to Creative Technology is because
they are such jerks. I was nice to them at first but they were mean to
me. So I took revenge but being impolite to them. It's their fault.

But that wouldn't have been much, becuase the FM
you like so much comes actually from the Yamaha OPL3 FM chip (used in
lots of cards and even on some motherboards of Pentium 2 vintage); not
~designed~ by Creative Labs, just used by them.

The FM synthesis was initiated by Yamaha. However, I suspect that
Creative Technology made some alterations to it before putting it on the
SB16 card. These alterations could possibly change the way the synth
sounds. This is something they will not discuss because they are such
sick stingy secretive f--ks.

I am hoping this is not the case. I am hoping the SB16 ISA FM synth is
just the OPL3 given a different name but otherwise is exactly the same
as the Yamaha OPL3 FM chip -- this would really make my life a lot easier.

You will find loads of OPL3-related info on the net - I even found a
patent about emulating it. There are documents outlining the exact
configuration of FM operator nodes, and how the mixture of 2-operator
and 4-operator tones are organised. Not so long ago, once could
actually buy the OPL3 chip, and use it as the foundation of a diy sound
board (and yes, there is an example of just such a project on the net).
However, it is so old now that supplies have almost certainly dried up.

This will only make sense if you know what the term "operator" means
with respect to FM synthesis. That is what "learn about the technology"
means. Nobody else can do that for you. Suffice it to say, people have
done whole emulations of a full-blown DX7 using Csound. With digital,
FM is FM is FM; if you know the operator structure (which ~is
documented; search on OPL3 and it will pop up pretty quickly) you can
emulate it in software. FM synthesis is one of the most comprehensively
documented synthesis techniques ever. There is a vintage Csound opcode
that does basic 2-operator FM, and of course more elaborate structures
can be built up using groups of basic oscillators.

And, guess what - there is a complete open-source OPL3 emulator
available on the net, in the form of a load of C++ code - look for
"adplug". It is used for a Winamp plugin module to play OPL3 music
files, such as you may be using even now on your Soundblaster. Of
course, to make use of it you have to be comfortable reading, building
and if necessary modifying C++ code.

If you read the links to the two messages I posted, you'll find that I
don't like emulation.

I want my synth to be hardware. I want it to be on a chip. It should
freshly-generate its tones in real-time -- just like the SB16 ISA FM
synth [i.e. Creative Music Synth] does.

Creative Music Synth is on an FM chip. It's purely hardware. That's what
I like. I don't want any sort of emulation or softsynths. Emulation stinks.

My Avance sound card uses OPL3 emulation. It sounds disgusting. I
returned the Avance piece-of-human-f**k and got the money back.

Nothing like the the real FM in my older SB16 ISA card.

 

On Nov 7, 7:46 am, "robb" <s...@where.on.net> wrote:

no shorts on any of the power regulator chips 5v L387 or the
L298s

and still get 76 ohm continuity between 5v an 0v ref.

Ummm, what's wrong with that? I = E/R: 66mA. This
(static) current isn't blowing the fuse.

TM

 

[NeeekUsenet@gmail.com]

On Oct 5, 4:16 am, murray.james.com....@gmail.com wrote:

I Want To Share Computer Security Information To All Internet Netter.

Thank you as I am studying MCSE and Security+.

 

[Michael Black]

"Jon Slaughter" (Jon_Slaughter@Hotmail.com) writes:

"Jonathan Mcdougall" <jonathanmcdougall@gmail.com> wrote in message
news:1191843018.047481.325550@19g2000hsx.googlegroups.com...
On Oct 8, 3:13 pm, "Jon Slaughter" <Jon_Slaugh...@Hotmail.com> wrote:
Sorry for all the cross posting but I'm interesting in getting a serious
discussion about how usenet has become lately.

Usenet is usenet. What you want is a discussion forum. There are
plenty
of implementations available freely that you may modify to suit your
needs.


I'm trying to see if the community is interested in moving into something
better.

Please, don't cross-post to unrelated newsgroups and understand that
you are currently part of this "spam" category. Time to use this
"spam-repellent" on yourself.



Hmm... But yet its ok for you to do it? I knew someone would say such a
thing but I guess you rather me post individually to each group?

How are we supposed to know which newsgroup you are actually reading when

you cross-post? That forces us to keep the cross-posting in the replies,
bozo.

There are newsgroups for discussion of usenet, but you are too lazy
to find them, just like the bozos who post beginner questions in
..design or anything else that's off-topic.

There is no difference between you and the problem.

Michael

 

[Jon Slaughter]

"Michael Black" <et472@FreeNet.Carleton.CA> wrote in message
news:fedj66$qpo$1@theodyn.ncf.ca...

"Jon Slaughter" (Jon_Slaughter@Hotmail.com) writes:
"Jonathan Mcdougall" <jonathanmcdougall@gmail.com> wrote in message
news:1191843018.047481.325550@19g2000hsx.googlegroups.com...
On Oct 8, 3:13 pm, "Jon Slaughter" <Jon_Slaugh...@Hotmail.com> wrote:
Sorry for all the cross posting but I'm interesting in getting a
serious
discussion about how usenet has become lately.

Usenet is usenet. What you want is a discussion forum. There are
plenty
of implementations available freely that you may modify to suit your
needs.


I'm trying to see if the community is interested in moving into something
better.

Please, don't cross-post to unrelated newsgroups and understand that
you are currently part of this "spam" category. Time to use this
"spam-repellent" on yourself.



Hmm... But yet its ok for you to do it? I knew someone would say such a
thing but I guess you rather me post individually to each group?

How are we supposed to know which newsgroup you are actually reading when
you cross-post? That forces us to keep the cross-posting in the replies,
bozo.

There are newsgroups for discussion of usenet, but you are too lazy
to find them, just like the bozos who post beginner questions in
.design or anything else that's off-topic.

There is no difference between you and the problem.

Um, cause I only posted to 5. The 5 I frequently visit. If you posted only
to one then I would see. Check out the dotnet group and you would see.
Several stopped the cross posting and I replied to them just fine.

Maybe you do not know as much as you think?

 

[glen herrmannsfeldt]

JosephKK wrote:

(snip)

The distinction between 'tuner' and 'converter' is fuzzy.
I don't believe that there is a convenient way to block convert
the ATSC input to NTSC output. One could build a box with
multiple tuners, decoders, and modulators but I doubt that
would be for the consumer market.

While i have not see one, there is nothing that prevents it
technologically. I have seen receivers that can receive the entire
AM band (in stereo as broadcast) at the same time. I have seen
receivers that receive over half of the FM band (in stereo)
simultaneously. Only ADC, DAC, and compute power available preclude
block conversion. Dig around bit on software defined radios and you
can find the done devices that i have found.

You can block convert a band to another, shifted, band with a
single mixer. I suppose processors are fast enough now to
demodulate a downshifted group of FM band signals, maybe
AM without downconversion.

I think I said before that a block ATSC to NTSC converter might
be useful in a commercial setting, such as a hotel. I would
seem to have a very small advantage for home use, more than I
would expect for the cost difference.

-- glen

 

[John Fields]

On Thu, 11 Oct 2007 16:31:34 -0700, Lester Zick
<dontbother@nowhere.net> wrote:

On Thu, 11 Oct 2007 14:25:18 -0500, John Fields
jfields@austininstruments.com> wrote:

On Wed, 10 Oct 2007 17:12:04 -0700, Lester Zick
dontbother@nowhere.net> wrote:

On Wed, 10 Oct 2007 13:30:21 -0500, John Fields
jfields@austininstruments.com> wrote:

the contraction of "it is" isn't possessive.

Or you might consider placing carets under the phrase objected to
instead of whatever else strikes your fancy.

---
If you can rouse yourself from your self-admitted drunken stupor you
might try using a non-proportional font like Courier or Courier New.

Usually I prefer truth.

---
No, you don't.

Sure I do.

---
Well, you may _prefer_ truth, but you certainly don't seem to be
bound by your preferences.
---

You prefer whatever comes along which will allow you to be an
argumentative, deceitful troublemaker.

And the difference would be what exactly?

---
What difference?
---

That I prefer truth instead of kissing your ass?

---
Well, that may be your "preference" but it certainly doesn't stop
you from lying.


--
JF

 

[Gary Tait]

JosephKK <joseph_barrett@sbcglobal.net> wrote in news:1BAPi.7909$6p6.3126
@newssvr25.news.prodigy.net:

While i have not see one, there is nothing that prevents it
technologically.

For a $40 box, it won't be a blik digital to analog convertor.

 

[Michael A. Terrell]

Michael Press wrote:

In article <470F511B.DF279A05@earthlink.net>,
"Michael A. Terrell" <mike.terrell@earthlink.net
wrote:

465C7552.DFCAE84C%40earthlink.net

Not found on my server,
and not found by the Google Message-ID
look up widget.

--
Michael Press

It is a group of photos from our Veteran's park earlier this year.
It was posted to news:alt.binaries.schematics.electronic and
news:alt.binaries.pictures.radio

Subject:
Only in America - Memorial Day photos! 766 KB
Date:
Tue, 29 May 2007 18:47:39 GMT
From:
"Michael A. Terrell" <mike.terrell@earthlink.net>

It is still on the Supernews servers, but I put it up as a temporary
web page until I launch my new website.


http://home.earthlink.net/~fay.terrell/Memorial-day-2007.html

These are reduced images, because of the 10 MB limit for that website.



--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Ross Herbert]

On Tue, 9 Oct 2007 16:38:19 -0400, "robb" <some@where.on.net> wrote:

Is it necesary to repair lifted traces/pads ?

its actually a pad at the end of a trace to mount a wire/pin
connection to another board (not a hole)

if one does need to repair then how does one ree-glue or repair
a lifted trace/pad ?

thanks for any help,
robb

Usually, a lifted pad will not withstand the heat from a soldering
iron when using adhesives such as cyanoacrylate and I have not found
this method to be all that successful. The best way is to fit a swaged
thru-hole eyelet in place of the pad and then run a length of small
gauge wire (kynar wire-wrap wire or similar) from the eyelet back to
the pcb track which noramlly goes to that pad. The advantage of this
method is that the eyelet will support a thru-hole component lead with
good strength.

You can get a PCB repair kit eg.
http://www.solder.net/PCB/pcb_repairkit.asp
http://www.intertronics.co.uk/products/crc2012100.htm

but these won't be cheap.

If you can find a supplier for the eyelets themselves then you can
make do.

 

[Michael Black]

billcalley (billcalley@yahoo.com) writes:

Hi All,

I keep reading that the high-gain front-end stages of a microwave
receiver almost completely sets the entire radio's NF and sensitivity,
and that the following stages (the I.F.) have little effect except to
amplify the signal and the noise equally to a higher amplitude for the
radio's detector. This doesn't make complete sense to me, because the
I.F. would have a HUGE effect on the receiver's signal-to-noise ratio,
and therefore its sensitivity, if we simply narrowed the IF's
bandwidth down from, let's say, 1MHz to 1kHz!!

All an amplifier can do is amplify what's at its input. Whatever the
signal is in reference to the noise, that ratio will remain at the output,
even though the actual voltage level will be higher at the output of
the amplifier compared with the input.

To use a broad example, 1v of noise and 0.1v of signal at an amplifier's
input will mean 10v of noise and 1v of signal at the the output if
the gain is ten. You haven't altered the ratio, just made everything
louder.

It's like turning up the volume on a hearing aid to hear the person
next to you, but which also amplifies the other sounds in the room that
were already stronger than the person; you haven't actually fixed the problem
because the problem was that the person was weaker than the surrounding
sounds.

So if you have a first stage that adds noise to the mix, noise that
will help to mask the desired signal, then you've made things worse.
Forever down the signal chain, there is nothing you can do to fix
the problem, because once that noise is added, any later amplification
amplifies it along with the desired signal. If that stage in
the broad example generated 1v of noise, that equals the level of
the desired signal, and thus has made the situation worse.

So you want to get that signal up fast without adding any noise, or
at least as little as possible. So for low level microphones, you'll
often see a transformer to boost the signal, because it will introduce
less noise than an active stage.

A low noise first rf stage will indeed set the stage. It will
amplify the incoming signal (and the background noise equally) but will
add little of its own noise to mask the signal. If it's not low noise,
then any incoming signal has to be above a certain level to stay
above that noise.

There is background noise picked up by the antenna along with the
desired signal. That level varies with frequency, becoming more
significant the higher up you go. You can't do anything about
that, it's part of basic communication (well you can, but that's
another story). But you can work at making sure as little noise as
possible is added to the mix.

Later stages don't matter, because the signal is stronger
and the noise generated by later stages will not have the same impact.
So that previous broad example, 10v of noise and 1volt of signal out
of the first stage, the second stage will amplify that by ten again,
so its output is 100v of noise (I said that was a broad example) and
10volts of signal, but if the stage adds 1 volt of noise
that 1v is now 1/10th the level of the desired signal, when before
it was stronger than the desired signal.

Michael

 

[Steve]

"billcalley" <billcalley@yahoo.com> wrote in message
news:1193180277.682973.141980@e9g2000prf.googlegroups.com...

On Oct 23, 3:12 pm, Mark <makol...@yahoo.com> wrote:
On Oct 23, 4:36 am, billcalley <billcal...@yahoo.com> wrote:





On Oct 22, 11:17 pm, et...@FreeNet.Carleton.CA (Michael Black) wrote:

billcalley (billcal...@yahoo.com) writes:
Hi All,

I keep reading that the high-gain front-end stages of a
microwave
receiver almost completely sets the entire radio's NF and
sensitivity,
and that the following stages (the I.F.) have little effect except
to
amplify the signal and the noise equally to a higher amplitude for
the
radio's detector. This doesn't make complete sense to me, because
the
I.F. would have a HUGE effect on the receiver's signal-to-noise
ratio,
and therefore its sensitivity, if we simply narrowed the IF's
bandwidth down from, let's say, 1MHz to 1kHz!!

All an amplifier can do is amplify what's at its input. Whatever the
signal is in reference to the noise, that ratio will remain at the
output,
even though the actual voltage level will be higher at the output of
the amplifier compared with the input.

To use a broad example, 1v of noise and 0.1v of signal at an
amplifier's
input will mean 10v of noise and 1v of signal at the the output if
the gain is ten. You haven't altered the ratio, just made everything
louder.

It's like turning up the volume on a hearing aid to hear the person
next to you, but which also amplifies the other sounds in the room
that
were already stronger than the person; you haven't actually fixed the
problem
because the problem was that the person was weaker than the
surrounding
sounds.

So if you have a first stage that adds noise to the mix, noise that
will help to mask the desired signal, then you've made things worse.
Forever down the signal chain, there is nothing you can do to fix
the problem, because once that noise is added, any later
amplification
amplifies it along with the desired signal. If that stage in
the broad example generated 1v of noise, that equals the level of
the desired signal, and thus has made the situation worse.

So you want to get that signal up fast without adding any noise, or
at least as little as possible. So for low level microphones, you'll
often see a transformer to boost the signal, because it will
introduce
less noise than an active stage.

A low noise first rf stage will indeed set the stage. It will
amplify the incoming signal (and the background noise equally) but
will
add little of its own noise to mask the signal. If it's not low
noise,
then any incoming signal has to be above a certain level to stay
above that noise.

There is background noise picked up by the antenna along with the
desired signal. That level varies with frequency, becoming more
significant the higher up you go. You can't do anything about
that, it's part of basic communication (well you can, but that's
another story). But you can work at making sure as little noise as
possible is added to the mix.

Later stages don't matter, because the signal is stronger
and the noise generated by later stages will not have the same
impact.
So that previous broad example, 10v of noise and 1volt of signal out
of the first stage, the second stage will amplify that by ten again,
so its output is 100v of noise (I said that was a broad example) and
10volts of signal, but if the stage adds 1 volt of noise
that 1v is now 1/10th the level of the desired signal, when before
it was stronger than the desired signal.

Michael

Thanks Tom, Tim, Phil, and Michael for some great answers!

I guess I need time to digest all this. But what I still don't
get -- just taking Michael's terrific response as a good example -- is
while I know that the receiver's front-end sets the ratio between the
input signal and the receiver's noise, and that this S/N ratio cannot
then be improved by the receiver's I.F. *amplification* stages, why
can't the receiver's I.F. *filter* stages simply passband filter out
most of that wideband input noise to improve the receiver's SNR, which
should then improve the sensitivity of the receiver? That's the part
that still has me stumped...

Thanks All,

-Bill- Hide quoted text -

- Show quoted text -

another way to think of it is that the desried input signal has a
power DENSITY, i.e. power per Hz BW. and the front end ciruicts have
a noise DENSITY, i.e. noise power per Hz that is determined by the
noise figure. Then when the noise and signl go therough the IF
filter, the IF filter sets the BW. If the signal is very narrow, the
filter can be very narrow and will let in only the minimum possible
amount of noise. Both the noise figure and IF bandwidth are important
in determining sensitivity. But the IF BW cannot be less then the
desired signal BW. And the Noise figure can't be less than 0 dB.

I think one of the key concepts you may be missing is that even the
antenna picks up noise with the signal so there is a limit to the
acheivable sensitivity even if you had a "perfect" receiver. A
perfect receiver would have a 0 dB noise figure. That does not mean
there is NO noise, it means there is no EXTRA noise beyond that which
the antenna picks up.
The lowest noise floor for space communicarions is the 3degK floor.
For Earth comm its room temperature. The "perfect" receiver also has a
BW no wider than it needs to be to pass the desired signal but it must
be wide enough to pass the signal and therefore also passes that
amount of noise.

Mark- Hide quoted text -

- Show quoted text -


Thanks a lot guys. I think I understand all this now (at least I hope
I do!):

1. If we can decrease the receiver's NF *or* bandwidth (which will
decrease the added noise levels), then we will improve our SNR, and
therefore our sensitivity.

2. The NF dominates microwave receiver designs because that is
normally all we will have any control over when we are given the SNR/
BW/modulation that will be used in the system.

3. Since it is measured at a single spot frequency of 1Hz, NF itself
is completely independent of bandwidth.

4. After the receiver's high gain frontend receives the transmitted RF
signal-with-noise, and then adds its own frontend circuit noise, the
I.F. stages will only be able to, at best, maintain this same signal-
to-noise ratio as set by the frontend. No improvement in SNR will be
possible, since the I.F.'s bandwidth will be "set in stone" for the
specific modulation in use, and cannot be less wide than the
modulation itself. (Therefore, when the receiver's bandwidth is
fixed, then the system NF is directly related to the receiver's
sensitivity).

5. I guess I will logically have to assume that the calculation for
receiver sensitivity, -174+NF+10log(BW)+SNRmin, must take for granted
that the receiver's I.F. gain will be high enough to increase the
received signal power enough to properly drive the detector (even at
the lowest RF input signal levels), since gain is not part of this
sensitivity equation... why it is not, I have no idea!

Thanks for all of the unbelievably helpful responses!

-Bill

Rick H pointed out that my equations omitted gain as an additional term.
Sorry for the error. You are correct to expect gain to be in there.

Steve

 

[DJ Delorie]

"robb" <some@where.on.net> writes:

there is a 36 Ohm 1/4 watt resistor ( orng blu blk gold )
between (inline with) the 32V supply volts to a Vcc2 pin on an
IC, what is reason to use this setup and could it be another
mistake made by previous repairer ?

It creates an RC low-pass filter to smooth out the power even more
than just a capacitor can do. I do something similar on chips that
are especially sensitive to supply ripple.

 

[billcalley]

On Oct 25, 12:21 am, JosephKK <joseph_barr...@sbcglobal.net> wrote:

billcalley billcal...@yahoo.com posted to sci.electronics.design:





On Oct 23, 3:12 pm, Mark <makol...@yahoo.com> wrote:
On Oct 23, 4:36 am, billcalley <billcal...@yahoo.com> wrote:

On Oct 22, 11:17 pm, et...@FreeNet.Carleton.CA (Michael Black)
wrote:

billcalley (billcal...@yahoo.com) writes:
Hi All,

I keep reading that the high-gain front-end stages of a
microwave
receiver almost completely sets the entire radio's NF and
sensitivity, and that the following stages (the I.F.) have
little effect except to amplify the signal and the noise
equally to a higher amplitude for the
radio's detector. This doesn't make complete sense to me,
because the I.F. would have a HUGE effect on the receiver's
signal-to-noise ratio, and therefore its sensitivity, if we
simply narrowed the IF's bandwidth down from, let's say, 1MHz
to 1kHz!!

All an amplifier can do is amplify what's at its input.
Whatever the signal is in reference to the noise, that ratio
will remain at the output, even though the actual voltage level
will be higher at the output of the amplifier compared with the
input.

To use a broad example, 1v of noise and 0.1v of signal at an
amplifier's input will mean 10v of noise and 1v of signal at
the the output if
the gain is ten. You haven't altered the ratio, just made
everything louder.

It's like turning up the volume on a hearing aid to hear the
person next to you, but which also amplifies the other sounds
in the room that were already stronger than the person; you
haven't actually fixed the problem because the problem was that
the person was weaker than the surrounding sounds.

So if you have a first stage that adds noise to the mix, noise
that will help to mask the desired signal, then you've made
things worse. Forever down the signal chain, there is nothing
you can do to fix the problem, because once that noise is
added, any later amplification
amplifies it along with the desired signal. If that stage in
the broad example generated 1v of noise, that equals the level
of the desired signal, and thus has made the situation worse.

So you want to get that signal up fast without adding any
noise, or
at least as little as possible. So for low level microphones,
you'll often see a transformer to boost the signal, because it
will introduce less noise than an active stage.

A low noise first rf stage will indeed set the stage. It will
amplify the incoming signal (and the background noise equally)
but will
add little of its own noise to mask the signal. If it's not
low noise, then any incoming signal has to be above a certain
level to stay above that noise.

There is background noise picked up by the antenna along with
the
desired signal. That level varies with frequency, becoming
more
significant the higher up you go. You can't do anything about
that, it's part of basic communication (well you can, but
that's another story). But you can work at making sure as
little noise as possible is added to the mix.

Later stages don't matter, because the signal is stronger
and the noise generated by later stages will not have the same
impact. So that previous broad example, 10v of noise and 1volt
of signal out of the first stage, the second stage will amplify
that by ten again, so its output is 100v of noise (I said that
was a broad example) and 10volts of signal, but if the stage
adds 1 volt of noise that 1v is now 1/10th the level of the
desired signal, when before it was stronger than the desired
signal.

Michael

Thanks Tom, Tim, Phil, and Michael for some great answers!

I guess I need time to digest all this. But what I still
don't
get -- just taking Michael's terrific response as a good example
-- is while I know that the receiver's front-end sets the ratio
between the input signal and the receiver's noise, and that this
S/N ratio cannot then be improved by the receiver's I.F.
*amplification* stages, why can't the receiver's I.F. *filter*
stages simply passband filter out most of that wideband input
noise to improve the receiver's SNR, which
should then improve the sensitivity of the receiver? That's the
part that still has me stumped...

Thanks All,

-Bill- Hide quoted text -

- Show quoted text -

another way to think of it is that the desried input signal has a
power DENSITY, i.e. power per Hz BW. and the front end ciruicts
have a noise DENSITY, i.e. noise power per Hz that is determined by
the
noise figure. Then when the noise and signl go therough the IF
filter, the IF filter sets the BW. If the signal is very narrow,
the filter can be very narrow and will let in only the minimum
possible
amount of noise. Both the noise figure and IF bandwidth are
important
in determining sensitivity. But the IF BW cannot be less then the
desired signal BW. And the Noise figure can't be less than 0 dB.

I think one of the key concepts you may be missing is that even
the
antenna picks up noise with the signal so there is a limit to the
acheivable sensitivity even if you had a "perfect" receiver. A
perfect receiver would have a 0 dB noise figure. That does not
mean there is NO noise, it means there is no EXTRA noise beyond
that which the antenna picks up.
The lowest noise floor for space communicarions is the 3degK floor.
For Earth comm its room temperature. The "perfect" receiver also
has a BW no wider than it needs to be to pass the desired signal
but it must be wide enough to pass the signal and therefore also
passes that amount of noise.

Mark- Hide quoted text -

- Show quoted text -

Thanks a lot guys. I think I understand all this now (at least I
hope I do!):

1. If we can decrease the receiver's NF *or* bandwidth (which will
decrease the added noise levels), then we will improve our SNR, and
therefore our sensitivity.

2. The NF dominates microwave receiver designs because that is
normally all we will have any control over when we are given the
SNR/ BW/modulation that will be used in the system.

3. Since it is measured at a single spot frequency of 1Hz, NF
itself is completely independent of bandwidth.

Er, not quite. It is a tradeoff bewteen bandwidth versus noise versus
datarate. Please see Shannon's law



4. After the receiver's high gain frontend receives the transmitted
RF signal-with-noise, and then adds its own frontend circuit noise,
the I.F. stages will only be able to, at best, maintain this same
signal-
to-noise ratio as set by the frontend. No improvement in SNR will
be possible, since the I.F.'s bandwidth will be "set in stone" for
the specific modulation in use, and cannot be less wide than the
modulation itself. (Therefore, when the receiver's bandwidth is
fixed, then the system NF is directly related to the receiver's
sensitivity).

Except that there are dynamically programmable transmitter receiver
pairs that adapt bandwidth and datarate to manage current noise
environment. Space exploration vehicles like the voyager do this.
Newer software defined radios also do things like this.



5. I guess I will logically have to assume that the calculation for
receiver sensitivity, -174+NF+10log(BW)+SNRmin, must take for
granted that the receiver's I.F. gain will be high enough to
increase the received signal power enough to properly drive the
detector (even at the lowest RF input signal levels), since gain is
not part of this sensitivity equation... why it is not, I have no
idea!

Thanks for all of the unbelievably helpful responses!

-Bill

Please note that the current IF bandwidth sets the measurement
bandwidth for the S/N measurement. This property is called
selectivity. As discussed for 3. and 4. above this impacts S/N for
the total receiver.- Hide quoted text -

- Show quoted text -

-------------------

ME:

3. Since it is measured at a single spot frequency of 1Hz, NF
itself is completely independent of bandwidth.

JOE:
"Er, not quite. It is a tradeoff bewteen bandwidth versus noise
versus
datarate. Please see Shannon's law."
------------------
Thanks for the further info Joe. But now my head REALLY hurts!
I had no idea that a receiver's NF could change with a change in
bandwidth and/or data rate. I think I'm going to have to hit the
books yet again!!

Best regards,

-Bill