Jerry Stuckle wrote:
I never said that, either. But like the troll you are, you can't get
anything straight.

Your memory is failing Jerry.

Jerry Stuckle wrote in news:lrgjen$ao4$1@dont-
email.me:

I know EXACTLY what a picowatt is. And I also know what portable
receivers are capable of. Sure, if you feed a picowatt directly into
the front end of a receiver, a good receiver will hear the signal. But
what field strength do you need at the antenna for a portable FM
receiver to hear that signal? And most of your inexpensive portable
receivers will not hear much of a signal (if at all), even if you do
feed a picowatt directly into the front end (not that you can without
major surgery on the receiver).


Which begs the question of whether that front end is a high resistance input
or not. I don't know if it's 50R, 75R, or whatever, but I do know that if
it's a high resistance then talk of power means nothing, it needs spelling
out in volts.

I think one reason this thread got so long is that context is everything, and
people (including me) didn't say enough about it from the off. Cranking the
numbers means little in a case where a smarter question might well be 'how
long is a pice of string?'.

What is helping me a lot here is the direct accounting of people's experience
with various powers, in specific buildings and such, using specific
antennas.. Thanks for those, they give me the quickest grasp of the scale I
need to work with.

Jerry Stuckle wrote in news:lrgjen$ao4$1@dont-
email.me:

Sure, but you're also talking a 5Khz deviation (actually about 12Khz
bandwidth). Commercial FM uses 75Khz deviation (typically around 180Khz
bandwidth). A huge difference.


Does that degrade the signal quality compared a really good FM broadcast? (If
it does so a lot, it amazes me how little people are willing to accept from
their portable MP3's and DAB radios, but that's another matter...) Whatever I
end up doing, I want to avoid things like catching the FM, truning to audio,
rebroadcasting with all the losses involved, then back to audio yet again!
Sounds to me like a disaster, I'd likely end up with bigger problems than I'm
trying to fix now.

Jerry Stuckle wrote in news:lrglvk$ub7$1@dont-
email.me:

And as a matter of fact, I train the people who work with me. I've been
in the electronics business for over 40 years, working on everything
from $40 dollar CB sets to multi-million dollar computer mainframes. I
doubt you've even touched a soldering iron.


Sorry about the tad bit of schadenfreude I'm getting here, but you two remind
me of the Lone Gunmen in that amazing X-Files episode, just before Signy
Coleman showed up. I think we need Signy Coleman in here.

On 01 Aug 2014 17:48:22 GMT, Rob wrote:

Oh yes I do! dBm, meaning dB over a milliwatt.
And in the cable industry, dBuV, meaning dB over a microvolt.

Also dBmV for cable and OTA TV (into 75 ohms):
http://www.tselectronic.com/tech_notes/db.php

For FM tuners, it's dBf (dB over 1 femtowatt) usually into 300 ohms
but sometimes into 75 ohms:
http://mail.audiokarma.net/forums/showthread.php?t=29525
http://community.crutchfield.com/car_audio_and_video/f/27/receivers/t/3088/fm-sensitivity#13128

Plenty more to choose from:
http://en.wikipedia.org/wiki/Decibel#Suffixes_and_reference_values

In America, where everything is bigger, probably dB over a millivolt,
but not expressed as dBm!

Bigger is better. FCC broadcast EIRP specs are most often expressed
in dBW (dB over 1 watt) but sometimes dBk (dB over 1 kilowatt).

My own version for data sheets and press releases is dBr (dB better
than reality).


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

Jeff Liebermann wrote in
:

For FM tuners, it's dBf (dB over 1 femtowatt) usually into 300 ohms
but sometimes into 75 ohms:


The Tecsun PL-390 uses dBµ (micro). Most of this is new to me, but I read
that Tecsun's dB referencing makes them useful to EMI and RFI engineers, and
one related radio beign especially useful for tracing noise, having a plug-in
rotatable magnetic loop antenna as well as a long(ish) whip.

At this point pouring scorn or praise on Tecsun radios is interesting to me
either way, because for the first time in a while I have found a radio I care
enough not to be indifferent to it.

On 8/1/2014 2:58 PM, Lostgallifreyan wrote:
Jerry Stuckle wrote in news:lrgjen$ao4$1@dont-
email.me:

Sure, but you're also talking a 5Khz deviation (actually about 12Khz
bandwidth). Commercial FM uses 75Khz deviation (typically around 180Khz
bandwidth). A huge difference.


Does that degrade the signal quality compared a really good FM broadcast? (If
it does so a lot, it amazes me how little people are willing to accept from
their portable MP3's and DAB radios, but that's another matter...) Whatever I
end up doing, I want to avoid things like catching the FM, truning to audio,
rebroadcasting with all the losses involved, then back to audio yet again!
Sounds to me like a disaster, I'd likely end up with bigger problems than I'm
trying to fix now.


I won't get into the math here, but due to the sidebands (yes, FM has
sidebands, also - the number and strength of the sidebands is
proportional to the deviation and modulating frequency), frequency
response of the modulated signal is proportional to the bandwidth of the
channel and deviation. A 5 kHz deviation can theoretically pass up to
about 5Khz of audio, but in practice it's limited to about 3 kHz (to
avoid adjacent channel interference). This is fine for voice, but does
not work well for music (try listening to music on the AM band, for
instance).

A 75 kHz deviation can easily be modulated at 15 kHz, providing for
better quality music.

Back in the late 60's and early 70's, there were some hams on 2 meters
running 15 kHz deviation. It's amazing how much better the audio
quality was, even with just voice. But that's back when there were few
repeaters; I'm glad it didn't catch on. Here in the Washington, D.C.
area, it's impossible to get coordination for a 2 meter repeater and
difficult on 440 Mhz. I can't imaging what it would be like with 1/3 of
the channels available!

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

On 8/1/2014 1:58 PM, Lostgallifreyan wrote:
Jerry Stuckle wrote in news:lrgjen$ao4$1@dont-
email.me:

Sure, but you're also talking a 5Khz deviation (actually about 12Khz
bandwidth). Commercial FM uses 75Khz deviation (typically around 180Khz
bandwidth). A huge difference.


Does that degrade the signal quality compared a really good FM broadcast? (If
it does so a lot, it amazes me how little people are willing to accept from
their portable MP3's and DAB radios, but that's another matter...) Whatever I
end up doing, I want to avoid things like catching the FM, truning to audio,
rebroadcasting with all the losses involved, then back to audio yet again!
Sounds to me like a disaster, I'd likely end up with bigger problems than I'm
trying to fix now.

Not really a disaster, I do it daily. The drawback is, if I want to
change stations, I need to run to my bedroom where the internet radio is
and push buttons. One of these days, I'll breakdown and get myself a
portable internet radio.
Mikek

PS, I'll bet both of you stations stream on the internet. If you
have wifi, that will eliminate your noise problem.
Mikek

---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com

Jerry Stuckle wrote:
I won't get into the math here, but due to the sidebands (yes, FM has
sidebands, also - the number and strength of the sidebands is
proportional to the deviation and modulating frequency), frequency
response of the modulated signal is proportional to the bandwidth of the
channel and deviation. A 5 kHz deviation can theoretically pass up to
about 5Khz of audio, but in practice it's limited to about 3 kHz (to
avoid adjacent channel interference). This is fine for voice, but does
not work well for music (try listening to music on the AM band, for
instance).

A 75 kHz deviation can easily be modulated at 15 kHz, providing for
better quality music.

You keep amazing me, Jerry! Keep on going, I need some fun going into
the weekend!

Jerry Stuckle wrote in news:lrgvk8$5er$1@dont-
email.me:

I won't get into the math here, but due to the sidebands (yes, FM has
sidebands, also - the number and strength of the sidebands is
proportional to the deviation and modulating frequency), frequency
response of the modulated signal is proportional to the bandwidth of the
channel and deviation. A 5 kHz deviation can theoretically pass up to
about 5Khz of audio, but in practice it's limited to about 3 kHz (to
avoid adjacent channel interference). This is fine for voice, but does
not work well for music (try listening to music on the AM band, for
instance).


Thankyou, that's great help. I'll have to be careful about buying one of
those widgets... I did suspect that something that had a narrower bandwidth
would reduce frequency response (based on playing with the AR-3000 on
narrowband FM). That's one reason I was wondering about boosting the
broadcast signal directly for low level rebroadcast in a building, to keep
what fidelity I can as best possible.