David wrote:
On 28 Nov 2005 08:59:00 -0800, wrote:


David wrote:

Up until about 30 years ago, almost every radio station on the air was
feeding audio to their transmitters via unshielded wire phone lines.
No buzz.

Optoisolators as suicide devices.
+++++++++++++++++++++++++++++++++++++
Now I get it.
I am trying to recieve signals near or at the noise floor which is set
first by the local QRN. there are as amny different levels as
refference
books, so I will use John Doty's figures which are wildly optimistic in
my
experience. I will post links to my refferences so others may follow
them.

From:http://anarc.org/naswa/badx/antennas/grounding.html

"According to "Reference Data for Radio Engineers"
(Sams, 1975), the wintertime level of natural noise in
my area at 10 MHz should be about 32 dB above the
thermal reference level: this would produce a noise
floor of -104 dBm in this bandwidth with a perfectly
efficient antenna. "

A very handy chart that converts dBm to Volts can be found at:
http://www.minicircuits.com/dg03-110.pdf

Sherwood Engineeringhttp://www.sherweng.com/table.html gives
the R2000 noise floor as -130dB in the SSB Mode.

So I am trying to capture signals in the range of -130dB=0.058uV to
-119dB= 0.251uV.

Your refference to audio being delivered over balanced line is at 0dBm
(nominal) for a voltage of 0.775V. (*600Ohm) or 0.225 at 50 Ohms.

There is more then a slight voltage level diffference.

Can we agree that:
Adding 1uV of noise to a 1uV(-107dBm) signal will significantly degrade
the
SN ratio.

Adding 1uV of noise to a 0dBm 50 or 600 ohm line will result in
minimal,
as in I would like to see it measured, degradation of the overall SN
ratio.

And I bet you won't try to run the output of a moving coil phono
cartridge
over ~70' of balanced audio line.

In a uV world I will stick to single ended, unbalanced,
coaxial/shielded cable
interconnects. If you are lucky enough to deal with signals in the
0.1V range
then twisted or parallel cable will work just fine.

Terry

On 28 Nov 2005 10:47:37 -0800, wrote:


David wrote:
On 28 Nov 2005 08:59:00 -0800, wrote:


And I bet you won't try to run the output of a moving coil phono
cartridge
over ~70' of balanced audio line.

In a uV world I will stick to single ended, unbalanced,
coaxial/shielded cable
interconnects. If you are lucky enough to deal with signals in the
0.1V range
then twisted or parallel cable will work just fine.

Terry

You can't send a MC phono signal 70' on co-ax either.

David wrote:
You can't send a MC phono signal 70' on co-ax either.
++++++++++++++++++++++++++++++++++
You mihgt find the story
at:http://broadcastengineering.com/mag/broadcasting_future_video_utp/
intersing.
It discribes using UTP (unshielded twisted pair) for video.


Mention is made of crosstalk.
For CAT5 cable 53dB of isolation at 4.2MHZ is acheived.
CAT6 gies 63dB at 4.2MHz.
Crostalk increases with frequency.

Another good refference that shows "failure" modes for twisted pair:
http://www.extron.com/technology/archive.asp?id=utptechnology

I have lost my bookmarks to a couple of links for coax cable "leakage"
and crosstalk specificitions. I will have to pull them from a backup
later this
week.

Why do you suppose that 99.99% of all CATV operations use coax for
the coper connections instead of twisted pair? Twisted pair is less
expensive,
so if it was "as good" as coax I suspect they would switch to it.

It has never been my contention that twisted and parallel balanced
pairs
have no place in the world. I just accept that while they do have many
usefull applicaitons, low level RF distribution isn't 'one of them.

By the way we are rolling out some component HDTV in house distribution
with CAT6 UTP. Looks pretty darn good after a 200' run. The CEO wanted
this and it was much cheaper to pull in good CAT6 then 4 coax cables.

Terry

On 29 Nov 2005 06:52:04 -0800, wrote:


David wrote:
You can't send a MC phono signal 70' on co-ax either.
++++++++++++++++++++++++++++++++++
You mihgt find the story
at:http://broadcastengineering.com/mag/broadcasting_future_video_utp/
intersing.
It discribes using UTP (unshielded twisted pair) for video.


Mention is made of crosstalk.
For CAT5 cable 53dB of isolation at 4.2MHZ is acheived.
CAT6 gies 63dB at 4.2MHz.
Crostalk increases with frequency.

Another good refference that shows "failure" modes for twisted pair:
http://www.extron.com/technology/archive.asp?id=utptechnology

I have lost my bookmarks to a couple of links for coax cable "leakage"
and crosstalk specificitions. I will have to pull them from a backup
later this
week.

Why do you suppose that 99.99% of all CATV operations use coax for
the coper connections instead of twisted pair? Twisted pair is less
expensive,
so if it was "as good" as coax I suspect they would switch to it.

It has never been my contention that twisted and parallel balanced
pairs
have no place in the world. I just accept that while they do have many
usefull applicaitons, low level RF distribution isn't 'one of them.

By the way we are rolling out some component HDTV in house distribution
with CAT6 UTP. Looks pretty darn good after a 200' run. The CEO wanted
this and it was much cheaper to pull in good CAT6 then 4 coax cables.

Terry

I think the context is shortwave radio.

David wrote:

I think the context is shortwave radio.
+++++++++++++++++
I was tryihng to show the isolation of good quality UTP is around 63dB.
63dB is very good for a 1V video(RF from 0~5MHz), not so very good
for antena supplied RF.

Not near quite enough for my location.

Feel free to use any cable you wish.

I was trying to help newbies avoid the mistakes that I had already
made.

Terry

On 29 Nov 2005 07:34:07 -0800, wrote:


David wrote:

I think the context is shortwave radio.
+++++++++++++++++
I was tryihng to show the isolation of good quality UTP is around 63dB.
63dB is very good for a 1V video(RF from 0~5MHz), not so very good
for antena supplied RF.

Not near quite enough for my location.

Feel free to use any cable you wish.

I was trying to help newbies avoid the mistakes that I had already
made.

Terry

You lose me with all those numbers. I just look for symmetrical
bowties.

David wrote:
You lose me with all those numbers. I just look for symmetrical
bowties.
++++++++++++++++++++++++
Sorry I thought this news group was about Shortwave, receivers and
antennas.

A special sub-part of the hobby is antenna and feedline inter-reaction
and how to get the strongest, cleanest RF signal from the antenna to
the
receiver.

I had hoped that we were having a somewhat serious fact based
conversation.

Sad to see how wrong I was.

Anyway, you are the very first person I have killfiled.
I had wrongly assumed that inpiste of your repeated OT politcal
comments
that you were a serious SWL. Sorry to waste our time.

Terry