On Sat, 13 Dec 2003 20:50:47 +0000,
said...
On Sat, 13 Dec 2003 11:58:39 GMT, (John Crighton)
wrote:

Hello Paul,
have a look here,
http://www.alphalink.com.au/~parkerp/noapr97.htm

Hi John,

Always nice to have your input. I did actually come across the circuit
you point to above during my search of the Web, but rejected it as
probably not being sensitive enough. I thought I could maybe do a
little better by having a stab at it myself - with the assistance of
LTSpice of course!
Many thanks to the other respondents to this thread, but no one seems
to have been able to SWAG the actual likely signal level in mV or uV.

Because you didn't provide enough info, dude. That much could've
been inferred from the eqs I gave you. And you asked for "field
strength" in the wrong units. it's V/m or mV/m or uV/m. Hell I'd
give it to you in kV/m if you wanted. You'll never know what it is
if you can't determine the voltage present at the meter antenna's
terminals and it should be a dipole.

So I thought what the hell and built my original design from
yesterday. I've just finished it and am surprised and pleased to
report that it worked fine first time! The sensitivity is a little on
the low side, but *remarkably* close to what I'd set out to achieve.
With a 100mW transmitter some 4 feet away, I can tune for 40Mhz and

clues. so you're still on that project.

tweak the sensitivity and get a peak at S9 on the CB radio type signal
meter I'm using for this purpose.

! Adjust the meter to get the answer you want. Ok.

That would have done me just fine
had you not suggested making the measurements from some greater
distance! So I either live with it as it is and use is at say 6 feet
away or stick in an extra voltage amplification stage for 'far field'
testing (do I *really* need this for my purposes?)

lessee 40MHz is 7.5m lambda so the far field starts at around 3.75
meter per the eq I gave you for that.

I think that 1st eq I gave was for a vertical and it's ****ing with
me.

I'll use a distance of 6m.

since you seem to want to know power try the path loss eq

32.45 + 20log(f) + 20log(d) = 20db

f in MHz, d in km

10log(Pr/Pt) = -20dB

but EIRP = Pt.G

G is antenna gain and you didn't give that info.

so I'll use G = 1

Pr = 1mW

Pr.G = E^2/Z voltage at input to Rx

G is Rx antenna gain, I'll use 1

E = 224 mV rms

Let me know if I f'd up anything. Lots of distractions and I'm
trying to hurry and do other work.

Mike

Buy 'em books, send 'em to school, and all they want to do is eat
the teachers




Incidentally, you were dead right about the tea-tray idea. It turns
out the grounded areas of the PCB really need to be earthed to a
decent, proper ground/earth rod via the mains supply. It makes a
*huge* difference to the sensitivity and drastically reduces the
annoying effects of hand capacitance when tuning and tweaking.
I'll post the schematic I arrived at later under another thread and
maybe someone can suggest a few mods that might up the sens. without a
complete redesign. Is it really that important to make the
measurements from 10 feet or more away?

In (rec.radio.amateur.homebrew), Michael A. Terrell wrote:
Scott Stephens wrote:

Scott

**********************************

DIY Piezo-Gyro, PCB Drill Bot & More Soon!

http://home.comcast.net/~scottxs/

**********************************

Your web site is very hard to read with the dark blue background and
black text. A lot of people have vision problems, and can not read this
color combination.

On my system (FreeBSD) with the Mozilla FireBird browser, the text
and images are in light-colored windows inside the dark background,
and it's not at all difficult to read. The Netscape 4.6 browser on
the same system _does_ put the black text directly on the dark-blue
background, and it is decidedly unpleasant.

A newer browser might be nice, but it also would be good if web page
designers built pages with older code in mind.

It _definitely_ has some cool stuff. Thanks, Scott!

--
Comparing Knuth with O'Reilly books is like comparing
Unix with Windows.
-- Abigail, in the Monastery

In (rec.radio.amateur.homebrew), Michael A. Terrell wrote:
Scott Stephens wrote:

Scott

**********************************

DIY Piezo-Gyro, PCB Drill Bot & More Soon!

http://home.comcast.net/~scottxs/

**********************************

Your web site is very hard to read with the dark blue background and
black text. A lot of people have vision problems, and can not read this
color combination.

On my system (FreeBSD) with the Mozilla FireBird browser, the text
and images are in light-colored windows inside the dark background,
and it's not at all difficult to read. The Netscape 4.6 browser on
the same system _does_ put the black text directly on the dark-blue
background, and it is decidedly unpleasant.

A newer browser might be nice, but it also would be good if web page
designers built pages with older code in mind.

It _definitely_ has some cool stuff. Thanks, Scott!

--
Comparing Knuth with O'Reilly books is like comparing
Unix with Windows.
-- Abigail, in the Monastery

It's too bad it isn't that simple.

A 1V/m field doesn't result in one volt at the feedpoint of a perfectly
matched one meter dipole or monopole, and the value it does induce
depends on the quality of the impedance match as well as the fraction of
a wavelength the one meter antenna length represents. And, if one volt
does appear at the feedpoint, it's very unlikely that a simple circuit
will measure it as one volt.

Probably best to stick with your $1.5 kilobuck meter if you really want
to measure field strength.

Roy Lewallen, W7EL

Active8 wrote:
On 13 Dec 2003 03:50:41 -0800, said...

What you are descrbing is a "signal sniffer", not a signal strength meter.


Who are you replying to? Paul did not say Signal Stength Meter, but
the guy you replied to kinda hints at it when he mentions power
level.

I would have to say that my 1GHz Signal Level Meter, which cost
$1500 would be the better than a relative field strength meter, but
if he measures say, 1V with his Tx off and 2V with it on, then
that's 1V and if his Rx antenna is a 1m dipole, that's 1V/m.

Mike

It's too bad it isn't that simple.

A 1V/m field doesn't result in one volt at the feedpoint of a perfectly
matched one meter dipole or monopole, and the value it does induce
depends on the quality of the impedance match as well as the fraction of
a wavelength the one meter antenna length represents. And, if one volt
does appear at the feedpoint, it's very unlikely that a simple circuit
will measure it as one volt.

Probably best to stick with your $1.5 kilobuck meter if you really want
to measure field strength.

Roy Lewallen, W7EL

Active8 wrote:
On 13 Dec 2003 03:50:41 -0800, said...

What you are descrbing is a "signal sniffer", not a signal strength meter.


Who are you replying to? Paul did not say Signal Stength Meter, but
the guy you replied to kinda hints at it when he mentions power
level.

I would have to say that my 1GHz Signal Level Meter, which cost
$1500 would be the better than a relative field strength meter, but
if he measures say, 1V with his Tx off and 2V with it on, then
that's 1V and if his Rx antenna is a 1m dipole, that's 1V/m.

Mike

On Sat, 13 Dec 2003 17:39:27 -0800, said...
It's too bad it isn't that simple.

A 1V/m field doesn't result in one volt at the feedpoint of a perfectly
matched one meter dipole or monopole, and the value it does induce
depends on the quality of the impedance match

you mean antenna to free space, right?

as well as the fraction of
a wavelength the one meter antenna length represents.

amplify, very please. por favor. Refresh my ram.


| E(uV/m) |
V (dBmV) = 20log | --------- / 1000 |
| 0.021f(MHz) |

plus correction for distance (regulations for limits are for
specific measuring distances), etc. I'll mull the above eq over.
Gotta figure out where the .021 came from, but not now. My eyes are
getting fatigued from this 'puter.

And, if one volt
does appear at the feedpoint, it's very unlikely that a simple circuit
will measure it as one volt.

It would have to be calibrated to compensate for the circuit. Maybe
that's why it's called a "relative" field strength meter. Relative
to another signal or no signal


Probably best to stick with your $1.5 kilobuck meter if you really want
to measure field strength.

I don't. He does At least not tonight. But my SLM *will* measure
field strenth using a cheap ass dipole cut to the frequency of
interest with or without an external preamp and do it to the
satisfaction of the FCC, assuming it's calibrated. I even have a
near-field probe, not so cheap. It beats guess work.

I wouldn't expect his sniffer to be real accurate but he did ask
for guesstimates. Started off as "around 4 feet" for a half watter
now we're at 100mW - prob his reference Tx.

BRs,
Mike



Roy Lewallen, W7EL

Active8 wrote:
On 13 Dec 2003 03:50:41 -0800, said...

What you are descrbing is a "signal sniffer", not a signal strength meter.


Who are you replying to? Paul did not say Signal Stength Meter, but
the guy you replied to kinda hints at it when he mentions power
level.

I would have to say that my 1GHz Signal Level Meter, which cost
$1500 would be the better than a relative field strength meter, but
if he measures say, 1V with his Tx off and 2V with it on, then
that's 1V and if his Rx antenna is a 1m dipole, that's 1V/m.

Mike

On Sat, 13 Dec 2003 17:39:27 -0800, said...
It's too bad it isn't that simple.

A 1V/m field doesn't result in one volt at the feedpoint of a perfectly
matched one meter dipole or monopole, and the value it does induce
depends on the quality of the impedance match

you mean antenna to free space, right?

as well as the fraction of
a wavelength the one meter antenna length represents.

amplify, very please. por favor. Refresh my ram.


| E(uV/m) |
V (dBmV) = 20log | --------- / 1000 |
| 0.021f(MHz) |

plus correction for distance (regulations for limits are for
specific measuring distances), etc. I'll mull the above eq over.
Gotta figure out where the .021 came from, but not now. My eyes are
getting fatigued from this 'puter.

And, if one volt
does appear at the feedpoint, it's very unlikely that a simple circuit
will measure it as one volt.

It would have to be calibrated to compensate for the circuit. Maybe
that's why it's called a "relative" field strength meter. Relative
to another signal or no signal


Probably best to stick with your $1.5 kilobuck meter if you really want
to measure field strength.

I don't. He does At least not tonight. But my SLM *will* measure
field strenth using a cheap ass dipole cut to the frequency of
interest with or without an external preamp and do it to the
satisfaction of the FCC, assuming it's calibrated. I even have a
near-field probe, not so cheap. It beats guess work.

I wouldn't expect his sniffer to be real accurate but he did ask
for guesstimates. Started off as "around 4 feet" for a half watter
now we're at 100mW - prob his reference Tx.

BRs,
Mike



Roy Lewallen, W7EL

Active8 wrote:
On 13 Dec 2003 03:50:41 -0800, said...

What you are descrbing is a "signal sniffer", not a signal strength meter.


Who are you replying to? Paul did not say Signal Stength Meter, but
the guy you replied to kinda hints at it when he mentions power
level.

I would have to say that my 1GHz Signal Level Meter, which cost
$1500 would be the better than a relative field strength meter, but
if he measures say, 1V with his Tx off and 2V with it on, then
that's 1V and if his Rx antenna is a 1m dipole, that's 1V/m.

Mike

Mike Andrews wrote:

On my system (FreeBSD) with the Mozilla FireBird browser, the text
and images are in light-colored windows inside the dark background,
and it's not at all difficult to read. The Netscape 4.6 browser on
the same system _does_ put the black text directly on the dark-blue
background, and it is decidedly unpleasant.

A newer browser might be nice, but it also would be good if web page
designers built pages with older code in mind.

It _definitely_ has some cool stuff. Thanks, Scott!

--
Comparing Knuth with O'Reilly books is like comparing
Unix with Windows.
-- Abigail, in the Monastery

I have several other browsers, but I prefer using Netscape 4.79. Some
websites are a royal pain. I recently ran into an electronics
distributor who put their entire website in "Flash". There is no way I
will wait five minutes or more per page to download and run stupid
animation when I am looking for parts. I have seen a bunch of sites with
a white background and a very pale yellow text.


My website isn't perfect, but I but a lot of work into making it easy
to use and I asked for, and used, feedback from members of a couple
newsgroups. You can see it at:
http://home.earthlink.net/~mike.terrell/ I still have a lot of work to
do to the site, but a website is never really finished, is it?
--
11 days!


Michael A. Terrell
Central Florida

Mike Andrews wrote:

On my system (FreeBSD) with the Mozilla FireBird browser, the text
and images are in light-colored windows inside the dark background,
and it's not at all difficult to read. The Netscape 4.6 browser on
the same system _does_ put the black text directly on the dark-blue
background, and it is decidedly unpleasant.

A newer browser might be nice, but it also would be good if web page
designers built pages with older code in mind.

It _definitely_ has some cool stuff. Thanks, Scott!

--
Comparing Knuth with O'Reilly books is like comparing
Unix with Windows.
-- Abigail, in the Monastery

I have several other browsers, but I prefer using Netscape 4.79. Some
websites are a royal pain. I recently ran into an electronics
distributor who put their entire website in "Flash". There is no way I
will wait five minutes or more per page to download and run stupid
animation when I am looking for parts. I have seen a bunch of sites with
a white background and a very pale yellow text.


My website isn't perfect, but I but a lot of work into making it easy
to use and I asked for, and used, feedback from members of a couple
newsgroups. You can see it at:
http://home.earthlink.net/~mike.terrell/ I still have a lot of work to
do to the site, but a website is never really finished, is it?
--
11 days!


Michael A. Terrell
Central Florida

On Sat, 13 Dec 2003 23:59:21 GMT, Active8
,invalid wrote:

clues. so you're still on that project.

Well, it's *related* to "that" project, yes.

tweak the sensitivity and get a peak at S9 on the CB radio type signal
meter I'm using for this purpose.

! Adjust the meter to get the answer you want. Ok.

Yes! I'm only interested in *relative* field strength. That's why I
asked for a "ballpark figure" to be plucked from the air. I think you
may be thinking of some fancy type of instrument like some guy
mentioned he had that cost 1500 bux. These ham-type jobs I'm
interested in cost just pennies to make as they don't need any
absolute standard of accuracy; only a relative indication. You tweak
the meter's sensitivity control to show antenna A of the TX giving
rise to say S5 on the meter. You then change to antenna B and see if
the reading is any higher or lower. It's really as simple as that.

I'll use a distance of 6m.

Noted, thanks.



--

"I expect history will be kind to me, since I intend to write it."
- Winston Churchill