Paul Burridge wrote:

Hi all,

I wanted to build an RF relative field strength meter, so set about
searching on the Web for any existing designs. Those I turned up
weren't particularly impressive, so I decided to start from scratch
and design my own. I've just completed that this afternoon. I've
allowed for 0.25mV input to give rise to FSD on the microammeter.
Question being, however, is that going to be sensitive enough?

Yes. If it's not, either move closer, or add an op amp with
a gain control after the diode(s) & cap. Mine uses 2 gain
controls - 1 on the input to the op amp, and one that sets
the gain of the op amp. A further improvement is the use
of a cheap DPM - no parallax and a wider "full scale" range
with no loss of sensitivity. The downside of the cheap DPM
was the need for 2 9 volt batteries. (I have since built a
small DC-DC converter that occupies the volume of a single
9V battery. That may allow using a single rechargeable
9V to power the converter - but I haven't tried it yet
to be sure that the converter doesn't produce noise that
would be detected by the instrument. The converter does
produce dual 9V fully isolated outputs at at least 10 ma
per output, way more than the instrument needs.)


Does
anyone have any idea what the field strength in microvolts or
millivolts is from a half Watt transmitter at about 6 feet away? I
guess I should have posed this question *before* designing it, but who
among us can honestly say they haven't designed something without
knowing what the spec is? :-)
Anyway, ballpark figures gentlemen, please.

p.
--

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

Mike Andrews wrote:

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.

Mozilla 1.4a doesn't have any problems.

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

Like trying to accommodate fighting parents, having Micro$oft constantly
extending and subverting standards.

It _definitely_ has some cool stuff. Thanks, Scott!

Thanks. Any things you like more than others? When I make time, I plan
on documenting my tinkering with windows html/hta app to md5 sign and
test your pc files, laser-pointer velocimeter and interferometers, PIC
hardware and software for alarm system, and micro-power radar sensors. I
should update the bookmarks and clean all the dead-links too.

--
Scott

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

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

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

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

Mike Andrews wrote:

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.

Mozilla 1.4a doesn't have any problems.

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

Like trying to accommodate fighting parents, having Micro$oft constantly
extending and subverting standards.

It _definitely_ has some cool stuff. Thanks, Scott!

Thanks. Any things you like more than others? When I make time, I plan
on documenting my tinkering with windows html/hta app to md5 sign and
test your pc files, laser-pointer velocimeter and interferometers, PIC
hardware and software for alarm system, and micro-power radar sensors. I
should update the bookmarks and clean all the dead-links too.

--
Scott

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

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

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

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

Paul Burridge wrote:

I'll add that my Optoelectronics handi-counter's fsm bargraph can detect
a few hundred milliwatts at several feet away.

I visualize a radio-field power density being grid-lines painted on a
balloon around a 1/2 wave dipole. As the balloon is blown up, the
grid-line expand, given by 4 pi r^2.

For some good app notes on designing electrically small antennas and
radio link calculations:

Goto -
http://www.rfm.com/corp/apnotes.htm

Checkout:
http://www.rfm.com/corp/appdata/antenna.pdf
http://www.rfm.com/products/tr_des24.pdf

HP (now Agilent) has some app-notes on designing diode detectors, and
has some utility programs that will help you design and calculate
performance. Some I think, in context of RFID reading devices. But they
point out you get a square-law for small signals, which gets nonlinear
for larger signal levels. And what bias the detector diode has on it.


--
Scott

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

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

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

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

Paul Burridge wrote:

I'll add that my Optoelectronics handi-counter's fsm bargraph can detect
a few hundred milliwatts at several feet away.

I visualize a radio-field power density being grid-lines painted on a
balloon around a 1/2 wave dipole. As the balloon is blown up, the
grid-line expand, given by 4 pi r^2.

For some good app notes on designing electrically small antennas and
radio link calculations:

Goto -
http://www.rfm.com/corp/apnotes.htm

Checkout:
http://www.rfm.com/corp/appdata/antenna.pdf
http://www.rfm.com/products/tr_des24.pdf

HP (now Agilent) has some app-notes on designing diode detectors, and
has some utility programs that will help you design and calculate
performance. Some I think, in context of RFID reading devices. But they
point out you get a square-law for small signals, which gets nonlinear
for larger signal levels. And what bias the detector diode has on it.


--
Scott

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

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

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

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

Michael A. Terrell wrote:

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.

Sorry. The next time I update it I'll see if I can find a better color.
I think I noticed that once while I was developing it - I think it is
due to a low-color VGA mode. I spent too long fooling around trying to
develop the fractal-smith chart background (thanks to da GIMP) to mess
with it any further. You can always edit the HTML yourself and change my
background color. Its not like I've got advertisers paying me.

--
Scott

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

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

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

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

Michael A. Terrell wrote:

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.

Sorry. The next time I update it I'll see if I can find a better color.
I think I noticed that once while I was developing it - I think it is
due to a low-color VGA mode. I spent too long fooling around trying to
develop the fractal-smith chart background (thanks to da GIMP) to mess
with it any further. You can always edit the HTML yourself and change my
background color. Its not like I've got advertisers paying me.

--
Scott

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

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

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

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

On Mon, 15 Dec 2003 00:50:09 +0000,
said...
On Sun, 14 Dec 2003 16:47:09 GMT, Active8
,invalid wrote:


I remember the 40MHz part, but I'm not sure what yer up to. Just
curious

You once referred to me as the "battlebots guy" - although I post on
many other aspects of electronic design as well, so that's not
entirely accurate. I trust this jogs your memory. :-)

Yes, but I thought the 40MHz project was *not* bot related.

Mike

On Mon, 15 Dec 2003 00:50:09 +0000,
said...
On Sun, 14 Dec 2003 16:47:09 GMT, Active8
,invalid wrote:


I remember the 40MHz part, but I'm not sure what yer up to. Just
curious

You once referred to me as the "battlebots guy" - although I post on
many other aspects of electronic design as well, so that's not
entirely accurate. I trust this jogs your memory. :-)

Yes, but I thought the 40MHz project was *not* bot related.

Mike

On Mon, 15 Dec 2003 07:16:35 GMT, Active8
,invalid wrote:

Yes, but I thought the 40MHz project was *not* bot related.

Nope. *All* the 40Mhz stuff I post about is 'bot related. That's the
r/c band we're permitted to use. There's an alternative option to use
something up in UHF but I'm giving that a miss for obvious reasons.
:-)
--

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