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

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/

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

On Mon, 15 Dec 2003 06:59:30 GMT, said...
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.



Any particular search string to use for that Agilent stuff? They're
usually good for info on stuff like that.

Mike

Active8 wrote:

On Mon, 15 Dec 2003 06:59:30 GMT, said...

HP (now Agilent) has some app-notes on designing diode detectors

Any particular search string to use for that Agilent stuff? They're
usually good for info on stuff like that.

I though Agilent made you answer a bunch of questions before they would
let you at their stuff. Doing a web search on one of the app notes I
downloaded, I get:
http://rf.rfglobalnet.com/library/Ap...s/1/An1089.pdf

RF Globalnet's got lots of good stuff. Probably where I got the design
apps from too.

HP app notes I collected:

pin diode pi atten an1048
pin diode switch an1049
x-band mixer an1052
pin diode freq mult. an1054
(comb gen)
pin diode t/r switch an1067
schottkey diode apps an1069
schot. diode det - RFID an1089
atf-36163 10GHz LNA an1091
pin diode switch an957-1,2,3
z-mtchng for mix & dets an963
0-bias schotky diode an969
broadbnd mixers an976
square-law detectors an986
diode bias an987
zero-bias an988
harmonic mixing an991
shttky diode mixer an995
choke network design ana001
osc design ana008
vco design anm024
5ghz active mixer ans010
transistors primer1
noise and s-parms primer2
thermal primer3
thermal primer3a
gasfets primer4
HP product line quickguide

"Designing Detectors for RF/ID Tags Application Note 1089"

--
Scott

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

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

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

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

On Tue, 16 Dec 2003 23:56:14 GMT, said...
Active8 wrote:

On Mon, 15 Dec 2003 06:59:30 GMT, said...

HP (now Agilent) has some app-notes on designing diode detectors

Any particular search string to use for that Agilent stuff? They're
usually good for info on stuff like that.

I though Agilent made you answer a bunch of questions before they would
let you at their stuff. Doing a web search on one of the app notes I
downloaded, I get:

I don't remember having to do that. I better get a sneakemail
(.com) addys ready for the next registration proceeses, though

http://rf.rfglobalnet.com/library/Ap...s/1/An1089.pdf

Ah. RFID. Big market in the works.

RF Globalnet's got lots of good stuff. Probably where I got the design
apps from too.

Thanks. You're right. I haven't had time to hit RF Globalnet in a
while. I used to get the news letter. Tnx for the reminder.

I wish I had more time. Maybe someone has the time to collect all
our app notes and get permission to organize them with
comprehensive synopses and mirror them on a free site. Maybe
qsl.net or something.



HP app notes I collected:

That's all? Oh, just from HP, ok.

Mike

pin diode pi atten an1048
pin diode switch an1049
x-band mixer an1052
pin diode freq mult. an1054
(comb gen)
pin diode t/r switch an1067
schottkey diode apps an1069
schot. diode det - RFID an1089
atf-36163 10GHz LNA an1091
pin diode switch an957-1,2,3
z-mtchng for mix & dets an963
0-bias schotky diode an969
broadbnd mixers an976
square-law detectors an986
diode bias an987
zero-bias an988
harmonic mixing an991
shttky diode mixer an995
choke network design ana001
osc design ana008
vco design anm024
5ghz active mixer ans010
transistors primer1
noise and s-parms primer2
thermal primer3
thermal primer3a
gasfets primer4
HP product line quickguide

"Designing Detectors for RF/ID Tags Application Note 1089"

On Tue, 16 Dec 2003 23:56:14 GMT, said...
Active8 wrote:

On Mon, 15 Dec 2003 06:59:30 GMT, said...

HP (now Agilent) has some app-notes on designing diode detectors

Any particular search string to use for that Agilent stuff? They're
usually good for info on stuff like that.

I though Agilent made you answer a bunch of questions before they would
let you at their stuff. Doing a web search on one of the app notes I
downloaded, I get:

I don't remember having to do that. I better get a sneakemail
(.com) addys ready for the next registration proceeses, though

http://rf.rfglobalnet.com/library/Ap...s/1/An1089.pdf

Ah. RFID. Big market in the works.

RF Globalnet's got lots of good stuff. Probably where I got the design
apps from too.

Thanks. You're right. I haven't had time to hit RF Globalnet in a
while. I used to get the news letter. Tnx for the reminder.

I wish I had more time. Maybe someone has the time to collect all
our app notes and get permission to organize them with
comprehensive synopses and mirror them on a free site. Maybe
qsl.net or something.



HP app notes I collected:

That's all? Oh, just from HP, ok.

Mike

pin diode pi atten an1048
pin diode switch an1049
x-band mixer an1052
pin diode freq mult. an1054
(comb gen)
pin diode t/r switch an1067
schottkey diode apps an1069
schot. diode det - RFID an1089
atf-36163 10GHz LNA an1091
pin diode switch an957-1,2,3
z-mtchng for mix & dets an963
0-bias schotky diode an969
broadbnd mixers an976
square-law detectors an986
diode bias an987
zero-bias an988
harmonic mixing an991
shttky diode mixer an995
choke network design ana001
osc design ana008
vco design anm024
5ghz active mixer ans010
transistors primer1
noise and s-parms primer2
thermal primer3
thermal primer3a
gasfets primer4
HP product line quickguide

"Designing Detectors for RF/ID Tags Application Note 1089"

Active8 wrote:

On Mon, 15 Dec 2003 06:59:30 GMT, said...

HP (now Agilent) has some app-notes on designing diode detectors

Any particular search string to use for that Agilent stuff? They're
usually good for info on stuff like that.

I though Agilent made you answer a bunch of questions before they would
let you at their stuff. Doing a web search on one of the app notes I
downloaded, I get:
http://rf.rfglobalnet.com/library/Ap...s/1/An1089.pdf

RF Globalnet's got lots of good stuff. Probably where I got the design
apps from too.

HP app notes I collected:

pin diode pi atten an1048
pin diode switch an1049
x-band mixer an1052
pin diode freq mult. an1054
(comb gen)
pin diode t/r switch an1067
schottkey diode apps an1069
schot. diode det - RFID an1089
atf-36163 10GHz LNA an1091
pin diode switch an957-1,2,3
z-mtchng for mix & dets an963
0-bias schotky diode an969
broadbnd mixers an976
square-law detectors an986
diode bias an987
zero-bias an988
harmonic mixing an991
shttky diode mixer an995
choke network design ana001
osc design ana008
vco design anm024
5ghz active mixer ans010
transistors primer1
noise and s-parms primer2
thermal primer3
thermal primer3a
gasfets primer4
HP product line quickguide

"Designing Detectors for RF/ID Tags Application Note 1089"

--
Scott

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

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

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

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

On Mon, 15 Dec 2003 06:59:30 GMT, said...
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.



Any particular search string to use for that Agilent stuff? They're
usually good for info on stuff like that.

Mike

On Fri, 12 Dec 2003 16:41:06 +0000, 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.
PA0SE made a good one for 136kHz and higher, believe you'll find it
described on http://www.qsl.net/on7yd/ and many other places

73
Jan-Martin, LA8AK
http://home.online.no/~la8ak/c.htm
--
remove ,xnd to reply (Spam precaution!)

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