Malfunctioning homebrew field strength meter
 

"amdx" wrote in news:4f6f2$46a49e2b$18d6b40c$11917
@KNOLOGY.NET:

I built the circuit from the page below.

http://www.atvinderby.co.uk/2.4Ghz_SWR_Meter.htm

The I get 0v out when held near my wireless router, if
I put it near the microwave oven, the high input impedance
meter bounces up and down between 7mv and 80mv and
everything in between.
I used a 1N416E diode and a 1500pf filter capacitor. The
tuning cap doesn't have any affect.
Should this circuit work? If so what could I be doing wrong?

Mike



Mike,

In this part of the world, WLAN equipment at 2400MHz is restricted to
10dBm EIRP. (A microwave oven delivers almost 60dBm to its load, leakage
is hopefully much less.)

If you were to place your quad at 1m (meaning 1 metre) from the router,
and lets assume your router had 0dBi gain, that your quad is actually
optimised (including impedance matched to the load) and delivering 7dBi
gain, you would expect to develop around -23dBm in a 50 ohm load. That is
a pretty small voltage, and you would expect to get around 1mV DC from a
microwave detector if the source was a continuous source... but is it?

Owen

Malfunctioning homebrew field strength meter
 

"Jerry Martes" wrote in message
news:Ih5pi.1716$9A6.1649@trnddc01...

"amdx" wrote in message
...
I built the circuit from the page below.

http://www.atvinderby.co.uk/2.4Ghz_SWR_Meter.htm

The I get 0v out when held near my wireless router, if
I put it near the microwave oven, the high input impedance
meter bounces up and down between 7mv and 80mv and
everything in between.
I used a 1N416E diode and a 1500pf filter capacitor. The
tuning cap doesn't have any affect.
Should this circuit work? If so what could I be doing wrong?

Mike

Hi Mike

That device looks so interesting to me that I will build one.
Have you thought about the reason for using the Quad? It seems that
complexity of the Quad+Reflector with the tuning capacitor might be used
for some reason other than gain. A dipole over a piece of copper would
be about the same "gain".
And, since the output of this device never needs to connect to a coax,
why do you suppose the *right angle* BNC is used?
I'll learn something from this project.

Jerry
I skipped the BNC connector altogether, soldered directly to the banana
plug connector.
I thought the Quad+Reflector was just for more gain and he says it is
horiz and vert polarized.
I have got a more stable output now, I tried it on my older microwave
(1988 model) and I got a more stable signal of as high as .8V, yea I had
to switch from the 200mv scale to the 2V scale. I decided to put a glass
of water in the microwave, then I could only get about 350mv. BTW the
measurements were taken on the outside of the oven at the door :-)
I need to go back to my tuning capacitor, I just grabbed a tiny air
variable from a
scrap pcb thinking it would be big enough, I'm questioning that decision
now.
Mike

Malfunctioning homebrew field strength meter
 

"Owen Duffy" wrote in message
...
"amdx" wrote in news:4f6f2$46a49e2b$18d6b40c$11917
@KNOLOGY.NET:

I built the circuit from the page below.

http://www.atvinderby.co.uk/2.4Ghz_SWR_Meter.htm

The I get 0v out when held near my wireless router, if
I put it near the microwave oven, the high input impedance
meter bounces up and down between 7mv and 80mv and
everything in between.
I used a 1N416E diode and a 1500pf filter capacitor. The
tuning cap doesn't have any affect.
Should this circuit work? If so what could I be doing wrong?

Mike



Mike,

In this part of the world, WLAN equipment at 2400MHz is restricted to
10dBm EIRP. (A microwave oven delivers almost 60dBm to its load, leakage
is hopefully much less.)

If you were to place your quad at 1m (meaning 1 metre) from the router,
and lets assume your router had 0dBi gain, that your quad is actually
optimised (including impedance matched to the load) and delivering 7dBi
gain, you would expect to develop around -23dBm in a 50 ohm load. That is
a pretty small voltage, and you would expect to get around 1mV DC from a
microwave detector if the source was a continuous source... but is it?

Owen
I don't know but, I'll go fire up the laptop and see if I get more signal
while
I'm loading my homepage.
Mike

Malfunctioning homebrew field strength meter
 

"amdx" wrote in message
...

"Owen Duffy" wrote in message
...
"amdx" wrote in news:4f6f2$46a49e2b$18d6b40c$11917
@KNOLOGY.NET:

I built the circuit from the page below.

http://www.atvinderby.co.uk/2.4Ghz_SWR_Meter.htm

The I get 0v out when held near my wireless router, if
I put it near the microwave oven, the high input impedance
meter bounces up and down between 7mv and 80mv and
everything in between.
I used a 1N416E diode and a 1500pf filter capacitor. The
tuning cap doesn't have any affect.
Should this circuit work? If so what could I be doing wrong?

Mike



Mike,

In this part of the world, WLAN equipment at 2400MHz is restricted to
10dBm EIRP. (A microwave oven delivers almost 60dBm to its load, leakage
is hopefully much less.)

If you were to place your quad at 1m (meaning 1 metre) from the router,
and lets assume your router had 0dBi gain, that your quad is actually
optimised (including impedance matched to the load) and delivering 7dBi
gain, you would expect to develop around -23dBm in a 50 ohm load. That is
a pretty small voltage, and you would expect to get around 1mV DC from a
microwave detector if the source was a continuous source... but is it?

Owen
I don't know but, I'll go fire up the laptop and see if I get more signal
while
I'm loading my homepage.
Mike much more than
Ok, I have the field strength meter about 1ft from the router and it reads
about 3mv,
while loading the homepage it jumped to 15mv and loading a pdf file caused
it to go to
25mv. However I get 0v if I move much more than a foot away.

Malfunctioning homebrew field strength meter
 

"amdx" wrote in
:
....
I thought the Quad+Reflector was just for more gain and he says it is
horiz and vert polarized.

That is not the only thing in the article that doesn't make sense.


Owen

Malfunctioning homebrew field strength meter
 

"amdx" wrote in message
...

"John Passaneau" wrote in message
...
"amdx" wrote in news:4f6f2$46a49e2b$18d6b40c$11917
@KNOLOGY.NET:

http://www.atvinderby.co.uk/2.4Ghz_SWR_Meter.htm

Hi:
That circuit should work. The exact value of the filter capacitor is not
critical. Lead length is important. If your copy look EXACTLY like the
pictures then it could work. The diode pictured is important. A common
glass type diode will not work well. Also the pictured diode type is very
static sensitive and should come to you wrapped in metal foil. If it
wasn't
likely the problem is a bad diode. Building things for this high of
frequency is tricky and if any short cuts are taken it will probably stop
the device from working well.

John Passaneau
W3JXP

Hi John,
I tried to keep leads short, I built it per the pictures and dimensions.
I did use a microwave diode (1N416E) I did ruin one diode soldering
#14 wire to it (I think). So I just soldered a small diameter wire to the
next diode and attached the small wire to the circuit.
The problem is the erratic reading near the microwave oven. Seems like
the filter cap would smooth that.
Mike


An erratic reading near a microwave oven doesnt surprise me. The oven uses a
stirrer to move the beam around inside the oven.



Jimmie

Malfunctioning homebrew field strength meter
 

On Mon, 23 Jul 2007 21:14:07 -0400, Jimmie D wrote:

An erratic reading near a microwave oven doesnt surprise me. The oven
uses a stirrer to move the beam around inside the oven.

Do you normally read earlier followups and post those answers as yours?

Message-ID:

Malfunctioning homebrew field strength meter
 

amdx wrote:

[...]

Interesting; why bother?

You know about "hotspot finders?"

http://www.iogear.com/main.php?loc=product&Item=GWF001
http://www.jiwire.com/detector-shootout-contenders.htm
http://www.pctoday.com/Editorial/art...2t08.asp&guid=
http://www.trendnet.com/products/TEW-429UB.htm

Most all detectors will give a 1-4 or 1-5 led "readout" of signal
strength. A couple will tell you the type of encryption being used by
the wireless device, signal strength, channel, etc.; and the tew-429ub
is BOTH a "Wireless USB Adapter AND Wifi Detector!"

The iogear unit is available at most walmarts for $19.??

Regards,
JS