Directional antenna to locate RFI

I came across a few Proxim RangeLan2 7200 cards the other day. I've
hooked one up and tested it out as a poor man's spectrum analyzer. So
far so good.

Now, I would like to hack in a very directional antenna so I can use it
to try to track a source of RFI. The antenna on these is actually
located on a box that is connected to the card via a 4 inch or so cable
and an odd connector (looks similar to ethernet dongle connectors I've
seen). But inside that box, the antenna connects to a PC board via what
looks very much like the antenna connector used on Apple's Airport
cards (a little tiny thing, I suspect it may be a fairly standard
connector for that size)

First, would a directional antenna work to let me see where the source
of the RFI is? I figure I could point, let it scan for a bit, then move
and repeat. When I see the RFI appear on the graph, I can then head in
that direction and repeat until I narrow down where the source is. Does
this sound reasonable?

Second, what kind of antenna would be ideal for this? How directional
should I be looking (and what is the correct term called so I know what
to look for). I'd think if I get one that has too small of a reception
area, then I'd never be able to narrow down the location because even
the smallest move would radically change the end pointing spot, so I'd
have to be looking almost dead onto the source to pick it up at all. On
the other hand, one that is too large a field would never let me narrow
it down enough to have any idea where the source is.

Has anyone done this already? If not, any tips, hints, suggestions, or
otherwise to point me in the right direction is appreciated.


-chris

(ps: I apologize in advance for spelling or other errors, my news
client lacks spell check and I'm the type that really needs it)

On Tue, 26 Apr 2005 03:44:15 GMT, Chris Bartlett <(E-Mail Removed)>
wrote:

>First, would a directional antenna work to let me see where the source
>of the RFI is?

Sorta. Transmitter hunting is an art. Under ideal conditions, it's
almost trivial with a decent antenna and receiver. However, under
typical conditions, it's a nightmare. Reflections, multipath,
multiple sources of RF, limited rx dynamic range, antenna side lobes,
and such cause nothing but trouble.

>I figure I could point, let it scan for a bit, then move
>and repeat.

The "snoop" program scans at 3 speeds. None are ideal. If you have a
CW or FM source, that's always on, then it might be possible.
However, if the transmitter is on only erratically, or moves around,
or drifts (as in a microwave oven), the time that it will take the
snoop program to move across the band is far too long to be useful.

>When I see the RFI appear on the graph, I can then head in
>that direction and repeat until I narrow down where the source is. Does
>this sound reasonable?

Quite reasonable, under ideal conditions. It really depends on what
you're chasing, what else is around, and how much time do you have to
do this. The method I use is to direction find on the move. I pick a
location, and draw a line of position on a map to where the antenna
points. I then move several hundred feet in hopefully a perpendicular
path to the source, and take another line of position. Repeat a few
dozen times and you will find the map has one location where most of
the lines converge. There will be some lines off into some strange
directions. These are reflections and can be discarded. Where the
lines converge is the transmitter.

However, you're not there yet. I've done this and found myself facing
the outside wall of an apartment building with no clue which apartment
is the source of the interference. The signal is strong enough that
the directional high gain antenna overloads the receiver. So, I have
to use an attenuator in the receive path. 2.4GHz step attenuators are
not cheap or easy to build. For paying work, I use an MMDS
downconverter and a borrowed portable spectrum analyzer.

For close in work, a simple 2.4GHz field strength meter will be
sufficient if used with a high gain antenna. However, walking down
the hallway with a 3ft diameter dish antenna is not a good idea. I
use a butchered microwave oven leakage detector, RF amplifier, and
19dBI dish antenna.

>Second, what kind of antenna would be ideal for this?

Parabolic dish. The bigger the better. 24dBi gain and 5-7 degree
beamwidth.

>How directional
>should I be looking (and what is the correct term called so I know what
>to look for).

Look for the horizontal (azimuth) -3dB beamwidth specification. The
narrower the better for direction finding. The beamwidth is roughly
proportional to the gain. The more gain, the narrower the beamwidth.

>I'd think if I get one that has too small of a reception
>area, then I'd never be able to narrow down the location because even
>the smallest move would radically change the end pointing spot, so I'd
>have to be looking almost dead onto the source to pick it up at all. On
>the other hand, one that is too large a field would never let me narrow
>it down enough to have any idea where the source is.

Yeah, something like that. 5-7 degrees is a very narrow beamwidth.
You need the gain at long ranges, where you start hunting. However,
the narrow beamwidth will make it difficult to point the antenna.
However, as you get closer, the gain is less and less important, while
the beamwidth becomes more critical (as in the apartment building
example).

>Has anyone done this already? If not, any tips, hints, suggestions, or
>otherwise to point me in the right direction is appreciated.

Been there, done that, etc. One aspect of ham radio are transmitter
hunts. Although not directly applicable to 2.4Ghz hunting, read:
http://members.aol.com/homingin/
The book is generally worth a read although microwave xmitter hunting
isn't mentioned.



--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831.336.2558 voice http://www.LearnByDestroying.com
# (E-Mail Removed)
# (E-Mail Removed) AE6KS

In article <(E-Mail Removed)>, Jeff
Liebermann <(E-Mail Removed)> wrote:

> >I figure I could point, let it scan for a bit, then move
> >and repeat.
>
> The "snoop" program scans at 3 speeds. None are ideal. If you have a
> CW or FM source, that's always on, then it might be possible.
> However, if the transmitter is on only erratically, or moves around,
> or drifts (as in a microwave oven), the time that it will take the
> snoop program to move across the band is far too long to be useful.

Without getting into expensive equipment, is there a better option out
there for a poor man's spectrum analyzer?

> Been there, done that, etc. One aspect of ham radio are transmitter
> hunts. Although not directly applicable to 2.4Ghz hunting, read:
> http://members.aol.com/homingin/
> The book is generally worth a read although microwave xmitter hunting
> isn't mentioned.

Thanks, I'll check it out.

And thanks for all the other info as well (I wasn't going to quote it
just to say Thanks... no sense wasting the bandwidth)

-chris

On Thu, 28 Apr 2005 02:47:20 GMT, chris <(E-Mail Removed)> wrote:

>Without getting into expensive equipment, is there a better option out
>there for a poor man's spectrum analyzer?

No. What you have (Proxim 7200 or 7400 card) is about the cheapest
and most functional spectrum analyzer around. However, it's not the
only card that will play spectrum analyzer. See:
http://www.allaboutjake.com/network/...lanexpert.html
which uses a Prism 1 chipset card. I've never gotten it to work, but
others have reported success. The big advantage is that it scans only
11 channels instead of 80, and is therefore faster.

There's also the Teletronics WL2000 PCMCIA card. It only does 802.11
(1 and 2 mbits/sec) but comes with a nifty spectrum analyzer program.
http://www.odessaoffice.com/wireless/survey.htm

>And thanks for all the other info as well (I wasn't going to quote it
>just to say Thanks... no sense wasting the bandwidth)

Y'er welcome. Undying gratitude, endless praise, and cold cash, are
always welcome.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831.336.2558 voice http://www.LearnByDestroying.com
# (E-Mail Removed)
# (E-Mail Removed) AE6KS

In article <(E-Mail Removed)>, Jeff
Liebermann <(E-Mail Removed)> wrote:

> and most functional spectrum analyzer around. However, it's not the
> only card that will play spectrum analyzer. See:
> http://www.allaboutjake.com/network/...lanexpert.html
> which uses a Prism 1 chipset card. I've never gotten it to work, but
> others have reported success. The big advantage is that it scans only
> 11 channels instead of 80, and is therefore faster.
>
> There's also the Teletronics WL2000 PCMCIA card. It only does 802.11
> (1 and 2 mbits/sec) but comes with a nifty spectrum analyzer program.
> http://www.odessaoffice.com/wireless/survey.htm

Sweet, at least I now know other brands should I decide to get more of
them (I looked on ebay for the Proxim RangeLan2 series... YIKES, I
guess now that people can use them for cheap analyzers, they aren't
cheap any more! I'm glad the box I found contained a few so I'm at
least set for the time being)

> >And thanks for all the other info as well (I wasn't going to quote it
> >just to say Thanks... no sense wasting the bandwidth)
>
> Y'er welcome. Undying gratitude, endless praise, and cold cash, are
> always welcome.

Alas, you will have to just have my gratitude and praise... if I had
cash, I wouldn't need the poor man's analyzer ;-)


-chris

Jeff Liebermann wrote:
> On Thu, 28 Apr 2005 02:47:20 GMT, chris <(E-Mail Removed)> wrote:
>
>
>>Without getting into expensive equipment, is there a better option out
>>there for a poor man's spectrum analyzer?
>
>
> No. What you have (Proxim 7200 or 7400 card) is about the cheapest
> and most functional spectrum analyzer around. However, it's not the
> only card that will play spectrum analyzer. See:
> http://www.allaboutjake.com/network/...lanexpert.html
> which uses a Prism 1 chipset card. I've never gotten it to work, but
> others have reported success. The big advantage is that it scans only
> 11 channels instead of 80, and is therefore faster.
>
> There's also the Teletronics WL2000 PCMCIA card. It only does 802.11
> (1 and 2 mbits/sec) but comes with a nifty spectrum analyzer program.
> http://www.odessaoffice.com/wireless/survey.htm
>
>
>>And thanks for all the other info as well (I wasn't going to quote it
>>just to say Thanks... no sense wasting the bandwidth)
>
>
> Y'er welcome. Undying gratitude, endless praise, and cold cash, are
> always welcome.
>

Not to hurt Marlon's influx of cold cash, but I bought a TT PCMCIA card
just for the SA functions, never could get a damn peep out of it. That
was early on in getting into wireless for me and I ended up throwing it
in the junk drawer with a bunch of other worthless crap.

On Thu, 28 Apr 2005 03:24:12 GMT, chris <(E-Mail Removed)> wrote:

>Sweet, at least I now know other brands should I decide to get more of
>them (I looked on ebay for the Proxim RangeLan2 series... YIKES, I
>guess now that people can use them for cheap analyzers, they aren't
>cheap any more! I'm glad the box I found contained a few so I'm at
>least set for the time being)

I bought 6 of the 7400 cards on eBay for $25 + $10 shipping recently.
The catch was that there were no antennas which was exactly what I
wanted. Unfortunately, 3 of the cards failed to survive someones
attempt at reflashing the cards with receive only firmware. I fixed
that but it was pure hell and a big waste of time. Incidentally, the
"snoop" program is part of the Windoze driver, not a stand alone
program.

There's one more I forgot about. I bought a Symbol medical computah
with a Spectrum24 card installed for $150.
| http://www.symbol.com/products/mobil..._ppt_4300.html
What got my attention was that it included a stand alone spectrum
analyzer program. Well, it turned out to be the same as the snoop
program in the Spectrum 24 7400 card driver. The computah is a 486/25
with 4Mbytes of RAM with a 640x480 VGA color display. It accepts a
PCMCIA memory card (or a CF card with an adapter). Unfortunately,
16MBytes maximum for the card. Meanwhile, I managed to kill the
battery and the stupid pen doesn't turn off eventually killing the
AAAA battery. (yes, it's the overpriced $3/ea AAAA battery). I'll fix
it eventually, but it's apparently no better than using the 7400 card
and a laptop. Bummer.

If you're serious about playing direction finder and wanna go the
spectrum analyzer router, there's no need to buy a 2.4GHz analyzer. A
much cheaper model that only goes to perhaps 500Mhz will work just
fine with a downconverter. I've butchered a Pacific Wireless MMDS
downconverter and my really ancient HP141T spectrum analyzer into a
useable system. It's certainly not portable, but it does work around
my neighborhood. The MMDS converter downconverts the 2.4Ghz to an IF
frequency of about 140Mhz. The converters normally receive 2.6-2.7Ghz
and might contain a 2.4Ghz notch filter, which is easily removed with
an xacto knife. I'll post photos when I do my next "site survey" or
antenna test.
| http://www.qsl.net/n9zia/2.4ghz_transverter.html
| http://www.qsl.net/g0ory/2.3g/lo2398/lo2398.html
| http://apache.airnet.com.au/~fastinfo/wireless/PacMon/
Plenty more MMDS converter modifications on the web.


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831.336.2558 voice http://www.LearnByDestroying.com
# (E-Mail Removed)
# (E-Mail Removed) AE6KS

On Wed, 27 Apr 2005 23:24:48 -0400, Rôgêr <(E-Mail Removed)> wrote:

>Not to hurt Marlon's influx of cold cash, but I bought a TT PCMCIA card
>just for the SA functions, never could get a damn peep out of it. That
>was early on in getting into wireless for me and I ended up throwing it
>in the junk drawer with a bunch of other worthless crap.

I never bought any of Marlon's kits. I'm too cheap. I bought just
the cards from Marlon and made my own kits. The nifty thing about the
cards was the built in and quite rugged R-SMA connector. There are 3
WL1000 cards sitting in a box at a former client's waiting for me to
pick them up and do something useful with them. They all work.

The problem you may have had with them was that Teletronics was
screwing around with the firmware when they came out with the 802.11b
version. The 802.11 (1-2mbits/sec) cards worked just fine, but I
could never get the spectrum analyzer to work with the 802.11b cards.
As soon as the driver would load, the whole laptop (or desktop with
PCMCIA adapter) would lock up and hang. Lonnie was doing battle with
Teletronics at the time and of course, nobody at Teletronics would
talk to me. I sold the card to someone cheap and never bothered
dealing with it again.

Normally, I would volunteer to re-flash it for you, but I'm a bit
buried in paying work and don't wanna deal with it. Don't toss it as
I think it can be resurrected.



--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831.336.2558 voice http://www.LearnByDestroying.com
# (E-Mail Removed)
# (E-Mail Removed) AE6KS

In article <(E-Mail Removed)>, Jeff
Liebermann <(E-Mail Removed)> wrote:

> There's one more I forgot about. I bought a Symbol medical computah
> with a Spectrum24 card installed for $150.
> |
> | http://www.symbol.com/products/mobil...uch_ppt_4300.h
> | tml
> What got my attention was that it included a stand alone spectrum
> analyzer program. Well, it turned out to be the same as the snoop
> program in the Spectrum 24 7400 card driver. The computah is a 486/25
> with 4Mbytes of RAM with a 640x480 VGA color display. It accepts a
> PCMCIA memory card (or a CF card with an adapter). Unfortunately,
> 16MBytes maximum for the card. Meanwhile, I managed to kill the
> battery and the stupid pen doesn't turn off eventually killing the
> AAAA battery. (yes, it's the overpriced $3/ea AAAA battery). I'll fix
> it eventually, but it's apparently no better than using the 7400 card
> and a laptop. Bummer.

Yeah, I looked at those and realized it was nothing more then a tablet
computer. I actually thought of buying a hardened Walkabout for $80 and
using it as an ebook reader as well (and hardened is good, I break
things easily... I'm kind of like Lenny, always in search of a rabbit
farm). But the dealer on ebay isn't selling them with power supplies
and wants another $60 for it. I couldn't tell from the specs and pics
if it was standard enough to be something I could replace with any of
the dozens in my box of orphaned wall warts.

So I just passed on the whole thing (besides, a Clio would be a nicer
looking ebook reader, and has a keyboard to boot... but then those are
WinCE, and the RangeLan2 7200 doesn't have WinCE drivers... dang
nabbit!)

> If you're serious about playing direction finder and wanna go the
> spectrum analyzer router, there's no need to buy a 2.4GHz analyzer. A
> much cheaper model that only goes to perhaps 500Mhz will work just
> fine with a downconverter. I've butchered a Pacific Wireless MMDS
> downconverter and my really ancient HP141T spectrum analyzer into a
> useable system. It's certainly not portable, but it does work around
> my neighborhood.

Well, when I started this quest, I had a particular site in mind to use
it. But the more I learn about it, the more I realize it just isn't
going to be practical to attempt where I wanted to attempt it (indoors
in a Drs office, where I'm surrounded by potential sources of RFI
trying to find the one that *might* be the source of the wireless
problems). And of course, I'm crossing my fingers their problem turns
out to be the power saving settings on their Intel 2200BG cards (they
*tell* me they are already set to CAM, but I just found out, they may
be lying... the hazards of debugging over the phone for a site 3 hours
away)

So portable was important, but now much less so as I'd likely use it
for kicks to go wifi hunting... but that implies I have time for fun...
every time I think I do, my wife corrects me on the issue :-)


-chris

Jeff Liebermann wrote:

> Normally, I would volunteer to re-flash it for you, but I'm a bit
> buried in paying work and don't wanna deal with it. Don't toss it as
> I think it can be resurrected.

The sentiment is appreciated. But it is/was one of the 1-2 meg units,
pre 802.11b. And I didn't mean to imply I bought one of Marlon's kits, I
seem to remember it was from Electromm. It was a "kit" but they didn't
have all the parts. What was missing was a little patch antenna, I
already had one so that didn't matter.

If I remember correctly, I thought maybe the antenna connector wasn't
soldered on correctly and I did some surgery. I don't think it'd be
worth the effort to try to bring it back to life, but I'll take another
look at it when I'm at the office.