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Author Topic: 2.4 GHZ Hunt without a spectrum analyzer  (Read 3148 times)
WA2OJT
Member

Posts: 6




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« on: November 13, 2004, 04:14:59 AM »

I'm trying to locate a 2.4 GHZ signal in the Catskill mountains but don't have a spectrum analyzer. Any suggestions?
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WB6BYU
Member

Posts: 13238




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« Reply #1 on: November 15, 2004, 12:26:06 PM »

Do you have any type of receiver that can detect and/or
demodulate the signal you are looking for?  If not, you
may have to build a down converter.

Is the signal (relatively) continuous, or just intermittent?
As long as the signal is on the air enough then a beam
antenna of some sort attached to whatever receiver you
have should do the job.  There should be a number of
antenna designs on the web.  A high gain antenna will
give greater detection range and more accurate bearings,
but needs to be turned more slowly when the signal is
intermittent due to the narrow beamwidth.
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WA2OJT
Member

Posts: 6




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« Reply #2 on: November 15, 2004, 02:02:47 PM »

It's a WISP that I'm looking for. The IP is bogus per Melissadata and other se's.

I'm not worried about the antenna. The i.f. input of some satallite receivers is about 1.5 ghz. I can use an analog field strength meter on the i.f. of it. But can I tun up to 2.4 ghz?

I'll probably look on ebay for stuff that operates in the 2.4 band.
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WB6BYU
Member

Posts: 13238




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« Reply #3 on: November 16, 2004, 10:48:38 AM »

What is the IF used in a wireless networking card?
You may be able to use that as a receiver, then couple
the IF to a VHF/HF receiver with an S-meter.

Any sort of downconverter could be pressed into service
if it receives somewhere near the desired frequency.
You can use one of the wide-band receivers like the
VR-500 as a tunable IF strip with most types of front
ends.  (CW or SSB modes can give you about 10dB better
signal to hunt than FM or AM.)  Check with Downeast
Microwave to see if they have any receive converters
that would work in this application.
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KE6PKJ
Member

Posts: 256




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« Reply #4 on: November 17, 2004, 01:50:51 PM »

The 2.4 ghz Radio Shack video receiver uses a varactor tuned local oscillator that sets each channel to frequency by a fixed resistor and trim pot instead of a PLL circuit. All you would need to do is bypass that little resistor/pot scheme with your own multi-turn trim pot to set up on your intended frequency. The i.f. is 479.25 mhz which you could tap off and run into any scanner, or you could simply sample the output from either the receivers baseband video or audio outputs into an opamp that drives a meter for a simple "S meter".
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W7DJM
Member

Posts: 1




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« Reply #5 on: November 18, 2004, 06:50:54 PM »

""""It's a WISP that I'm looking for. The IP is bogus per Melissadata and other se's.""""

I haven't got the least idea what that sentence means, but in a search on eBay for a spectrum analyzer and related parts, I see that there is some kind of lashup you can get with a wireless "WIFI" card that will show spectral activity (via software) of the WIFI spectrum.

Here's just one I found, go to the search page:

http://search-desc.ebay.com/spectrum-analyzer-WIFI_W0QQsatitleZQ22spectrumQ20analyzerQ22Q2cQ20WIFIQQsotextsearchedZ2

and I used        "spectrum analyzer", WIFI



and got:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=25397&item=3853702568&rd=1&ssPageName=WDVW
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KC2MMI
Member

Posts: 620




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« Reply #6 on: November 21, 2004, 08:53:13 PM »

WiFi is 2.4GHz. How about taking a $20 "WiFi hot spot locator" key fob and connecting it to a directional antenna?
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K4RAF
Member

Posts: 19


WWW

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« Reply #7 on: February 09, 2005, 05:35:16 PM »

Take a laptop, connect a PCMCIA 802.11B card, run NetStumbler in signal strength mode on the MAC & use a directional antenna...

Why are you looking for this WISP ?
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N5OOM
Member

Posts: 23




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« Reply #8 on: March 16, 2005, 03:13:43 PM »

It's a little late for this particular conversation, but for future use, netstumbler is very useable for this:  http://www.netstumbler.com.  The effects of antenna pattern are very clear when using netstumbler.

In addition, here is a link to a presentation on the North Texas Microwave Society site discussing the use of the Proxim Rangelan 7400 pcmcia card as a limited functionality spectrum analyzer.  This card runs around $30 on eBay.

http://www.ntms.org/files/$20%20WIFI%20SA.zip

The Proxim Rangelan 7400 is an obsolete (pre 802.11b) wireless network card that did frequency hopping in the 2.4GHz band.  The software for the card includes a signal strength scanning function for the 80 used channels in the band.
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SAIL_AWAY
Member

Posts: 19




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« Reply #9 on: November 16, 2005, 01:49:48 AM »

netstumbler will work, but not for everything.  it's better to use a linux box and do passive monitoring with kismet so you can see access points that aren't broadcasting an SSID.  kismet will let you see access points based simply on the packets being transferred between two points without revealing that you're looking.  netstumbler is very "noisy" in that it makes transmissions to stir things up and generate responses, and the default configuration of netstumbler on a pc can be easilly detected by anyone who knows what to look for.  kismet can detect wifi receive only without leaving a signature.

http://www.kismetwireless.net/index.shtml
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