EEVblog Electronics Community Forum
Electronics => RF, Microwave, Ham Radio => Topic started by: CopperCone on August 15, 2017, 05:56:20 pm
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I have a bicone hooked up to my SA and I found a weird pulsed signal on almost exactly 2GHz. It appears to be a very slow amplitude(on off) modulation, almost like a beacon. Like it turns on every 2 seconds for a second and turns off. Very slow. Literary like human seconds.
Any idea what this might be? I looked at it for a while and it appeared to be repetitive. :o
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Check you router or wireless modem , sometimes they can have certain features enabled. For example on my router there is a WiFi feature that in a way works like a beacon for WiFi reciever.
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Wifi is not 2Ghz, so... what?
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yes, it does not appear to be a frequency related to cell phones or wifi. appears to be fairly powerful too.
I will try to find it again. I saw it last month and its been bugging me since.
ok, thats different. it appears to be a bunch of spikes when I center around 2 GHz with 50MHz bandwidth. Kind of looks like some kind of digital communications.
Before there was just a pulse that went on and off. Maybe I remembered the frequency wrong...
What is the purpose of beacons anyway? I figure anything computer related would be alot faster then a few Hz frequency.
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Mobiles, sat phones and space according to:
https://www.ntia.doc.gov/page/2011/united-states-frequency-allocation-chart (https://www.ntia.doc.gov/page/2011/united-states-frequency-allocation-chart)
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There's GSM bands at 1850.2 – 1909.8 and 1930.2 – 1989.8 (MHz, uplink and downlink respectively).
I've seen GSM-850 around here, that looks like a picket fence of carriers with digital (flat topped) bands appearing within them from time to time.
Hmm, I didn't try demodulating it, I should. It ought to be that freaking bit-bit-beep-bit-bip GSM sound that bleeds into freaking everything...
Tim
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This is what I get off my specially tuned 2GHz paperclip.
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Most likely cellular downlink (tower to handset).
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I doubt it ever turns off. Check out band 2 LTE - 1930-1990 MHz, as w2aew mentioned this is the cellular base station to handset link.
If it is LTE you can expect carriers 5/10/15 or 20 MHz wide.
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This is what I get off my specially tuned 2GHz paperclip.
Yes, I see something similar on those frequency ranges, but with more resolution (maybe its my RBW?)
This signal I speak of was just a spike that appeared and disappeared. I believe I even put my instrument into receiver mode (0 Hz span) to check for modulation. It just appeared and disappeared with a very low frequency in the seconds.
When I look at the cell/wifi bands, I see spikes that dance around (probably because its only 10mS maximum update rate). I assume each is a data channel that someone is using. 2 modulated carriers per connection right, so its duplex. Digital stuff looks like... well its doing something fast.
This thing was slower then someone keying morse code.
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50 MHz span and 30kHz RBW, IIRC. Not sure about VBW.
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What I know in the US the use ~2ghz for Sat Radio and Sat Phones. :-//
There are more thinks like Zigbee for example.