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Freq ID'ing


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#1 Sn0w

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Posted 16 July 2011 - 08:20 AM

Scanning about with my R20 :biggrin: found something strange (to me anyway) what appears to be a trunked talkgroup at 3151mhz, I believe it's public safety related. I looked on the FCC, Radio Reference and CityFreq, and couldn't find anything.

Planning on setting it to VOX record on my PC and letting it hang out for a while. How can I track the talkgroup? Trunker + R20 + Optolinx or the Icom variant? Just try the separate channels?

#2 ticom

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Posted 16 July 2011 - 11:03 AM

Scanning about with my R20 :biggrin: found something strange (to me anyway) what appears to be a trunked talkgroup at 3151mhz, I believe it's public safety related. I looked on the FCC, Radio Reference and CityFreq, and couldn't find anything.

Planning on setting it to VOX record on my PC and letting it hang out for a while. How can I track the talkgroup? Trunker + R20 + Optolinx or the Icom variant? Just try the separate channels?


Here's a useful chart: http://transition.fc...le/fcctable.pdf

Looking at the chart, we see that 3151 is allocated for Radio Location & Space Research on the Federal side, and Private Land Mobile for Non-Federal. Assuming you are actually picking up a narrowband signal on 3151 MHz. and not a harmonic, image, or other spurious signal then I'd say you are likely picking up a non-communications emitter related to radiolocation, especially since you didn't find an LMR license for the frequency.

WA5VJB sells some nice PCB log periodic antennas that work well for getting a directional fix on a signal, and also has some information if you want to roll your own antenna for that frequency range.

Non-communications emitters, while uninteresting to listen to, are often an indicator of something interesting happening nearby when they are turned on (or off as the case may be).

#3 Sn0w

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Posted 16 July 2011 - 04:22 PM

It's weird, I was thinking it might be a harmonic or an image but I tried running my other scanner with all the freq's nearby (location-wise not frequency-wise) that I often hear and nothing yet.
I've uploaded (below) the sound file from scanner record from while I was asleep - it sounds a bit scratchy in the audio but on my radio it comes in loud and clear with a full signal (might be the patch cable).

It is the local police, not my regular frequencies, I just don't know what they're doing @ 3000. I still haven't found a frequency that's being duplicated, but I'm still hunting.

Anyway - file is here 15mb

Edited by Sn0w, 16 July 2011 - 05:51 PM.


#4 ticom

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Posted 16 July 2011 - 09:04 PM

It's weird, I was thinking it might be a harmonic or an image but I tried running my other scanner with all the freq's nearby (location-wise not frequency-wise) that I often hear and nothing yet.
I've uploaded (below) the sound file from scanner record from while I was asleep - it sounds a bit scratchy in the audio but on my radio it comes in loud and clear with a full signal (might be the patch cable).

It is the local police, not my regular frequencies, I just don't know what they're doing @ 3000. I still haven't found a frequency that's being duplicated, but I'm still hunting.

Anyway - file is here 15mb


One of two possibilities:

1. It's an image/spurious signal.
2. Your local PD is running an analog point-to-point link on 3 GHz.

I'd suspect #1 is more likely, especially if you're within a mile or two of the transmitter.

#5 Sn0w

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Posted 17 July 2011 - 05:24 AM

One of two possibilities:

1. It's an image/spurious signal.
2. Your local PD is running an analog point-to-point link on 3 GHz.

I'd suspect #1 is more likely, especially if you're within a mile or two of the transmitter.


I'm a little over a mile from their repeater, so that's probably it, :rolleyes: and I thought I stumbled onto something exciting!

#6 ticom

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Posted 17 July 2011 - 08:32 PM

I'm a little over a mile from their repeater, so that's probably it, :rolleyes: and I thought I stumbled onto something exciting!


Next time you might! That's the fun part about all this.

I've been into hobbyist SIGINT and communications monitoring for 28 years. Most of stuff I've heard was mundane. A lot informative on some level, either subtle or practical. A little bit was downright interesting. Definitely a hobby for the patient-type, or as background filler for when you're doing something else.

Over this weekend, I replaced the Diamond Discone antenna on the roof with a commercial VHF-high band antenna. I'm now scanning that frequency range to see what I gained in reception range.

#7 Sn0w

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Posted 18 July 2011 - 08:00 AM

Next time you might! That's the fun part about all this.

I've been into hobbyist SIGINT and communications monitoring for 28 years. Most of stuff I've heard was mundane. A lot informative on some level, either subtle or practical. A little bit was downright interesting. Definitely a hobby for the patient-type, or as background filler for when you're doing something else.

Over this weekend, I replaced the Diamond Discone antenna on the roof with a commercial VHF-high band antenna. I'm now scanning that frequency range to see what I gained in reception range.


I'll keep on scanning the airwaves! Found a couple more harmonic images, weird but interesting. Some weird stuttering from the local AFB, probably just lack of antenna range though.
Loving my R20 and the expanded search range, need to get an antenna up on the roof. Going to start studying for my tech class license again, hopefully I'll get it soon.

#8 bitTwiddler

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Posted 06 September 2012 - 06:58 PM

Is there a reasonably inexpensive method of scanning for RF in an area without using a radio? I have six different radios all dedicated to difference frequencies (e.g. 2 Meter, 60 Meter, 222 MHz, etc) so it isn't simple for me to scan full spectrum all in one go.

My reason for asking is I have noticed a number of new antennas in the area and curious as to what they are broadcasting. A couple of the antenna designs give hints at the broadcast frequency range but the others I am unsure about.

All the best

bT

#9 ticom

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Posted 06 September 2012 - 09:12 PM

Is there a reasonably inexpensive method of scanning for RF in an area without using a radio? I have six different radios all dedicated to difference frequencies (e.g. 2 Meter, 60 Meter, 222 MHz, etc) so it isn't simple for me to scan full spectrum all in one go.

My reason for asking is I have noticed a number of new antennas in the area and curious as to what they are broadcasting. A couple of the antenna designs give hints at the broadcast frequency range but the others I am unsure about.

All the best

bT


Spectrum Analyzer. You can build a decent one for around $100, or find an older used one like a HP8554 for a couple hundred.

If you look around, you might even find something like a CEI (Watkins Johnson) RS-125 receiver system which is what they used for TEMPEST back in the day.

#10 bitTwiddler

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Posted 06 September 2012 - 10:12 PM

Spectrum Analyzer. You can build a decent one for around $100, or find an older used one like a HP8554 for a couple hundred.

If you look around, you might even find something like a CEI (Watkins Johnson) RS-125 receiver system which is what they used for TEMPEST back in the day.


Much obliged. The Science Workshop link is worth the article alone. I was under the impression that a good one was ~US$10K.

TEMPEST - one of those things you dream of finding at the estate sale of a deceased alphabet soup agent ;-)

#11 ticom

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Posted 07 September 2012 - 06:30 PM

Much obliged. The Science Workshop link is worth the article alone. I was under the impression that a good one was ~US$10K.

TEMPEST - one of those things you dream of finding at the estate sale of a deceased alphabet soup agent ;-)


Good ones for hobbyist purposes are pretty cheap, and you always find them at hamfests.

Funny you mentioned estate sales, that's where I found my RS-125. It was wasn't the "-7" TEMPEST package, however.




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