Having trouble seeing signals in 2.4 GHz range with 6G Combo+

[Jason Rohrer]

Hi! I just got a 6G Combo+, and I'm learning how to use it.

Using the included grey Rubber Duck antenna (up to 1000 MHz) on the left SMA port, I was able to see a huge spike when transmitting on a hand-held radio that transmits at 462 MHz. The spike disappears when the radio stops transmitting. Great!


However, I'm trying to measure various 2.4GHz radios, and not having any luck. I have the black 5.8GHz Rubber Duck antenna on the right SMA port (which is also supposed to work for 2.4GHz), and I have that higher-frequency module activated. I've set the window to the FCC-listed range for these transmitters (2.402-2.48 GHz). But I'm not seeing any change on the RF-explorer's display when turning the transmitter on or off, nor when changing my distance from the transmitter.

I've tried two different 2.4 GHz transmitters, and confirmed that both are working (these are remote control systems, one for a robot, and another for a quad copter). The robot and the quad copter are both responding to the signal, so transmission is definitely happening.

Here's the robot transmitter:
https://fccid.io/UKU-RAD04

And these are for the quad copter transmitter:
https://fccid.io/BRWDAMTX12
https://fccid.io/BRWDASRX20


I do see some baseline noise on the display, and a few negligible spikes, but they don't seem to correspond to the transmitters at all (transmitters on or off, baseline and small spikes look and measure the same).

I have the calculation set to "normal," so the history line jumps around instantly, with no memory or averaging.


This makes me wonder:

1. Am I doing something incorrectly?

2. Is there something wrong with either the included antenna or the higher-frequency module?

3. Am I mis-understanding how these transmitters work?


Thanks!
Jason

[Mr Fame]

Hey Jason,

The 2.4Ghz transmitters usually transmit in super short bursts, So having a realtime sweep wouldn’t show much. Try setting a smaller span (20-40mhz), and using a peak-hold setting. Letting your analyzer sweep the channel repeatedly will give you a better response. When analyzing wifi, I try to look at each channel one by one, as opposed to reading the entire 2.4GHz spectrum at once.

Hope this helps!
-Jason
Sent from my iPhone

> On Nov 28, 2022, at 2:55 PM, Jason Rohrer <jason...@fastmail.fm> wrote:
>
> Hi! I just got a 6G Combo+, and I'm learning how to use it.

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[Jason Rohrer]

Yes, I was able to have much better results, and "catch" the signal, when using this technique.

My application was actually fox hunting... or rather, verifying that fox hunting of 2.4 GHz devices was impractical.

From what I've seen, given the short bursts, this seems to be the case.

I also tried fox-hunting a cell phone that was in the middle of a voice call (in the same room with me). I was able to catch some spikes in the 1850.2-1909.8 band.... but they were extremely transient, and they jumped around a lot in frequency within the allowed band. This was surprising to me, because I see a huge, non-transient spike for the duration of a 462 MHz FRS "push to talk" radio transmission.... I was guessing that cell phone voice would behave similarly. But I guess it's sending digital packets using some kind of spread-spectrum method.

I was hoping to use a log periodic antenna to "fox hunt" such signals, but my initial experiments with omni antennas makes me think that the signals are too transient and too jumpy to locate with a directional antenna.

Does this match the experience/expectations of others?

The end-game for me is "fox hunting" for cellular trail cameras that are sending data over 4G LTE.... but it seems like this is actually impossible, for the most part.

I'm actually trying to verify that it's impossible (or very difficult).... because I don't want someone to use such techniques to locate MY cellular trail cameras and steal them.

Jason

> https://groups.google.com/d/msgid/rf-explorer/277F5850-0D23-457C-AF07-4802E7FF15DC%40gmail.com.

[Mr Fame]

If I wanted to fox hunt a Signal like that:

-Sniff signal with omni antenna to find a reliable beacon (using peak hold and low sweep times aka higher rbw settings)

Once a reliable indicator is found (even a periodic burst at a given frequency can be zeroed in on of it repeats in time):

-switch to log periodic antenna.
-set analyzer to a small span (1 MHz will work for 2.4GHz)
-set analyzer to rms or some other averaging
-use the fastest sweep setting possible
-point antenna and wait

Eventually, the transmitter will use the part of the spectrum that you are watching, and you will “see” it. If you make note of the signal strength as you turn your antenna, you will start to see a stronger signal in a particular direction.

After that, typical fox hunting techniques apply.

It will take longer to find than a steady signal, but anything that transmits can be found, as long as it continues to transmit.

Just a side note: Cell phones use many bands simultaneously, and your trail cameras might as well. It wouldn’t be easy to find your transmitters, but it all boils down to who is looking for them (if anyone) and how they are looking. An antenna array can easily triangulate a signal source using only 1 transmission burst, but the handheld ones cost around 10,000$US so there is a barrier to entry there.

Whatever your project is, best of luck. Hope my limited knowledge helped!

-Jason
Sent from my iPhone

> On Nov 28, 2022, at 5:55 PM, Jason Rohrer <jason...@fastmail.fm> wrote:
>
> Yes, I was able to have much better results, and "catch" the signal, when using this technique.

> To view this discussion on the web visit https://groups.google.com/d/msgid/rf-explorer/13374a61-a228-483e-bfba-e02987ad1032%40app.fastmail.com.