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Author Topic: UHF FHSS Device  (Read 3913 times)

Cameron Stuckey

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Re: UHF FHSS Device
« Reply #10 on: November 02, 2016, 10:21:35 pm »

https://www.youtube.com/watch?v=Xzhepe4gEvU&feature=youtu.be

Great video, Jason.

I'm not a frequency hopping algorithm myself but this seems too random for my understanding FHSS. I'd expect a constant step size, constant amplitude, and constant linger time, if not constant than a predicable pattern.

The closest thing I have seen to something like this was a transmitter with a failing oscillator that couldn't maintain it's frequency. Fascinating stuff. I'll be on the look out.
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Jason Glass

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Re: UHF FHSS Device
« Reply #11 on: November 02, 2016, 10:44:00 pm »

Great video, Jason.

I'm not a frequency hopping algorithm myself but this seems too random for my understanding FHSS. I'd expect a constant step size, constant amplitude, and constant linger time, if not constant than a predicable pattern.

The closest thing I have seen to something like this was a transmitter with a failing oscillator that couldn't maintain it's frequency. Fascinating stuff. I'll be on the look out.
Hi Cameron,

Your post reminds me that I've seen a bad TR-825 pack show this sort of pattern when keyed on.

Hmm...

Sent from my mobile phone. Please excuse the inevitable spelling and grammatical errors.

Dan Currie

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Re: UHF FHSS Device
« Reply #12 on: November 03, 2016, 05:51:11 am »

Jason,
   Nice work at capturing that video.  Your span is .5mhz wide and the source looks like a FM signal that is being modulated constantly, no spars or change of bandwidth.  Obviously it is moving around freakishly.  Then again a BTR TX doesn't have the 'fork' look.  Trying to spark some synapses... some of the shapes this device makes are reminiscent of an 825 being keyed on.   



Or is that the trace left by the persistence leaving a 'flat top' trail' because it's moving so fast?  I can't locate an image right now of an 825 pack keyed on not but modulating or static.  By chance is there a TR-825 assigned to 534mhz?

I'm glad you appreciated the Hedy Lamarr reference.  There were two more rehearsals today with the show/web stream early afternoon.  I also brought in the 1302 to have a peek.  Both the BB60C and 1302 showed this noise.  I inserted a SAW filter in line which has the gak in its bandpass and it didn't go away.  So this isn't some sort of false image.  I did find it though.

 The signal IS roughly 20mhz of Tempest 900 noise!!  The Tempest on the show was spewing nonsense 400mhz--ish  lower than what it broadcasts.  Hedy has been found.  Peak to peak in the 902-928mhz range the tempest is 24mhz wide.  The other 4mhz are probably being masked by TV station 21 or is under the noise floor.

 If you have been seeing something similar to this and the range of the gak has been higher maybe there was a FHSS on the show in the 1.9 or 2.4ghz range releasing hash lower in the spectrum.  Keep us posted on what you find.
   
« Last Edit: November 03, 2016, 05:56:21 am by Dan Currie »
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Ike Zimbel

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Re: UHF FHSS Device
« Reply #13 on: November 03, 2016, 01:12:52 pm »

Jason,
   Nice work at capturing that video.  Your span is .5mhz wide and the source looks like a FM signal that is being modulated constantly, no spars or change of bandwidth.  Obviously it is moving around freakishly.  Then again a BTR TX doesn't have the 'fork' look.  Trying to spark some synapses... some of the shapes this device makes are reminiscent of an 825 being keyed on.   



  I did find it though.

 The signal IS roughly 20mhz of Tempest 900 noise!!  The Tempest on the show was spewing nonsense 400mhz--ish  lower than what it broadcasts.  Hedy has been found.  Peak to peak in the 902-928mhz range the tempest is 24mhz wide.  The other 4mhz are probably being masked by TV station 21 or is under the noise floor.

 If you have been seeing something similar to this and the range of the gak has been higher maybe there was a FHSS on the show in the 1.9 or 2.4ghz range releasing hash lower in the spectrum.  Keep us posted on what you find.
 
A few comments:
1) That is a cool video, if somewhat alarming. +1 on Dan's comments.
2) Tempest 900: I had one out on the Shania Twain tour last summer. The other gear in the rack (a dog's breakfast of com and RF gear) did not like having the antenna mounted on the base station...definitely induced some noise. I used the remote antenna right on top of the rack and things settled down. I have also seen them put out noise when the base station antenna and the remote antenna were in close proximity to each other.
3) I'm not sure if I have a screen shot of this, but on my most recent show I had some interference that was moving around over time. This was definitely intermods from the com system as I was able to listen to it. There were a number of things with the system that I was not too keen on, like two of the four BTR bases having only single TX outs instead of the split one, and those going through a combiner, so that was likely the culprit.
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Re: UHF FHSS Device
« Reply #13 on: November 03, 2016, 01:12:52 pm »


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