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Would you kind folk share your thoughts on my EzUhf Lite spectrum graph?

J

Jerry

Junior Member
Hi all,

I'm still pretty new to the UHF side and I am setting up my reciever. It is not installed, only plugged into the computer via long usb extension and sitting on my powered up quad. Its a QAV400 with an Eagle Tree Vector and FRSKY receiver. I had everything powered up, including all fpv gear (currently 5.8 600mw) and 2.4 radio gear. How does this graph look to your experienced eyes? Yes, I am working on my HAM as soon as I can, to stay as legal as I can.

Thanks for your time everyone!
Jerry

test.PNG
 
J

joshuabardwell

Senior Member
Mentor
I don't know about UHF or the 433 band specifically, but I am a wireless network engineer by trade, and have some familiarity with spectrum analysis, so I'll tell you what I see.

The noise floor is around -110 dBm, which I would consider to be normal. There is a narrowband spike at around 432 MHz. I would want to identify that spike if possible. You have "record peaks" turned on, which I think will lock in the maximum value seen on a frequency. If the spike was a temporary, short occurrence, "record peaks" would make it look like it was happening continuously. Therefore, I would consider turning off "record peaks" and looking at the instantaneous values to see if this transmission was a fluke, or if it was a regular occurrence.

I did some searching and found this sample image (http://beta.ivc.no/wiki/index.php/File:Ezuhf_spectrum_analyzer.png) which shows a spike in the same place, so that suggests this is some common thing.

The noise floor is slightly less stable above around 434 MHz, suggesting that there may be some very weak interference in that area. This is probably irrelevant, due to its extreme weakness.

What frequency range will your transmitter be using?
 
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J

Jerry

Junior Member
Thank you for the quick reply!

The spike at 432 came in when I powered up my transmitter, which is on 2.4GHz. When the transmitter is powered down, there is no spike and the signal is consistent with the rest of the plot. I have the transmitter and receiver set to "extreme hopping", that covers the range from 430 to 450 MHz. I will turn off the "record peaks" feature tomorrow and post that plot as well. However, the peak corresponds with powering on and off the transmitter, the graph refreshes ~10 seconds and it is there every time, but leaves when powered off. What does that mean to you?

Also, I'm glad you said that. Is there a way with the T8FG Super to turn off the 2.4 GHz transmission, and only use the UHF signal?

Thanks again!
 
J

joshuabardwell

Senior Member
Mentor
No need to mess with "record peaks" if the spike corresponds to a known transmitter. It's probably relatively constant. Do you know whether that spike is a harmonic of the 2.4 transmitter, or whether it is a component of the 400 MHz signal? 432 MHz shouldn't be a harmonic of 2.4, but you never know.

BTW, I just looked at your Y axis and I see that it peaks out at -70 dBm, so the "spike" is not as huge as I first thought it was. That being said, at the edge of your range, your ezUHF may have a pretty weak SNR, so even a modest spike like that might have an effect.

Your use of "extreme hopping" is ideal. Since you are operating in the range of 430-450 MHz, this spike, which covers roughly 431.5 to 432.5 MHz is a pretty small slice of your overall frequency bandwidth. You probably wouldn't even notice it if that entire 1 MHz slice was completely obstructed.

Below is how to disable 2.4 on the transmitter when you are using ezUHF. I would definitely recommend this, if only to save battery. But still, there's no need to be cluttering up the airwaves any more than necessary.

http://www.rcgroups.com/forums/showthread.php?t=1714980
 
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