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-   -   Poor Mans 2.4 Ghz Spectrum Analyzer Update (http://www.Wattflyer.com/forums/showthread.php?t=72719)

kyleservicetech 12-04-2013 01:19 AM

Poor Mans 2.4 Ghz Spectrum Analyzer Update
 
4 Attachment(s)
Back two years ago, I originated a thread on a "Poor Mans" 2.4 Ghz Spectrum Analyzer that showed some of the things that is going on with our 2.4 Ghz radio systems. Below is a link to that thread.

http://www.wattflyer.com/forums/showthread.php?t=63497

Since that time, the original Spektrum analyzer has become extinct, and along with that, they absolutely do not work with Windows 8. So, if you should see one of the original analyzers in Ebay, or similar, word to the wise.

So, a birthday present to me included a new Spektrum Analyzer, as shown below:
http://rfexplorer.com/models/ (The model I have is the 2.4 Ghz unit at $119.00)

So, do you need one of these for general flying on 2.4 Ghz? Absolutely NOT! But, if you're curious about these frequencies, this is one unit that will provide a lot of information. The RF Explorer is orders of magnitude more capable than the original unit listed above.

The unit has a built in LCD display in an aluminum case, with a built in battery that is good for hours of operation. Charging is by a USB cable. The analyzer can also interface with a PC, and display the information on your computer screen if desired.

Operating without a PC, this unit has a wide range of abilities, such as changing the frequencies scanned within the 2.4 Ghz band, showing the exact frequencies of any of the transmitted signals, accumulating scanned info, averaging scanned info, and quite a bit more.

One very nice thing, the operator can also change the "Sensitivity" of the unit for transmitters located a considerable distance away.

So, today I did a bit of testing with this unit, along with my Spektrum DX8 transmitter. The transmitter was placed about 50 feet behind my home, on top of a plastic garbage can. Its location was right along the line of sight of one wall of my home. Pacing off about 300 feet, the Spectrum Analyzer showed the normal signal level. And, stepping to the right about 5 feet put the home between the transmitter, and the Analyzer. The displayed signal dropped off. Really dropped off, as expected.

Next, the analyzer was put behind a 6S2P A123 battery pack, held in front of the analyzer by about 1/2 foot. The displayed signal level dropped completely to ZERO! Moving the analyzer closer to the battery pack, and some signal was picked up. Interesting.

The analyzer has a whip antenna, so the analyzer was rotated 90 degrees to see what would happen. Yup, the signal again dropped off noticeably. So, now you know why these 2.4 Ghz receivers require a second receiver with its antennas rotated from the master receiver. Or at least a single receiver with two antennas, one extended by perhaps 6 inches from the receiver. Those 2.4 Ghz signals are very definitely position and rotation sensitive.

Take a look at some photos of this unit, along with photos of the PC display when connected to the computer.

(Note, that wide band "Hump" on the left third of the DX7 display is from my computer modem, located about 15 feet away.)

pmullen503 12-04-2013 02:24 AM

Interesting data.

This seems like a good club purchase for investigating their flying field. Especially those fields with Bermuda Triangle like zones where planes regularly lose signal.

waytooslow 12-04-2013 03:27 AM

Quote:

Originally Posted by pmullen503 (Post 933078)
Interesting data.

This seems like a good club purchase for investigating their flying field. Especially those fields with Bermuda Triangle like zones where planes regularly lose signal.


But the spektrum never fails... or so I have heard [popcorn]

pmullen503 12-04-2013 03:42 AM

Spektrum has been rock solid for me for years, but so has FrSKy and even FlySky's cheap 2.4g. No one has trouble with Futaba either. Our flying environment must be quite benign in terms of interference.

That's not the case everywhere. I know a field not too far away has an area you don't fly over with 2.4g. It would be nice to know what's out there causing problems.

kyleservicetech 12-04-2013 03:57 AM

Quote:

Originally Posted by pmullen503 (Post 933087)
Spektrum has been rock solid for me for years, but so has FrSKy and even FlySky's cheap 2.4g. No one has trouble with Futaba either. Our flying environment must be quite benign in terms of interference.

That's not the case everywhere. I know a field not too far away has an area you don't fly over with 2.4g. It would be nice to know what's out there causing problems.

Yeah
I've had my original Spectrum analyzer at our club's field several years ago. And, NOTHING was picked up.

Tomorrow, I'm going to take this unit to the same field, it's far more sensitive to low level signals than the original unit.

kyleservicetech 12-04-2013 09:51 PM

Spectrum Analyzer at the club's field today
 
This unit was taken to our clubs field today for a few more tests.

The DX7 transmitter was placed on a table inside the club house, while the analyzer was walked to the end of our field, about 500 feet away. The signal level dropped off as expected on the units display. Rotating the unit 90 degrees again caused a loss of signal, but still quite sufficient to control any model airplane. This analyzer still showed a strong signal at the 500 foot distance.

Placing the analyzer about an inch above the ground resulted in ZERO SIGNAL! Their is a very slight rise of the ground level between the transmitter and analyzer, so those who are flying sailplanes, do not let your model go behind any location where the ground is in between the transmitter and receiver.

Placing the analyzer behind the club fields steel cyclone safety fence had only a slight difference in signal level. What was surprising was a significant signal difference between holding the 2.4 Ghz transmitter, versus placing the transmitter on a picnic table. Holding the transmitter resulted in a much stronger transmitted signal.

As for stray 2.4 Ghz signals, few were noted. For the most part, the analzyer showed -100 Dbm signal levels when all transmitters were off. A few quick transmissions did show up, with very strong signal levels, but they were gone in less than a second. These signals were narrow band, taking less than a few percent of the 2.4 Ghz frequency range.

This unit has a "Accumulation" mode where it displays and holds the peak signal level received since the signal was last cleared. For those clubs that have had 2.4 Ghz interference on their models, this feature would show up what's being transmitted. This accumulation mode would be less useful when monitoring the Spektrum DSMX or Futaba frequency hopping signals. These transmitted signals will fill up the analyzers accumulation mode of display in short order.

All in all, this is a very good unit for those curious about these 2.4 Ghz signals. And, again, no, its not needed for general model flying at 95% of the club fields.

For those that go to the giant scale flyin's where hundreds of radios are turned on at the same time, this unit might be quite useful.

CNY_Dave 12-04-2013 10:14 PM

When I was flying my champ I noticed under certain conditions it would not respond when on the pavement, if I was just the right distance/angle.

I'm glad to hear I wasn't paranoid in always using a satellite RX, and in being very certain the primary and satellite could not be 'shadowed' at the same time.

sidybee 03-04-2014 03:39 AM

Quote:

Originally Posted by CNY_Dave (Post 933156)
When I was flying my champ I noticed under certain conditions it would not respond when on the pavement, if I was just the right distance/angle.

this is exactly my problem except its flying and not on the ground .
and im having a bugger of a time finding out whats causing this......

kyleservicetech 03-04-2014 03:53 AM

Quote:

Originally Posted by sidybee (Post 941455)
this is exactly my problem except its flying and not on the ground .
and im having a bugger of a time finding out whats causing this......

If your 'Brownouts' are lasting half a minute or so, it might be a linear regulator in your ESC overheating, and shutting down.

As for me, I'll NEVER use an ESC with a linear receiver voltage regulator type BEC in any model with more than two LiPo cells, and two servos. Just to much risk of that BEC overheating, and shutting down.

Much better to use one of those high powered switching type BEC's that will add about 0.4 ounces weight to your model.

http://www.rcplanet.com/CASTLE_BEC_1...FcU-MgodIWAA8g

kyleservicetech 03-04-2014 03:55 AM

Quote:

Originally Posted by CNY_Dave (Post 933156)
When I was flying my champ I noticed under certain conditions it would not respond when on the pavement, if I was just the right distance/angle.

I'm glad to hear I wasn't paranoid in always using a satellite RX, and in being very certain the primary and satellite could not be 'shadowed' at the same time.

Out of curiosity, what brand of transmitter and receiver were you using? And was it a full range receiver?

I've got one of Spektrums "Back Yard Flyer" types of receivers. That thing was checked at over 1000 feet on the ground for range with no issues.


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