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Old Jul 02, 2015, 10:47 AM
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RFU and Telemetry Station Experience

Jim,

Attempted a Telemetry station session. Here is the sequence, starting with the XDP session to turn on telemetry in the RFU:

Entered programming mode in the RFU by holding the button while powering up the RFU. When it turns orange (almost immediately and it looks red) I let go of the button.

Then turn on the XDP and find the RFU. In advanced Mode and on the telemetry page I set the RFU to refresh the telemetry rate at 10. Then closed the telemetry window and saved the EEPROM on the main XDP page.

Power off Rx and install in aircraft.

Power on Tx and aircraft and see a good bind. The controls work as well.

When I turn on the Telemetry station it sees the Tx and Rx, but the signal Strength and Rx voltage remain as ???.

I sometimes get an error message about version 3.0, but I click OK and proceed from there.

Can you give me tips to get this working?

Paul
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Old Jul 02, 2015, 11:35 AM
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Got it working - had to upgrade my RFU from v1.0 to v1.4.

Now I need to understand the signal strength indicator.

I'm getting about -18db with the Tx about three feet from the Rx.

When I place the Tx behind me it goes lower to about -35db.

With the low power (range check) button pressed on the Tx it goes to about -40db. With the Tx behind me and the range check button pressed it goes down to about -60db.

The relative values make sense, but are the absolute values of -18, -35, -60db reasonable numbers? Perhaps so since the RFU specs say it's sensitivity is good down to lower than -100db!

Next will be to take it outside and put it far away and observe the signal strength.

Cool. Thanks,

Paul
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Old Jul 02, 2015, 12:51 PM
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Yes, these all make sense. The limiting factor here will actually be the Telemetry Station itself because it's sensitivity (to receive the transmission from the RFU) is not nearly as good.
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Old Jul 02, 2015, 02:26 PM
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Hmm. Is it then correct to think that the signal strength that is captured onto the PC is the signal strength that the Telemetry Station 'sees' and is not the signal strength that the Transmitter 'sees'... which may be quite different.... not because of location difference of the Transmitter vs. the Telemetry Station but because of the design differences of the two?
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Old Jul 02, 2015, 03:27 PM
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JH,

I agree with your assessment, but in my case due to physical location; Jim will have to comment on design differences.

I placed my PC with the Telemetry Station (TS) back at one location, then walked about 100 feet away to a better flying spot. So in my case my results were conservative because the TS was about 100 feet farther from the aircraft than my transmitter. Since I do not get the telemetry on my transmitter I cannot comment on the difference in RSSI values.

Jim, what happens if the RFU and telemetry station go out of range - does the displayed signal strength freeze at the last known value until new data becomes available?

Paul
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Old Jul 02, 2015, 03:31 PM
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Jim,

Nice touch to have the software write an excel file of the data. I noticed that the Telemetry Station software will not load a file greater than about 300Kb. Fortunately I can also get the data from the excel file.

So far the lowest signal strength I've seen is -75 to -79db when the craft is about 700 feet high and about 500 feet out. That is with no other transmitters aboard the aircraft; only the RFU.

Paul
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Old Jul 02, 2015, 05:35 PM
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Quote:
Originally Posted by JHeuler View Post
Hmm. Is it then correct to think that the signal strength that is captured onto the PC is the signal strength that the Telemetry Station 'sees' and is not the signal strength that the Transmitter 'sees'... which may be quite different.... not because of location difference of the Transmitter vs. the Telemetry Station but because of the design differences of the two?
No, that is not correct.

The signal strength shown is how the receiver sees the transmitter. So, the location of the Telemetry Station does not matter (other than for being able to receive the telemetry data from the receiver).
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Old Jul 02, 2015, 05:37 PM
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Quote:
Originally Posted by FlyingW View Post
Jim, what happens if the RFU and telemetry station go out of range - does the displayed signal strength freeze at the last known value until new data becomes available?
Yes, the data is frozen in place until the Telemetry Station receives more telemetry data.
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Old Jul 02, 2015, 05:42 PM
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Quote:
Originally Posted by FlyingW View Post
Jim,

Nice touch to have the software write an excel file of the data. I noticed that the Telemetry Station software will not load a file greater than about 300Kb. Fortunately I can also get the data from the excel file.

So far the lowest signal strength I've seen is -75 to -79db when the craft is about 700 feet high and about 500 feet out. That is with no other transmitters aboard the aircraft; only the RFU.

Paul
The file can be any size... I was saving/loading megs of data during testing.

The signal strength is affected by so many different things. It's something that I pretty much ignore now days. As long as the range test passes with 125+ feet (I typically get around 500 feet here), there are no worries about legal (visually un-aided, line of sight) flying.
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Old Jul 03, 2015, 12:17 PM
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Ok, first results:

Below is the test machine, equipped with the RFU-telemetry and a 1.3ghz, 200mx video transmitter. Also have a 2.4ghz "notch filter" installed on the video Tx to help reduce 2.4ghz interference. Video Tx antenna aft is about 16 inches from the RFU antenna up front behind the cameras.

With the video Tx turned off, flew out to about 700 feet high, 300 feet out and got -67db for the RFU's RSSI.

With the video Tx turned on, flew to about the same location and got -77db for the RFU's RSSI. Video reception was good. Control link was solid. In another flight I also turned on the Mobius and got about -75db.

So far so good. Will try it later with my prescription sunglasses and go out a little farther.
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Old Jul 03, 2015, 12:54 PM
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Jim,

I get this error on Windows XP, WIndows 7 and Windows 8. Thought is was just a glitch yesterday, but now I can reproduce it often.

It happens after I load a recorded file of data, and then attempt to play it back using the arrows.

Thanks,

Paul
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Old Jul 03, 2015, 01:08 PM
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You will have to send me the file. It contains something that it doesn't like. Send it to our tech support email address.
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Old Jul 03, 2015, 01:12 PM
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What are you plugging the RFU into? You would get better reception if you had one of the RFU's antenna's pointing forwards and the other pointing upwards. This puts one antenna perpendicular to the radiation pattern of the 1.3GHz antenna. 10dBm loss is quite a bit. Every 6dB doubles the effective range. So, your range going from -67 to -77 is a reduction of about 1/3rd of the total range.
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Old Jul 03, 2015, 01:22 PM
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Jim,

The PPM output of the RFU is plugged into a Naze32 flight controller.

I will try your suggested re-alignment of the RFU antenna and report back.

Also, I sent the xtd file to the XPS tech support email address.

Thanks,

Paul
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Old Jul 03, 2015, 01:32 PM
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I'm curious: In what orientation to the transmitted signal does an XPS Nano receiver get the best reception?
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