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Old Jul 08, 2012, 03:00 PM
flitelab's Avatar
Canada, NS, Halifax
Joined Feb 2010
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So the diversiry in the Tx merely switches back and forth? so half the time it could be worse than a standard single antenna I guess but basically avergaes out to better overall I guess.
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Old Jul 08, 2012, 03:12 PM
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richard hanson's Avatar
United States, UT, Salt Lake City
Joined Oct 2007
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I like the setup -
The radiated pattern switches ,which at the speed of the frames sent, simply covers more completely .
Wrong?
Right?
Frankly, mine works very well.
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Old Jul 08, 2012, 03:51 PM
No bounce, No play.
davidmc36's Avatar
Canada, ON, Ottawa
Joined Oct 2010
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Quote:
Originally Posted by freechip View Post
The 999+ value was most likely a bogus number recorded.
Sounds at least plausible to me. When I hooked up the Flight Log to a Rx that was not compatible that is what showed on the display.

Interesting topic though, will have to be sure and follow any updates from Mikael.
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Old Jul 08, 2012, 04:07 PM
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Vienna, Austria
Joined Oct 2010
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Okay, played a little around with my Airview Spectrum analyzer. Put the DX18 to DSM2 mode. I got 2 peaks in the 2.4GHz band, like it should be with DSM2. When covering one antenna, one peak gets weaker. When covering the other antenna, the other peak gets weaker. So my theory seems right that the DX18 switches between the antennas. Since there is only a switch between the 2 antennas, they will work seqentially.
So basically it is normal that you get more fades, since one antenna points in the direction of the model.

To be honest, I would have oriented the straight antenna downwards. At least for helis. For gliders, which fly high above, the orientation seems right.
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Old Jul 08, 2012, 05:19 PM
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Westranm's Avatar
United States, AZ, Chandler
Joined Jan 2011
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Quote:
Originally Posted by davidmc36 View Post
From AR7610 manual:

"Antenna fades—represents the loss of a bit of information on that specific antenna.
Typically it’s normal to have as many as 50 to 100 antenna fades during a flight. If any single antenna experiences over 500 fades in a single flight, the antenna should be repositioned in the aircraft to optimize the RF link.
Frame loss—represents simultaneous antenna fades on all attached receivers. If the RF link is performing optimally, frame losses per flight should be less than 20. A hold occurs when 45 consecutive frame losses occur. This takes about one second. If a hold occurs during a flight, it’s important to evaluate the system, moving the antennas to different locations and/or checking to be sure the transmitter and receivers are all working correctly."

From AR9020 manual:

"Note that DSMX hops through the band while DSM2 finds two quiet channels and
remains on those channels. Consequently because DSMX operates on quiet and
noisy channels, it’s common to have more Antenna Fades than when using DSM2,
when used in busy 2.4GHz environments. When taking flight log data readings, the
Frames and Hold Data are important and should be used a reference while Fades
are insignificant due to the nature of frequency hopping. A 10-minute flight will
typically result in less than 50 Frame Losses and no Holds."

I would maybe think about repositioning one of the antennas based on your description, but wouldn't get too bent out of shape about it.

Yes, Yes, Yes. Not exactly the same Rx's you are talking about, just noting the nature of DSMX would not give me any pause for concern.
I just popped into RCGroups to give my experience with the RF link today--ironically it seems to be a hot new topic. Up to this point I have been so focused on the screen issues of my DX18, I hadn't tested out what seemed to be lower RF performance.

A little background...I'm flying sailplanes (often well above 1000ft) in an area known to be a 2.4GHz hostile environment--even Futaba radios have experience lockouts here, though only briefly. I have found DSMX to be solid in this environment, flying with a DX6i that I had upgraded to DSMX. Note to Horizon: stop underselling DSMX...it is far superior to DSM2 in my experience. This is why I stuck with Spektrum and decided to purchase the DX18 as my long-term radio.

By far, my DX18 is not performing at long range as well as my old DX6i on DSMX. Testing with two sailplanes and switching between my DX6i and the DX18, I am finding that I am getting a lot of noticeable holds on the DX18 whereas the DX6i I am not when I get above 1000ft. In fact, I had one 1.5 hr flight where I had 50 holds (not a typo) with the DX18.

Using the same planes and transmitters/receivers, I completed extensive range testing today, hoping to reach some conclusions. Here is what I found...
  1. The DX18 range tested at less than 1/2 the distance of the DX6i. This might be meaningless, though, if the DX18 attenuates the power more than the DX6i.
  2. When I pointed the DX18's top antenna at the model, the range decreased drastically. The same happens with the DX6i when the antenna is unfolded and pointed directly at the plane. I expected this result on the DX6i, but not the DX18 with the second antenna.
  3. Given #2, I started thinking that the antenna in the handle must not be working, because I clearly didn't have diversity. I then proceeded to range test, covering up one antenna and then the other. I found that covering up the antenna in the handle never had any effect regardless of orientation! However, covering up the main antenna always resulted in a hold.

In a final test to get conclusive results, I covered up the handle, went to a distance where the plane would not react during range test mode and changed the orientation of the main antenna to match what the handle antenna would have if it was working. I found that my DX18 would reconnect with the model.

So, if you are still with me, I have concluded that my handle antenna is doing little to nothing. For the type of flying I am doing, that would totally explain why I am getting all the holds. The only question is whether the screen glitch issue is somehow related. I will be reporting this to Horizon.

BTW, I was supposed to receive a phone call from Horizon today regarding the screen glitch, but it appears they didn't get around to calling me given they are now closed. A real bummer...as I clearly have more than a cosmetic defect and will not be flying the radio any further.

-Randy
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Old Jul 08, 2012, 05:30 PM
Suspended Account
Rhode Island USA
Joined Aug 2010
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Quote:
Originally Posted by Mukenukem View Post
As far as I understand the diversity function in the DX18, there are 2 antennas, between them the TX switches permanently. One frame this antenna, the next frame the other. Since they are positioned differently, more fades can happen. When I opened the TX I saw the TX module, and between the two antenna connectors there is a diversity switch.

I also have more fades than before, but nothing which makes me worry.

Maybe you want to use a telemetry module so you can see the fades in real time ?
Why arent you worried about more fades?

VP
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Old Jul 08, 2012, 05:30 PM
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Westranm's Avatar
United States, AZ, Chandler
Joined Jan 2011
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Quote:
Originally Posted by Mukenukem View Post
Okay, played a little around with my Airview Spectrum analyzer. Put the DX18 to DSM2 mode. I got 2 peaks in the 2.4GHz band, like it should be with DSM2. When covering one antenna, one peak gets weaker. When covering the other antenna, the other peak gets weaker. So my theory seems right that the DX18 switches between the antennas. Since there is only a switch between the 2 antennas, they will work seqentially.
So basically it is normal that you get more fades, since one antenna points in the direction of the model.

To be honest, I would have oriented the straight antenna downwards. At least for helis. For gliders, which fly high above, the orientation seems right.
Regarding your glider comment...true, unless you are flying your glider casually, riding thermals for long periods of time while sitting down. In which case you may find the top antenna pointing straight at the model.

-Randy
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Old Jul 08, 2012, 06:33 PM
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freechip's Avatar
Canada, ON, Rockland
Joined Aug 2008
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Maybe an RF issue is causing the screen to glitch. Have it serviced and kill two birds with one stone.
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Old Jul 08, 2012, 07:26 PM
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richard hanson's Avatar
United States, UT, Salt Lake City
Joined Oct 2007
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Quote:
Originally Posted by freechip View Post
Maybe an RF issue is causing the screen to glitch. Have it serviced and kill two birds with one stone.
Not very likely that "screen fade" is an rf issue---- by the way, I have had none of this fade issue -
Clean livin!
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Old Jul 08, 2012, 07:47 PM
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Westranm's Avatar
United States, AZ, Chandler
Joined Jan 2011
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Quote:
Originally Posted by freechip View Post
Maybe an RF issue is causing the screen to glitch. Have it serviced and kill two birds with one stone.
The first time I sent mine in for service, the technician said the radio "passed all diagnostic tests. Who knows how extensively, if at all, the actual RF was checked or that the technicians really know how to service this new radio...clearly the one working on mine did not.

I'm just hoping at this point that Horizon will just send me a new radio. I'm tired of participating in their learning curve on supporting this radio.

-Randy
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Old Jul 08, 2012, 08:17 PM
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Westranm's Avatar
United States, AZ, Chandler
Joined Jan 2011
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Quote:
Originally Posted by richard hanson View Post
Not very likely that "screen fade" is an rf issue---- by the way, I have had none of this fade issue -
Clean livin!
I agree it seems unlikely...maybe it's affecting the actual encoding of the signal that is to be transmitted via RF? Who knows. I hope it is related rather than my radio having multiple defects.

Is there anyone here without the DX18 screen glitch (most evident on servo screen) who is getting significantly reduced RF performance on DSMX?

Conversely, is there anyone here with the screen glitch who is getting RF performance on par with their other Spektrum transmitters on DSMX?

Sailplane folks or others who fly at greater distances/altitudes, what experience are you having? Better or worse range, especially in terms of holds, on DSMX?

-Randy
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Old Jul 08, 2012, 08:20 PM
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Shadrack's Avatar
Winnipeg
Joined Feb 2002
5,851 Posts
Well hopefully Andy chimes in on this. I think this is pretty valid, considering the way that Westranm tested.
The top spektrum Tx should perform as well or better than the past models.
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Old Jul 08, 2012, 09:21 PM
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Westranm's Avatar
United States, AZ, Chandler
Joined Jan 2011
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Quote:
Originally Posted by Mukenukem View Post
Okay, played a little around with my Airview Spectrum analyzer. Put the DX18 to DSM2 mode. I got 2 peaks in the 2.4GHz band, like it should be with DSM2. When covering one antenna, one peak gets weaker. When covering the other antenna, the other peak gets weaker. So my theory seems right that the DX18 switches between the antennas. Since there is only a switch between the 2 antennas, they will work seqentially.
So basically it is normal that you get more fades, since one antenna points in the direction of the model.

To be honest, I would have oriented the straight antenna downwards. At least for helis. For gliders, which fly high above, the orientation seems right.
I pulled out my spectrum analyzer after seeing your post. For DSM2, I seem to see the same...one channel per antenna. So the antenna that doesn't appear to be transmitting properly for me on DSMX appears to at least transmit an RF signal.

Another test I tried is to compare the DSMX signal coming from my DX6i versus DX18 in terms of waterfall view across the 2.4gHz band. It appeared that the distribution of the signal from the DX6i was more highly populated across the band than my DX18, though the difference was not dramatic.

Take my results with a grain of salt given they come from a low-budget spectrum analyzer. Also, this may not be indicative of the performance of all DX18 radios as I believe mine is defective.

-Randy
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Old Jul 08, 2012, 09:41 PM
Detail Freak
target's Avatar
Harbor City, CA
Joined Oct 2003
21,672 Posts
I once had a new satellite Rx give me 999 fades on both antennas and the solution was to use a different new satellite RX.
The second one worked like a charm, installed exactly as the previous one was.
Thankfully, the Flight Logger let's you check for just this sort of thing.

You might try swapping the Satellite and extension.
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Old Jul 09, 2012, 02:01 AM
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Vienna, Austria
Joined Oct 2010
2,596 Posts
I also hat an AR12010, and got fades on one satellite even when sitting 5m around the TX. Swapped the sat, no fades anymore. Maybe the sat has an issue.

@VP: As long as there are no frame losses, I have no problem with fades.
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