[NSRCA-discussion] 2.4Ghz

Fri Jun 27 05:27:41 AKDT 2008

OK.... 2.4 question for everyone. 

I'm about 70% done with my first 2m pattern plane. All scratch built. It is an electric and will have 2.4 for guidance (Dx7 AR7000). 

The fuselage has carbon fiber veil laminated to the insides of the outer skin, and there is a 1/4" dia thin wall carbon tube on either side of the fuse, both below the wing and above the wing. 

My intention with this airplane is to mount the main reciever in the fuse behind the wingtube, and approximately 2" behind the 2 5S batterys in the fuse. I then intend to run the remote reciever out the bottom of the fuse and rearward approximately 4-5" from the main reciever. The satellite will be well behind the carbon fiber veil laminated area and should not be blocked by it in any way. 

My hope is that the satellite will be far enough away from the batts and all the carbon reinforcement to get a clear signal at all times. The main rcvr has the possiblity of being blocked by the veil in the fuse, the carbon tubes and wing tubes in the fuse and the batts. I am of course trying to get it as far away from these things as possible to prevent any blockage. 

Any thoughts on this? Should I remove the veil from the area where the main rcvr will sit so I can get a clear signal to it as well? 

From: ed_alt at hotmail.comTo: nsrca-discussion at lists.nsrca.orgDate: Fri, 27 Jun 2008 09:13:45 -0400Subject: Re: [NSRCA-discussion] 2.4Ghz

Great tips here from Troy. For reference, I almost never have a frame loss and I check after almost every flight.  I am getting roughly 40 to 80 fades in the main receiver, usually tens to twenties on the remotes after a 13 minute flight.  The main receiver is often a higher number of fades because it just naturally has more junk near it which either reflects or absorbs RF energy.  Wire bundles and closer proximity to the fuel tank and CF wing tube are what make the fades higher for the main receiver in my setup.   I have noticed a definite correlation of higher fades with being "blocked" by the fuel tank.  At one time, I had a remote on the fuselage side, adjacent to the tank.  That remote would give me about 120 fades per flight until I moved it away from the tank.  Think about how a microwave oven works. A cup of coffee heats up from the molecules being excited by the RF radiation.  The same exact principle is in effect with the minuscule power level of the signal reaching your model, so the fuel in the tank turns that RF energy into a miniscule amount of heat, while reducing the signal level that makes it through the other side.  It's a highly localized effect; just getting an inch or so away (ahead of behind the tank location) improves the performance noticeably.  This is just the physics of the beast, so it makes no difference what brand of 2.4 you fly, you want antenna placement to be in the clear as much as possible.  Ignore the marketing, pay attention to making unobstructed paths for your receivers!  The data monitor is a great tool to assure you have a good setup before you ever fly, then monitor performance for degradation from a known good starting point. Ed

Date: Thu, 26 Jun 2008 13:26:59 -0700From: troy at troynewman.netTo: nsrca-discussion at lists.nsrca.orgSubject: Re: [NSRCA-discussion] 2.4Ghz
Allan,

in a range test situation you are going to be getting the worst possible readings on the flight data log. You could be holding the range test button and be on the fringes of loosing range yet the system is still working. The Flight data device will tell you exactly that. Which it did.

Here is what I do with the data log device. I will use a second person to hold the model. I then will walk to a spot where the data starts to show lager numbers of fades. Its doing its job telling you the signal is getting weak.

I then will find the spot a little closer that has the best "low" fades. This is where the signal starts to get "fuzzy" and the range is still solid but further out it starts to increase the fades. With the model on the ground, and you on the ground "level with it" the range test button depressed you are giving the system its worst possible scenario. Of course the flt log will show this.

I then will make a note of this location where the range starts to fade.

Simply walking until it stops working like we did with 72mhz stuff is going to show a ton of fades....Remember this thing is taking readings 50-60 a sec. So to get 200-300-500 fades putting the range test process in place you are are only talking about 10 secs. tops with weak signal. So think about what is going on...this is a tool and along with it comes some analysis of what is really happening and what the numbers mean. Its not a device that is a green light for go and red light for NO.

So find the spot where you are not getting large numbers of fades..this is your range check distance. 

Now start up the engine and go to this same spot....you could have similar numbers of fades...remember that a given antenna may be blocked partially depending on model orientation to you and the TX. So I will walk around the model at this given distance and have my buddy looking at the flt data log. 

This tells me how its performing. Is this type of device for everybody Nope its not but its a powerful tool if you think about what the tool is telling you. The real test is in the air, because the data logger is going to rack up bigger numbers while under the range test scenario....but fly it and you will see what is happening.  Also in looking at those number 100fades is about 2-3 secs worth of weak signal....this is a really small amount of time, and it doesn't mean the system is in hold...it just means a given antenna is getting weak signal for that amount of time. Compared to the number of seconds in a flight...that's low, and beside a fade doesn't mean its not getting signal just that its weak signal...and the signal from other antennas are stronger and the system is using those. 

If you have a weak signal for all antennas at the same time you could get a frame loss. It takes 45 frame losses in a row to make the system go into hold and this all happens in less than a second. So to really look at these numbers they have to be really really high to have a problem..

For normal use in a pattern model I'm getting about 100-150 fades on the main A-B antennas and low numbers on the remotes. My remotes are behind the wing down the tail of a wood model. I have the remotes with antennas mounted in different axis and planes to get the best diversity possible. I often have single digit fades on the two remotes. Its common to get a few Frame losses but its also common to have zero. I have seen numbers as high as 20-30 on the frame losses...never seen any holds from a  flying situation.

Turning your RX on before the TX can affect your numbers and of course turning the TX off before the taking readings on the RX will also add to your numbers.

Obviously the instructions for this little device are not as clear as they could be but if you think about it and what the data is telling you...its well worth having it. Just think about the numbers mean and how quickly the tick marks can build up in a range test situation.

Troy Newman
Team JR

From: nsrca-discussion-bounces at lists.nsrca.org [mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of AWorrest at aol.comSent: Thursday, June 26, 2008 11:51 AMTo: nsrca-discussion at lists.nsrca.orgSubject: Re: [NSRCA-discussion] 2.4Ghz
I've got mixed opinions about the flight log. I flew my pattern ship all last year using a DX7 and the AR7000 with no problems. Later I bought the flight log and tested it on the AR7000. While it showed correctly there were two receivers in operation, some of the other readings were strange. It turned out my AR7000 wasn't upgraded to support the flight log. Still the flight log acted as if it did.Recently I bought a R921 on e-Bay. I range tested it with the flight log. The readings were terrible. I sent the R921 back to Horizon. They could find nothing wrong. When it returned I tested it again. Still bad readings. Talked to Horizon again. Was told to try it in a plane. Before doing that, one more time I range tested it on top of a paper box. Did the exact same thing with two receivers that I had successfully test flow in an airplane. This last test, the "bad" receiver had better numbers than the two "good" ones!I'm now wondering if these receivers retain some information after being turned off and this leads to erratic flight log readings. BTW, someone on one of the discussion lists says when there is a frame lost it is not counted as an antenna fade. I don't know if this is true but it does make the math work. Yes, I've had on occasion more frame losses than antenna fades.AllanIn a message dated 6/25/2008 9:20:15 AM Central Daylight Time, jlkonn at hotmail.com writes:
I am curious what other folk's experience has been with JR/Spektrum 2.4Ghz.I have experienced a frame loss when one satelite Rx showed -0- fades.  It's my understanding this shouldn't happen.  I have another 9ch Rx from the "Great Receiver Giveaway" I'm going to try but was wondering what others are finding is average for fades and frame losses per flight?Thanks!JLK**************Gas prices getting you down? Search AOL Autos for fuel-efficient used cars.(http://autos.aol.com/used?ncid=aolaut00050000000007) 

Introducing Live Search cashback . It's search that pays you back! Try it Now 
_________________________________________________________________
The other season of giving begins 6/24/08. Check out the i’m Talkathon.
http://www.imtalkathon.com?source=TXT_EML_WLH_SeasonOfGiving
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.nsrca.org/pipermail/nsrca-discussion/attachments/20080627/41c389f0/attachment-0001.html>