RX Antenna for Carbon based aircraft - feedback on best practice [Archive]

bOjO

Aug 01, 2007, 12:43 AM

Hi,

You can find some information here:

http://www.f3j.com/antenna.htm

This subject have been widely discussed in French forum and, after many experimentations, here is the best solution they found:

...put the antenna in the fuse, make an extension with electric wire to reach the tail and another extension of at least 50cm outside the fuse (if possible at 45 degree) with piano wire (0.3 - 0.5 millimeter diameter).

See this picture:

http://pierre.rondel.free.fr/images2/Freestyler3/pages/Freestyler30.htm

and the comments:

http://www.rcgroups.com/forums/showthread.php?t=666684&page=4

I've chosen this solution in my Trinity F3F full carbon and I never had any problem (MPX Synthesized DS IPD Receiver and MPX evo 9).

You can also try with a simple electric wire instead of the piano wire but it's less clean...

To be honest I've seen many F3F planes with the antenna simply lying in the fuse (straight in a tube at least !) and they don't seem to have any problem... but they fly closer in F3F.

I use this solution in my Nyx F3J (JR Synthesized Receiver + MPX Evo) because I was too lazy to add any extension and I never had any problem even when I fly really far away...

Note that I don't mention the problem of the tuned length, and I think you can't know how much a carbon fuse will screen the antenna so, according to me, it's useless to try to define an exact right length for the extension...

Hope this help,

Joel

SmokinJoe101

Aug 01, 2007, 12:58 AM

on most Kevlar carbon weave fuse you can run antenna inside the fuse with no issues I have for many years but complete carbon fuse is another issue I would run extensions out fuse.
SJ

pinolefm1

Aug 01, 2007, 01:02 AM

I just drilled a hole through the top of the fuselage on my planes and run the antennae out that and tape it to the top of the fuselage, :confused:

Steve

bOjO

Aug 01, 2007, 02:35 AM

Another example here:

http://www.f3x.com/htdocs/Aspirin/Freestyler3.htm

Regnar Petersen

Aug 01, 2007, 08:30 AM

Hi

I have used solution 4 (F3J.com) on my Pike.

I soldered a new antenna wire to the original one, so i doubeld the length. The range test was 450 meters with tx antenna extended and the plane 1 meter over the ground. In flying I have been very far away and never had any problems.

jgs99v

Aug 01, 2007, 01:31 PM

bOjO

Aug 01, 2007, 02:33 PM

Joel - thanks - very eloquent and clean - this is great!!!! I'll follow the thread.
So guys is it really as simple as taking my current rx antenna (without modification) running thru a hole in the top of the fuse and taping it down? The reason I'm asking is because I'm in the process of repairing a F3F Nxy and the previous owner modified the Rx antenna and I just wondered if I should take my new JR720/790 and modify it - and if there are specific fixes for specific aircraft/rx hardware.

To be safe, the best way is certainly not to tape the antenna (unmodified) on the fuse... it will work until it won't... :(

You should make an extension like this http://www.f3x.com/htdocs/Aspirin/Freestyler3.htm

That doesn't damage your receiver: just solder nicely a wire with shrinking tube, you just lose 0.5cm of your antenna even less, no problem at all.

But most important: make some test before flying in any case:
model at 1 meter from the ground, use one branch of your transmitter antenna and see how far you can walk away without random movements of the servos. You should have at least 80 meters. With my Trinity I have more than 120m. If you use the full length of your transmitter you may have a LOT more than ~100 meter (but you have to find a place to conduct this test :) )
... and most importantly : inactivate the IPD function of your receiver if there is, if not you will never see when the lost of signal occurs !!

Joel

jgs99v

Aug 01, 2007, 02:52 PM

Joel - IPD = fail safe PCM mode correct?

pinolefm1

Aug 01, 2007, 03:34 PM

To be safe, the best way is certainly not to tape the antenna (unmodified) on the fuse... it will work until it won't... :(

Joel
Are we talking 72 mhz here or 2.4ghz... :confused: I'll agree taping 2.4ghz antennaes seems to be problematic but all my planes (72mhz radios) have the antennae taped to the top of the fuselage for the last umpteen years ..carbon mini blade..trinity carbon...superblade...Flash hotliner...and a few own designs and I have never ever had a problem with taping them outside of the fuse :confused: I taped them outside specifically to help remove any chance of interference caused by running the antennae inside of the fuselages :confused:
Steve :)

bOjO

Aug 01, 2007, 03:35 PM

Joel - IPD = fail safe PCM mode correct?

No, it is the MPX system to get rid (ignore) invalid signals. if some invalid signals are received the receiver replace them by the last valid signal received. If the receiver don't receive valid signal for more than x seconds (0.5 sec I think) it switch to fail safe mode.
That mean that if you have this kind of system on your receiver (Jr 790 does have an equivalent ??) you can't see if lose of signal or perturbations occurs during the range test... and you may think that everything is ok :(

Joel

jcosta

Aug 01, 2007, 06:02 PM

Are we talking 72 mhz here or 2.4ghz... :confused: I'll agree taping 2.4ghz antennaes seems to be problematic but all my planes (72mhz radios) have the antennae taped to the top of the fuselage for the last umpteen years ..carbon mini blade..trinity carbon...superblade...Flash hotliner...and a few own designs and I have never ever had a problem with taping them outside of the fuse :confused: I taped them outside specifically to help remove any chance of interference caused by running the antennae inside of the fuselages :confused:
Steve :)

Steve,

72MHz seems to be less prone to interference from carbon fuses, but taping them to the fuse or running them inside is not much different. The fuse can still block the signal, depending on the position of the plane towards the TX.

Safest solution is to extend the antenna either with a piano wire hanging out the back, or just a trailing wire. At least 15 inches...

The most elegant solution is to run it up the tail, when it does not have carbon.

Anyway, what works on a slope definitely may not work on f3J/F3B/TD, distances are much bigger.

jgs99v

Aug 02, 2007, 03:54 PM

Well - Of the two planes I bought second hand:
The antennae was extended to the full length excluding the wire inside of the fuse.
Joe winded his, whilst David just taped them. I noticed that Darrell Z. complained about observing glitches on his Crossfire. So I was just trying to avoid any possible issues. So no specific test data leaves this open for experimentation to continue.

pinolefm1

Aug 02, 2007, 09:25 PM

Steve,

Anyway, what works on a slope definitely may not work on f3J/F3B/TD, distances are much bigger.

Well despite flying primarily slope I fly hotliners at the same slope on less than windy days and I can be found testing the absolute limits of my 20/20 on just about any given day with either the slope planes or the hotliners ;)

Steve

djklein21

Aug 03, 2007, 12:59 PM

Well despite flying primarily slope I fly hotliners at the same slope on less than windy days and I can be found testing the absolute limits of my 20/20 on just about any given day with either the slope planes or the hotliners ;)

Steve
Jcosta is still correct, because hotliners are much smaller than a 3.7 m F3J plane. The F3J plane specked to your visual limit will be considerably further away. I learned this fact well when I made the jump to TD/F3b flight. We really push the limits of our reception, so a rock solid RF link is a must. I have never had a glitch at the slope after I started setting up my planes for TD flying.

pinolefm1

Aug 03, 2007, 02:13 PM

Jcosta is still correct, because hotliners are much smaller than a 3.7 m F3J plane. The F3J plane specked to your visual limit will be considerably further away. I learned this fact well when I made the jump to TD/F3b flight. We really push the limits of our reception, so a rock solid RF link is a must. I have never had a glitch at the slope after I started setting up my planes for TD flying.

Just to clarify my experience since it appears that you discounted partially what I said....
I have had my 3.1M superblade to 1000' AGL (measured by on board eagletree) and have flown near or above that altitude on many many occasions.Surprisingly without loss of my airplane due to signal loss ;)

You "probably" can't go wrong with a 15" stinger hanging out your backside but I'm just relating my own experiences..YMMV ;)

Steve

bobthenuke

Aug 07, 2007, 02:56 PM

No, it is the MPX system to get rid (ignore) invalid signals. if some invalid signals are received the receiver replace them by the last valid signal received. If the receiver don't receive valid signal for more than x seconds (0.5 sec I think) it switch to fail safe mode.
That mean that if you have this kind of system on your receiver (Jr 790 does have an equivalent ??) you can't see if lose of signal or perturbations occurs during the range test... and you may think that everything is ok :(

Joel

Reading the instructions that come with the MPX IPD receivers, ;) , you're directed to disable the IPD while performing the range check...with it in this "dumb" state problems will become self evident. Additionally, the receiver records 3 different error conditions; low voltage, field strength fluctuations (blind spots), and signal interference. Fail Safe mode is not automatic - it must be set, same for IPD mode.

Going back to the original question regarding best practice, in the past I've placed my antennas in different places and positions depending on the specific model and my general attitude towards the setup at the time, but any performance data (negative or postitive) means only something to someone with the same model, same Tx/Rx, same configuration from nose to tail, flying in the same conditions and geographical location. For larger models I'm sticking to the old tried and true method of pulling the antenna out directly behind the wing and attaching it as close to the top of the vertical stab as possible. I'd hate to think that trying to eliminate that tiny extra bit of drag or getting rid of that old, funky antenna look would ever cost me my ship some time if conditions were such that I needed that last little "grunt" of reception to keep it in control.

...bob

mlachow

Aug 07, 2007, 06:29 PM

Are we talking 72 mhz here or 2.4ghz... :confused: I'll agree taping 2.4ghz antennaes seems to be problematic but all my planes (72mhz radios) have the antennae taped to the top of the fuselage for the last umpteen years ..carbon mini blade..trinity carbon...superblade...Flash hotliner...and a few own designs and I have never ever had a problem with taping them outside of the fuse :confused: I taped them outside specifically to help remove any chance of interference caused by running the antennae inside of the fuselages :confused:
Steve :)

OK, everyone believes there are problems with 2.4, especially those that don't use them.

Substitute 2.4 for FM, for digital trims, for digital servos, etc, etc....

I also like reports that guys lost control at a distance. You have to consider two questions. 1) Did the radio link fail and 2) did the visual link fail. A short loss then recovery is often the visual link failing since after recovery, the model is generally at a lower altitude which should be worse for the radio link.

jcosta

Aug 07, 2007, 06:44 PM

I also like reports that guys lost control at a distance. You have to consider two questions. 1) Did the radio link fail and 2) did the visual link fail. A short loss then recovery is often the visual link failing since after recovery, the model is generally at a lower altitude which should be worse for the radio link.

In my case I know when the radio link failed. Because the receiver tells me so when I retrieve the plane, and because the fail safe is activated, in full crow braking.

Also, I suggest you put a 2.4GHz receiver in a carbon fuse and go fly. But with a plane you paid US$1500-2000. Will you do it?

And 2.4GHz is illegal in Portugal, as in most European countries.

Still, I am very happy that the car and power plane crowd are using it, it means a cleaner 35MHz band for me... I strongly advice anyone who asks me to convert... ;)

mlachow

Aug 07, 2007, 07:34 PM

Also, I suggest you put a 2.4GHz receiver in a carbon fuse and go fly. But with a plane you paid US$1500-2000. Will you do it?
;)

I'll top you one. I put them in my scratch built molded model. $1500 is a lot cheaper than a month of evenings laying up a new model not to mention the price of materials. I doubt that I could even get the high modulus carbon I use in the spars today, better than anything in any Euro moldies I know if.

F3X

Aug 07, 2007, 08:50 PM

pinolefm1

Aug 07, 2007, 10:02 PM

OK, everyone believes there are problems with 2.4, especially those that don't use them.

Substitute 2.4 for FM, for digital trims, for digital servos, etc, etc....

I also like reports that guys lost control at a distance. You have to consider two questions. 1) Did the radio link fail and 2) did the visual link fail. A short loss then recovery is often the visual link failing since after recovery, the model is generally at a lower altitude which should be worse for the radio link.
My post only reflects what I read here and elsewhere.Wasn't meant as an argument for or against 2.4ghz ..only that there may be potential problems.
For example...... http://www.rcgroups.com/forums/showthread.php?t=657685&highlight=copper+patches
Hope this helps :rolleyes:
Steve

mlachow

Aug 08, 2007, 10:05 PM

Hi Mike,
Maybe you can help clear this issue up for many potential users of the JR 2.4 system. Some may not know you are on Team JR and have the opportunity to test the new system.
John and Peter flew 2.4 at the Nat's this year in unlimited and F3J I believe.

Maybe you can tell us what models has the 2.4 system been use successfully in and if there were any modifications made for better reception? This info would be very useful.

I am flying things I build myself, so none of them are kits. Except for 2M at the Nats, everything I flew was with the Spektrum module in a 9303 or 10X so those are available now.

I flew a 9303 2.4 in my 2M at the nats. Basically similar to an Aegea 2M. My RES is a bubble dancer but the pod is really my F3b pod built light for RES. Also the same pod Tom Kiesling and Mark Drela use for thier Supra's. Only my RES and 2M are on the 9303, unlimited and F3j are on a 10X. 2M and RES were with R7000 RX and the Unlimited/F3j models used the R9000. I put two remotes on the R9000 just to test how well they worked in different locations. The R9000 will read out how many signal losses you have for each of the receivers in the system. Really nice for those who like to have data. Unfortunately we don't have that kind of data on 72 and 35 systems. That would be interesting to have.

Most of my fuselages are a mix of glass and carbon. Pylon areas have carbon cloth in that area, carbon strip runs full length of pod and booms are all carbon. I use a solid bar for ballast in my RES ship. That sits right next to the receivers. No problem with the ballast. I never had any problems with R770's and R790's in these fuselages. It's sure nice not having to snake the long 72 antennas down the fuselage.

I also have flow the RX in my 1/3 scale Salto with no problems.

Peter Goldsmith flew 2M with a Duck and Unlimited and F3j with a Sharon. He also has a Tragi 705 that he flies with 2.4. There were probably a half dozen DX-7's or modules in the RES ships at the Nats including things like Ava's. But Peter and myself were the only two to fly Unlimited ships at the nats.

It was really nice at the Nats not having to worry about frequency pins, especially for evening flying.

It was nice to try the 9303 2.4 native TX. If you fly anything fast or want better response, get the native TX, not the module. The 2.4 TX sends updates faster than the module transmitter. I can tell the difference, anyone who flies anything fast might notice.

mlachow

Aug 08, 2007, 10:14 PM

My post only reflects what I read here and elsewhere.Wasn't meant as an argument for or against 2.4ghz ..only that there may be potential problems.
For example...... http://www.rcgroups.com/forums/showthread.php?t=657685&highlight=copper+patches
Hope this helps :rolleyes:
Steve

There is potential for problems in any system. Most comments I hear are about problems with 72MHz RX's in fuselages and adding wire.

Fortunately everything you hear on the Internet is true :eek: and lots of folks can repeat what they read on the Internet to give modellers thier expert :rolleyes: opinions.

pinolefm1

Aug 08, 2007, 11:35 PM

There is potential for problems in any system. Most comments I hear are about problems with 72MHz RX's in fuselages and adding wire.

Fortunately everything you hear on the Internet is true :eek: and lots of folks can repeat what they read on the Internet to give modellers thier expert :rolleyes: opinions.
Did you even read the thread I linked?? Are you saying they went through all that testing and effort for no reason.That thread is not the only instance of 2.4ghz being problematic :rolleyes:
Your post seem to say that there are absolutely no issues with 2.4ghz and that I and others are fabricators of 1/2 truths and lies :confused: :rolleyes:
I recognize there can be problems with 72mhz systems as well and the primary fix is to simply run the antennae exterior either by drilling a small hole in the fuselage or some people apparently prefer adding a stinger out the backside.
Amazing to think you represent some professional RC group with your snide remarks and attitude.:rolleyes:
I wonder what your qualifications are that makes you believe you opinions are "expert" :rolleyes: opinions ??
Steve

Andrew McGregor

Aug 09, 2007, 02:23 AM

As the author of that thread... I can state with complete certainty, it IS the case that 2.4GHz CAN be a problem in all-carbon layups. But I can also state with complete certainty, it isn't necessarily. I've seen a Carbon Destiny set up with an AR7000 bunged inside and just work. My Mini-Blade is still trouble... although I now have a 2.4GHz spectrum analyzer I can borrow from work so I can finally debug it properly.

I actually measured the signal loss inside the Mini-Blade's fuselage before I put the patches on it... 17dB, or four thousand times signal strength reduction. That's the same as six kilometers of empty air... no wonder it doesn't work properly without extreme measures.

raschow

Aug 09, 2007, 05:13 AM

I wonder what your qualifications are that makes you believe you opinions are "expert" opinions ??

Pretty darn good IMO! Let's see - He wears Team JR & Team Spektrum shirts, scratch builds magnificent composite F3X airplanes, constructs F3X timing/signaling systems, consistently wins and/or places high in regional, national & national team selection RC soaring events. He knows way more than he typically volunteers to tell, but is very forthcoming and carefully analytical if one takes the trouble to ask. When he talks, I listen! Good Lift!
PS: He married well too (I think)!

djklein21

Aug 09, 2007, 12:45 PM

mlachow does know what he is talking about.

pinolefm1

Aug 09, 2007, 01:05 PM

Pretty darn good IMO! Let's see - He wears Team JR & Team Spektrum shirts, !

So....he pimps radio systems ,wears spiffy team gear and builds airplanes like the rest of us.I don't think I'll fall to my knees in admiration if that's OK :rolleyes:
Doesn't surprise me that he's posted what he did.
Maybe the team manager pulled him aside and said "Hey Mike..someone needs to go online to try to squelch this talk of 2.4ghz not being perfect as it's costing us radio sales"

as far as him "knowing what he's talking about "apparently he doesn't have all the answers based on Andrew McGregor's post just above this one
At least he admitted in a backhanded way that there are potential problems with any radio system...which includes 2.4ghz ;)
Steve

jgs99v

Aug 22, 2007, 08:46 PM

Guys - This was posted in another group - thought if referenced this might be of help:
http://www.rc-cam.com/ant_exp.htm

target

Sep 27, 2007, 08:12 PM

Dave Klein-

What method will you use for your CERES antenna (assuming a 72MHz Rx.)?

Thanks,
Target

mlee8249

Sep 27, 2007, 08:45 PM

Hi Guys,

Just thought I would add my $.02

I fly mostly F3J models and with carbon fuselages. Lately, it has been the Shadow and Vision. Both models were initially set up with 72-mHz JR 9303 systems. I could not get a good ground check with the stock antenna inside and was running them outside on the fuselage. But I did some experiments along with a friend who was flying a Sharon and another Shadow.

I first range checked with the antenna laying sideways to the plane outside. Perfect range check, all angles. Next, I placed the antenna inside and got only 1/4 of the range check distance. NFG. So, I now spliced 12 inches of antenna wire to the stock length and ran it inside the fuse with the 12-inches hanging out. My range check actually increased by 25%...whoa! That was unexpected! So, for the heck of it, and the fact that I don't want 12 inches of wire hanging out, I started to clip an inch off at a time and then did the range check. It wasn't until I got the extra wire down to 7 inches that the range dropped. So, I spliced an 8 inch length on the stock antenna, with heat shrink on the splice, and flew it. No problems! I then taped the 8 inch piece to the fuse so that it wouldn't be just flopping all over. No problem. And that's the way I left it from then on. Perfect reception. My friend arrived at the same conclusion using a Futaba 14-MZ system, same type of testing, independent of my testing.

I now started messing with the JR X9303 DSM2 system. Did the same test sequence and got the same initial result...poor range check. I then spliced some sheilded wire from the reciever case out for about 6 inches and then added one inch of unshielded wire which pokes out of the fuselage. Now, my receiver set up uses the 9000 series reciever with the secondary receiver also in use. The secondary rx is sitting with the antennas pointing down the bottom of the cockpit area and out the skin. So, if you look at the nose of the plane, the "whiskers" are sticking out at the 10:00, 2:00, 4:00 and 8:00 o'clock positions. Last Sunday was the initial flight in a contest environment. Perfect even at extreme distance. Nobody even knew I was flying 2.4 until they noticed the shorty antenna on the tx. Even Team JR pilot Larry Jolly couldn't tell until he looked closely for the whiskers. So, this can be done, and the drag from the whiskers is not nearly as bad as a single wire going all to the way up to the tip of the tail. I'm happy with it. Your mileage may vary!

Mike

djklein21

Sep 28, 2007, 01:39 AM

Dave Klein-

What method will you use for your CERES antenna (assuming a 72MHz Rx.)?

Thanks,
Target

Target, I will be doing solution number 2 from Samba's website

http://www.f3j.com/antenna.htm

I plan on flying these planes in Europe in the future, so I will set them up as if I had to deal with 35MHz. I did this too my X-21 and had no issues. I also like Pierre Rondel's Idea of using a brass threaded solder link to make a removable music wire antenna. I will mount mine under the tail cone though. You can see Pierre's solution performed on his Freestyler on the TUM webpage.

target

Sep 28, 2007, 03:28 AM

roydor

Sep 28, 2007, 06:37 AM

Mlee,

I ordered a 9303 DSM2 system and planning to install it on my Perfect. I am very interested in your solution with splicing shielded wire to extend the antenna. Could you please explain where and how you spliced it, inside the receiver, outside, what sort of wire etc. Pics would be really nice also, of the fuse too if possible.

Roy

eye_rc_soar

Sep 28, 2007, 09:20 AM

Hi Guys,

Just thought I would add my $.02

...

I now started messing with the JR X9303 DSM2 system. Did the same test sequence and got the same initial result...poor range check. I then spliced some sheilded wire from the reciever case out for about 6 inches and then added one inch of unshielded wire which pokes out of the fuselage. Now, my receiver set up uses the 9000 series reciever with the secondary receiver also in use. The secondary rx is sitting with the antennas pointing down the bottom of the cockpit area and out the skin. So, if you look at the nose of the plane, the "whiskers" are sticking out at the 10:00, 2:00, 4:00 and 8:00 o'clock positions. Last Sunday was the initial flight in a contest environment. Perfect even at extreme distance. Nobody even knew I was flying 2.4 until they noticed the shorty antenna on the tx. Even Team JR pilot Larry Jolly couldn't tell until he looked closely for the whiskers. So, this can be done, and the drag from the whiskers is not nearly as bad as a single wire going all to the way up to the tip of the tail. I'm happy with it. Your mileage may vary!

Mike

Mike, can you post a picture of your install of the AR9000 and the "whiskers"?

Thanks,
Don

djklein21

Sep 28, 2007, 11:22 AM

I was thinking of using that same style music wire setup in the tail, but with a small gold single connector tying the tail wire to the main wire. That way, I can remove the tail planes and just unplug the extension...
Not sure if I'll feel as secure as if it was soldered, though.

Maybe the connector, and a piece of shrink tube to help insure it stays connected...
Hmmm :confused:

T
I would feel comfortable as long as each extension had their own connector. That way, If one were to come loose the other would still be ok. I am also going to add the steel music wire exiting the tail. That way I will have three orthogonal antennas, covering all orientations. Plus I think the wire exiting the tail looks cool.

djklein21

Sep 28, 2007, 11:27 AM

BTW, I strongly recommend using an FM (not a PCM) receiver for testing your antennas. The PCM receiver will mask a weak/poor signal before it goes into fail safe. An FM receiver will show the noise in fluttering control surfaces, letting you know that you are approaching the edge of no reception. I also prefer an FM reciever in flight, since I will get the same warnings before I get total loss of control. I think this is more important on a thermal field than on the slope since the distance we fly at are much further. There also tends to be a lot more transmitters on at the same time at a thermal comp when compared to a slope race.

djklein21

Sep 28, 2007, 11:28 AM

Mr Mike Lee, I am really enjoying your input on your 2.4 experiences. I have a 9303 with a Spektrum module. I am only using 2.4 in my Trex right now, but I would love to transition to it for my sailplanes as well.

mlee8249

Sep 28, 2007, 11:48 AM

Hi Roy,

The wire I used for the 2.4 Ghz rx's is just shielded audio wire from Radio Shack. What I did was to use 2-conductor shield wire, carefully removing the outer insulation. When you do that, you will have two 28-ga wires wrapped in wire shielding. I only need one wire, so I pulled one of the wires out, and then placed thin heat shrink back over the remaining wire with the shielding intact. I now have a single conductor shielded wire.

I clipped the stock antenna from the rx as close as comfortable to the rx casing. I then soldered a length of the shielded wire to the reciever antenna (what is now left of it) long enough to fit my needs, and then added the one-inch of unshielded wire to replace the portion I clipped off originally. I placed only enough heat shrink on the solder joints to prevent having a bare wire showing. Nothing hard about the process, just careful soldering.

Don, I'll try and get a pictorial story going on this to show what I did and how it looks on the plane. I used to think that having them whiskers out there would be pretty hoakie, but then I also thought it sure beats having a wire going from the canopy all the way to the top of the fin, or trailing off the tail for me to step on, or hanging around the wing saddle for my hand to catch on while launching. My next experiment is to tape the whiskers to the side of the fuse completely so that they don't hang out at all. Should be fun!

Andrew McGregor

Sep 28, 2007, 12:28 PM

Ok, here's a couple of bits of clue...

1) Audio wire doesn't work at 2.4GHz, and you're probably getting conduction down the shield... in other words, it's working, but not for the reason you think it is. Use WiFi antenna cable instead... it's about 8x the price, but works a dream. There's a very thin kind of WiFi antenna cable that weighs next to nothing. Satellite TV cable would also work, but it's really heavy.

2) Taping outboard antennas to a carbon fuse doesn't work. I tried that, found out by experiment, and then found an article about radar reflections that explains why it doesn't work. Carbon-epoxy is an almost perfect microwave damping material, so there can be no signal near the surface and parallel with it. This also explains why carbon DS gliders are hard to pick up on radar. Trying this might well be the wrong kind of fun as your plane suddenly becomes a free-flight model. Mine did, on a slope site, on the backside. Fortunately it came down in long grass and somewhere I could find it.

3) You don't need to solder antennas at 2.4GHz. Instead, just remove the shield from exactly 31mm of cable, lay it alongside the existing antenna, and tape it on with non-metallic tape (or heatshrink it on).

4) External antennas if they stick out need to be either 31mm exactly or 62mm exactly (plus or minus about 0.5mm). You need to be fairly precise about that 31mm. Measure from the end of the shield if you're using shielded cable, otherwise measure from the surface of the carbon.

5) There are ways to make flush external antennas work, but I don't have a design I like yet... the damping from the carbon messed up my last try at it.

Avaldes

Sep 28, 2007, 12:32 PM

Hey Mike,

Unless you tie the shielding to a ground plane, you are just carrying extra weight. Maybe there is some capacitance effect from having the conductor close to the foil? For real RF shielding you need to ground it (ideally at both ends).

Might be worth an experiment to see if regular wire gives the same results.

-Aaron

Andrew McGregor

Sep 28, 2007, 12:51 PM

Ordinary wire will work, just not as well as shielded, even if you don't tie the shield to anything (for kind of the same reason you can just lay conductors alongside each other at these frequencies). For runs of a few centimeters, it's not worth the trouble... unless the fuse is more than 50mm in internal diameter, where the wire will start to radiate inside the model.

roydor

Sep 28, 2007, 02:33 PM

Andrew,

If I understand it correctly 2.4 GHz is 125 mm in length ( 3e8/2.4e9 ). 31.25 mm is 1/4 of the wave length which probably means that the receivers electronics are tuned with the antenna to achieve good reception with only a quarter of the required wave lenght. Isn't it plausible that adding 125 mm to the existing 31.25 mm (a total of 156.25 mm = 5/4 wave length) and extending only 31.25 mm of the antenna out of the fuse should give a good result.

In this case the 125 mm extension should be an RF "clean" extension. Am I wrong?

Roy

Andrew McGregor

Sep 28, 2007, 03:28 PM

Ok, you're half right.

Yes, the part of the antenna outside the fuse should be 31mm long.

However, the inside length doesn't actually matter. The electrical environment inside the fuse is a single non-resonant cavity, so there is no meaningful wavelength in there. The overlap with the RX antenna should be 31mm because that matches to the receiver.

roydor

Sep 28, 2007, 06:31 PM

But if you add an entire wavelength you could avoid having to overlap pieces of 31 mm wire and just solder on the 125 mm. You could solder 125 mm to the end of the existing antenna and just stick out a piece of that out the fuse.
Should be easier to make and maintain.

tewatson

Sep 28, 2007, 11:17 PM

By actually gluing wire into the hinge line, or using the method shown in the Ceres build doc? The nice thing about the Ceres tail is they have provided a means to do this (holes in the tail roots for music wire to poke into).

The only drawback to the Baudis method is when you remove the tails, you have the wire antennas out the fuse in the tail positions. I suppose with a connector one could make that removable too.

Tom

Target, I will be doing solution number 2 from Samba's website

Pilebuck

Sep 29, 2007, 12:21 AM

This is working very well in my F3X models...http://www.rcgroups.com/forums/showpost.php?p=5414484&postcount=25

Just need to find a suitable connector that will allow the use of a removable banjo wire as an antenna.

Sam

mlee8249

Sep 30, 2007, 10:39 PM

Hi Aaron and Andrew,

I did some more testing on my setup, and here is what I found. Aaron mentioned that the shielded wire has to be grounded to work. Well, I guess not! Mine is not grounded and when I used only the shielded wire without anything of the antenna, the rx was blind. Add the one inch of antenna on top of that, and the rx worked. Makes sense when you consider the poor penetration level of 2.4-Ghz.

Andrew said not to use audio wire. I did use a premium grade of audio wire, multi stranded...not the cheap stuff. When I treid to use servo wire with shielding, no difference. Andrew also mentioned not to stick the antenna to the side of the fuselage. This is true. My testing found that when I stuck them to the fuse, my ground check range went down an immediate 30%....tooo dangerous to risk. Let the whiskers hang out, and range returns to normal. Someone else mentioned that the length of antenna hangig out the fuse is critical. Well, I did not find this to be true. I went about making my antenna length rather hap-hazardously and so some are longer or shorter than others. Works fine. It may be that the two internal rx's and single remote rx are working well to cover up.

I do have photos coming on my method of making the system work. And thanks to Aaron and Andrew for the help!

Mike

mlee8249

Sep 30, 2007, 11:02 PM

Okay, back to the photos. Here we go!

mlee8249

Sep 30, 2007, 11:31 PM

Part two of the project showing the installation of the rx inside and out. BTW, this is my Shadow model I am installing into.

Andrew McGregor

Sep 30, 2007, 11:39 PM

The audio wire clearly works... but probably not as shielded cable at that frequency. It doesn't really matter what sort of audio wire, as there are only a few kinds of coax that work at 2.4GHz and higher, and they're all expensive and designed for the purpose. So most likely, you'd get on just as well with a bit of plain hookup wire.

mlee8249

Oct 01, 2007, 12:30 PM

Hi Andrew,

Geez, this is great being able to converse with people on the other side of the earth! You're right that any wire should work, and that is proven more than rarely as I read about people using piano wire trailing out the tail, super thin mag wire in the hinge line of HLG's, and even one guy I knew of using the landing gear strut that just happened to be the length he needed for the antenna. The one thing I won't use is a single strand wire as it is too prone to breakage at any given time. Even fine multi-strand wire has been known to break somewhere in the middle. I can't even count the number of times someone has related to me that their range check failed and then by checking the continuity of their antenna wire, they found that there was a break in the wire. So, you can never be too careful. This should be a real wake up call to anyone to make it part of their routine maintenance check to make sure the antenna wires are good. Could save them a plane someday. Thanks for the info, Andrew. All I know right now is that the shielded wire I am using is working in the real world, I am getting good ground check range and no problems in the air. So, whatever the case might be, I have managed to get it right or at least one of my planes would be still be smoldering in that smoking hole in the ground caused by a crash. Right now, I can happily state that both planes are sitting smug in the hanger and flying fine...on 2.4 GHz.

Mike

eye_rc_soar

Oct 01, 2007, 01:37 PM

Mike

Just to be very clear on your "whiskers" final or best position, in the photos you posted the whiskers appear to be nearly parallel and next to the fuselage surface. Was this during your experiment to try them taped to the surface? When you had the success flying were the whiskers sticking out more perpendicular to the surface?

Thanks,
Don

Avaldes

Oct 01, 2007, 01:54 PM

Hey Mike,

Great results and pictures that you posted here! It is interesting that the shield is attenuating the 2.4 signal without a ground.

-Aaron

mlee8249

Oct 01, 2007, 10:39 PM

Hi Don,

You're right in that the whiskers are stuck to the sides of the fuselage and that was shot right before I did the ground testing again. So, whatever you do, let them stick straight out. You'll get used to them faster than you will get used to not having a long whip antenna on the Tx.

Aaron, thanks for the reply. You know me well enough that you know I'm no electronics whiz. I'm really a hack. But this one works and what can I say?

Now I have a question for you other whiz people...we all know that you're not supposed to point a regular Tx antenna directly at the model as this is the worst part of the radiation pattern. But, does anyone know where the worst part of the radiation pattern is on these itsy-bitsy short 2.4 GHz Tx antennas? I see some guys angle them up, and mine I haven't bent at all. (because I'm not a bent-wick). Anyone?

acw

Oct 07, 2007, 10:53 AM

For what is worth, I have just decided to try installing the antenna inside the fuse of my carbon Nyx. After a positive range check, I flew all day without any problem. I'm using some futaba PCM Rx (no mods) and a 12S Tx

I wonder how much signal loss to expect. At least in slope soaring it appears to be just fine.

AW

Andrew McGregor

Oct 07, 2007, 11:11 AM

Now I have a question for you other whiz people...we all know that you're not supposed to point a regular Tx antenna directly at the model as this is the worst part of the radiation pattern. But, does anyone know where the worst part of the radiation pattern is on these itsy-bitsy short 2.4 GHz Tx antennas? I see some guys angle them up, and mine I haven't bent at all. (because I'm not a bent-wick). Anyone?

Same as the FM antennas, the null is straight off the end. Best is broadside on. This is the same for receiver antennas.

target

Oct 07, 2007, 11:47 AM

The setup I used on the all carbon fuselage of the CERES worked like a charm. You can see pics and a description on my Blog.

Target

mlee8249

Oct 08, 2007, 12:21 AM

Hi Andrew,

I didn't get to read your answer prior to going into competition again with the set-up. And I found out the hard way about the antenna position being what you said....No, I didn't lose a plane or nothing, just got a couple of lock-outs until I bent the tx antenna up and that stopped any loss. It was perfect for the entire Visalia event. So, the correct way to hold the antenna is any way as long as you don't point at the plane.

Thanks!

dbarker

Oct 21, 2007, 08:20 PM

FYI - I started a new thread where I used Mike Lee's ideas on antennaes on a carbon/kevlar Supra fuselage. It works!

http://www.rcgroups.com/forums/showthread.php?t=760393

roydor

Nov 09, 2007, 01:27 PM

Today I test flew my carbon fuse Perfect with a 2.4 9303 system.

I used 62 mm extensions which I attached with a heat shrink to the original antenna so that the extension runs along side the original antenna for its entire length and extends an additional 31 mm over the original length. I then drilled two holes under the elevator servo and another in front of the servo and extended the antenna's through them for 31 mm. The secondary receiver is placed under the elevator servo and the primary in front of the elevator servo.

Range was 50 meters in almost every direction while in aspects some it was only 40-45 meters (still plenty).

in the air it worked great, this system is awesome (flew with a Stylus before) the response is incredible and the system is comfortable and the mixing options were great.

The plane feels as though its on steroids, its much more agile and just feels alive.

Thanks to all in this forum for the info, it helped allot.

Roy