SilentPilot

2.4Ghz Antenna Mounting

49 posts in this topic

I recently range tested my repaired Pike WR and the results were disastrous!

There may be a few contributing factors. I'll try explain here with the hope I get some advice on how best to alter my setup if that is needed.

I've got two remotes installed because the actual Rx (and its main antennas) is in a Carbon / Kevlar nose cone which totally blocks the signal. So that gives me a total of four antennas that I use. Two taped to the fuselage, under the trailing edge either side, and another two in front of the wing. One taped on top of the fuselage and one below. 

This arrangement worked very well before. Now it doesn't...

There are two big differences now. One, the repair. My dad fixed it up and used Carbon I believe. Two, one of the remote antennas has had the 'active' part of one wire broken off.

I installed all the antennas as before but now the damaged one (that would have been the lower front antenna) is just pushed back in the hole and taped over.

Is this the problem? If the broken antenna has ended up touching bare Carbon would that lead to range problems?

Any ideas greatly appreciated :) 

 

Tony 

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Hi Tony. What RC system are you using? You mention remotes so does that suggest Spektrum?

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Tony, the broken antenna must be fixed/replaced before you can use it again. 

Assuming that you have a Spektrum receiver, you can open the receiver case / satellite and check to see if the antenna is soldered on board or plugged in with U.FL connector. If it is soldered then, you have to send it in to be professionally serviced, otherwise, you can replace it yourself.  

The genuine SPM4648ANT is a suitable replacement that HH sells at https://www.amainhobbies.com/spektrum-rc-spm4648-spm4649t-replacement-receiver-antenna-4-spm4648ant/p520524

HK has longer ones that fits perfectly well too: GR300-Ant/25381 OrangeRX replacement antenna: https://hobbyking.com/en_us/orangerx-gr300-replacement-antenna.html

I've also tested these that I bought from aliexpress: https://www.aliexpress.com/item/150mm-FrSky-2-4G-Receiver-Antenna-Futaba-2-4G-Receiver-Compatible/1913171866.html

Carlos

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Thanks Dave and Carlos :)

 

Yes, it is a Spektrum installation. 

I figured the broken antenna would be an issue. I have spares, just not enough time, the satellite is buried in the rear fuselage! I have unplugged the satellite with a broken antenna to see if I can pass a thorough range test with just one (two antennas). 

With my DX8 I was very particular (some may say too much so!) to arrange antennas in all 3 axis, so preventing any chance of the Tx / Rx antennas being orientated pointed at each other. Now I've got a DX9 with its dual diversity antennas there is no chance that this can happen, so I guess as long as the Tx sees an Rx antenna the signal will get through.

 

I did some reading regarding 2.4 installation on the Samba (Pike manufacturers) website. Paying particular attention to installing antennas in Carbon airframes. They say not to have it parallel to any Carbon structure. I had mine taped to the fuselage which I assumed to be a Carbon/Kevlar layup. Is this bad practice?

My original range tests were very good before the repair. Now I'm wondering why it isn't so any more... 

There is a possibility that the model was on damp grass for a while and some dew seeped into the tape. Also possible that when I picked it up to do a hand held test from differing orientations I accidentally held my hand over an antenna :o

 

If I were to start again should I try to use the 'whisker' type mounting that clears away from the fuselage altogether?

 

Tony 

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2 hours ago, SilentPilot said:

If I were to start again should I try to use the 'whisker' type mounting that clears away from the fuselage altogether?

Tony 

Yes !

taping the antennae flat onto a carbon fus is very bad (or so I've read elsewhere)

Phil.

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Cheers!

I'll call in at T9 and see what they've got :) 

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I've used heatshrink to protect my external whisker antennae and this also stiffens it up, stopping the chances of it being blown bag and in line with the fuselage.

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I've had another thought regarding this...

I think I'm going to cut a hatch into the nose cone so I can thread the main Rx antennas outside once the nose is on.

 

Any reason not to do this? I'm thinking of a round hole to save stress points, with either the antennas coming out of the actual hatch sides, or through drill holes on the sides of the nose. I think I'd prefer them coming out of the sides but one hole is probably better than three...

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21 minutes ago, SilentPilot said:

I've had another thought regarding this...

I think I'm going to cut a hatch into the nose cone so I can thread the main Rx antennas outside once the nose is on.

 

Any reason not to do this? I'm thinking of a round hole to save stress points, with either the antennas coming out of the actual hatch sides, or through drill holes on the sides of the nose. I think I'd prefer them coming out of the sides but one hole is probably better than three...

Before making any holes in the fuselage, I suggest that you make a test by fixing the antenna at the nose using scotch tape and then do a range test. If you have telemetry, you can use the readings to determine the correct place that presents the best results.

Keep in mind that no matter the lenght of antennas are, only the last 31.25 mm of antenna must be kept away from carbon, but there is a caveat on this rule...

Everytime I change flying locations, I always repeat the range test for my peace of mind; A range test failed last weekend on a sailplane that I fly quite often for more than two years. I was almost giving up when I decided to pull both antennas out from the exit guides about three inchs (about 8 centimeters) and then passed the range test. I flew about two hours without having any hiccups

What can I say out of this experience? I really don't know, but one thing I know for sure. I will try to repeat testing more often than I did before.

Carlos

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The trouble is my Pike has a Carbon nose. 

No signal gets through. Telemetry has to be turned off or it affects range checks. It's like the nose cone acts like a satellite dish and reflects all the telemetry signal onto the remote antennas swamping the signal. 

There is no way to thread the antennas outside once the nose cone is on, hence the need for a hatch. 

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Use the shark teeth outside the fuselage. 

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I will do this on the remote receiver, but it's not possible to thread any through the nose...

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50 minutes ago, SilentPilot said:

Telemetry has to be turned off or it affects range checks. It's like the nose cone acts like a satellite dish and reflects all the telemetry signal onto the remote antennas swamping the signal.

If Telemetry has to be turned off for range check, then your setup has a bigger problem. Telemetry shouldn't affect communication between radio and receiver. It must work always, specially while range checking.

FWIW, the Spektrum telemetry transmission is based on when it hears a message from the transmitter in your hands - hear a control message, wait a little, then send a telemetry message. There is never transmition and receiving of data packets at the same time.

A receiver gets a signal. It decodes the signal. It generates pulses, 1 at a time in a legacy receiver. Sometime in there it listens again (remember, there are 2 transmissions every 11ms). And then it waits a few ms. On newer receivers, it has to make sure the timing is perfect so it can send telemetry. Meanwhile, it's generating pulses.

I strongly recommend that you clear this issue out before flying your plane next time.

Carlos

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Is it possible that the Rx got the telemetry signal from the satellite antenna?

The telemetry got instructions what to send, but can only transmit from the main Rx antenna, which is shielded and so causes the interference?

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If your "broken rx aerial" still has some length to it that is as long as the normal aerial section (about 31.5 mm I think) then you can very carefully remove the outer sheathing for that last 31.5mm and bingo you have a new aerial.

Beware of unsupported whiskers, they can vibrate in the airflow and break off, I have had this happen over time.

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2 hours ago, SilentPilot said:

Is it possible that the Rx got the telemetry signal from the satellite antenna?

The telemetry got instructions what to send, but can only transmit from the main Rx antenna, which is shielded and so causes the interference?

No, that's not the way it works.

Which receiver are you using?

Carlos

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1 hour ago, f3fman said:

If your "broken rx aerial" still has some length to it that is as long as the normal aerial section (about 31.5 mm I think) then you can very carefully remove the outer sheathing for that last 31.5mm and bingo you have a new aerial.

Beware of unsupported whiskers, they can vibrate in the airflow and break off, I have had this happen over time.

Antenna length  = 1/4 * Wavelength which in our case translates to 31.25mm

Whenever is possible, I rather replace the antenna with a new one instead of repairing the old, but there are cases this might indeed be a viable option. If the antenna is soldered and if there is enough lenght of wire intact, a repair can still be attempted before sending it in to be professionaly serviced. 

I was researching details on how to do this repair when I found an excellent reading, full of images that I believe, will guide the OP in this task.

http://rcsci.blogspot.com.br/2016/11/receiver-antenna-repairreplacement-guide.html

Carlos

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Thanks, but I'm not planning on repairing the broken antenna, I've already replaced it. It was indeed the push on connector that was in the link. 

I still don't understand this telemetry. All I can say for sure is that it worked properly when telemetry was off. Excellent range check and no problems in flight. 

Things have only gone wrong since the repair. I swapped the broken antenna and the remote it was connected to was still acting strange. Kind of flickering instead of a solid light to indicate that it is working. Maybe that's more evidence that the broken antenna touched some Carbon creating a short which in turn damaged the circuit. 

 

I think my best way forward now is to somehow route the main Rx antennas outside also, however, the nose cone makes this awkward. 

Cutting slots would be easiest so I can slide on past the antennas but I think a hatch that can be taped back on would likely be stronger.

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I had an all carbon (including sheath nose) Blade XL and was faced with a similar problem to you regarding the routing and positioning of the antennae. I ended up using an AR6250 receiver with the long extended whisker antennae. It worked fine up to the point where the receiver failed on the ground just before launch. Spektrum then had the recall on those receivers and they were all swapped for the AR6255 which I then had and used without any problem.

The long whiskers allowed me to position one antennae vertically out of the fuselage just in front of the wing behind the where the sheath ends and the other pointing roughly 45 degrees downwards out of the fus.

Obviously this receiver doesn't have any telemetry but maybe better to live without this facility than risk a model having it and erratic reliability.

 

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