Aerial placement

[Old School]

A basic question, but very few boats these days have an external aerial, so how is the aerial lead mounted in the hull, please?

[rol243]

you can buy an antenna kit with comes with the alloy mount / tube and push on top cap. the antenna goes inside this short tube and you just bend the last 1/2 inch and push on the cap to make it waterproof. [ rc boat bitz ]

[Old School]

Thankyou, that is for an external aerial mount, however, many boats do not seem to have external antennae. I will have a look on the site.

[rol243]

sorry it all depends on what type of receiver your using , i use Futaba with a single antenna wire i prefere to have this in line of transmitter sight for better range. also if you have a carbon fibre hull you don,t want to run the antenna inside the hull as you will lose range.

[Prodrvr]

You don’t bend 2.4g antennas.

[Old School]

I also prefer line of sight so was surprised that so many run their antenna inside the hull.

[rol243]

yes you can bend the last 1/2 inch where there is no insulation. the bend is what holds the antenna from slipping back down the tube when the cap is pushed on.

[Mxkid261]

You can use something like this. https://www.offshoreelectrics.com/pr...prod=aero-6028

Sometimes I just used a piece of aluminum tubing, silicone it into the hull, and put a plastic tube in it held in by some tygon fuel line. Simple and free if you have stuff laying around.

22141145_10159406185800716_3089018734855408953_n.jpg

[Fluid]

yes you can bend the last 1/2 inch where there is no insulation. the bend is what holds the antenna from slipping back down the tube when the cap is pushed on.

Sure you can - if you want to damage your antenna. Futaba specifically warns not to repeatedly bend the antenna to avoid compromising the antenna internals. That last 1” of the antenna is the only part which receives a signal from the transmitter, damage it and no reception. Too, folding it over reduces it’s effective length so lowered reception again. This is likely one reason folks report poor range on a radio which used to work fine.

You “can” do it, just as you can text while driving or smoke cigarettes - but it is ill-advised and not necessary.



.

[NativePaul]

yes you can bend the last 1/2 inch where there is no insulation. the bend is what holds the antenna from slipping back down the tube when the cap is pushed on.

The uninsulated part at the end of the antenna is the only part that is actually working as an aerial, the rest is shielded, and is only there as an extension so you can get the aerial out or a carbon hull/fuselage/chassis or up past your motor/battery/ESC etc that can block the signal. You can do what you want with the insulated part as long as you dont damage it, but for best reception the uninsulated part should be kept straight and oriented in the same plane as the TX aerial.

Nearly all the aerials I have seen on 2.4ghz RC sets (all with good performance) are tuned to a quarter wavelength which is 31.25mm for a direct mounted (internal) antenna like on a Tactic RX, or as the dieletric effect of the 50ohm coaxial slows down the radio waves a little it is 28.8mm on extended antennas.

If you bend it, it will no longer be a tuned length and reception will suffer dramatically, best case scenario is that you bend it exactly in half and make it 1/8 wave length (not nearly as good as straight, but much better than a random length). There is no need to bend it over the top, the low mass of the wire and its stiffness means that you can just poke it up any reasonably sized tube, and it wont fall back down.

If you only have 1/2" uninsulated at the end of your antenna I suspect that it has been broken off at some point, and I would advise you to check out the length of a brand new one at your LHS. If it is indeed shorter than stock, open up the RX, many have the antennas easily user replacable with a U.fl plug/socket, and replacements are made by Futaba, Spektrum, Frsky that I know of and likely many more that I don't, any will do as they all use the same U.fl connector, 50 ohm Coax, and 28.8mmm aerial length. If it is soldered to the board as some low end sets are, you could very carefully strip the coax back leaving 28.8mm of the inner aerial that looks uninsulated (it is actually insulated to stop it shorting on the coax sheath, but with very thin transparent insulation) poking out , buy a new RX, or if you run solo on a private lake, feel free to carry on with what you have and hope for the best.

[MadProps]

I had no external antenna mount and found anywhere near the limits of the range the signal would get lost in hard turns as the antenna would be below the water line. I installed an external antenna and all is well with extended range

[Old School]

Thankyou all for your replies

[rol243]

i have fitted my 2.4 gig antennas like this since i first started using 2.4 gig radio and have had not one single issue atall with range , its not that i would bend and re bend this end every time as just about all of my receivers stay in the boat and are not transfered to other boats as there only about $50 a pop to buy.
maybe i should just leave the antenna inside the hull and hope for better range. lol

[CraigP]

The uninsulated part at the end of the antenna is the only part that is actually working as an aerial, the rest is shielded, and is only there as an extension so you can get the aerial out or a carbon hull/fuselage/chassis or up past your motor/battery/ESC etc that can block the signal. You can do what you want with the insulated part as long as you dont damage it, but for best reception the uninsulated part should be kept straight and oriented in the same plane as the TX aerial.

Nearly all the aerials I have seen on 2.4ghz RC sets (all with good performance) are tuned to a quarter wavelength which is 31.25mm for a direct mounted (internal) antenna like on a Tactic RX, or as the dieletric effect of the 50ohm coaxial slows down the radio waves a little it is 28.8mm on extended antennas.

If you bend it, it will no longer be a tuned length and reception will suffer dramatically, best case scenario is that you bend it exactly in half and make it 1/8 wave length (not nearly as good as straight, but much better than a random length). There is no need to bend it over the top, the low mass of the wire and its stiffness means that you can just poke it up any reasonably sized tube, and it wont fall back down.

If you only have 1/2" uninsulated at the end of your antenna I suspect that it has been broken off at some point, and I would advise you to check out the length of a brand new one at your LHS. If it is indeed shorter than stock, open up the RX, many have the antennas easily user replacable with a U.fl plug/socket, and replacements are made by Futaba, Spektrum, Frsky that I know of and likely many more that I don't, any will do as they all use the same U.fl connector, 50 ohm Coax, and 28.8mmm aerial length. If it is soldered to the board as some low end sets are, you could very carefully strip the coax back leaving 28.8mm of the inner aerial that looks uninsulated (it is actually insulated to stop it shorting on the coax sheath, but with very thin transparent insulation) poking out , buy a new RX, or if you run solo on a private lake, feel free to carry on with what you have and hope for the best.

Paul, are you saying that the plastic insulation on the antenna is a magnetic shield? You do realize that an antenna works on principles of electromagnetic radiation, right? The plastic only comes into effect if the frequency is super high, then it gets a bit lossy. But gigahertz antennas are very short. The orientation of the antenna is, is you any many pointed out, very important.

[NativePaul]

Rol243, you are doing well in getting the aerial up above the hull, I am glad you have not had any issues and I hope you never do, I just wouldn't feel right in not pointing out that the bend is far from optimal, and that you may have broken part of the tip off making it less optimal still.

CraigP, No, of course I don't think the plastic insulation on the antenna is a magnetic shield, the grounded woven metal sheath of the coaxial cable is the shield. Do you not know how coaxial cable works?

[CraigP]

I've never seen a coax cable used as an aerial... The only antennas I have seen are a solid, bare wire (old school) and a stranded cable with a plastic insulation on it. A coax is designed to transmit a signal from one end to the other over a controlled impedance to arrive on the receiving end as undistorted as possible. The shield as two functions, as an external shield for external fields not considered as the signal and to set the impedance of the cable, usually 50 or 75 ohms. The shield is usually grounded to drain extraneous energy and to set the impedance relative to ground, which is usually established as a ground plane. If a coax works as an aerial for you then that's a good thing!

[fweasel]

Craig, modified coax cables are used as antennas all the time and I don't see how the 2.4GHz receivers using them are any different, in your eyes.

[CraigP]

The length of an antenna is 1/4 the wavelength of the desired signal to receive. The older transmitters, running 500khz or so, needed at least a 20" antenna. As the frequency increases, the antenna grows shorter. I agree that you could modify a coax for GHz reception. But that wasn't the point Paul was making. You still need 1/2 a 1" unshielded portion even for GHz. That would be trick to raise the reception point over the boat and still make it effectively receive the carrier. My reciever has the antenna inside of it on a PCB strip line. It's attached with Velcro on the under side of the deck, pointing up. I'm getting full range for a boat, but wouldn't trust it in a plane. Your cell phone has the same type of antenna. The benefit of a PCB strip line is that you can set the capacitance of the antenna, and make a better tuned circuit. I have designed antennas for a living, working for Wilson Electronics. If you use a coax, you should be well versed in antenna theory or you could easily make a unidirectional antenna out of it, something you really don't want. These antennas need to be omnidirectional in RC craft. Some of these problems being posted could be suffering from that.

[CraigP]

Im just going to leave this topic for others to discuss... This is some pretty deep theory, so just keep doing what you do. I shouldn't have said anything

[rol243]

the coaxial cable is like an extension lead for the main antenna as used for television reception, you need both the inner copper wire and the woven copper wire mesh to connect , just like positive and negative on battery terminal connections.

[fweasel]

The length of an antenna is 1/4 the wavelength of the desired signal to receive. I agree that you could modify a coax for GHz reception.

Agreed

But that wasn't the point Paul was making.

What specifically do you not agree with what Paul said? Because, it all sounds in line with my understanding of the topic, from a non-EE, practical application point of view.

[CraigP]

Paul is saying that the exposed end of the coax is the only part that is acting like an antenna, which IS true, IF the shield is tied to the ground reference of the antenna, inside the receiver. This is where I may be wrong... iF the receiver comes with an SMA or other, high speed, impedance controlled connector, then you can use the shield as he references. But I've never seen a boat receiver with a SMA connector on it.

My point is, if the shield is not tied to a good, antenna referenced ground, then the shield will be capacitively coupled to the inner conductor and it will move with the signal but not in phase, so it loads, or makes the signal weaker. So where is the shield being tied, is the big question. The grounds on the servo ports are no good, because most GHz antenna front end circuits are Capactively coupled to an isolated ground within the IF radio section of the receiver.

I'm sorry, complex explanation! But it's a complex subject matter and just recommending these generic uses can invite more trouble than it fixes.

But this discussion has made me think. IF we had that SMA connector, it would be great to feed the non-connector end of the coax up through the middle of the vertical stabilizers found on many hydros and just expose the 1/2" of bare metal at the top of the stabilizer. That would be a trick antenna position! Also, for my education, are there receivers that come with a micro coax cable coming out of it? Again, I've only seen stranded single conductor, but there are new things out everyday...

[buckman]

Howdy boys, I use 30 feet of coax cable to receive 2.4 ghz signal underwater from enclosed GoPro to I-pad, How you may ask, simply bare 6inches of copper wire from both ends of coax and tape one end to GoPro and other end to I-pad and you have 2.4ghz antenna.
lol
Buckman

[Bp9145]

[QUOTE=CraigP;701862]" But I've never seen a boat receiver with a SMA connector on it."

Actually I thought that is why some receivers have interchangeable antennas because it has some sort of SMA connectors on it? Others have modified their receivers just for that purpose to put whatever antenna they choose to use. For example, a guy who had a metal boat had a hard time receiving RF signals so what he did was open the receiver and inside the receiver the original wire antenna is connected with a connector style called U.FL and using a short U.FL to SMA cable he was able to use two matching antennas on the deck, one for his Futaba, and one for his XBee communications. I don't have extensive knowledge about 2.4ghz antennas but just enough to understand how it works. But here's an image of it. . .a boat receiver with a SMA connector on it. Check our Degi-key they lots of antennas with SMA connectors on it.Screen Shot 2017-10-04 at 11.44.47 AM.jpg

[CraigP]

Yes, I see... I owe Paul an apology, I didn't realize they had this. Man, thanks for letting me know, it gives me some ideas. I use Digi-Key a lot! Also Mouser Electronics. With that connection, you should be able to get any type of antenna you need!

[CraigP]

I'd like to hear more about this "metal boat", sounds cool!

[Bp9145]

YIPPPEEEE. . .we're all in agreement. Now let's brainstorm some really cool ideas we could all implement in this crazy hobby of ours.

[NativePaul]

Craig, I did say earlier that the sheath of the coax is grounded, like you say it wouldnt work otherwise, but they are, so they do. SMAs are pretty big for model RX usage, I did say earlier that they use the U.fl connector which much smaller but does the same thing. For comparison between the 2 this is a U.FL to SMA adapter.

And for scale, the surface mount u.flplug.


All the top brands ie Futaba, Spectrum, Sanwa/Airtronics, JR, Multiplex/Hitec and Frsky all use RX aerials based on 50ohm coax with the U.fl connector, and likely more that I have not seen inside too. I have seen some budget off brand RX that are still based on the 50ohm coax but soldered to the RX, this is inferior as the connection is not shielded as it is with the U.fl socket, and it is not replaceable in the event of antenna damage, but on the other hand some are so cheap you can see why they dont include a connector. I did also allude to Rx with non coax internal aerials with slightly longer full 31.25mm 1/4 full wave, my mistake not to specify that the aerial would be A PCB trace not a wire, I thought that would be implied by the ease of manufacrure, considering that there is nothing to gain by adding a wire while still keeping it internal to the case.

In case you still dont believe me here are a few replacement aerials from well known manufacturers.

[Bp9145]

Ok then we're all good. This was a learning experience for everyone involved and for future boaters to learn from. . .like I've said in the past this is a place that we can share our knowledge with everyone and that's why I love it. Some will have more knowledge than others but we all contribute somehow. . .peace I'm out my fellow boaters.

[CraigP]

Oh I more than believe you Paul! I have used this stuff in radio gear for our remote telemetry systems running all over in Texas, Colorado and New Mexico. This is what I'm used to seeing. Impedance matching is critical... Our competition takes it rather lightly, and we can pluck out cell signals where they can't using some pretty high gain boosters. I'm sorry I was so forceful, it's just that I know how finicky it all is.

We have our field guys put too tight a bend radius on a coax and what do you know, it don't worky no more! I just spent yesterday on this very problem, with raking with a guy that doesn't "get it", so I was sensitive to the subject. But no excuses, I've got to keep my mouth shut, lesson learned, trust the Paulman!