Receiver antenna
- Thread starter tward
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mjmccarron
Member
No. The antenna leads are cut to a specific length to match the wave length that they are being used at. Altering the length will alter the performance and not in a good way.
bstanley72
Member
Yes, what he said, you can't do this, will alter the frequency that it will receive, this is very bad.
What are you trying to accomplish? Maybe there is another way.
What are you trying to accomplish? Maybe there is another way.
mjmccarron
Member
It's difficult to explain but it's something like trumpeting into a Christmas wrap tube. If you get the right note, (frequency) it will resonate a specific tone. Change the length of the tube and the note (frequency) changes. The same thing happens with the antenna wire. It's sized to resonate a signal of a specific frequency which is very small in amplitude. (microvolts) If you change the length of the wire, it will not resonate at the frequency of your transmitter, it will be tuned to a frequency different from what you are sending. It may be able to be extended but you will need to calculate the length based on the frequency and harmonics of the signal. Well beyond most of our capabilities. Best to just leave it alone. There is no reason to extend it that I can see. Unless you are encasing it in carbon fiber, or other conductive material, the balsa, foam board plastic or whatever is around it is invisible to radio signal. It doesn't require "clear view". A properly designed extension cable would introduce loss and reduce the range.. RC equipment is very low power compared to Two way radios used for communication.
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It *CAN* be done, but not easily.
Effectively you'll need to keep the radiating portion of the wire the same while insering a waveguide inbetween.
And what's a waveguide? Just a section of wire where radiation and absorption of RF are confined from occuring.
In this case *IF I HAD TO DO IT* I'd use a piece of coaxial cable with the shield grounded to the board and the center tap wired between the board's RF input and the tuned length of antenna. The RF is trappped in the coax, guided away from the antenna, and the exposed antenna, free from the coax's grounded confinement, resonates on the remaining antenna lenght.
Many of the "Long antenna" versions of 2.4 RX's do this, but handmaking one would be a BEAR. Keep in mind, we're not talking about your typical TV cable coax, we're talking very fine stuff -- not much thicker than the wire on the ORX 615's now, and there might not be a handy grounding point anywhere near the RF output for you to tap off of.
All told, if you can afford to pick up the *slightly* more expensive long antenna ORX's you'll be better off.
Effectively you'll need to keep the radiating portion of the wire the same while insering a waveguide inbetween.
And what's a waveguide? Just a section of wire where radiation and absorption of RF are confined from occuring.
In this case *IF I HAD TO DO IT* I'd use a piece of coaxial cable with the shield grounded to the board and the center tap wired between the board's RF input and the tuned length of antenna. The RF is trappped in the coax, guided away from the antenna, and the exposed antenna, free from the coax's grounded confinement, resonates on the remaining antenna lenght.
Many of the "Long antenna" versions of 2.4 RX's do this, but handmaking one would be a BEAR. Keep in mind, we're not talking about your typical TV cable coax, we're talking very fine stuff -- not much thicker than the wire on the ORX 615's now, and there might not be a handy grounding point anywhere near the RF output for you to tap off of.
All told, if you can afford to pick up the *slightly* more expensive long antenna ORX's you'll be better off.
tward
Junior Member
I see. The specific length is kinda like SWR's on the old CB antaennas. Got it. I believe I will just find a long wire version of said Rx. The whole question stems from worrying about interference from other electrical stuff, lights, FPV etc. Besides that I think it looks pretty good with a antenna mast sticking up with the "mushroom" and all.
Thanks to all for the info.
Tony
Thanks to all for the info.
Tony
Speaking as somebody who often winds myself up trying to solve potential problems that have never even occurred, let me just say that maybe you don't need to worry about this at all. Give it a test. Give it a good range check and see. There will certainly be some noise affecting the signal, but maybe your system has enough margin that it doesn't actually affect your flying. Or go ahead and fiddle with it if that's what you enjoy. Gosh knows I understand that...
Mostly Harmless
Member
The short answer is a qualified yes. As with most technical topics, the devil is in the details:
If the antenna is designed for the frequency to be received (2.4 GHz), any length of suitable coaxial cable (coax) can be used to extend the antenna without ill effects, with the following caveats:
- Conventional coax (e.g., the typical CB or Ham radio coax from Radio Shack) introduces large losses at such high frequencies. A high-quality coax specifically designed for these frequencies is needed to reduce signal losses in the cable.
- Connections between the original cable and the extension must be done cleanly so as not to introduce impedance values (a resistance to RF signals, to put it simply) different from the original cable. Impedance mis-matches also result in loss of signal in the cable.
- Some antenna designs (but not those used in our receivers, I believe) use a specific length of coax to match the impedance of the antenna to the coax to the receiver. Altering the length of the coax lead in this case alters the overall impedance of the antenna system -- resulting in loss of signal strength delivered to the receiver.
I lost an antenna from a receiver (bad crash due to pilot error, of course). I didn't realize the antenna had broken off until after I left the crash site. Using some high-quality coax left over from a satellite receiver and basic antenna design principles, I fabricated a new antenna (a simple coaxial dipole for those interested) with a longer lead. It seems to work as well as the original (although I have no quantifiable measurements to confirm this).
I love being able to combine an old hobby (ham radio) with a new one.
If the antenna is designed for the frequency to be received (2.4 GHz), any length of suitable coaxial cable (coax) can be used to extend the antenna without ill effects, with the following caveats:
- Conventional coax (e.g., the typical CB or Ham radio coax from Radio Shack) introduces large losses at such high frequencies. A high-quality coax specifically designed for these frequencies is needed to reduce signal losses in the cable.
- Connections between the original cable and the extension must be done cleanly so as not to introduce impedance values (a resistance to RF signals, to put it simply) different from the original cable. Impedance mis-matches also result in loss of signal in the cable.
- Some antenna designs (but not those used in our receivers, I believe) use a specific length of coax to match the impedance of the antenna to the coax to the receiver. Altering the length of the coax lead in this case alters the overall impedance of the antenna system -- resulting in loss of signal strength delivered to the receiver.
I lost an antenna from a receiver (bad crash due to pilot error, of course). I didn't realize the antenna had broken off until after I left the crash site. Using some high-quality coax left over from a satellite receiver and basic antenna design principles, I fabricated a new antenna (a simple coaxial dipole for those interested) with a longer lead. It seems to work as well as the original (although I have no quantifiable measurements to confirm this).
I love being able to combine an old hobby (ham radio) with a new one.
IMO, one should never direct-splice RF coax. Either remove the old lead and solder an entire new one to the pads, or put an appropriate RF connector (SMA, RP-SMA, N, etc...) on the old lead and connect the new lead. As long as your soldering skills are up to snuff, and you have the correct crimp tool, you should be able to keep your line losses relatively low. Like many people, I don't want to spend several hundred dollars on a crimp tool and dies for the small coax that we use in RC flight, so I just buy pigtails and cut one end off. For example, I would buy an SMA to u.fl pigtail, cut off the u.fl end, and solder it to the pads of the device I was working on.
Mostly Harmless
Member
Generally true, Joshua... However, given that the antennas in our receivers are of the coaxial dipole type (see http://www.gonzales.com.au/joe/projects/videolink2/video_link_2.htm for an example -- this antenna is described about half way down the page), splicing a cable to the antenna is pretty much the same thing as a direct splice to coax cable. Direct splicing can be done, but is quite challenging to do well -- especially with the size of the coax used here. Barrel connectors would add needless complexity, cost, and weight.
After thinking about it, it would probably be more advantageous (and easier) to simply create a whole new antenna with a longer lead from scratch. Of course, you still have to solder the end of the coax to the receiver.
After thinking about it, it would probably be more advantageous (and easier) to simply create a whole new antenna with a longer lead from scratch. Of course, you still have to solder the end of the coax to the receiver.
The difference, to me, is that an antenna is physically designed to attach to the coax, whereas a naked end of a coax cable is not designed to attach to another naked end of a coax cable. How are you going to solder the center conductors together and then cover them back up with a piece of dielectric? How are you going to make sure the grounding sheathes overlap without a gap? RF connectors are physically designed to bridge the gap (literally) between pieces of coax.
Mostly Harmless
Member
We're probably in the weeds here, but in this antenna design, the coax is integral to the antenna itself. One cannot disconnect the coax from the antenna without taking the antenna completely apart -- in order to extend the feedline from this antenna (without rebuilding it), one would have to splice coax to coax (or add a few connectors).
I've done field repairs of coax where I had to splice ends together (I didn't have appropriate connectors on hand) -- some scrap dielectric, solder, electrical tape, and coax sealer did the trick. I'm sure I added some impedance mis-matches, but it worked. Of course, it was the much larger coax used for HF work -- The smaller coax would be much tougher to splice, but I could probably make it work... maybe (albeit not nearly as well).
With connectors, you're adding a lot of cost, bulk, and weight. Many of the designs we're flying here probably are not very tolerant of excesses in all 3 categories.
Hence my assessment that it would be MUCH easier (not to mention cheaper and lighter) to rebuild the antenna from scratch using a longer length of coax.
Of course, all my points are relative to the integrated, wire-like antennas included on most R/C receivers. If you get to things like the clover-leaf designs with integrated connectors, then extensions are a bit easier -- just add a pigtail extension. When I fixed my FlySky receiver, I wasn't quite as interested as saving the $15 for a new one as I was in having fun making the fix and building an antenna from scratch. YMMV...
I've done field repairs of coax where I had to splice ends together (I didn't have appropriate connectors on hand) -- some scrap dielectric, solder, electrical tape, and coax sealer did the trick. I'm sure I added some impedance mis-matches, but it worked. Of course, it was the much larger coax used for HF work -- The smaller coax would be much tougher to splice, but I could probably make it work... maybe (albeit not nearly as well).
With connectors, you're adding a lot of cost, bulk, and weight. Many of the designs we're flying here probably are not very tolerant of excesses in all 3 categories.
Hence my assessment that it would be MUCH easier (not to mention cheaper and lighter) to rebuild the antenna from scratch using a longer length of coax.
Of course, all my points are relative to the integrated, wire-like antennas included on most R/C receivers. If you get to things like the clover-leaf designs with integrated connectors, then extensions are a bit easier -- just add a pigtail extension. When I fixed my FlySky receiver, I wasn't quite as interested as saving the $15 for a new one as I was in having fun making the fix and building an antenna from scratch. YMMV...
You can buy an extension cable. You would also need plug ends to mod your receiver.
http://www.readymaderc.com/store/in...id=776&zenid=681e5eb0a1a1f17875db820e00eaadf4
http://www.readymaderc.com/store/in...id=776&zenid=681e5eb0a1a1f17875db820e00eaadf4
You're right about that. I would never suggest a splice on a system on an airplane. Get a piece of coax in the correct length and solder it to your receiver. Or, better yet, just buy a receiver with the desired antenna(s), or one with u.fl connectors.
But if one absolutely had to join two cables, I would say suck up the cost, bulk, and weight, and use connectors. I am highly, highly skeptical of almost anybody's ability to splice coax directly without messing it up (present company excluded, naturally). At the best, I suspect that they will fubar the impedance and create unwanted emissions. At worst, they will create a failure point that is going to make an issue for them in the future.
tward
Junior Member
Gentlemen,
With all this being said, what about a satellite RX with the long wires? If only I can find out how to hook one up. I don't even know if a R615X will or can be used with one. I think I will just run with what I have, at least for the time being. I'm still in the short range testing mode for flight characteristics etc. I want to make sure all test out to my satisfaction be I start running farther down range. I was also trying to stay one step ahead of any problem that might be encountered. Improving my odds of not trashing my investment early on as it were. So far it has cost me around $1.00 a second to fly (props) because of an overlooked setting on the FC. So...... this is just a couple of questions that have come up during my research. Any and all info is catalogued in some fashion or another and is totally appreciated!!
One more Question.... can a antenna from a 2.4 Ghz transmitter be used on the receiver?
With all this being said, what about a satellite RX with the long wires? If only I can find out how to hook one up. I don't even know if a R615X will or can be used with one. I think I will just run with what I have, at least for the time being. I'm still in the short range testing mode for flight characteristics etc. I want to make sure all test out to my satisfaction be I start running farther down range. I was also trying to stay one step ahead of any problem that might be encountered. Improving my odds of not trashing my investment early on as it were. So far it has cost me around $1.00 a second to fly (props) because of an overlooked setting on the FC. So...... this is just a couple of questions that have come up during my research. Any and all info is catalogued in some fashion or another and is totally appreciated!!
One more Question.... can a antenna from a 2.4 Ghz transmitter be used on the receiver?
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A satellite requires that the receiver you've got be capable of utilizing it. I'm sure anything is possible with enough time and determination, but in general, if your receiver isn't already satellite-capable, you've probably got better options than modifying it to use one. I did a modification to my original FlySky receiver that came with my 9x, to put an antenna on it with a long piece of coax, to let me put my antenna near the tail while keeping my receiver accessible near the cockpit.
tward
Junior Member
I'm not gonna make any mods like that. 1. Time. 2. Knowledge. I give it a whirl with what I've got and go from there. With the info that I have gleaned so far I don't think I will have any problems. There are a couple of electronical gurus where I work. The coax resolution will be our next topic of discussion when we meet again.
Once again, many thanks.
Tony
Once again, many thanks.
Tony
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