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Repeater antennae

Piotrsko

Active member
#1
Since it sometimes seems everybody has radio glitches that could be attributed to lack of signal strength or poor S/N ratio, has anybody ever experimented with a long thin wire buried in the wing or fuselage about 6 wavelength long?

A piece of 30 ga wire wrap about 18" long with one end pointed at the radio antenna in the plane but not connected to anything could function as a longwire repeating antenna, kinda like those cheapo cellphone things back a couple of years ago only actually working. {2piFL *(.486)*6} .486 is a efficiency factor indicated by my wire wrap supplier.

Same principal as repeating antenna in tunnels just really short cuz we be in the ghz range anymore
 

Hai-Lee

Old and Bold RC PILOT
Mentor
#2
Since it sometimes seems everybody has radio glitches that could be attributed to lack of signal strength or poor S/N ratio, has anybody ever experimented with a long thin wire buried in the wing or fuselage about 6 wavelength long?

A piece of 30 ga wire wrap about 18" long with one end pointed at the radio antenna in the plane but not connected to anything could function as a longwire repeating antenna, kinda like those cheapo cellphone things back a couple of years ago only actually working. {2piFL *(.486)*6} .486 is a efficiency factor indicated by my wire wrap supplier.

Same principal as repeating antenna in tunnels just really short cuz we be in the ghz range anymore
Many of my planes use pushrods made of wire and effectively pointing to the Rx antenna/s. I have used such for many years and they are open circuit at each end. Sadly they did little to prevent LOS and associated issues which I have since totally eliminated from all of my flying models through careful radio system selection and very careful and considered antenna placements.

Since adopting my current radio system and antenna installation requirements I have NEVER had a single LOS or interference issue and I fly between 20 and 100 times each week!

Every metal item installed in a model aircraft can and does effect the Rx signal sue to the re-radiating of the transmitted signal and the reflected/re-radiated can provide a very complex mixing of in phase and out of phase signals that can effectively cancel out the transmitted signal at the Rx antenna and cause a LOS or even a pseudo interference scenario.

The placing of the Rx antenna away from ALL metal structures as far is as practicable can decrease the strength od the unwanted reflected/re-radiated signals and give a better or stronger line of sight signal directly from the Tx. Whilst there will always be a small amount of unwanted reflections Etc the ratio of wanted to unwanted signals is vastly improved and to date allowed me to fly without any fear or incurring Rx signal issues.

Tunnel radio propagation is different to free space communications because inside a tunnel complex there is rarely a direct radio path between devices and the re-radiating systems are there as the simplest method of allowing the signal to radiated into areas that cannot Rx a direct transmission signal. Adding a second source of signal to a Rx receiving a direct signal is a recipe for disaster if the signals are out of Phase and equal in signal level. Make the direct path signal from the transmitter strong and reduce all other signal paths and you will never have a LOS unless you have a Tx or Rx failure!

Just what works for me and what I was taught!

Have fun!
 

Piotrsko

Active member
#3
OK so short answer is: nobody has done this. Hai-Lee's response shows that education of proper practices is really lacking in our sport and that the application of a panacea is moot.
 

FDS

Well-known member
#4
Most people do know where not to put antennae after they make that mistake once!
Many more modern receivers are very reliable, given that most countries limit you to 500m or full line of sight only then any improvement beyond that is not really necessary.
Long range systems like the TBS Crossfire will usually keep a very reliable signal well beyond legal limits.
I am sure people have tried almost every possible design for antennae over the years, maybe not with every possible radio control frequency but for FT type line of sight flying, you should never need to worry about range.
 

Headbang

Well-known member
#5
I happen to do this stuff for a living. A single antenna would not repeat, or at least not with any sort of effectiveness. In order to have any real world effect you would need something to the tune of a 24db antenna receiving. That would be around a 2ft dish in 2.4ghz. That would have to feed something like a 2db whip. Not mention a passive repeater is not legal in many countries.

Better solution is to use remotes on a single rx. More diversity. Better chance of signal getting through. Or do something antenna wise on the tx end, but remember the only way to increase antenna strength is to focus it, so for every 3db gained you have to effectively double the focus.

All of this is the simplified version, it is all a lot more complex then one might expect.
 

evranch

Active member
#6
I also deal with a lot of wireless stuff, have my ham license and yep, passive repeaters just don't work, as Headbang clearly describes. You need to gather enough signal to reradiate, and that means you need to gather a LOT once you add up the losses. The long wire across the wingspan particularly won't work. You may be thinking more of a reflector such as you would find as the back element of a yagi antenna. The problem is, a reflector will just direct your signal in one direction from the airplane, and airplanes turn. Also, you will have to space it very precisely from your active element, and 6 wavelengths is way too long.

If you want to add directionality, add it to your transmitter antenna and point it at your plane. This is what ultra-long range setups use, with GPS, telemetry, and a tripod-mounted antenna tracker with a high-gain antenna. Not practical for casual flight.

Since I switched to the FrSky diversity receivers I just don't see how you can fly far enough to worry about RC dropouts. I have flown over a mile away with zero dropouts using a basic $30 receiver. You can even upgrade the antennas from the little bendy whips to a pair of PCB strip dipoles that will always be straight:

Accidentally bent dipole antennas i.e. flexible whips always perform poorly. Tack them straight with some hot glue or something.

Further than that, R9 or TBS crossfire are what you need. I have an R9 and have never seen it drop below 4 bars of telemetry signal.