Is 2.4GHz Suitable For Marine Use?
One of my current significant interests is learning to fly electric helicopters, and as an owner of an e-Flite Blade 400, I have a Spektrum 2.4GHz DX6i transmitter, and a Spektrum park flyer AR6100e receiver. However for marine use I use an aging two channel Futaba 27MHz AM set. So wouldn't it be nice if I could use my new Spektrum DX6i for my boating exploits too?
With no crystals to worry about, no frequency clashes, and no telescopic aerial to break or to cause significant injury to others. The DX6i has a ten model memory, and six channels, mixing, a count up/down timer, so why not? A little searching of the Internet reveals various thoughts on the subject, much of which is often subjective. |
Interestingly the Spektrum website hosts this page on the subject of "Basic Boating Safety" (http://www.spektrumrc.com/Articles/Article.aspx?ArticleID=1566), which contains the quote "Another way to prevent frequency conflicts would be to upgrade your radio system to a Spektrum 2.4 GHz DSM system". The implication is that Spektrum believe that 2.4GHz is suitable for marine use.
Futaba equally make the occasional reference to 2.4GHz used for boats.
Prior to investing any more money in Spektrum radio gear, I sent an e-mail to Horizon Hobby, listing my concerns and asking for advice. Sadly this has so far gone unanswered.
So What Are The Issues?
It's an obvious one, but 2.4GHz is a much higher frequency than the 27MHz and 40MHz bands. This gets the signal away from the potential interference of electrical equipment, and metallic structures, so this is a good thing. Also at higher frequencies the path the radio signal takes is less compliant around obstructions and curvature of the earth (otherwise known as signal propagation). In layman’s terms range tends to be more line-of-sight, making this bad news. Higher frequencies are also more easily blocked by dense substances such as water (ruling out 2.4GHz for submarine use), the human body, or even other models. This is also not good.
Shared Frequency Band
In the UK, 27MHz, 35MHz, and 40MHz are all licensed bands exclusively for modelling use. However 2.4GHz is available for a number of other uses, including WiFi lans, video senders, and portable phones such as the DECT standard. So we have to share the 2.4GHz band with a number of other users. Assuming you're some distance from residential or commercial population this isn't much of an issue, but in urban area's this could be a problem. Spektrum 2.4GHz radios attempt to get round this by listening before selecting any of the eighty designated channels in the 2.4GHz band. So in an ideal world, where other transmissions in the 2.4GHz band are already operating and you switch your transmitter on, then it works fine. Your 2.4GHz radio should select free channels. However if other devices start transmitting after your radio has initialised, then this could possibly result in issues.
Damage Limitation
Both Futaba and Spektrum have their own workarounds to sharing the 2.4GHz band with other devices. Futaba with their FASST (FHSS) system, use a frequency hopping mechanism, switching channels every few milliseconds. So if a channel is in use by another device, it may cause an issue only for a fraction of a second, by which time another channel is selected automatically. Spektrum have their own mechanism whereby they select two channels, and transmit on both at the same time (DSSS). Loss of one channel, is compensated for by using the second.
Recommendations for Marine Use
Receiver Placement
Place the receiver high up in the hull or superstructure. Whatever you do, ensure it's above the waterline. Higher frequencies suffer significant attenuation (loss) when passing through dense materials such as water.
Aerial Orientation
Ensure that the orientation of aerials of both the transmitter and receiver are the same. The majority of the power is radiated from the transmitter in a donut shape around the axis of the aerial. Similarly the receiver aerials are most sensitive in the same plane, around the aerials in a donut form.
Many marine modellers will be using radio gear designed for aircraft use. Aircraft operate in a 3D environment, where the orientation of the model to the transmitter changes significantly in flight. Because of this, guidelines recommend that where used, aerials of primary and secondary receivers are placed at right-angles to each other, or when using a single receiver it's aerials placed at right angles to each other.
However marine craft should be operating in a 2D environment, in other words we would expect a boat to be sitting on the water in a horizontal attitude most of the time. So for marine use, I would personally recommend pointing both receiver aerials vertical, or at least close to vertical. There may be a slight advantage in having the aerials just slightly off the vertical plane. Similarly flip the transmitter aerial up to a vertical position.
Well this is just about as much as we can do to mitigate against the problems.
But Does It Work?
Well so far I can only comment on Spektrum equipment, specifically the DX6i, with the park flyer receivers (AR6100e/AR6200). These were chosen only because it's what I have available for testing. But I would expect Futaba FASST to behave similarly.
The trial was with a Model Slipway Club 500, at the lake in Southchurch Park. The receiver was mounted on the inside of the hatch cover with velcro, with aerials positioned vertically through the hatch cover.
In testing I had full control for the length of the lake available to me, of approximately 90 metres (around 295 feet). With the range check function of the DX6i enabled, I appeared to loose control at around 85 metres (approximately 279 feet), which significantly exceeds the minimum specified distance of 90 feet quoted in the Spektrum handbook.
During testing I attempted to place a number of obstructions in the path between the transmitter and the model, which included larger boats, people, and metal fencing. Control was maintained throughout.
The receiver was subsequently trialled in a second boat, a Veron Pilot Launch. Here the receiver was in a slightly lower position, at approximately water level. Again control was maintained throughout, and the range (when using the range-check function) was similar.
Since the initial trial I have used the DX6i almost exclusively for Club 500 racing, and have not (yet) noticed any issues with range, or loss of control. Nor have I experienced any issues with loss of binding between the transmitter and the receiver.
So Would I Recommend It?
Well, so far I have found that the Spektrum DX6i to work fine in a marine environment with both the 6100 and 6200 receivers. However I’m not disposing of my 27AM crystals just yet, but I think I’ll certainly invest in a few more Spektrum receivers!
Miscellaneous Notes
Here in the UK, as part of the EU, we're limited to 100mW output in the 2.4GHz band. Whilst investigating the various menu options of the DX6i, it appears to offer the option of switching from EU-328 (EU300-328), to US-247.
Sadly we've not yet got a webcam looking over the Southchurch Park lake yet, but If you want to see the Southchurch Park boating lake in Google maps, click here: Google Maps Link to Southchurch Park
Futaba equally make the occasional reference to 2.4GHz used for boats.
Prior to investing any more money in Spektrum radio gear, I sent an e-mail to Horizon Hobby, listing my concerns and asking for advice. Sadly this has so far gone unanswered.
So What Are The Issues?
It's an obvious one, but 2.4GHz is a much higher frequency than the 27MHz and 40MHz bands. This gets the signal away from the potential interference of electrical equipment, and metallic structures, so this is a good thing. Also at higher frequencies the path the radio signal takes is less compliant around obstructions and curvature of the earth (otherwise known as signal propagation). In layman’s terms range tends to be more line-of-sight, making this bad news. Higher frequencies are also more easily blocked by dense substances such as water (ruling out 2.4GHz for submarine use), the human body, or even other models. This is also not good.
Shared Frequency Band
In the UK, 27MHz, 35MHz, and 40MHz are all licensed bands exclusively for modelling use. However 2.4GHz is available for a number of other uses, including WiFi lans, video senders, and portable phones such as the DECT standard. So we have to share the 2.4GHz band with a number of other users. Assuming you're some distance from residential or commercial population this isn't much of an issue, but in urban area's this could be a problem. Spektrum 2.4GHz radios attempt to get round this by listening before selecting any of the eighty designated channels in the 2.4GHz band. So in an ideal world, where other transmissions in the 2.4GHz band are already operating and you switch your transmitter on, then it works fine. Your 2.4GHz radio should select free channels. However if other devices start transmitting after your radio has initialised, then this could possibly result in issues.
Damage Limitation
Both Futaba and Spektrum have their own workarounds to sharing the 2.4GHz band with other devices. Futaba with their FASST (FHSS) system, use a frequency hopping mechanism, switching channels every few milliseconds. So if a channel is in use by another device, it may cause an issue only for a fraction of a second, by which time another channel is selected automatically. Spektrum have their own mechanism whereby they select two channels, and transmit on both at the same time (DSSS). Loss of one channel, is compensated for by using the second.
Recommendations for Marine Use
Receiver Placement
Place the receiver high up in the hull or superstructure. Whatever you do, ensure it's above the waterline. Higher frequencies suffer significant attenuation (loss) when passing through dense materials such as water.
Aerial Orientation
Ensure that the orientation of aerials of both the transmitter and receiver are the same. The majority of the power is radiated from the transmitter in a donut shape around the axis of the aerial. Similarly the receiver aerials are most sensitive in the same plane, around the aerials in a donut form.
Many marine modellers will be using radio gear designed for aircraft use. Aircraft operate in a 3D environment, where the orientation of the model to the transmitter changes significantly in flight. Because of this, guidelines recommend that where used, aerials of primary and secondary receivers are placed at right-angles to each other, or when using a single receiver it's aerials placed at right angles to each other.
However marine craft should be operating in a 2D environment, in other words we would expect a boat to be sitting on the water in a horizontal attitude most of the time. So for marine use, I would personally recommend pointing both receiver aerials vertical, or at least close to vertical. There may be a slight advantage in having the aerials just slightly off the vertical plane. Similarly flip the transmitter aerial up to a vertical position.
Well this is just about as much as we can do to mitigate against the problems.
But Does It Work?
Well so far I can only comment on Spektrum equipment, specifically the DX6i, with the park flyer receivers (AR6100e/AR6200). These were chosen only because it's what I have available for testing. But I would expect Futaba FASST to behave similarly.
The trial was with a Model Slipway Club 500, at the lake in Southchurch Park. The receiver was mounted on the inside of the hatch cover with velcro, with aerials positioned vertically through the hatch cover.
In testing I had full control for the length of the lake available to me, of approximately 90 metres (around 295 feet). With the range check function of the DX6i enabled, I appeared to loose control at around 85 metres (approximately 279 feet), which significantly exceeds the minimum specified distance of 90 feet quoted in the Spektrum handbook.
During testing I attempted to place a number of obstructions in the path between the transmitter and the model, which included larger boats, people, and metal fencing. Control was maintained throughout.
The receiver was subsequently trialled in a second boat, a Veron Pilot Launch. Here the receiver was in a slightly lower position, at approximately water level. Again control was maintained throughout, and the range (when using the range-check function) was similar.
Since the initial trial I have used the DX6i almost exclusively for Club 500 racing, and have not (yet) noticed any issues with range, or loss of control. Nor have I experienced any issues with loss of binding between the transmitter and the receiver.
So Would I Recommend It?
Well, so far I have found that the Spektrum DX6i to work fine in a marine environment with both the 6100 and 6200 receivers. However I’m not disposing of my 27AM crystals just yet, but I think I’ll certainly invest in a few more Spektrum receivers!
Miscellaneous Notes
Here in the UK, as part of the EU, we're limited to 100mW output in the 2.4GHz band. Whilst investigating the various menu options of the DX6i, it appears to offer the option of switching from EU-328 (EU300-328), to US-247.
Sadly we've not yet got a webcam looking over the Southchurch Park lake yet, but If you want to see the Southchurch Park boating lake in Google maps, click here: Google Maps Link to Southchurch Park