Is 35Mhz dead? (Availability issues).

[Bearair]

Posted by Erfolg on 07/12/2013 12:14:06:

I personally still use 35 and have no issues with it other than the potential for frequency clash.

Phil Green makes a very relevant point, the benefit from 2.4 to my mind is the spread spectrum modulation.

I also take the point that Phil has made with respect other users and the increase of usage on 2.4.

It does seem to me that this is an area where the BMFA would serve its general RC members well by campaigning and actively seeking a band with the width for the sole usage of RC models. We should recognise that the purpose of our hobby is fun and pleasure, which we obtain from flying models. Safety is an issue which we should take seriously. It is arguable that 2.4 spread band technology has conceptually and actually achieved this desirable objective. Rather than the BMFA being hung up on CE marking, and misquoting what they mean. That is at the point of sale the equipment is compliant with EU regulations, and there is still an obligation of any user to ensure that the equipment when used is compliant, however obtained. The CE mark only indicates at the time of purchase it was compliant, hence many companies undertaking safety inspections on equipment on a recorded and regular basis. Far more benefit to members and the wider community would be gained from a dedicated spread spectrum band. It would be show us members that the BMFA is working towards future proofing the hobby, via a publicly visible campaign and not the interests of the modelling retail trade.

In total agreement with what you say. But I feel that until such time as we get such a Band (and I do not know if 35mhz could be that band) we should continue to defend the only band we do have dedicated to our use.

Roger

[Simon Chaddock]

I have only recently added (note added) 2.4 equipment but still use 35 for the majority of my planes.

In the environment that I fly I can find no performance difference between them.

It is still possible to buy 35 Rxs (Giant Shark & Hobby King) although it looks like most are now of the synthesised type (no crystal needed).

So like most I would say if you have got 35 keep using it but if you are starting from scratch 2.4 is easier to get!

Edited By Simon Chaddock on 07/12/2013 13:43:45

[Simon Chambers]

Posted by Erfolg on 07/12/2013 12:14:06:

It does seem to me that this is an area where the BMFA would serve its general RC members well by campaigning and actively seeking a band with the width for the sole usage of RC models.

We do!

Its between 458.5 to 459.5MHz and is reversed especially for model flyers - the old UHF frequency that equipment used to come in. This frequency is commonly used by FPV guys nowadays as its not as polluted as the ~430MHz band (Amateur Radio frequencies and other licence exempt devices) that is often used by the LRS (Long Range Systems). It's not a huge band, but large enough to have a few channels to hop around in and fit a decent modulation system in. Also there are many commercial volume ICs (thanks to keyfobs, temperature sensors, etc) that can tune into that frequency (usually these ICs can tune a whole range between at least 400-500Mhz) so transmitters and receivers don't have to be that expensive either.

Staying on the theme of FPV, those that are on here who think they can use 2.4GHz video at the flying field with a 35MHz transmitter will find out quickly its a bad idea. Firstly those poor guys still on DSM2 will find when a model flies near them with a video transmitter with a decent power output will start to have problems. Secondly, you'll find that all the other 2.4GHz RC transmitters that are hopping all over the frequency band will stomp all over your analog video signal! This is why most FPV guys (in the UK) now use 5.8GHz for video and 2.4GHz for control.

The other great leap forward that we benefit from on 2.4GHz equipment is the nearly total integration of the RF circuitry into a single IC. That IC contains all the tuning, mixing, demodulation, etc that has been under a laser in the factory to calibrate, tune and match it all directly on the IC's silicon die. As devices produced for the 2.4GHz frequency band as so wide spread and have been for a while - a lot is known on how to produce reliable devices. After all, companies can't afford large returns with faulty goods.

Look inside any 35MHz receiver and you'll find its cluttered with chokes, inductors, capacitors and other passive components that have had to be tuned by hand in a factory. As these parts are large and have a lot of mass in them, they have to be physically glued to the PCB to prevent them being destroyed by vibration and shock. So in answer to those who say will 2.4GHz be around in 25 years - it probably will be, however most of your 35MHz receivers won't be!

One reason 2.4GHz suffers less interferences from on-board electronics than 35MHz is because most EMF interference (from motors, ESCs, switching contacts, etc, etc) ends up at 1GHz. So 2.4GHz is high enough to be far enough away from this source of interference.

The obvious downside is that it is much more Line of Sight than 35MHz - so pretty much anything solid from a distance will block the signal. However for us this isn't a big deal for most of us as its pretty hard to fly behind trees, etc! Even for FPV use, there is the requirement that the model has to be visible by your observer - so again its still LOS.

Cheers,

Si.

[Glyn R]

I keep reading these long drawn out frequency discussions. The real trick with modern 2.4ghz Radios is the use of Digital technology. The provision of the GUID based systems is the real advance. The frequency has to be high enough for the frame rate to be practical. Each data packet carries the Globally Unique Identifier the frequency used is not the really clever bit.

[Simon Chambers]

Posted by Glyn R on 07/12/2013 22:34:25:

I keep reading these long drawn out frequency discussions. The real trick with modern 2.4ghz Radios is the use of Digital technology. The provision of the GUID based systems is the real advance. The frequency has to be high enough for the frame rate to be practical. Each data packet carries the Globally Unique Identifier the frequency used is not the really clever bit.

eh?

You realise PCM on 35MHz is digital data right? Adding 16 to 32bits extra hardly will increase the frame rate at all.

Even with a GUID if you're transmitting on a very small frequency band that each 35MHz channel uses, if someone else transmits on that same channel you'll still get stamped out...

With 2.4GHz its wide enough band to be able to hop and/or spread over a 80MHz frequency range. Of course this wouldn't be possible if you had to keep in a very small space as you do with the 35MHz band (to avoid hitting the older systems).

Also having GUID and packet based data transmissions doesn't solve the interference susceptibility issue of the lower frequencies. Here for example is a spectrum anaylser plot between 1MHz and 1000MHz (1GHZ) of a cheap 3v DC motor (commonly used in toys) showing in purple the noise when the dc motor is running and the yellow is the baseline ambient (motor off) state: (remember the scale is in dB's)

This is the motor in question:

Note how the noise rolls off at the higher frequencies. Even this little low powered motor is a sizable noise source which will cause problems if left next a sensitive receiving RF section. Again remember most 35MHz receivers don't have their RF sections shielded either (unlike modern RF Chipsets such as those used for 2.4GHz with the RF sections in silicon), so will be even more susceptible to noise.

Si.

[Simon Chambers]

I would point out though, due to the low frequencies involved, its pretty easy to design and make 35MHz receivers with commercially available off the shelf parts. So along as we have access to the 35MHz band, its perfectly achievable to still have working receivers for it. Of course it depends on the market for it, but I would be surprised if there wasn't always a cottage industry around to support 35MHz systems.

But at the same time, much is true for 2.4GHz too for the future. Many people in the RC world appear to find 2.4GHz devices as 'black-magic'. This signal somehow magically is received onto a PCB into a little black IC that pumps out the servo signals.

The reality is, even though there is more going on, its not rocket science and still pretty simple. The majority of 2.4GHz systems out there use common and pretty simple modulation techniques. Even though the biggest risk on 2.4GHz systems is that certain ICs will become discontinued, it doesn't necessarily mean the system will become dead. As the modulation techniques are pretty standard (for FHSS based systems that usually means the modulation is either FSK or GFSK based), there will be a whole load of replacement RF Chipsets that can do the same job.

So even in 25 years, it's entirely plausible that 2.4GHz RC transmitters and receivers will still exist and still be compatible.

Incidentally, given how much 2.4GHz stuff is out there commercially (WiFi, Bluetooth, Cordless phones, Microwave ovens, etc, etc, etc), it's not a band that will disappear quickly. Also as we all fly out in the middle of open spaces well away from buildings and other structures (well you should be anyway), even as 2.4GHz gets pretty crowded, there is little risk for us to be blocked out.

Just how far can you go before too much 2.4GHz traffic is too much? Well I'd put money on that if you're walking down regents street this time of year, your low powered 2.4GHz Bluetooth headset will still be happily chatting with your phone...

Incidentally the 35MHz band is set at a EU level (the spec is detailed in the ETSI document EN 300 220). So its unlikely that we will loose the band anytime soon.

Si.

[GONZO]

Further to Simons comments on the 459mHz band; There are already systems available that hop within the band, some more DIY than others, that can be used by almost all current and past Tx that have a trainer port. The new Tx unit is attached to the Tx or the Tx stand and gets its information and power from the main Tx. One such unit that has a good reputation **LINK**

At the moment this choice is not cheap due to low numbers but if your OK at coding and reflashing firmware then the DIY/ semi kit route is the way to go. Search for LRS systems or systems on 430mHz should give you some leads.

HTH

[Rob Jones 2]

If I had several hundreds of pounds worth of 35Mhz equipment (some people have thousands of pounds worth), I would be very peed of at the rapid change round to where they have became worthless from the resale point of view.

I would also be inclined to deny the advantages of the 2.4 "newcomer" .It is just human nature. I personally resisted getting a computer radio, feeling that my old steam-powered 5 channel Tx was good enough. In the end I bought a Futaba 7c , it didn't improve my flying skills one jot but has provided me with many hours diversion playing with all the functions.

But I believe it is quite simple to get "modules" to change a 35 Tx to 2.4.

But I stand by my suggestion that it might be better to resell sooner rather than later.

[Former Member]

[This posting has been removed]

[Bernie]

I fly on both 2.4 and 35 .never had any problems with either. cheers from a happy flyer .

[Erfolg]

I am pretty sure that most modellers are satisfied at the performance of both the prime RC aircraft channels of 35 and 2.4.

I do believe that it is very easy to be complacent and assume that all will be well into the future with our existing frequencies and equipment. I believe that now is the time for the BMFA to consider the issues raised by Phil Green. If the issues are real, to set about establishing a solution such as a dedicated band where frequency hoping is practical.

With respect to 459, I remember when this was going to be the answer to all our problems. I have only ever seen one Reftec set in use, the user did not find it that reliable, Rx difficult to obtain at reasonable cost, going to 35 thereafter. So I guess an issue will always be the commercial availability of equipment at reasonable prices, whilst maintaining reliability.

In short we can all now appreciate the convenience and probably the more important aspect of improved safety from the ability to frequency hop. The BMFA will have recognised the safety benefits, now is the time press the regulators before a issue becomes established and press for a dedicated frequency for us RC modellers. Keeping the membership informed on their thought and actions in this area, will be more than a passing interest to the membership.

[Rob Jones 2]

Andrew Ray:

Personally in use I don't see a clear winner, they both control my models, both have failsafe capability and they are both subject to some sort of issues due to the propagation characteristics of the signal. My biggest concern is remembering to extend the aerial when using the 35Mhz set.

Regarding the loss in value of 35Mhz gear, some have used this to their advantage, I have, I bought some top notch receivers recently for not a lot of money. As far as the value of the two Tx's I have, it doesn't matter as they are still serviceable and a few years old so I guess they would not be worth much anyway.

I agree. I noticed earlier that 35Mhz 7cs, new, have sold on eBay for about £40, whereas the 2.4 version sells for about £200.If I was starting out to buy gear now, I would be very inclined to stock up on 35Mhz, as long as I believed 35Mhz will continue to be protected. At my age, I only have to look 10 to 15 years ahead anyway!