Converting a 35MHz model to 2.4GHz

If you flew in the 2000s, there's a fair chance a 35MHz helicopter or plane is sitting in a loft somewhere, with a long telescopic aerial on the transmitter and a crystal in the back. They can fly again. The question is how much to change.

Why 2.4GHz replaced 35MHz

Old 35MHz radios used a fixed channel set by a pair of crystals, one in the transmitter and one in the receiver. Two people on the same channel meant one of them crashed, which is why clubs used peg boards to show who was on which frequency. Long aerials, interference from other electronics, and the cost of crystals added to the hassle.

2.4GHz radios hop between many frequencies and lock to one specific transmitter when you bind them. No crystals, no frequency clashes, short aerials. By around 2010 most new models came with 2.4GHz, and 35MHz faded out.

Is 35MHz still usable in the UK?

Legally, yes. Ofcom still lists 34.945 to 35.305MHz as licence-exempt for model aircraft only, at up to 100mW (Ofcom licence-exempt radio models). Practically, crystals are now hard to find and old transmitters and receivers are ageing. If your old set still works and you only fly on your own, you can use it. For anything you care about, converting is the safer choice.

The three ways to revive an old model

Route 1: new transmitter and receiver

The simplest and usually the best option. Buy a modern transmitter and fit a matching receiver in the model, plugging the existing servos, speed controller and gyro into it.

This works well for any model with separate components: most collective pitch helicopters such as an Align T-REX 450 or E-Sky Belt-CP, and most planes. A radio you buy now will also fly your next model. Our guide to RC transmitters explained covers which to choose.

Route 2: convert the old transmitter

Some older transmitters can be converted by fitting a 2.4GHz module in place of the 35MHz radio-frequency board. Two types exist:

• Plug-in modules for transmitters that already had a removable RF module, such as some Futaba and Graupner sets. These are straightforward.
• Solder-in or DIY modules for transmitters with a fixed board. You remove the old RF board and wire the new module to the transmitter's signal output. Model boating and flying magazines have published step-by-step conversions of sets such as the Futaba Skysport (Model Boats conversion article).

It's satisfying, and cheap if you're comfortable with a soldering iron. But you end up with a transmitter that still has an old set's limited features and a tired battery. Worth it only if the transmitter has sentimental value or you want to match it to models you already own.

Route 3: replace the model's electronics

Many small helicopters from the 2000s combined the receiver, servo mixer, gyro and speed controllers on a single board. E-Sky's 4-in-1 board on the Honey Bee and Lama is the best-known example. You can't just plug a new receiver into the servos, because there are no separate servos to plug in.

Your options are:

• A replacement 2.4GHz version of the board, if one was made and you can still find it.
• A modern multi-function flight controller for small helicopters, plus a receiver, if you're comfortable rewiring.
• Rebuilding the electronics with separate parts. Practical on bigger models, rarely worth it on a toy-grade coaxial.

People do get these conversions working, but owners regularly report trouble: a modern receiver often only drives part of the old mixer, so the gyro or mixing stops working properly.

Model-by-model notes

The E-Sky, Walkera and Align brand pages cover these models in more detail.

A note on multi-protocol radios

Transmitters with a multi-protocol module can talk to dozens of different receiver systems, including several older and toy protocols such as some Walkera and DSM2 receivers (multiprotocol module protocol list). This doesn't help with 35MHz receivers, but it is very useful if you have a mix of early 2.4GHz models from different brands.

Is it worth it?

A sensible rule of thumb:

• Hobby-grade helicopters and planes in good mechanical condition: convert. A receiver costs less than a set of blades.
• Toy-grade coaxials and fixed pitch models: usually not. A modern stabilised helicopter costs less than the parts and flies far better. See best RC helicopters for beginners.
• Anything you're buying second-hand: factor the conversion into the price. Our checklist for buying a used RC helicopter helps.

After converting, set the failsafe on the new receiver so the motor stops if the signal is lost, and range-check the model before it flies. All our radio and electronics guides are on the Electronics hub.