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[Edward Pinniger]

I've got a serious problem with the radio on my scratchbuilt R/C steam yacht (this problem is one of the reasons I haven't done any work on this model for months). Basically, when out of the water, the radio has a good range - at least 20-25m. When the boat is in the pond, the range is reduced to a couple of metres - making it completely unusable.

The transmitter has an aerial about 50cm long - I've checked the aerial connection inside the transmitter box. The boat - which is about 3' long - has an aerial wire wound around the inside of the hull, well above the waterline, connected to a further length of wire which goes up inside the funnel - maximum height above the waterline about 13cm.

Initially I got this problem when running the boat in a neighbour's swimming pool and I thought it may have been caused by the pool's metal lining (if any). However, I

Any clues as to what could be causing the problem, and how to fix it other than completely replacing the radio gear? Is this (range reduction when the boat is in the water) a standard phenomenon or just a particular problem with my radio?

[wideawake]

I've got a serious problem with the radio on my scratchbuilt R/C steam yacht (this problem is one of the reasons I haven't done any work on this model for months). Basically, when out of the water, the radio has a good range - at least 20-25m. When the boat is in the pond, the range is reduced to a couple of metres - making it completely unusable.

The transmitter has an aerial about 50cm long - I've checked the aerial connection inside the transmitter box. The boat - which is about 3' long - has an aerial wire wound around the inside of the hull, well above the waterline, connected to a further length of wire which goes up inside the funnel - maximum height above the waterline about 13cm.

Initially I got this problem when running the boat in a neighbour's swimming pool and I thought it may have been caused by the pool's metal lining (if any). However, I

Any clues as to what could be causing the problem, and how to fix it other than completely replacing the radio gear? Is this (range reduction when the boat is in the water) a standard phenomenon or just a particular problem with my radio?

Hi Edward

My immediate reaction is that something's amiss.   For a start, I'd not regard 25 - 30m as good range.  I'd immediately suspect a problem.   I'd certainly not expect such a significant reduction in range due to operating over a water path either.   It's difficult to diagnose whether the fault lies in the tx or rx without either test gear or the ability to swap out one or the other.

If you know anyone with compatible gear, try another tx with your boat.   If OK the fault is in your tx.  Double check by trying your tx with the other rx.   If not then it's likely to be your rx.  Again cross check.  BTW obviously you need to find someone with a tx/rx on your frequency or swap the crystals around.

HTH

Guy

[Edward Pinniger]

Sorry for not making this clear in my original post, the TX/RX (all the running gear, in fact) in my model is taken from an old Nikko RTR motorboat. (It's not a really cheap low-end RTR system, it does have a rudder, but isn't exactly top quality). I ran the original boat several times and its in-water range (even with the aerial removed!) was certainly much greater than the 2-3m I'm getting now.
I didn't actually measure the maximum range, just turned the boat + TX on and walked over to the other side of the house! The maximum range (out of the water) may be greater than this distance.  25-30m is more than adequate for me as I rarely run boats more than 10-15m away from the shore.

I may try adding a higher, temporary aerial to the boat and see if this has any effect.

[Arrow5]

Has the aerial been shortened ( or lengthened) ?  The supplied manufacturer`s length should not be altered as it is a "tuned" length.  Is it live steam ie lots of metal or if electric is the motor suppressed ?  Any carbon fibre in the construction of the model?   Do you have an alternate route for the aerial, say up the mast ? 50cm seems too short. Range shouldnt be affected on or off water.

[Arrow5]

Consider a cheap , but effective radio for under £35. My Springers have a range of at least 300m and possbly more using such a set.

[Edward Pinniger]

Thanks for the information -I didn't realise the aerial lengths on RC sets were tuned; I just assumed the longer the better! The aerial on the original RTR boat was quite short - about the length of an average transmitter aerial. Would shortening the aerial in the boat - removing the loop running around the hull - actually improve things?

My model isn't live steam (if I could afford a steam plant I'd definitely buy a decent radio set to go with it!) it has a plastic hull, no carbon fibre. The only metal is in the masts and the deck fittings (most of the latter aren't added yet).

I'm considering replacing the entire radio and motor setup with something decent quality; after the amount of time I put into the build it would probably be worth it. The main problem is removing the deck without damaging the planking or wooden superstructure.

[wideawake]

Has the aerial been shortened ( or lengthened) ?  The supplied manufacturer`s length should not be altered as it is a "tuned" length.  Is it live steam ie lots of metal or if electric is the motor suppressed ?  Any carbon fibre in the construction of the model?   Do you have an alternate route for the aerial, say up the mast ? 50cm seems too short. Range shouldnt be affected on or off water.

All very good questions!   Now I know the origin of the r/c gear I see that my original suggestions weren't appropriate.   However I think that the loss of range still sounds more drastic than any of the possible simple problems would cause.   I still suspect something a bit more drastic.   Has is ever worked properly since you removed it from the RTR boat?   Is it possible that the PCB got cracked during removal or something got disturbed when you extracted it?

BTW I particularly agree that the aerial should be kept at it's original length.

HTH

Guy

[tigertiger]

RTR boat radios have a big problem

Range of 30m is possible. However as soon as another radio is in the vicinity the radio signal is swamped.

When you were testing the boat I am assuming that another RC set was being used nearby.

This could be the problem.
The only solution is to buy a standard RC radio set, not expensive. Especially if you can get a two channel set without servos included. And even if the model shop only has a box set of TX, RX and servos, some will buy the servos back.

[Edward Pinniger]

Thanks to all for the advice. I've decided to (eventually) buy a decent radio set (and motor + rudder servo) for this model. I don't often do this, but after the amount of work I put into building the model, which looks very good so far, it should be worth it.

BTW, interference is probably not the cause of the problem; I was testing the boat on a gravel pit several hundred metres from any houses (or phone/radio masts) and there were no other R/C models running nearby.

[787Eng]

Something also to consider is the Output transistor can be damaged by having the TX antenna retracted and the radio on. The technical reason is due to whats called SWR (standing wave ratio) where the transmitted RF is reflected back into the RF power transistor. This causes heat to be generated in the transistor and as we all know heat and electronics is a no no (lets the electronic smoke out )

Most radios even the expensive module radio, JR Futaba etc have poor heat heatsinking on the transistors so even if the antenna is extended every time over time the output Transistor degrades over time.

Its best to send the radio in for a check every couple of years for a checkup.

I learnt the hard way, after flying planes for several years....should have know better being a radio Ham as well.  After that I sent the radio in for a check every year.  cheap insurance and yes they did identify the o/p was on the decline again on a test done about 2 years later

Mark