Techniques > Radios

Radio interference at Bray Head (35 MHz)

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Fergal Gordon:
Hi Everyone,

Taking your questions and comments in order, Alan, I was flying my RCRCM Typhoon.  It is very tight for space in the cockpit, it took me some time to figure out how to fit everything in.  The Rx in is under the deck in the nose, with the connectors facing forward.  All the servo cables have to be routed by the antenna to reach the Rx.  Currently the antenna is internal, housed in a tube running the length of the fuselage.

I could route the antenna externally, but it would still have to exit near the wings, as the cockpit is covered by a removable cone.  So the antenna would still have to be routed near the servo cables for most of their length.

This could be part of the problem, but does not explain why I only had this problem on one occasion.  On the other hand, I flew at Bary Head with a different glider with a similar radio set up and I had no problems, suggesting the problem is the Typhoon and not the location.

Ralph, you mentioned HT cables, always to be avoided.  As far as I know, the DART cables would are low tension and possibly DC.  And John's input also suggests that the DART lines are not the problem.

Joe you suggested I might have picked up interference from Shankhill MFC.  There are two things against this, the interference was short lived in each occasion.  Also, I left the model on and switched off the Tx, and there was not a sound from the servos.

As regards the phone, on this occasion I had the phone off.  I don't always remember to switch it off, but it was off on this occasion.

In the short term I will try routing the servo wires away from the antenna. though there is not much scope for this.  Is there any point in wrapping some shielding around the servo cables, such a aluminium foil.

Longer term, probably next winter, I will send my Tx back to Multiplex for an upgrade to 2.4 MHz.

Thanks for all your input.


Best regards,


Fergal

Happy Days:
Years ago, in the days of sailing ships, (I don’t actually remember them,……..I think I must have been away at the time) the navy’s of the world placed almost all their cannons along the sides of their ships. Ideally, when in battle, the battleships would try to sail along side the enemy and fire the max number of cannon “broadside.”  If the “target” ship sailed towards or away from the ’Man o’ war’ it presented a much smaller small target and was less likely to be hit.

The antennas that we use for our rc amusement work just like those battleships of old. The Tx antenna “fires” virtually all it’s radio energy off of it’s sides. In real terms no radio waves come off the end of the antenna at all.

And the receiving antenna only receives radio waves on it’s sides. (Biggest target).

Running  part of a rx antenna close to any electrically conductive material shields the antenna from the transmitters signal for the duration of that length. In other words it reduces the “target” for the radio waves to hit. (Not strictly true,...but good enough for this posting :oops: ) In addition, servos produce small radio waves themselves, (interference)  which is radiated along their wires. Because the servo leads are close to the rx antenna this has a negative double whammy effect on the receiver.

The servo leads are absorbing some of the Tx radio signal, so the receiver is “hearing” a weaker signal from your transmitter. AND the receiver is hearing  louder background noise from the servos. (Because the antenna is close to the servo leads)
Couple this with any additional interference you may have got from the trains’ electric motor,(HT or LT) and or the possibility that at that time you may have been flying towards or away from the Tx, (Not broadside to it,) and it’s more than probable that for a few moments your receiver couldn’t ‘hear’ the Tx at all.

Re-routing the antenna, so that it’s as far away from the servo/battery leads (and any carbon fibre) as possible, (even a few millimetres away,) for the max distance as possible will help the radio signal find the antenna easier, and reduce the amount of interference it picks up from the servos.

Wrapping the servo leads in metal foil might prove to be counter productive. Although it could reduce some of the interference from the servos, (Not much however, unless the foil is “earthed”) it will also tend to pick up more of the tx signal, thereby increasing the shielding of the rx antenna.


Good luck Fergal


K.

Aidan:

--- Quote from: "Fergal Gordon" ---Longer term, probably next winter, I will send my Tx back to Multiplex for an upgrade to 2.4 MHz.
--- End quote ---

If you're interested in moving to 2.4GHz but would prefer not to be without your transmitter while it's upgraded you might consider the Jeti Duplex system. It's a similar system to M-Link but you can easily convert the transmitter yourself. Also the Jeti receivers are cheaper (at least the telemetry capable ones are). The Jeti TMe module is made specifically for the Multiplex EVO providing you don't upgrade the firmware to v3.XX. We converted my Dad's EVO 9 in about 10 minutes last weekend. It seems to work perfectly and will probably get road tested at Toutinna this weekend. The conversion is completely reversable too except for the hole to mount the antenna as it's just a plug in module. I think you could also mount the antenna where the existing 35MHz one is if you didn't want to modify the case at all.

I've just bought a second hand EVO 12 that I'm going to upgrade with the universal Jeti TU2 module so I will be able to use either 35MHz or 2.4GHz at the flick of a switch.
The only downside I can see with Jeti Duplex compared with M-Link is that the telemetry is displayed on a separate LCD (the Jetibox or Jetibox Mini), not the EVO screen. So it's not quite as tidy but I'm just going to mount the Jetibox Mini on top of hinged screen on the EVO and I think it'll be very acceptable. All Jeti 2.4GHz receivers are telemetry capable with RX voltage monitoring built in as standard whereas only specific larger and more expensive Multiplex receivers are telemetry capable.

Aidan

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