Radio interference at Bray Head (35 MHz)

[Fergal Gordon]

HI everyone,

A couple of weeks ago I flew at Bray Head on a nice evening with a fresh breeze.  Myself and Ed flew about 500 m south of the cross, as there were 6 para-gliders there.

3 or 4 times during an hours flying I had some glitching.  I have never had glitching before, except for the time I did not extend my antenna before take off.  Initially I though it was severe turbulence, but the wind was not that strong and you would not expect much turbulence coming from the sea.

I landed and did a radio check, all OK.  I switched off the Tx and there was not a sound out of the servos.  Everything seemed OK.

I completed another couple of flights, again with intermittent glitching.  The last incident was close in at eye level and this one was more valiant and at one stage sent the glider towards the sea.  Control was reestablished, followed promptly by a safe landing.

I checked it out at home and all seemed to be OK and have flow since on the slopes in Wicklow without any problem.  At this stage I am guessing that the problem came from the overhead electric cable of DART line.  We we standing back from the edge and were not aware of the trains below, so I don't know if there was a train passing when the glitching occurred.

Here are the technical details of my system:

Tx: Multiplex Royal Evo 9, 35 MHz, synth, operating on Ch 80

Rx: Multiplex Rx-6-Synth light, operating on Ch 80

Servo: Hytec HS82MG x 2, Hytec HS125MG x 4

Ed was flying on 2.4 GHz and had no problems.

Does anyone have any similar experience at this or similar locations?  I presume I should move to 2.4 GHz to fly safely at Bray Head, or is there some other way to address this problem.


Best regards,


Fergal

[Alan_Perse]

Hi Fergal. Welcome to the Forum.

Just wondering what model you were flying?

I had similar problems like that before with my DHLG. I think I told you about it before. Thanks to Ralph I have finally solved the problem. My receiver antenna was to close to the mess of servo and battery cables in the fuselage. Just rooting it away solved the problem.
 
I know that you never had any problems before with your models, so this may not help. So it could be an interference problem at Bray.

Alan.

[rogallo]

Hi Alan and Fergal

HI Tension Electric Cables CAUSE RF interference, Stay away.

We have power lines scattered across the farm we fly in and suffer from interference on 35mhz near the cables.

Also stay use lower channel numbers (I am on 80  )

Just me twopence worth

Ralph

[joe]

Hi Fergal.
Maybe someone was flying at the Shankill club on your channel?
Shankill club is just south west of the sugar loaf. If they had a powerful TX I guess it could cause problem???

[JohnPearson]

Hi Fergal

Looked at the possible reasons you give for problems on 35MHZ, here's what I think!!

1. We fly of the beach beside a railway line at castle rock,trains pass close to us, and we have had no interferance on 35 or 2.4.
2. Power lines, I lost a small electric jet on 35, after flying under a local power line a few weeks ago, the model never give me any problems before that day.
3. Running your antenna near other cables can cause big problems, I always place the antenna out side the fuselage.
4. mobile phones can cause problems to 35 using synth system, i.e phone in your pocket when flying, The BMFA do not allow any mobiles on the flight line at any shows in England.

We had a  problem at our club with operating on 35MHZ over the last year, with models crashing for no reason and bad interferance on some channels, we got equipment in to check out the flying site for local transmitters operating near the 35 band and strong transmissions on other freq's, we found nothing, therefore all our pilots fly on 2.4, problem solved.

I think the idea which Joe put forward about shankel may be possible, to check barrow a channel monitor if possible when you next go to bray.

Hope some of this info helps

johnp

[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]

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

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