Gutted

[Paul Williams]

Tim, I have been fliting through the settings on the dx6i, whats the power setting for? two different modes are avaiable. EU 328 and US 247

[Lew Weaver]

Eric

Exactly what I was going to ask next -is there no such equipment available?

Also what does it take to swamp a Speccy Rx?

[Former Member]

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[Tim Mackey]

Paul Williams wrote (see)

Tim, I have been fliting through the settings on the dx6i, whats the power setting for? two different modes are avaiable. EU 328 and US 247

EU 328 is the only legal output power setting for the UK ( 100m/w )

The US247 is for, well,,, the USA only! 

[Brian Parker]

Eric,

 The 144 Mhz. Amateur band is harmonically related to 2.4Ghz (*108).

Therefore 144Mhz Amateur equipment could readily be used as a tuneable IF in conjunction with a ‘simple’ 2.4Ghz converter. Are there no published converters in Amateur circles linked to your 2310-2450Mhz Amateur band?

[Lew Weaver]

The worst bit about these crashes is that my laddie had taken up the hobby again and I persuaded him to buy 2.4 gear.

He built this

[Lew Weaver]

We have researched the local area today for possible sources of our problem and discovered that a BT mast is transmitting on a line that crosses the flying site we were using.

This 12 metre high mast which is located maybe 5 miles away is transmitting a point to point radio system and the power leaving the mast is 200mW according to the palnning permission document.

 Could this be the cause of our crashes?

[Brian Parker]

I’m probably a little out of date (or incorrect) but my understanding is that BT use mainly 1.9Ghz with some transmission on 2.4Ghz. So they may in fact be transmitting on 2.4Ghz. They use ‘adaptive frequency hopping’ transmissions, the range is enhanced/increased by capturing reflected transmitted signals.

For what it’s worth (probably not much) I’m still of the opinion that the majority of problems users encounter are due to antenna orientation degrading the signal…. from the transmitter to the model and/or…. weak received signal due to the receivers antennae not fully optimised to receive reflective in phase signals.

 The BT transmissions may possibly have an effect due to this signal degrading but their coding and data steaming makes this unlikely. Also the fact is that not all users are affected.

Just my opinion. 

[Lew Weaver]

but is a BT broadband transmitter not likely to be using 2.4GHz? 

 ok - let me get this straight, and please correct me if I'm wrong (very likely!)

A Spektrum Tx selects 2 free channels when switched on, so if it selects 2 channels that it "sees" as "free", what happens if the model passes through a transmission beam that is using the selected channels?

[Brian Parker]

The receiver once bound to the transmitter becomes its slave and will (should) only act on the control information it samples if it recognises the protocol of its master. Error detection (and correction?) in all probability uses redundant information coding techniques to prevent acting on incorrect information.

 BT transmissions will be in ‘packets’ of a few milliseconds and will have sophisticated encapsulated protocols to prevent unauthorised interception of their transmissions. I understand that there is no transmitted signal between packets.

Not sure of the bandwidth of either transmissions but it’s becoming pretty crowded out there (35mhz faces greater challenges).

Don’t forget radio waves travel at the speed of light and the receiver is designed to receive and filter unwanted information.

Probably now in trouble from forum modulators for technical drifting/waffling.

 

I can’t answer to the extent of BTs utilisation of 2.4Ghz. Someone is sure to come up with the facts.

[Tim Mackey]

Nah...your OK so far Brian

[Tom Foreman]

So does the Spektrum system which locks onto two 'free' available frequencies suffer more from 'swamping' than the Futaba system, which frequency hops frequently ,  or does it make no difference?

Tom

[Brian Parker]

Is either system prone to ‘swamping’ if care is taken in installation?

 

Certainly below 50Mhz signals are often down in the background noise (both manmade and natural interference). 35Mhz sits in this noise.  The 35Mhz receiver is unable to recover wanted signals if this noise is beyond a certain level even with increased receiver sensitivity. Above 50Mhz the noise is much lower. Above 100Mhz the signal is clear from noise. Communication can thus be achieved at much lower signal levels.  Therefore surely at 2.4Ghz the limiting/critical factor is antennae location/orientation provided the receiver’s sensitivity enables it to respond to the wanted signal.

[Former Member]

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[Brian Parker]

Eric, Thanks for the reply.

As to the masked signal, I assume (correctly or incorrectly) that the coding is robust enough ensure continued contact.

[Tom Foreman]

Thanks for the reply Eric, I wondered whether the Frequency hopping might help in this respect as I have seen less Futaba problems reported than Spektrum, although you could argue that the Spektrum is more prevalent and therefore more people are likely to suffer problems if there is a larger user base.

[Former Member]

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[Keiran Arnold]

Did a scan of 2.4Ghz  to see if there was any noticeable usage on the band for about an hour. Nothing seen although it is not a busy area around here.

[Lew Weaver]

Keiran - how did you do that scan?

We have also found that there is a privately owned self-help relay station close by for analogue and digital broadcasts - that shouldn't  be a problem should it?

[Former Member]

[This posting has been removed]

[Keiran Arnold]

 I had access to a wideband Microwave Search Receiver with an Antena at 20m

[Former Member]

[This posting has been removed]

[Lew Weaver]

Further to the previous post, we have discovered that the BT broadband "point to point " transmission from the main mast to the receiver does not pass directly over our secondary flying site. We are not sure however if the signal is then relayed to other points.

Flew the repaired Pfalz with the same gear at our main field today with no problems.

It is really frustrating not finding the crashes cause.

[Lew Weaver]

Since the unexplained crashes at our second flying site I purchased one of Spektrum's Flight Logs.

Used it on about a dozen flights at our main site, trying as best I could to keep the flight path the same

Every second flight was with the aerial at 90 deg compared to sticking straight up for the others.

The Log showed that there were antenna fades with the aerial straight as opposed to all zeros with the aerial at 90 deg. The antenna fade numbers were mostly low with only one at 190 and Spektrum states that you should expect 50 to 100 per flight.

So, does that sort of confirm the aerial orientation points made on the previous posts?

Now I need to go fly at our secondary field to see if I can have another "unexplained" crash, but this time with the winter hack.

[Paul Williams]

This topic has gone round in some circles since I first posted it. I never proved the fault which caused several crashes but what I did do was act on advice given from a friend after making his own inquires. I don't know if you are aware but some of the spektrum gear has been baned at flying clubs due to faulty battery connections. The one I know of is the dx6i the spring clips holding the AA's have been proven to cause power loss which of course leaves the rx to shut down. I did a mod to correct this possible fault and after a run of crashes I have now flown 50 times or so without incident. I cant prove the mod cures all but for a few quid it has left me with the confidence to use this equipment again. Rawtenstall models have the mod for sale at 12 quid if you don't fancy making your own. Happy flying.