2.4 GHz dead zones

[TonyS]

Hi all,

Interesting feedback.

I'm not at all sure about all this. I have to say I'm becoming deeply suspicious that it's not my fault and if that's the case it could well be my DX 7.

Strangely I took my Futaba 35MhZ set out tonight to test fly my FPV mule and, as I've noticed before the throttle response is appalling so, sorry Chris but I don't think I'll be going 35MhZ....

I may have to try an alternative 2.4 GhZ Tx set - thinking maybe the Aurora 9 reviewed in this months mag? Expensive but not as expensive as the three planes that I've lost due to broken contact on the radio.......

Has anyone else had issues with Spektrum Tx's? 

T

 

PS Thanks Ian for the chat tonight - lots of food for thought. 

[Ajohnw]

Nosing about on the web 2.4ghz offers 80 channels. Some set ups use 2 channels so that can result in 40 really being available. When powering up the transmitter must scan the channels and detect one or in some cases 2 that are not in use. This is  part of what the ce sticker is about..

 

It would also seem that some set ups switch channels every few milliseconds. This is or will probably be eventually an attempt to gain more effective channels as a 2msec loss of control is regarded as un important - Futaba who use 2 aerials. It seems Spektrum use 2 receivers and 2 channels.

 

2.4gig  is also used for data links in local area networks. It seems these may be from one building to another. There are other uses of the band too. As there is no information I could find on rc channels spacing etc it's difficult to know if these could interfere and even then much would depend on the quality of the receivers. That goes back to an earlier point some one made where a strong near by signal prevents the reception of the wanted signal. Some car radio's suffer from this on FM when they go past certain transmitters eg maybe an ambulance services etc. I would hope that the CE sticker takes reasonable care of these sorts of problems but it will probably be with a commercial bent. No good laying down specifications that price equipment off the market.

 

I use the word seems often as it's not wise to accept info on the web as gospel but the same sort of information is available in a number of places.

 

2.4gig is really in the microwave realm,  That's an odd sort of place. I would be inclined to keep the transmitter aerial vertical and hope.

 

 

All of the above and more is why I have asked if anyone has a sanwa 8 channel 35mhz set up for sale.  I need more channels and don't feel inclined to go 2.4gig yet.

 

John

 

 

[Martin Harris - Moderator]

Touching something wooden as I type, I'm unaware of ANY problems at our club due to interference to 2.4 GHz equipment despite the proximity of a microwave towerwhich has been suspected of causing occasional problems to 35 MHz gear.

 

Reading the thread, a couple of questions come to mind:

 

In our club (and I'd guess this would be similar for most others) the majority of people use Spektrum, followed by Futaba, Jeti and there's one user of a high quality (German, I think) dual transmitter set-up installed in a Mutiplex transmitter. However, no-one in our club is using one of the "budget" sets. Although I have no reason to question their quality, I have read about a vulnerability to interference from one of the budget outfits to early Jeti equipment (swiftly rectified by Jeti, I'm glad to say, being a Jeti user) so is there a possibility that other systems might be similarly affected? It's always troubled me that Spektrum only locks on to 2 channels for the duration of a session which must limit its resilience but to be fair, I've never heard of a case where this has been proven to be ineffective.

 

Re. the Spektrum "low output" mentioned earlier, I believe the power output is software controlled - is there a possibility that the software is being corrupted and putting the output to 10mW?  Is there any way of the user checking this setting?

Edited By Martin Harris on 30/07/2010 00:23:17

[Vecchio Austriaco]

The low output is software controlled only at the DX6 and it will be also on the DX8. The DX7 doesn´t have a user controllable function to change the output power. In any case even the switchable output doesn´t switch between 10mW and 100mW but between 100mW and the American 120mW (not sure about the exact value they allow but it is in this range). The problems I had where in a distance where also a parkflyer (10mW) system would have worked.

 

I absolutely don´t want to be responsible for an anti 2,4 or anti Spektrum movement. I am very happy with those radios, never had any issue after the repair, in the family there is also a DX6i in use and a DX7SE. none of those ever had any problems and they are used for F3A trainers and IC powered helis. The helis are not flying too far away, even if we speak about 600 size, but the F3A trainer (Sebby angel 50) does.

 

Thinking back to the time using 35MHz despite the trouble of finding a free channel (even having two quartzs sets with me all the times) was sometimes annoing and the odd glitch or the short timeout when in PCM mode during every flight were normal. And this was a Futaba set, not a chineese copy.

 

Even I had the technical problem on my transmitter I don´t want to change and I am very happy with the price-performance ratio of the Spektrum series.  

VA (not paid by Spektrum...)

Edited By Vecchio Austriaco on 30/07/2010 06:02:04

[Martin Harris - Moderator]

Vecchio,

 

I'm certainly not anti Spektrum which is by far and away the most popular system at our club and one which I've never had cause to worry about but I do feel that it can't be as resilient as a frequency hopping system. That factor influenced my personal choice of system but as a club chairman I have absolutely no reservations about members choice of Spektrum radios.

 

My reason for posting was to suggest possible reasons why people have experienced problems - and my impression from reading the thread - and similar ones - is that most have come from Spektrum users -BUT - as I've already said, I believe them to be the majority so this may be just due to their popularity and not any reflection on the system.

 

You've certainly de-bunked the software based scenario if your info is correct but it might be interesting to know a little more about the cause of your low output, though.

 

I do agree that the attitude of some people who delight in "bashing" other systems is deplorable but this shouldn't prevent sensible discussion about possible problems -  of which Spektrum/Horizon have an excellent record of rectifying efficiently and quickly.

 

I wonder if Stephen Grigg could state whether his problem system was one of the mainstream or budget systems, without being too specific?

[Ajohnw]

I'm not knocking the merits of any system but it should be appreciated that the frequency hopping technique does have one flaw. Each time it hops the system must detect an unused channel. Fine but another transmitter is very likely to be doing the same thing at the same time. There is always a time lag between systems that detect and then act so it's possible for 2 transmitters to start using the same channel at the same time. The rational for not being too concerned about this aspect is that it will not happen too frequently and the loss of 2msec worth of data doesn't matter. Arguing that this approach avoids interference is a bit bizarre and seems more appropriately related to other 2.4g rc transmitter generated interference while they are controlling other nearby models. One thing is for certain these clashes will occur and will be more frequent as the number of transmitters go up. By trade I am an automotive design engineer and have spent rather a lot of time working on comms some of which have exactly the same problem.

 

On this basis the 2 channel approach is more reliable leaving nothing to chance other than local conditions causing an apparently clear channel and of course signal drop out. which is why they have presumably opted for 2 channels.

 

My view really is that the whole comms link for model aircraft control should be the subject of an international standard. There are several used in other fields already. In this case the physical layer is a 2.4ghz signal. Some use wire, others use light some use rf at various frequencies. In many cases the problems are very similar and standards set out the steps needed to negate their effect to an acceptable level. The alternative is relying on some software engineer some where figuring it out for themselves. That's not a good idea when safety is of concern.

 

 

John

[Martin Harris - Moderator]

John,

 

Good point about standardisation but I can't really follow your logic on the 2 fixed frequencies being more resilient.

 

I accept that the 2 frequencies are at an acceptable noise floor when selected but this gives no protection against a "dirty" user or two - such as video downlinking - using the frequencies pre-selected at a later stage in the flight - especially if the "random" channels selected are close to each other or even adjacent which I believe can occur.  Should a large chunk of the available spectrum be lost this way, a FHSS system will merely reject a frequency or two until it finds an acceptable one - even looking at 79 channels before finding one usable one would only take less than 1/5 of a second - maybe a just noticeable glitch...

 

In an ideal world this scenario shouldn't happen, but given the vagaries of the RF world - especially at GHz frequencies and the open nature of the 2.4 GHz band it's certainly not inconceivable.

[Ajohnw]

The 2 channels are established and there after shouldn't be interfered with by other legitimate transmitters even the hopping ones as they should detect the channel is in use. Hop and it has the flaw I mentioned more so with increasing numbers of transmitters in use. Throw in noise and what ever and it's rather hard to make a judgement as to which is better but I would still be inclined to favour all using fixed channels.

 

On down linking from memory the official frequency for that is something around 500mhz at 10mw. I wouldn't have thought that would be a problem given sensible 2.4ghz receivers. 4.8ghz transmissions may be but microwave does have the advantage that such signals are well away from the wanted signal so can easily be filtered out. I think the US made a sensible decision on adopting 70 odd mhz on that basis and also propagation but have no definite information on that. I suppose 2.4ghz and the current apparent free house and complete lack of compatibility between systems worries me especially the 2.4 part. Having had some limited involvement with spread spectrum communications I am also rather curious as to what form it takes in the model area. It can be a rather nebulous term.

 

Off topic but some (long) time ago I had a vision of model fliers towing a flight simulator hooked up to there model behind their cars when they went flying. Video linked drones  are already in use. A simulator is only a step away but a lot more expensive. I wonder where it all will go next?

 

John

[flytilbroke]

Seems quite a lot of confussion here. So just a little light on the subject of our 2.4GHz systems

 

Forget consumer video senders.

Forget consumer gadget controllers.

Forget car key and now car radio remotes.

 

They are all low powered devices which at the distance concerned, any model 2.4GHz receivers which are used at our flying will never detect them, never mind them being strong enough to be a problem.

 

Airborne video senders in a model may well, even are likely to cause unacceptable unwanted signal to our receivers, except where they are designed as part of the system

 

Permitted Frequency hopping happens so rapidly that there is virtually no chance of sufficient interferance to affect the model in flight.

 

Systems which use two channel "lock-up" are not reliant only on the radio signal. The Data being sent and received is the main operating factor. Again this happens so fast that the chance of extended blocking is so nearly impossible that it can be disregarded.

 

The wanted Radio signal can be limited and blocked by the materials used in our models, the manufacturers recognised this and produce designs which overcome this problem.

 

The chance of our models in flight having thier Receivers overloaded by other model Pilots' transmitters are truly miniscule.

 

Point to Point Radio Communication signals could well overload a model receiver for a short time as the model transits the narrow beam from thier source.

 

That leaves the Pilot as the extreamely likely cause of any mishap, whether by poor flying or not finding a fault in the model

[Dusty]

 

That leaves the Pilot as the extreamely likely cause of any mishap, whether by poor flying or not finding a fault in the model

 Cant agree more!

[John Privett]

Posted by Ajohnw on 30/07/2010 13:43:19:

The 2 channels are established and there after shouldn't be interfered with by other legitimate transmitters even the hopping ones as they should detect the channel is in use.

 

 

That's not quite how it works John.  The "hopping" transmitters hop from one frequency to another in a pseudo-random pattern regardless of whether or not the frequency they are hopping to is clear or not.  Both tx and rx know the algorithm and hop in sync from one frequency to the next.  To miss out occupied frequencies would require data to be transmitted both ways between tx and rx and multiple acknowledgements.

 

One other aspect that hasn't (I don't think) been mentioned here is that, rather like our mobile phones, our 2.4GHz txs do not transmit continuously.  They transmit a packet of data and then standby until it's time to transmit the next packet.  They are only transmitting something like 10% of the time. 

[Peter Beeney]

   As I have also recently been the victim of a malfunction by Spektrum radio, I’ve read this thread with some interest.
   Regarding John’s post about TETRA, (TErrestrial Trunked RAdio), when this first came into operation there were complaints about it interfering with many other operators, all on different frequencies. Close proximity, it appeared, was the common factor. It seems that one of the facilities of the emergency services radios is that they can automatically raise their own transmission power levels to a point capable of overcoming any ‘local difficulties’, such as hills etc. There was some debate in the article that I read about this as to whether this action was legal or not. But as it was the Police who were generally responsible, who was going to question this anyway? These power levels were not disclosed, nor likely to be, leading to a question in Parliament; the answer given by the then Minister of State for Transport was typical, this ruling would stand and it was the responsibility of the other operators to make sure their equipment was secure against interference. Whereas I suspect the opposite is what is actually meant to be the law.
   So John and empeabee may have a very valid point. A total swamping situation, perhaps? I don’t have any proof of this, of course, it would take some extensive checking out to establish any evidence. The situation may well have changed now, although, although I think unlikely.
   Regarding the actual lower power type interference, as I understand it each of the 83, (I think), channels is about 1MHz wide. The receiver is looking for a predetermined code from it’s transmitter and will not respond to any other signal. So any other signals in this channel just get ‘lost.‘ Is it a case that our required milli-second pulse signal is relatively so slow and so undemanding that in fact some of this can go missing but the model doesn’t see this? If we were sending vast reams of data every millisecond, which I believe is normally the case with other types of 2.4GHz communications systems, then it might make a difference. Does this then explain the item that I read, that the Americans had amassed 120 2.4GHz transmitters, switched them all on at once and they all worked perfectly. This may be just a story, but I suspect at least an element of truth. 35MHz PCM radio, it is said, will ignore interference for up to half a second. So in theory is it possible you could have a pulse of interference, up to half a second long, once every second, and the model would not notice this. But now half the information’s missing! I think the radio link, and the servos, would just slow down, as the MPX IPD rx is suppose to do, when right on the limit of radio range. Interesting again, I have perused a small item which said that once upon a time the Military used a frequency hopping system to send their clandestine messages but due to the radio waves getting ever more crowded it slowed the system down to a point where they had to give up on it. I don’t know what they use now.
   I’ve used MPX radio for many years, and many, many other sets, very predominately Futaba, with beginners, and I can honestly say that I’ve had more problems with Spektrum in a few months than I have with all the rest in 30 plus years! This is with buddy leads and piling up someone else’s model.
   Another club member who is learning has had two ‘loss of contact‘ experiences, and he has now received a new set. He mentioned his problems in a very well known model shop and they said he’d had a ‘lock-out’, (a new buzz word?), which is as Chris said, when a tank full of fuel, or the battery, or motor can apparently mask the signal. They also said there has been at least one case when a number of 2.4 models all crashed simultaneously. See TETRA, above? Also, as has already been noted, Manny Williamson remarked in the BMFA news there’s been a sudden increase in insurance claims. What’s brought that on? He speaks about engines stopping but I’m not entirely convinced. Is it more like models going out of control? A really accurate breakdown of the figures and a report might be interesting!

   Although I shall carry on using Spektrum, there are still beginners to help etc., I think I might be a tiddly bit apprehensive, waiting for the next incident.
   I shall continue to use, when ever possible, my couple of ancient SkySport 4’s for buddy purposes. They are really showing their age, but using MPX crystals they have never missed a single beat in years and years. I only use the MPX crystals as my own personal preference, nothing wrong with Futaba at all!                              PB

[Ajohnw]

Hi John. That just goes to show the dangers of believing every thing on the web.

 

From one site I had gathered that spectrum use 2 channels and do not hop. Futaba hop but I suspect they still have to look for a clear channel, see the pdf link below.

 

Time can be used to get round the point you mention about bi directional transmission. The receiver can expect a signal at some particular time and if it doesn't  get it or gets something that looks like it's not for it or even corrupt move on to the next frequency. There are all sorts of variations on this.

 

 

Few links that might be of interest

 http://www.bmfamid.co.uk/forum/index.php?topic=20.45;wap2

 

The IMS use of the band is entirely correct. eg but there are many uses

 http://en.wikipedia.org/wiki/IEEE_802.11 

 

And finaly on the seek unused channel and locking etc

http://www.google.co.uk/url?sa=t&source=web&cd=3&ved=0CBwQFjAC&url=http%3A%2F%2Fwww.mpba.org.uk%2FPDF%2520Files%2FUKRCC.pdf&ei=KSBTTPjOFYKQjAfHjuDCBA&usg=AFQjCNGxtwHPo-lfredYRnxDgyv0cUgPxA

 I took that as a ce requirement.

 

On only transmitting 10% of the time could be that they are always transmitting a carrier and only sending actual data 10% of the time. Locking on 2 empty channels permanently would be a bit of an issue if not.. The spread spectrum system I worked on effectively worked like that. The carrier was always there and the data was sent periodically in the form of so called chirps. The data can contain various things to allow it's integrity to be checked or even reconstructed if some is missing or corrupt.

 

If anyone knows of any hard information on the technical machinations of these systems on the web that isn't advertising etc I would be very interested.

John

[flytilbroke]

It is not neccessary for a two channel system to transmit continuously. Ten percent of the time can for example break down to 1/1000 of a second and 100 times in that second.

 

A second transmitter/receiver outfit can easily recognize which "channels" are in use and avoid them.

 

So, different to our 35MHz systems which use FM, requiring a continuously transmitted signal.

[Mark R]

Not adding to the 'blame' this manufacturer or that one....but about 4 weeks ago i lost my travel air to lock out? fail safe? donut of death? pilot stupidity??? pick one?  I had obtained my transmitter off eblay and thought i had performed faultlessly up until i was binding my F16 edf when i could only get 3-4 paces away from it til it refused to work, ar6200 (hmmm sorry bit of a giveaway as to who made the transmitter), after fiddling around did get a good range check from it, spool forward to 4 weeks ago and plane hammering itself quite succesfully into the ground.  At that point i thought it definately wasnt pilot stupidity, wasnt receiver pack failure, or as i had done a year before, forgotten to recharge receiver battery and ended up burying my ready 2 (was using 35mhz then).  So i decided to speak to the manufacturer and sent tx and rx off to be checked.  Outstanding customer service, both back in my hands within 2 days of posting, imagine doing that with the car or motorbike you bought for umpteen thousands of pounds!!!  Rx no problems, tx on the other hand....hmmmm aerial broken, could i tell it was broken beforehand? nope, could any of my friends at model site tell if  theirs was broken or frayed? erm no!  also it wasnt putting out enough power to the board or something technical like that...now there wasnt anyway of me knowing any of these problems beforehand, problems getting a good range check COULD of been down to lousy positioning of the rx, or a poor voltage or rx battery or perhaps mars was rising in uranus and the gods just didnt like me that day.   So what exactly am i trying to say with my previous drivel?  Is there really a donut of death or dead zone, hmmm maybe or is it the newer 2.4ghz systems are perhaps not as robust as the 35mhz ones of old, do we treat the new stuff gently?  Putting them away in the car banging against things, thudding them on the ground, are we 'abusing' them the way we used to with our 35mhz stuff.  Are WE  causing problems through day to day or week to week 'abuse'?  Just a thought as i would never of been able to tell, without sending off my radio to be looked at, what is the cause of the 'problems'  I and we are experiencing.

Edited By Mark Rowse on 31/07/2010 10:12:40

[Ajohnw]

2 msec is 500 times a second and it's not possible to guess how long a transmission lasts without hard information. They might update all channels in one go but as typical servo's move through 60 degrees in 90msec there wouldn't be a lot of point. No doubt some servo's may be quicker but human aspects come into it as well.

As to detection using simple numbers to pick up a signal that occurs every 2msec a channel needs monitoring for 2mses as all transmitters will not transmit at exactly the same time. That's an ideal situation in the real world where environmental effects might prevent detection one might look for a signal for say  10msec or even a lot longer. So if scanning 80 channels that would take 800msec. Big problem though. By the time all channels have been scanned some one might have started using one that was clear or some one else might have also marked it as clear and be about to use it..

Say the data transmissions are 100usec long to detect those the microcontroller that's probably doing the job would have to look and see at interval sligtly shorter than 1/2 of that or more than 20,000 times a second. There are several other approaches to this that can do the same sort of thing but all have cost aspects and then there are things called asic's/ Application Specific Integrated Circuits. Also microcontrollers that are tailored to do a specific job much used in the automotive industry. No point working out what this means as above because we have no idea how long the data takes to send or if it differs between manufacturers. Again it will take longer than some might think.

Detection is really easy flytilbroke isn't it.

Ok so the transmitter and receiver have found maybe found their channels what's next? Can't spend ages looking for activity on the channel as transmissions have to be sent every 2msec and little can be done anyway as the model might be in the air. Might be nice if the receiver  light a beacon if it thought that it was getting too much garbage but this might not be good for sales.

Hopping is interesting but it's rather difficult to generate true random numbers. Most methods generate the same sequence of numbers over and over again but there are ways of improving them a little by using methods that increase the chances of the  numbers used by each transmitter being different. The length of the sequence is a measure of it's quality. Mixing hopping with fixed has some interesting implications as to which one stomps on the other most often..

Lastly the 2msec interval. This is likely to be rather precise as it's in radio equipment but this introduces another problem. No 2 transmitters are likely to be exactly the same so the signals slowly drift across each other. The lower the difference the slower the drift and once they collide the longer they will  take to drift clear.

All sounds like futaba and jr might win out but it could also be dependant on how many of one particular transmitters are in use. There's lots of scope for problems and it all comes down to probability in the end and just how many times and how often the aircraft has to be updated to work in an acceptable manner. Then there are the increasing numbers of other makes - who knows what they do.

John

PS Maybe amateur radio people us 2.4gig for moon bounce communication. Best not fly when there is a full moon.

[TonyS]

"That leaves the Pilot as the extreamely likely cause of any mishap, whether by poor flying or not finding a fault in the model"

 

Sorry Flyilbroke (and Dusty) but in this case I can't accept responsibility.

 

Today, yet again, flying my Twister on a DX7 Tx I experienced some seriously troubling drop-out on the controls - luckily this time I got it back and landed it pretty darn fast.

At the time I was performing a relatively docile left-hand bank. The model had been up in the air and working fine for around 3-4 minutes before the problem arose. Battery check on landing - still 28% left according to my Smartguard.

 

I know I'm not the worlds greatest or most experienced RC pilot but I think I can recognise a communications glitch when I see one. In a model that has performed perfectly well on a number of occasions prior to the 'glitch' I can fairly well rule out, not having checked the model out thoroughly enough before flying or interference from badly positioned components etc etc.

 

I've no axe to grind with Spektrum. It was recommended to me and I've flown nothing but Spektrum (but for a tiny dabble with 35Mhz on the FPV set-up) since I began model flying again. Indeed I even recommended them and bought them for friends. Three lost planes due to lost comms link and another glitch today though and I sense a pattern.

I'm a great believer in not ignoring the obvious. If it looks like a duck, walks like a duck and quacks like a duck...it's probably a duck. In this case, it's probably a problem with the TX and Rx.

[Tim Mackey]

Sounds like the best thing would be to send them both off to HH for a health check Tony.

[Vecchio Austriaco]

Tony,

Question about your flying style: are you turning your body or your head if the plane is left or right from you?  (if it is the second it may be that the antenna was pointing to the plane and you transmitted less signal)

In any case it shouldnt happen. So do as Tim adviced.

 

Has anybody around you the Spektrum flight log? see details here. if yes you can check the connection quality. When I had the problems with my DX7 I purchased one of those, since the transmitter is repaired I just check new models after their first flights as it is always ok.

 

The flight log - when connected to the receiver before disconnecting the battery shows you information about transmittion quality as well as voltage problems (brown outs). Only snag of the flight log: works only with AR 7000 upwards and I use mainly AR6200.... 

[David Turner 5]

I was chatting to a bloke who designs wireless LAN systems. He was telling me that, in built-up areas, he was having to use 5-point-something GHz, because there are just too many 2.4 sources which interfere with his systems.

 

I can't predict how this will work out.

 

What I can tell you, is that when 35 Meg was introduced, it was also hailed as the "panacea".

 

Ultimately, you have a small fortune dangling on the end of a radio link.

 

[Tim Mackey]

" Ultimately, you have a small fortune dangling on the end of a radio link".  

 

Now that's a fact.

[Delta Whiskey]

There is an easy test you can do !..................................go fly somewhere else and see if you experience the same issues?

[Ajohnw]

I just looked at the manual for a walkera helicopter that comes with a 2.4ghz transmitter. It notes that the transmitter and receiver take 10 secs to lock and asks multiple users not to lock their set ups at the same time. It would be interesting to know what recommendation the other makes state.

John

[Peter Beeney]

   I think I would definitely have to agree with Tony here. However biased you are towards, or against, one particular brand of radio, and many people certainly seem to have their favourite, it would seem that there is a pattern emerging.
   If these crashes and glitches were always down to conditions such as uncharged batteries, poor radio and model installation and maintenance and pilot disorientation then these would have been prevalent to all frequencies and brands of radio since it all started. Of course, these situations have always existed, to some degree, and in a random pattern, but invariably I’m sure this is eventually recognised by the pilots and other observing modellers. Here we seem to be experiencing a total unexplained loss of control.
   Would not the same criterion also apply to the micro wave beams and other possible sources of interference to 2.4GHz? I’m sure it would affect all 2.4 systems in exactly the same way.

   With regard to the LAN being overcrowded, there was once a little query from a computer user about his system slowing down and he couldn’t discover why. The answer, from the expert, was to try disconnecting some of his local wireless peripherals. Thus freeing up some overloading of the airwaves immediately in the vicinity. It appeared he’d had exactly the same problem. So it occurred to me at the time that as Wi-Fi and WiMAX continue to increase in usage will that slow the 2.4 system down? That’s if they use the 2.4 bandwidth, and I’m pretty convince that some parts of these do. But, as I said, does it matter anyway? Is the modulating signal, that operates at eye/brain/hand speed, so relatively slow that it can go largely unnoticed?

   In a word, if one particular brand of radio constantly has problems that other similar systems don’t have, then it seems logical to suggest that that brand does have some specific problems. What other explanation could there be?

   Perhaps on a brighter note, I think I can say that I’ve never knowingly experienced a case of unknown interference on 35. There have been problems, of course, but eventually always accountable. Years ago, circa nineteen seventies, I bought a Realistic scanning radio from Tandy. Expensive, but it was the only one at the time that I could find that would cover the 35MHz band. I used it a lot back then, and I never once picked up any extraneous signals at all.

   Today I’ve been involved with buddy leads, yet again. I’d have never believed that a couple of mono plugs could be such a complicated issue. Or pain in the neck!       PB

[David Turner 5]

With regard to wireless LAN.

 

I recall that the designer, to whom I was speaking, told me that there was a high-end motor car which gave him particular problems.

 

It seems that, whenever one of these cars drove by a particular set of offices, the offices'  2.4 systems fell apart.

 

Can't remember whether it was BMW or Merc. However, the roadway passed beneath the "line" of a communications transmission ... apparently. All a bit too techy for me.

 

 

 

Trying to look at this simplistically, I come to the following conclusions. The frequency, itself, isn't magic. The magic is in the encoding, as far as I understand. Now,it's not that I have little faith, but I seem to recall that PCM, too, would be the "golden bullet". How'd that work out?

 

 

And, I have a suspicion that some of these systems are put onto the market too early. Is it a legitimate strategy to have the consumer perform your product development? I guess that an element of that is unavoidable; the question is, "How much is acceptable?"

Edited By David Turner 5 on 02/08/2010 06:59:11