Should PCM receivers really cost more?
 

Judging by the size of the box (like that matters), it seems a PCM receiver shouldn't cost any more to produce than a "standard" FM receiver. Is there any justification for charging twice as much for the PCM boxes? It seems like they would have recouped their development costs by now.

Tom

Should PCM receivers really cost more?
 

They will keep recouping it for as long as they can. I am looking for a TCAS for my real plane. It is 2X3X10, cost is over $25,000. There can't be a couple hundred bucks worth of stuff in there. If they dropped it to something like $5000 it would be in every plane in the world and they would make a ton, but they are trying to make as much as they can, as fast as they can. Really dumb. Happens in every aspect of life as well. Do you really think a harley costs $20+ grand to build?

Should PCM receivers really cost more?
 

Flyboy,

The cost of the actual hardware is insignificant compared to the engineering/certifcation etc... And the certification level is at least 'B' for a TCAS, which really drives the cost.


Now, I agree with you that the price of PCM could come down some. But as long the coding is proprietery, that is not going to happen soon.

Azhar

Should PCM receivers really cost more?
 

Yes, the added complexity of the decoder circuit warrents the increased price, in fact it is a bargin for what the additional design and circuit components cost. I'm not a fan of PCM but, being an electrical engineer, I do understand the increased costs.

Should PCM receivers really cost more?
 

azhar, I agree. They will just keep selling them for as much as they can get for them till it slows down, then drop the price and sell a bunch more (both the PCM and TCAS).

For me, the PCM is easy to justify. There are lots of people who don't feel that way and fly FM. Nothing wrong with that either. Both work well.

Like you said, I don't think you will see a huge drop in price, but they have come down a bit. I can get recievers now for about $50 cheaper than say a year ago.

Should PCM receivers really cost more?
 

I haven't seen the circuitry, but PCM is just another integrated chip isn't it?

If it is, then forget about the unit costs, it's only the development costs, the software and tooling costs that are being recovered, and you don't see physical evidence of any of those in the product itself.

After all, the material the chips made of is silicon, and that's available by the ton, free, on any beach!

-David C.

Should PCM receivers really cost more?
 

Rodney.. PCM receivers can cost over 150 dollars and all it does is receive and decode a 9600bit/sec RF signal at 72MHz... Now lets compare that to a moment to say a USB wireless card. Which can transmit, recieve, decode, encode, encrypt and route a 11mbit/sec signal at 2GHz which (checking on pricewatch) can go for as little as 33 dollars... Justify the cost of a PCM receiver knowing that... It is all in the development cost. There are more people willing to buy wireless adapters now so companies are willing to spend big bucks developing them, they know they're going to get their money back. Aren't enough RC users to justify the same development costs for a product.

Should PCM receivers really cost more?
 

Probably a lot more USB wireless cards sold than PCM receivers already. And when more are sold they will be down to 14.95. That's how it works. Volumes speak volumes about pricing.

Should PCM receivers really cost more?
 

I have to agree with Lynx, here. Look at it this way, the difference in price of a PCM radio "package" and an FM package is usually about $30-40. .maybe as high as 60. The difference is probably close to 50% actual part cost increase and 50% additional profit.

Look at a Sony Walkman. . AM, FM, tuneable, Cassette or CD, headphones, less than $60 in some places, and it has a ton more circuitry than our receivers.

They use the same basic casing for most receivers form a manufacturer, unless they change the size. Look at most receivers and they seem to be just a re-labelling of the previous model, with a slight "improvement" in the internal circuitry. PCM has been out for over 10 years now, FM for over 25, and the encryupted 'bits' code-train in PCM is the same, except for polarity, for each manufacturer (It's an FCC rule)

Are we getting "gouged". . . you bet!! Just like 8411 servos going for $115 at most places when you can get the more robust 5945 HiTecs for as little as $75. . . . .someone is making a KILLER profit margin.

Should PCM receivers really cost more?
 

At least the prices are starting to come down some. JR has the new 770 for $99 street price. Maybe some of the others will drop in price again too or at least drop the price on new models. It boils down to competition and what the end user is willing to pay.
Ed M.

Should PCM receivers really cost more?
 

If the development cost was $10 million and you sold 1 million you'd have to price each at 10 dollars to cover the costs.

If, however, you only sold 100,000 you would have to charge $100 for the same thing.

Since the unit cost is so low, it hardly enters the equation.

How many potential Network Interface Card buyers are there compared with RC radios receiver buyers?

-DC

Should PCM receivers really cost more?
 

Since PCM is proprietary by manufacturer, there is no competition to encourage lower prices.

Should PCM receivers really cost more?
 

All the pro flyers that ive talked to(paul skinner e.t.c) hate PCM- they would rather have FM glitches that they could fight rather than have a completely locked in fail safe plane that they can't do anything about.
Hey well guys, we all know the real definition of PCM.
Its not pulse code modulation, its Probably Costs More!
Now you can get a Multiplex IPD(intelliegent pulse decoder) reciever which is loads better(all the advantages of PCM and FM) for a lot less(FM receiver prices). When these catch on, pcm will probably become extinct(unless they lower their prices by a hell of a lot), so we will no longer have debates about the overpriciness of PCM!
yipee
Luke

Should PCM receivers really cost more?
 

Not necessarily so, since the mfg is usually pitting their PCM receivers against their PPM receivers. They tout the benefits, but people will only pay so much for them. I got an 8 channel PCM receiver for Futaba for 100 bucks - that's a good deal.

Should PCM receivers really cost more?
 

No way is IPD better. Check the resolution of the system. If you don't care about performance fine but don't claim it is better. In fact I'd say it has the disadvantages of both.

IPD Receivers
 

I have flown FM, Futaba 1024 PCM and Multiplex IPD receivers for many years now and feel no advantage of resolution of one over another, and I fly F3A which requires very precise equipment. I have not encountered any interference at my flying field that I felt, but if there is interference then the IPD receiver does become less precise as shown in the following advertisement, but less precision and some control may possibly be better than failsafe and no control:

"The new IPD process is a MULTIPLEX development which combines the best features of two different systems: the advantages of PPM - speed and compatibility - with the safety of PCM - to detect and suppress interference.
As fast as PPM
Compatible with other PPM transmitters
Detects invalid signals
No servo jitter with transmitter switched off
Servo Hold function
Servo Failsafe function
No servo travel beyond set limit values.

IPD receivers can be operated with all standard FM PPM transmitters on the appropriate frequency. In the event of radio interference, IPD receivers will help you maintain control, and in the event of unrecoverable interference, the receiver’s behaviour is similar to that of PCM receivers, with the servos moving to a pre-set failsafe position.

IPD stands for Intelligent Pulse Decoding, and the receiver incorporates a processor which analyzes the incoming signal for validity. Like a PCM system, IPD filters out invalid signals.

The difference between IPD and PCM is that the receiver does not 'switch off' the 'dirty' signal as field strength declines, but instead widens its tolerance. If the signal weakens, the receiver software starts to calculate an average pulse width using the values of subsequent pulses, which are normally slightly different caused by the jitter of the signal. The so called "floating average" suppresses the effect of jitter. As an additional help, the resolution of the signals, sent to the servos, is also reduced. Those two effects result in a slower reaction of the model, which you can take as an warning of interference. This "visible" warning enables you to take action (e.g. change direction of flight, hold the tx up, ...) This means that control becomes less precise as field strength falls away, but remains usable for longer (greater range). The result is that you can infer the approaching limit of range from the model’s behaviour, whereas PCM suddenly robs you of control.

An IPD receiver sees all usual PPM formats as valid, which means that all standard FM PPM transmitters on the same frequency can be used with IPD receivers

IPD is faster than PCM because there are no check cycles.

The user programs the fail-safe positions of all channels into the IPD receiver. The transmitter is used to set all servos to the desired positions.

Practical testing has shown that IPD and PCM produce comparable results when unrecoverable interference occurs. But please don’t get complacent: Like PCM, IPD is not an excuse for incompetent RC installation and careless cable deployment, and thorough suppression of electric motors and ignition systems is still essential."

Re: IPD Receivers
 

[QUOTE]Originally posted by MPX_4000
[B]I have flown FM, Futaba 1024 PCM and Multiplex IPD receivers for many years now and feel no advantage of resolution of one over another, and I fly F3A which requires very precise equipment. I have not encountered any interference at my flying field that I felt, but if there is interference then the IPD receiver does become less precise as shown in the following advertisement, but less precision and some control may possibly be better than failsafe and no control:

If you get a chance borrow a Hitec servo programmer which will allow you to measure the pulse width of the signal coming out of the receiver. In a good PCM system you will be able to change the pulse width in increments as small as 1.17 microseconds as I recall. I don't remember what I measured on the IPD but I remember I was shocked by the loss of resolution as a result of the signal processing they do. It does get rid of the jitter but at a high cost in terms of resolution. If you are happy with it don't by good servos because it will be a waste.

Should PCM receivers really cost more?
 

Is the resolution worse than 512?

I confess my flying accuracy isn't good enough to notice a step of 1/512th of the total movement. Let's see, the elevator only moves about 1/4 inch, so that 1/2048th of an inch per click.

That'll do me!

-David C.

Should PCM receivers really cost more?
 

IPD is just a filtered PPM signal, so it's fully analog (no stepping at all)

Re: Re: IPD Receivers
 

[QUOTE]Originally posted by OhD
[B]That is not true. I use IPD with the JR8411 digital servo and the notion that the IPD receiver gives poor resolution is simply false. If you are getting a normal strength signal the IPD does not do any processing, that only occurs at the extremes of range or otherwise impaired signal where data is poor but not so poor that failsafe needs to kick in.

Harry

Should PCM receivers really cost more?
 

Analog PPM is a thing of the past, it started dying when first computer radios came to market.

There is stepping that originates from A/D conversion in the transmitter and there is stepping that comes from timing circuits in IPD receiver MCU. No matter how strong the signal is its resolution can't be better than four times MCU clock pulse period and that is only if MCU has 16 bit timer/PWM circuits. If it has 8 bit timer/PWM circuits then things get worse.

Should PCM receivers really cost more?
 

sooooo.. . IPD is nothing more than a normal FM reciever, with some signal reception and amplification circuits thrown in, a PCM-type failsafe function thrown into the mix, and better resolution (within the limitations of the PPM timing window).

So, it can still go into "failsafe" (how do you program that with your standard FM radio?????) which means a lockout, and being FM is more prone to interference than PCM, no matter what kind of fancy receiver doo-dads you come up with to increase sensitivity. It seems that the way that sensitivity is increased, by actually widening the frequency "window" in the RF and IF amplifiers, would make it more prone to interference at the lmiit of sensitivity, which is pretty darned undesirable if the receiver is losing signal due to interference from something on the very edge of the frequency. You are still limited to the "narrow band" for your frequency, for total frequency bandwidth, and being that these "bands" are really bell-curve areas of sensitivity, the outer edges of that "sensitivity range" would actually be outside the desired 10khz (if I recall properly) of maximum frequency deviation allowed by the FCC for transmitters.. . . .

You know. . .U-control and solid steel cables is starting to look more attractive all the time. :)

There are advantages and disadvantages to every signal and receiver design. The ABC&W from JR is not living up to it's hype, dual conversion still has the upper hand, IPD gives you the worst-case scenarios of "lockout", FM is subject to getting hits from somebody sneezing hard at the other end of the flightline, and AM is a disaster.

Think I'll go over to HAM band so I can transmit 500 watts. . . . . Interfere with THAT!!!!!

Should PCM receivers really cost more?
 

PCM better than IPD? errrrmmmmmmm welllll .
IPD is not just an FM reciever.
I can't be bothered to get out the sheet with all the info about them but i can remember some of it.
They are faster than PCM so you get better control- snap rolls can be exited when they exit rather than before- walls are also better with IPD vs. PCM
They filter out any interference(rather than increase sensitvity) up to a certain intolerable level where they go into fail safe. You can tell when its almost going into failsafe or out of range because the controls become more slow and sluggish( the low resolution of the signal filtering that OhD was experiencing), giving you time to turn back towards yourself or raise the transmitter aerial vertical, or turn the plane away from the crowd, or land it really quickly e.t.c .This is something that PCM doesn't do. It filters out a bit and then....... bam into failsafe without any warning.
IPD failsafe programming is very easy. there is a plug in the reciever that you take out, set your controls to the desired positions, and then put the plug back in and the fail safe is memorised by the reciever.
What do you guys think are the best conrol movements for a failsafe? I think that having both ailerons go up about 60 degrees , throttle back and full up 60 degrees elevator would slow down the plane like anything and then have the plane go into a stable elevator.or am i just talking nonsense?
This thread is really interesting, so lets not ruin it by turning this into a pointless argument.
Luke :D :p

Should PCM receivers really cost more?
 

I found out the HARD way that the "crowd saving" low-throttle snaproll failsafe is NOT the best way to set it up. I lost two planes at Joe Nall this year, because the Transmitter seemed to go intermittent after I removed then replaced the transmitter module.

I'd imagine a minor climbing turn, with about 1/8 throttle, would be the best way to both save the crowd, and possibly save the plane, in the event of failsafe lockout.

Should PCM receivers really cost more?
 

The movements i described do not make the plane snap roll.
it makes it go into a parachute.
the thing is though, with an aerobatic model, its not going straight and level . If you program it to do a climbing turn when its doing the inevitable inverted flight, you get a spiral dive- not good.
Aerobatics models are unstable so they won't stay level in a climbing turn- then will come down somewhere rather fast so it could hurt someone badly.Maybe a trainer could be programmed to do a climbing turn but then where does it go? up and up and up so far that youve lost your plane.
I think that the best bet is to make the plane go into a parachute manuver.Even the most unstable 3d planes are stable in a parachute, and come down slowly. Even if the plane is inverted it will still enter a parachute- but the only manuver this won't work is understandably on a low inverted flyby.
I think that the only way you can find out which failsafe setting is the best is to experiment by climbing up high and turning the transmitter off and seeing what it does at various attitudes e.t.c
Luke

Should PCM receivers really cost more?
 

Those statements demonstrate that you don't understand our radios. Your PCM radio IS an FM radio. Your PCM receiver is nothing more than a normal FM receiver. You need to learn quite a bit more about the workings of model radios before sending posts about what system is better than another.

Harry

Should PCM receivers really cost more?
 

IPD receiver is in fact equal to other brands PCM receivers. It consists of RF deck followed by a microprocessor rather than simple PPM decoder (4017 + diode and capacitor).

I bet if one was crazy enough it would be possible to wirte a program that would allow IPD receiver to receive other mfgs PCM signals. I even think it would require LESS processing than it goes on in IPD.

Should PCM receivers really cost more?
 

Plenty of errors there to deal with!!

When signal strength is weak the IPD widens its selectivity. Note that word selectivity. No-one said it widens the range of frequencies it looks at. It widens its selectivity. On that frequency.

Since it does not alter the frequencies that it sees, it does not look outside of its 10khz band.

Germany is one of the few, perhaps the only country in this world that has strict laws regarding receivers. Most of us just have laws regarding transmitters. Because this is Multiplex's big market (as well as being its home) Mpx receivers are extremely high quality. The notion that its receivers alone take such a scattergun approach to frequency selection is not just technically wrong since you have confused selectivity with something else, it is not legal for Mpx!

A lot of impressionable people read these threads Kris, and will assume that you know what you are talking about. Please do not send posts that are are derogatory to a specific brand or system until you actually understand model radios. When you can explain to us why it is physically impossible to compare PCM against FM, we will know that you are beginning to understand!

Harry

Should PCM receivers really cost more?
 

Harry,
For sometime now I have been trying to obtain the schematic for an IPD receiver. It seems you may be the man to answer a few questions I have relating to IPD operation.

Quote.
"When signal strength is weak the IPD widens its selectivity"

Q1. Is this the RF signal strength in your statement ?

Q2. IPD - If it means Intelligent Pulse Decoding how can it digitally decode the RF signal which is A.C. ?

Q3. How does it change the selectivity and when does it know to do this?

Q4. What is the composition of the circuitry that allows this function to operate correctly in the close vicinity of other transmitters ?

Quote
"It widens its selectivity. On that frequency."

Q5. Is it feedback that makes it frequency selective on that frequency and if so where is it being sensed from ?

Q6. What happens to the sensitivity if the selectivity is increased on that freqency ?

Q7. Is this a technique using only passive components or are active components also used ?

I'm sure a lot of technical readers out there would also like to understand the vagueries of IPD. I for one look forward with interest to you de-mystifying IPD.

DavidO

Should PCM receivers really cost more?
 

David, I hope that I can answer most of your questions, though not the ones concerning the exact mechanisms that Mpx uses to create some of the features.

I think we need to start by separating out two different things that have arisen and are getting jumbled together, when in fact they are different. One is the selectivity issue which is purely a radio receiver thing, and the other is the IPD error detection which is a data thing - the failsafe part of the Rx.

In FM Capture Theory an FM Rx whether using PPM data or PCM data (note Kris, both are FM!) will be very good at selecting the strongest signal and ignoring weak signals. Assuming that you are the only Tx on your frequency then any other Tx bleeding over will be relatively very weak, as will background static, intermodulations etc. My Tx has a frequency scanner built in and if I switch it to high sensitivity then when 2 Tx are on, several other channels light up with low strength signals, if 3 Tx are on lots and lots of channels light up with low strength signals. So as well as the channels that are genuinely in use, our Txs mix the frequencies and the whole band can soon light up with these low power intermodulations. Your Rx can afford to be extremely selective and behave as if it is almost deaf - so it only hears the Tx that is shouting at it and can't hear the quieter IMs, static etc. But signal strength decays very quickly with distance and if your model is some distance away then the signal it hears from you may be down near the power of other Txs nearer to it, background static and so on. Now it can't afford to be so picky, other signals on that frequency may equal or occasionally overcome your signal strength. So IPD widens its selectivity - that is it becomes less deaf to your frequency so it can still hear you in amongst all the other noise, and not capture one other false but slightly stronger intermittent signal. Why not do that with normal PPM Rx? Well, they could but of course it would be getting some intermittent false data and would be glitching so it is of no benefit. To get any benefit from the lower selectivity you need error detection and the IPD part gives it that. Also, if the filed strength of the signal is strong the data is passed unmodified to the servos. Where field strength is weak the IPD will start to process the data. I don't know what the process is except that it uses recent past data so I suspect that it is a moving average or similar. This has the effect of slowing the servo response and giving you a warning that if you push any further you are likely to lose contact.

Error detection and failsafe works after the radio part has been stripped out, IPD only works on the servo data. It is not rocket science, it is the same as goes on in after-market failsafe devices, electric motor ESCs, gas turbine ECUs etc. It is just that Mpx has put it all into one Rx covering all channels and with a user programmable failsafe setting to drive the servos to, thus meaning that anyone with a PPM Tx, whether a computer or humble 2 channel non-computer Tx can have the benefit of error detection and failsafe that was previously only available in higher cost computer Tx with PCM and PCM Rx. PPM data is a time length pulse for each servo. There are max and min times that each pulse can be. If the pulse is longer or shorter than those time limits it must have been corrupted. So we have detected an error. It can not detect a corruption that has altered the time length but kept it within the normal time limits, however interference that can do that is phenomenally rare and not worth worrying about. If you turn your Tx up to 150% travel max for JR or 140% max for Futaba you generate a pulse that is either 0.9ms or 2.1 ms long. IPD's limits are set at a pulse of min 0.89ms or max 2.35ms (it needs to take account of Mpx Txs able to drive further than Far Eastern Tx). So if IPD sees a servo pulse shorter than 0.89ms or longer than 2.35ms, it says "error, impossible!!" It then holds at the last good position for 1/2 second, then if still in error it sends all servos to the user programmed position. It keeps receiving and the instant it gets good data it comes out of failsafe. By way of amusement, Mpx made a slight error!! Their 3030 Tx is capable of generating a signal outside the IPDs limits if you set it to some weird extreme values, and so is capable of sending the IPD into failsafe on a valid signal! hee hee! Mpx had to issue a tech notice to warn 3030 users about it and what conditions lead to it.

I hope this has helped to clear up a lot of confusion that still surrounds these IPD Rx. I use many of them, 7 channel single conversion, 9 channel d/c and 12 channel d/c (with built-in dual battery backer) since I like failsafe, and my Mpx Tx does PCM but Mpx stopped making PCM Rx in favour of IPD. They work superbly, only once in the last 3 years have I had an Rx go into full failsafe (throttle closed in my programming) for a fraction of a second. Woketman who posts regularly in the jets forum has used them in his jets without a hint of problem since they went on sale and I am about to entrust my £3k jet to the 12 channel IPD.

Harry

Should PCM receivers really cost more?
 

Harry,
I have great problems with your first paragraph. What you have given is a not very good text book generalisation. Detail of how the receiver RF circuitry operates in conjunction to IPD receivers is flawed.

"FM Capture Theory" - Why quote this when AGC and a double tuned front end take care of this.

"quieter IMs," - 3rd order Intermodulation products are hard to measure with 4th order nigh impossible as the power reduces dramatically.

"So IPD widens its selectivity - that is it becomes less deaf to your frequency so it can still hear you in amongst all the other noise." - Do you mean digital variable bandwidth ? How the heck can IPD change RF selectivity ?

Your statement above is a contradiction in terms and shows you have no understanding regarding the action of Selectivity and Sensitivity in RF sections.

I have no problems with your second paragraph its typical digital signal processing.

Could be something has been lost in the translation of documents you have used for reference.

DavidO

Should PCM receivers really cost more?
 

The IPD appears to be a conventional Narrow band FM receiver with a microprocessor used to process the information out of the discriminator. The term selectivity is used to describe the bandwidth of the receiver and is determined by a fixed ceramic filter in the IF. Also NBFM has no ability to capture like wideband FM.
Some time ago I tested the IPD extensively and found it very stable in terms of pulse width jitter right up to the point where it went into failsafe. I saw no slowing down of the response as the signal got weaker. In other words there was no warning just like PCM.
The thing I didn't like was the resolution which seems to be limited to about 4 microseconds. Someone asked if it was worse than 512, well this is more like 256. I have a low end MPX transmitter with digital trims and one click equals 16 microseconds. I don't see how you could trim a pattern plane with that kind of resolution.
The update rate is determined in the transmitter and with my Futaba the frame rate is the same in PPM as PCM so it wouldn't be any faster. The Multiplex transmitters might be faster but not by much. If you are happy enjoy IPD but don't tell anyone it is better than PCM.
As far as the original question, PCM should not cost much more and I believe we can see prices coming down slowly.

Should PCM receivers really cost more?
 

David, it's all terribly generalised and simplified because this forum is for a wide audience not just for radio techs, and simplifications always introduce problems. Judging by Mpx manuals their stuff on IPD may well have got a bit altered in translation. "Quieter IMs" referred to the 3oIM being quieter than the main signal, not all the umpteenth IMs. By all means pull it apart and put it back in proper tech language.

H

Should PCM receivers really cost more?
 

Mpx is not any faster as it uses standard PPM. Mpx claim that PPM is faster than PCM, I have always had doubts about that. Since each brand has its own PCM system which PCM are they comparing to? I guess it is to their own PCM which they no longer make. I believe early PCMs had a slower update but more modern versions give differing priorities to which channels get updated in each cycle and therefore can keep up the refresh rate on those channels that need it. I don't know for sure but I have a sneaking suspicion that the Mpx PCM was a bit outdated and therefore slower than the more modern systems, hence Mpx claim for PPM.

I, for one, have not said that IPD is better than PCM, though some others have said it. We went through this a while back (on the jet forum I think it was) and I pointed out that PCM does have an advantage over IPD. Since IPD is PPM it relies on a synchro pulse and uncorrupted data all the way through each cycle. Any corruption loses all subsequent data in that cycle even if it was good data since the Rx loses where it is in the cycle and needs to wait for the next synchro pulse. If the synchro pulse alone is hit and the Rx can't find the start of the cycle, all the good data for all the servos is lost for that entire cycle. Some PCM systems break the cycle into two halves each with its own PCM version of synchro so you don't lose as much data if it cam't synchronise, and if each servo's data is individually identified rather than just relying upon the sequence, any little hits on one servo don't necessarily scupper the data for all the subsequent servos in that cycle. So when interference is short in time and repeating rapidly, such as spark ignition, PCM still has an advantage as although it experiences the same hits on an individual servo, it does not tend to lose all the following servos' data in that cycle like PPM does.

H

Should PCM receivers really cost more?
 

OHD,

I believe that your measurement was flawed as the resolution of the system is indeed quite good, at least as good as my Futaba 1024 PCM by feel in the air where it really counts. I have flown Futaba 512 a long, long time ago and it is certainly much finer than that. I routinely set my trim authority (MPX 4000) to 10% which has about 40 clicks of trim full travel and moves the servo very little from one extreme to the other and I can feel (see) a change of one click of trim in the air. There is no problem with resolution with IPD (PS. I use only high quality digital servos).

Should PCM receivers really cost more?
 

Harry, interference is interference. . be it a resonance from two nearby sources, hi-energy saturation from a bad ignition, or just being too far away from the transmitter with a low-power transmitter on the same frequency near the plane. When a receiver attempts to improve it's sensitivity by "widening" it's receptive window (as you described) it also opens the possibility of interference from adjacent frequencies. I don't like that idea, as it sounds like an accident waiting to happen. I look at it this way. . if your signal to the receiver is that weak where an IPD receiver has to widen it's bandwidth (or any other receiver has to do it either), then you are too far out anyway. If you are being jammed by another transmitter on the same frequency, no amount of "sensitivity increase' is going to matter. Every receiver can be blanked by RF interference from ignitions and other sources. No amount of special circuits or different types of modulation/encryption can change that.

By the very nature of PPM coding (as admitted by yourself) all information is lost or garbled when the receiver loses signal or is jammed, even partially. PCM (yes I know how it works), however, still gets part of the signal and can "function" up to the limit of being totally blanked out. IPD, as you described it, is still limited by the characteristics of FM/PPM (PWM???), and then throws in a "failsafe" on top of it all.

It may work, you may like it, but I consider the shortcomings (as described by you) to be less desirable than PCM's foibles (lockout can be a pain) I didn't like IPD when it first came out. . I still don't like it.

Should PCM receivers really cost more?
 

If there's a USB wireless card that can survive in the same conditions as our receivers, is as small and light, and doesn't weigh any more, I'll take fifty for $33 a pop. :)

Should PCM receivers really cost more?
 

Harry,
From reading your interpretation of a german technical translation again it isn't any wonder that things come out back to front. A friend who speaks German has great difficulty in reading/interpreting technical German - it's another ball game altogether.

The front end signal processing you have partly described is in fact ABC&W. Yes, it's JR's principle and baby of many years. Looks as though the Patent has run out and its open season on ABC&W.
The front end schematic for 1995/7 Mini 9's and 1997 Micro 5/7's show identical circuitry to JR's ABC&W. Even the Multiplex 12ch DC receiver uses it.

It isn't possible for the IPD principle to control Sensitivity, Selectivity, Dynamic Range or Front End Bandwidth. Any reference to this must be taken as translation error.

ABC&W is an active form of monitoribg frequency selection whereas Dual Conversion is a fixed form of selection. An ABC&W receiver is very good at moving its centre frequency (Window) while still retaining its selectivity - ie. no need to retune when changing JR crystals, about fifteen spots either way (even at 20khz) and your still safe.

All other frequencies which will come in along with the one you want are all ATTENUATED, which means their strength will be very much reduced leaving the one you want shouting head and shoulders above the rest.

IPD and PCM are only as good as the FM circuitry in front of it.
DavidO

Should PCM receivers really cost more?
 

The original post was " Should PCM cost more ?"

Cost has nothing to do with selling price, only the P & L statement.

In a free market price is set by the competition PERIOD . You either compete or you do not compete .

There are ways around this, ---- they just aren't legal ! Collusion and price fixing are examples there are others .

Should PCM receivers really cost more?
 

In that case, why aren't Ferraris sold at, say, $29 each to get more sales volume?

It's a lot more accurate to say the top boundary of the price is set by competition, and the bottom boundary by cost.

This especially applies to electronics, where the unit cost is almost negligible. For example, if you buy a faulty calculator and you send it back to the manufacturer, they will simply throw it away and give you a new one. It's cheaper for them to do that than to fix it.

If a manufacturer wants to produce a new product, using new technology, the finance man (who has the final word!) will ask only three questions. How much will it cost, how many will they sell, and what price can they get. If one of those doesn't fit the equation, it won't fly, no matter how cool or accessible the technology is.

In the case of using LAN technology in RC, all three answers will stop the project dead in it's tracks.

There are two provisos to this. If the technology can be applied from another area (where the costs have been covered already) and the system is backward compatible to some extent (that is, people can use some of their existing equipment) things might change.

If the technology is desirable, it might end up on the wish list, but it won't come true without acceptable answers to all three of the above questions.

-David C.