Is PCM and Elec. Ign. a must? Is PPM OK?
01-11-2006, 12:48 AM
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RE: Is PCM and Elec. Ign. a must? Is PPM OK?
ORIGINAL: mglavin
Real world random NOISE is known to be approximately -125dBm. Today’s typical PPM RC RX looses its ability to operate at approximately -90dBm while the PCM RX is strong all the way to -100dBm.
Real world random NOISE is known to be approximately -125dBm. Today’s typical PPM RC RX looses its ability to operate at approximately -90dBm while the PCM RX is strong all the way to -100dBm.
A ten db improvement in the transmission efficiency is a very large improvement. It is the same as increasing the transmitter power by a factor of 10. I seriously doubt that is the case. More like 3db. Even so its a considerable improvement
01-11-2006, 05:57 AM
#77
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RE: Is PCM and Elec. Ign. a must? Is PPM OK?
Hi,
I have one final comment then my interest in this thread is exhausted.
In my application, I need a rx which is able to reject:
1) Gas ignition noise (many choices)
2) 1.5 watt tx on board the aircraft (fewer choices). One rx will reject 5 watts at the range of 4" across the frequency range of 27 mhz - 900 mhz. Most rxs cannot even deal with 1.5 watts.
3) Metal on metal noise (metal gears on metal gears operating under extreme loads). Dual 24" and 29" fine mesh nets mounted on the airplane require metal moving links and metal worm gear box driven by an electric motor to open and close the nets. ( 2 choices so far and neither is a PCM).
While these "challenges" are not purposely tackled by most RC flyers, it really illustrates the wide range of variation in receivers and brands to deal with and reject interference.
As usual, all generalities are wrong. There is such variation between rx models and brands, that the statement "PCM is better than PPM" is incorrect. There are PPM rxs that blow the shorts off the best PCM models in my testing regime and there are also some PPM rxs which are real junk.
It has been a good discussion
Cheers Elson
I have one final comment then my interest in this thread is exhausted.
In my application, I need a rx which is able to reject:
1) Gas ignition noise (many choices)
2) 1.5 watt tx on board the aircraft (fewer choices). One rx will reject 5 watts at the range of 4" across the frequency range of 27 mhz - 900 mhz. Most rxs cannot even deal with 1.5 watts.
3) Metal on metal noise (metal gears on metal gears operating under extreme loads). Dual 24" and 29" fine mesh nets mounted on the airplane require metal moving links and metal worm gear box driven by an electric motor to open and close the nets. ( 2 choices so far and neither is a PCM).
While these "challenges" are not purposely tackled by most RC flyers, it really illustrates the wide range of variation in receivers and brands to deal with and reject interference.
As usual, all generalities are wrong. There is such variation between rx models and brands, that the statement "PCM is better than PPM" is incorrect. There are PPM rxs that blow the shorts off the best PCM models in my testing regime and there are also some PPM rxs which are real junk.
It has been a good discussion
Cheers Elson
01-11-2006, 07:25 AM
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RE: Is PCM and Elec. Ign. a must? Is PPM OK?
Agreed, except
standard ceramic filters adhere to the 10 kHz raster. Widening the range is no option, unless you don't mind receiving your neighbour's channel output.
An RX’s ability is a secondary quandary. As noted above PCM and PPM receivers use the same RF, FM/IF demodulator IC and the same IF strip with the exception of a wider ceramic IF filter to accept and pass wider band information of PCM.
01-11-2006, 11:55 AM
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RE: Is PCM and Elec. Ign. a must? Is PPM OK?
ORIGINAL: rc bugman
Hi,
As usual, all generalities are wrong. There is such variation between rx models and brands, that the statement "PCM is better than PPM" is incorrect. There are PPM rxs that blow the shorts off the best PCM models in my testing regime and there are also some PPM rxs which are real junk.
It has been a good discussion
Cheers Elson
Hi,
As usual, all generalities are wrong. There is such variation between rx models and brands, that the statement "PCM is better than PPM" is incorrect. There are PPM rxs that blow the shorts off the best PCM models in my testing regime and there are also some PPM rxs which are real junk.
It has been a good discussion
Cheers Elson
01-11-2006, 01:22 PM
#80
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RE: Is PCM and Elec. Ign. a must? Is PPM OK?
ORIGINAL: dirtybird
Noise threshold is dependent on the temperature and the bandwidth. The minimum is -173 dbm at absolute zero and one cycle bandwidth. The telemetry systems used in the space program had a noise threshold of -153dbm using a cryogenic cooled MASER (liquid helium bath)and a bandwidth of 50HZ.
A ten db improvement in the transmission efficiency is a very large improvement. It is the same as increasing the transmitter power by a factor of 10. I seriously doubt that is the case. More like 3db. Even so its a considerable improvement
ORIGINAL: mglavin
Real world random NOISE is known to be approximately -125dBm. Today’s typical PPM RC RX looses its ability to operate at approximately -90dBm while the PCM RX is strong all the way to -100dBm.
Real world random NOISE is known to be approximately -125dBm. Today’s typical PPM RC RX looses its ability to operate at approximately -90dBm while the PCM RX is strong all the way to -100dBm.
A ten db improvement in the transmission efficiency is a very large improvement. It is the same as increasing the transmitter power by a factor of 10. I seriously doubt that is the case. More like 3db. Even so its a considerable improvement
Information I have suggests 3db is atypical of capture ratios, todays equipment falls easily within these numbers some fall short no doubt.
My assertion or claim of 10dBm differential was realized when a "loss of control" or interference is established at a dB level to cause +/- 40 us servo jitter. Zero reference is based on -50 dBm input power to the RX's antenna.
01-11-2006, 01:26 PM
#81
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RE: Is PCM and Elec. Ign. a must? Is PPM OK?
ORIGINAL: preivers
Agreed, except
standard ceramic filters adhere to the 10 kHz raster. Widening the range is no option, unless you don't mind receiving your neighbour's channel output.
Agreed, except
An RX’s ability is a secondary quandary. As noted above PCM and PPM receivers use the same RF, FM/IF demodulator IC and the same IF strip with the exception of a wider ceramic IF filter to accept and pass wider band information of PCM.
01-11-2006, 03:31 PM
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RE: Is PCM and Elec. Ign. a must? Is PPM OK?
mglavin, Please don't take this the wrong way but sometimes I get a tightening of the skull when I try to decipher some of your posts!
01-11-2006, 05:56 PM
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RE: Is PCM and Elec. Ign. a must? Is PPM OK?
ORIGINAL: mglavin
My assertion is based on the typical ambient noise generated of and within an RC RX not of more sophiscatted equipment your obviously referencing.
Information I have suggests 3db is atypical of capture ratios, todays equipment falls easily within these numbers some fall short no doubt.
My assertion or claim of 10dBm differential was realized when a "loss of control" or interference is established at a dB level to cause +/- 40 us servo jitter. Zero reference is based on -50 dBm input power to the RX's antenna.
ORIGINAL: dirtybird
Noise threshold is dependent on the temperature and the bandwidth. The minimum is -173 dbm at absolute zero and one cycle bandwidth. The telemetry systems used in the space program had a noise threshold of -153dbm using a cryogenic cooled MASER (liquid helium bath)and a bandwidth of 50HZ.
A ten db improvement in the transmission efficiency is a very large improvement. It is the same as increasing the transmitter power by a factor of 10. I seriously doubt that is the case. More like 3db. Even so its a considerable improvement
ORIGINAL: mglavin
Real world random NOISE is known to be approximately -125dBm. Today’s typical PPM RC RX looses its ability to operate at approximately -90dBm while the PCM RX is strong all the way to -100dBm.
Real world random NOISE is known to be approximately -125dBm. Today’s typical PPM RC RX looses its ability to operate at approximately -90dBm while the PCM RX is strong all the way to -100dBm.
A ten db improvement in the transmission efficiency is a very large improvement. It is the same as increasing the transmitter power by a factor of 10. I seriously doubt that is the case. More like 3db. Even so its a considerable improvement
Information I have suggests 3db is atypical of capture ratios, todays equipment falls easily within these numbers some fall short no doubt.
My assertion or claim of 10dBm differential was realized when a "loss of control" or interference is established at a dB level to cause +/- 40 us servo jitter. Zero reference is based on -50 dBm input power to the RX's antenna.
The other day I had the spark plug RFI cap come loose on the airplane I was flying with a PPM receiver. I had a very interesting time getting it down in one piece. I replaced the receiver with a PCM receiver and got a good range check. I decided not to fly it and see how it would perform.
02-28-2006, 11:23 AM
#84
RE: Is PCM and Elec. Ign. a must? Is PPM OK?
dirtybird: How you going to see how it performs...if you do not fly it? Seems like your leaving out something? Capt,n[:-]
03-01-2006, 06:57 AM
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RE: Is PCM and Elec. Ign. a must? Is PPM OK?
i read some answers about "is pcm and elec. ign. a must? " and i whant to tell about my experience...
my first gas engine was a quadra 30cc magneto ignition , and i fly it with my ppm radio and don´t have any problem,,, well then i have my second gas plane with a brisson 3.2 with elec. ign. and the first fly i do with my ppm radio. near the plane i don´t have problem and i get up and fly........... my friends said to mi " don´t do loop on the take of,,, feel your plane and then do 3d" but i don´t do anythig,,,, the plane go whenever he whant,,,, loops, roket wing,,, up and down,,,, i try to land a lot of times... i have a great interference,, at last i can land but my landig gear break out,, ...
then a friend take of his pcm rx and radio and put on my plane ,, and i dont have more problems...
DON´T FLY ELEC. IGN. WITH PPM...................
my first gas engine was a quadra 30cc magneto ignition , and i fly it with my ppm radio and don´t have any problem,,, well then i have my second gas plane with a brisson 3.2 with elec. ign. and the first fly i do with my ppm radio. near the plane i don´t have problem and i get up and fly........... my friends said to mi " don´t do loop on the take of,,, feel your plane and then do 3d" but i don´t do anythig,,,, the plane go whenever he whant,,,, loops, roket wing,,, up and down,,,, i try to land a lot of times... i have a great interference,, at last i can land but my landig gear break out,, ...
then a friend take of his pcm rx and radio and put on my plane ,, and i dont have more problems...
DON´T FLY ELEC. IGN. WITH PPM...................
04-18-2006, 08:48 AM
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RE: Is PCM and Elec. Ign. a must? Is PPM OK?
ORIGINAL: rc bugman
Hi,
I too am looking forward to the spread spectrum radios.
Dirtybird:
In my definition, rejecting interference is filtering out the noise before it reaches the internals of the RX. A PPM which shows no jitters is rejecting interference. A PCM which is not on "last command hold" is rejecting interference. Once the receivers show a response to the interference (PPM=jitters, PCM= last command hold), the rejection circuits in the rx have failed. (Please bear with me, since I work in academics, all discussions include definitions so we are on "the same page")
As you mentioned, competition pilots use PCM for its last command hold to make their flying look better, not because of superior interference rejection.
Elson
Hi,
I too am looking forward to the spread spectrum radios.
Dirtybird:
In my definition, rejecting interference is filtering out the noise before it reaches the internals of the RX. A PPM which shows no jitters is rejecting interference. A PCM which is not on "last command hold" is rejecting interference. Once the receivers show a response to the interference (PPM=jitters, PCM= last command hold), the rejection circuits in the rx have failed. (Please bear with me, since I work in academics, all discussions include definitions so we are on "the same page")
As you mentioned, competition pilots use PCM for its last command hold to make their flying look better, not because of superior interference rejection.
Elson
And by the way, Multiplex developed PCM for radio control in the first place and they also have moved on to better things.
If you fail safe without PCM, you have Multiplex IPD's, FMA, and a few others, I have a PCM on the shelf gathering dust and will only fly PPm and at this time, Multiplex IPD's
Roger
04-18-2006, 08:49 AM
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RE: Is PCM and Elec. Ign. a must? Is PPM OK?
ORIGINAL: EL TEMUCANO
WITH PPM - ANTENNA DOWN - 20 MTS, SOMETIME BEGUN GLITCHING NEXT TO THE PLANE .
WITH PPM - ANTENNA DOWN - 20 MTS, SOMETIME BEGUN GLITCHING NEXT TO THE PLANE .
WOW, then you do have a problem, I'm getting over 150 meters with my Multiplex PPM IPD's with engine running...
Roger
04-18-2006, 10:50 AM
#90
RE: Is PCM and Elec. Ign. a must? Is PPM OK?
Has anyone ever done any testing of PPM Rx's by brand regarding their ability to reject RF noise so that us less fortunate can know which brands to be wary of.
Karol
Karol
