Crystal Swapping.. Again
04-04-2004 | 10:21 PM
#76
Senior Member
RE: Crystal Swapping.. Again
Say what? Ground use only?
Must be the reason their logo is a helicopter.
Ooops!
Must be the reason their logo is a helicopter.
Ooops!
ORIGINAL: mr_matt
And just to clear up some things. The Model Avionics system is for surface use only. Planes are an entirely different animal, because of the 3d maneuverability.
And just to clear up some things. The Model Avionics system is for surface use only. Planes are an entirely different animal, because of the 3d maneuverability.
04-04-2004 | 10:27 PM
#77
Senior Member
RE: Crystal Swapping.. Again
ORIGINAL: BasinBum
Expensive innovations have a trickle down effect that eventually benifit the average modeler when the economics of scale bring the price down to what is percieved as reasonable.
Expensive innovations have a trickle down effect that eventually benifit the average modeler when the economics of scale bring the price down to what is percieved as reasonable.
04-04-2004 | 11:18 PM
#78
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RE: Crystal Swapping.. Again
What else is USING the 900mhz and 2.4 ghz seftions of the RF spectrum ALREADY? Lest see... garage door openers for one... lets make everyone impound thoier keychains and the garage door opener remotes out of thier cars at the flying field because they DON"T check to see if something else is on the same frequency before sending uot thier signals. (they just broadcast thier code...) I've been walking around outside with a keychain remote in my pocket and accidentally opened my garage door. (because something in my pocket hit the button.)
What else is going to be out at the field that can wipe out a model? (aren't some Cell phones using 2.4 ghz? Aren't we now recommending that people take cell phones tot he field in case someone needs to call EMS?)
Wouldn't that be the same basic logic for not wanting to be on 27 mhz with our systems for aircraft? (aside fromt he "toys" like Cox/Estes's Sky Rangers) Too much stuff already using the frequencies and too high a chance of interference.
What else is going to be out at the field that can wipe out a model? (aren't some Cell phones using 2.4 ghz? Aren't we now recommending that people take cell phones tot he field in case someone needs to call EMS?)
Wouldn't that be the same basic logic for not wanting to be on 27 mhz with our systems for aircraft? (aside fromt he "toys" like Cox/Estes's Sky Rangers) Too much stuff already using the frequencies and too high a chance of interference.
04-04-2004 | 11:22 PM
#79
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From: right \'round here someplace
RE: Crystal Swapping.. Again
ORIGINAL: FHHuber
What else is USING the 900mhz and 2.4 ghz seftions of the RF spectrum ALREADY? Lest see... garage door openers for one... lets make everyone impound thoier keychains and the garage door opener remotes out of thier cars at the flying field because they DON"T check to see if something else is on the same frequency before sending uot thier signals. (they just broadcast thier code...) I've been walking around outside with a keychain remote in my pocket and accidentally opened my garage door. (because something in my pocket hit the button.)
What else is going to be out at the field that can wipe out a model? (aren't some Cell phones using 2.4 ghz? Aren't we now recommending that people take cell phones tot he field in case someone needs to call EMS?)
Wouldn't that be the same basic logic for not wanting to be on 27 mhz with our systems for aircraft? (aside fromt he "toys" like Cox/Estes's Sky Rangers) Too much stuff already using the frequencies and too high a chance of interference.
What else is USING the 900mhz and 2.4 ghz seftions of the RF spectrum ALREADY? Lest see... garage door openers for one... lets make everyone impound thoier keychains and the garage door opener remotes out of thier cars at the flying field because they DON"T check to see if something else is on the same frequency before sending uot thier signals. (they just broadcast thier code...) I've been walking around outside with a keychain remote in my pocket and accidentally opened my garage door. (because something in my pocket hit the button.)
What else is going to be out at the field that can wipe out a model? (aren't some Cell phones using 2.4 ghz? Aren't we now recommending that people take cell phones tot he field in case someone needs to call EMS?)
Wouldn't that be the same basic logic for not wanting to be on 27 mhz with our systems for aircraft? (aside fromt he "toys" like Cox/Estes's Sky Rangers) Too much stuff already using the frequencies and too high a chance of interference.
04-04-2004 | 11:33 PM
#80
My Feedback: (10)
RE: Crystal Swapping.. Again
SoCal, call them and ask them if you can get one for your sailplane.
I know it is very hard to understand a spread spectrum system, when all one has been exposed to is a narrow band system. THese systems are designed to coexist in a given band of frequencies. If I can find some links I will post them. I am not an expert but I have learned a lot in the last couple of years. Our flight system is frequency hopping, and I am using a Direct Sequence system at work for an automotive application.
I know it is very hard to understand a spread spectrum system, when all one has been exposed to is a narrow band system. THese systems are designed to coexist in a given band of frequencies. If I can find some links I will post them. I am not an expert but I have learned a lot in the last couple of years. Our flight system is frequency hopping, and I am using a Direct Sequence system at work for an automotive application.
04-05-2004 | 12:00 AM
#81
My Feedback: (3)
RE: Crystal Swapping.. Again
ORIGINAL: mr_matt
SNIP
IMHO, the reason it has not been done by the radio manufacturers...the current stuff works OK, and a new SS radio would be very expensive to make, with a limited market. Same exact reason you do not see any mass market Asian turbines, and likely never will.
SNIP
IMHO, the reason it has not been done by the radio manufacturers...the current stuff works OK, and a new SS radio would be very expensive to make, with a limited market. Same exact reason you do not see any mass market Asian turbines, and likely never will.
BasinBum,
I am NOT against new stuff. In fact I was thinking that maybe we should require ALL turbines to be guided by SS radios as a requirement of the waiver (VBG). At least then we would KNOW that they work and are worth the extra cost. When enough folks jump out and get a SS radio, they will no longer be a specialty item.
04-05-2004 | 01:12 AM
#82
Senior Member
RE: Crystal Swapping.. Again
FHHuber, With out getting into the gritts of spread spectrum I can only say it doen't work that way.
Heddy Lamar where are you when we need you?
Heddy Lamar where are you when we need you?
04-05-2004 | 04:09 PM
#83
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From: stoke on trent, UNITED KINGDOM
RE: Crystal Swapping.. Again
hi there
to all you US flyers, very confused as to why you are not allowed to change youre crystals, over here i carry about 10 diffrent frequencys, all my models are on one TX ff8, but certain events call for us to nominate other frequencys that we can swap to to avoid 'clogging up' on just a few, as the 'end users' does this mean that you have to have qualifications that allow you to change the channel on your TV's???????
confused uk
to all you US flyers, very confused as to why you are not allowed to change youre crystals, over here i carry about 10 diffrent frequencys, all my models are on one TX ff8, but certain events call for us to nominate other frequencys that we can swap to to avoid 'clogging up' on just a few, as the 'end users' does this mean that you have to have qualifications that allow you to change the channel on your TV's???????
confused uk
04-05-2004 | 05:07 PM
#84
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From: St Augustine, FL,
RE: Crystal Swapping.. Again
ORIGINAL: hurricane527
hi there
to all you US flyers, very confused as to why you are not allowed to change youre crystals, over here i carry about 10 diffrent frequencys, all my models are on one TX ff8, but certain events call for us to nominate other frequencys that we can swap to to avoid 'clogging up' on just a few, as the 'end users' does this mean that you have to have qualifications that allow you to change the channel on your TV's???????
confused uk
hi there
to all you US flyers, very confused as to why you are not allowed to change youre crystals, over here i carry about 10 diffrent frequencys, all my models are on one TX ff8, but certain events call for us to nominate other frequencys that we can swap to to avoid 'clogging up' on just a few, as the 'end users' does this mean that you have to have qualifications that allow you to change the channel on your TV's???????
confused uk
Actually we can change them, we're just constrained from posting adverts telling everyone that we have done so. There may be some peer pressure applied to one that is dense enough to change the crystal and then continue to display a Tx tag for the previous frequency. That pressure might be in the manner of a good caning with one's own Tx antenna. As for enforcing any sanction against the practice, the AMA jackboots have limited presence at most flying venues, and the FCC is far too occupied with auctioning off the ether to be bothered.
As for changing channels on the telly, that must be done under the direct supervision of SWMBO, when she is granting audience.
Abel
04-05-2004 | 05:59 PM
#85
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From: stoke on trent, UNITED KINGDOM
RE: Crystal Swapping.. Again
hi Abel
thanx for the clarification, one more question, is your frequency for the exclussive use of aircraft, we use the 35meg range and this is only for model aircraft. i agree there will always be the danger of some airhead not changing his frequency pennant on his tx no matter where we fly, i see the same is true about TV, this is why im on forum SWMBO has the remote!!!!
thanx for the clarification, one more question, is your frequency for the exclussive use of aircraft, we use the 35meg range and this is only for model aircraft. i agree there will always be the danger of some airhead not changing his frequency pennant on his tx no matter where we fly, i see the same is true about TV, this is why im on forum SWMBO has the remote!!!!
04-05-2004 | 09:36 PM
#86
My Feedback: (1)
RE: Crystal Swapping.. Again
ORIGINAL: hurricane52
one more question, is your frequency for the exclussive use of aircraft
one more question, is your frequency for the exclussive use of aircraft
No, Our primary air band 72 mHz and possibly the 75mHz surface only band has commercial industrial primary users between the hobbiest channels and we are considered secondarey users. The adjacint hobbiest channel is not our nearest adjacint channel.
John
04-10-2004 | 10:57 AM
#87
RE: Crystal Swapping.. Again
We need a communications theroy expert here to explain the limitations and tradeoffs of spread spectrum. I'm not that person. I know enough to know it is an enormous subject, very complicated, non-intuitive, and SS is a generic term that refers to many different modulation schemes, not just one. SS is not a cure all. It will not eliminate the possiblity of losing your aircraft due to a weak signal. It will (depending upon the multiplexing technique) make beign 'shot down' much less likely.
The tradeoff, I think, is that range will become more of an issue. This is mainly due to path loss, but also, multiple simultaneous SS users will reduce range. For example, 4 simultaneous users would reduce the range of each user by a factor of 2. Multiple users do not interfere with each other directly but increase the noise level for each user.
The tradeoff, I think, is that range will become more of an issue. This is mainly due to path loss, but also, multiple simultaneous SS users will reduce range. For example, 4 simultaneous users would reduce the range of each user by a factor of 2. Multiple users do not interfere with each other directly but increase the noise level for each user.
04-10-2004 | 11:15 AM
#88
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RE: Crystal Swapping.. Again
ORIGINAL: JPMacG
This is mainly due to path loss, but also, multiple simultaneous SS users will reduce range. For example, 4 simultaneous users would reduce the range of each user by a factor of 2.
This is mainly due to path loss, but also, multiple simultaneous SS users will reduce range. For example, 4 simultaneous users would reduce the range of each user by a factor of 2.
This is not true. For frequency hoppers (FHSS), as more users come on, you start to loose data in a statistically deterministic way. You can model this loss and account for it with redundant data. This loss does not affect the range at all, just the amount of data that gets through (per unit of time)
And with new FCC rules, you can intelligently avoid frequency bins that are showing signs of interference, so you just hop around them. It used to be that you had to hop on all 75 bins equally. This is a big improvement in the regulations.
Direct Sequence (DSSS) is totally different.
EDIT Actually, more users in theory does indeed reduce the range even for a frequency hopping system. After the maximum range is reached (you have begun to use up all of the redundant data) then more users will cause more data to be lost. But I do not think this happens by some inverse square law like 4 users yields 2x reduction
04-10-2004 | 04:03 PM
#91
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RE: Crystal Swapping.. Again
Well we think that the limit of users that we can still maintain full performance is about 13-16. We are not really sure yet as we have not built that many radios! THis is an area where theory only goes so far, we really need to test it.
When more users (than the maximum allowed) try to turn on, there TX will inhibit itself and tell you to wait for someone to turn off first. But even if things get hairy, the system degrades gracefully, maybe with an audible warning to tell you you are loosing data.
We are making our second system on 900 Mhz now, and it will have different performance. Same princepal but different data rates. We like 900 because of the much reduced path loss.
When more users (than the maximum allowed) try to turn on, there TX will inhibit itself and tell you to wait for someone to turn off first. But even if things get hairy, the system degrades gracefully, maybe with an audible warning to tell you you are loosing data.
We are making our second system on 900 Mhz now, and it will have different performance. Same princepal but different data rates. We like 900 because of the much reduced path loss.
04-18-2004 | 07:26 AM
#92
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From: Memphis,
TN
RE: Crystal Swapping.. Again
[link=http://www.rcuniverse.com/forum/Tx_crystal_swapping!/m_1733329/tm.htm]crystal swapping thread..check it out .. tell me what you think[/link][X(]
