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FM transmitter in a vehicle
Happy New Year!
If I have an FM transmitter in a vehicle, do I need to worry about the vibration frequency? Is there such a thing as intermodulation from vibrating objects attached to an FM transmitter? I'm curious. |
#2
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FM transmitter in a vehicle
Is there such a thing as intermodulation from
vibrating objects attached to an FM transmitter? Well, in case you have faulty coils inside the transmitter - you may expirience something what one of my friends called "microphoning" - their inductance may slightly change according to the vibrations, which may lead to somewhat unruly behaviour of the device. Best Regards, Peter |
#3
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FM transmitter in a vehicle
On Fri, 30 Dec 2005 22:37:19 +0100, Antey wrote:
Is there such a thing as intermodulation from vibrating objects attached to an FM transmitter? Well, in case you have faulty coils inside the transmitter - you may expirience something what one of my friends called "microphoning" - their inductance may slightly change according to the vibrations, which may lead to somewhat unruly behaviour of the device. Your biggest problems might be microphonic tubes in the mic-preamp and/or oscillator circuit. HI!HI! HNY es 73 Jonesy -- Marvin L Jones | jonz | W3DHJ | linux Pueblo, Colorado | @ | Jonesy | OS/2 __ 38.24N 104.55W | config.com | DM78rf | SK |
#4
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FM transmitter in a vehicle
"Ron J" wrote in message
oups.com... Happy New Year! If I have an FM transmitter in a vehicle, do I need to worry about the vibration frequency? Is there such a thing as intermodulation from vibrating objects attached to an FM transmitter? I'm curious. Short answers: Worry - Probably not Intermodulation - No. Really long answer... Not sure what you mean by "vibration frequency". Here's the logic for what is called "Environmental Desensitization", or "Environmental Desense" for short...sort of. The type of transmitter is not important for this discussion. The antenna produces an RF field around it and the vehicle (the desired effect since it extends out to infinity). Any conductor relatively near the vehicle or a conducting part of the vehicle (call it a parasitic conductor or "PC" for short) will have RF currents flowing in them as a result of the transmitter (this occurs whether it is near or not - actually the distance only affects the strength of the current, but for close spacing, the effect is easier to see & understand). More simply stated: "Everything in the world is a receiving antenna." The strength and relative phase of the current in the PC (compared to the transmitted signal) will depend on many things (distance to main antenna, shape, size, orientation, frequency, other objects and conductivity) These PC RF currents will also produce an RF field in the region (around the PC and vehicle). It is no different than the intentional transmitting antenna except it is not cut to a desired length and shape, but accidental. The PC RF field(s) will sum with the field from the transmitting antenna thus producing a slightly modified field - I'll call the "Sum-Field". The actual "Sum_Field" amplitude and phase depends on the relative strength and phase of the two fields at any point and is therefore complex. These fields sum in a vector addition manner. Sounds all pretty random up to here... However, we can say for sure that: If the current in the PC changes, the resulting "Sum-Field" will change. If the position of the PC changes, the current in the PC will change. If the size of the PC changes due to an intermittent connection with another near-by PC, the current in the PC will change. And we know that: If the PC current changes, the resulting PC field will change. And most certainly If the PC field changes, the "Sum-Field" will change. Keeping in mind that: A receiver near or far away will receive the "Sum-Field" at its location. This means that if we have a conductor near the transmitter that, due to any of the above changes, it can "modulate" the field in some way. The modulation must have some relation to the change causing it. It will indeed contain the same characteristic that causes the changing current / field. Therefore, the "modulation" will have the same characteristic as the original change, and it will most certainly contain that vibration frequency or the noise which is the intermittent contact. So, the bottom line is that the vibration (or noisy contact) will modulate the signal at the receiver. This modulation must most certainly be a combination of amplitude and phase modulation. This effect is there and usually small enough to be unnoticeable, therefore it is of little to no concern most of the time. It can be the cause of noise in a mobile instillation from things like tail pipe vibration, hood (bonnet) hinges and latch and the like. P.S. this same argument explains how directional antennas work, such as the common Yagi-Uda and all phased arrays whether parasitic or driven (phased). 73, Steve, K9DCI P.S. The Apollo recovery and communication ships had this problem due to the High power HF transmitters causing RF current in the Deck railing chains which caused noise sidebands which extended up into the microwave frequencies interfering with the radars...believe it or not - don't know if this is on the web, but I have the NASA papers somewhere. |
#5
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FM transmitter in a vehicle
Answer-- Don't worry about it! tho, during WWII, there was
the use of a "WOBBULATOR" in some 450 MHz airborn , Friend or Foe radio sets, these were pre- crystal, P.L.L. type radios, Broad as a barn (kinda like tuneing a Grid Dip oscillator to a fm freq, and then YELLING at it-- it will fm it, but, it won't be reliable for communications)! But, with todays technology , you will get more phase flutter from multipath than anything else! Jim NN7K Steve Nosko wrote: "Ron J" wrote in message oups.com... Happy New Year! If I have an FM transmitter in a vehicle, do I need to worry about the vibration frequency? Is there such a thing as intermodulation from vibrating objects attached to an FM transmitter? I'm curious. Short answers: Worry - Probably not Intermodulation - No. Really long answer... Not sure what you mean by "vibration frequency". Here's the logic for what is called "Environmental Desensitization", or "Environmental Desense" for short...sort of. The type of transmitter is not important for this discussion. The antenna produces an RF field around it and the vehicle (the desired effect since it extends out to infinity). Any conductor relatively near the vehicle or a conducting part of the vehicle (call it a parasitic conductor or "PC" for short) will have RF currents flowing in them as a result of the transmitter (this occurs whether it is near or not - actually the distance only affects the strength of the current, but for close spacing, the effect is easier to see & understand). More simply stated: "Everything in the world is a receiving antenna." The strength and relative phase of the current in the PC (compared to the transmitted signal) will depend on many things (distance to main antenna, shape, size, orientation, frequency, other objects and conductivity) These PC RF currents will also produce an RF field in the region (around the PC and vehicle). It is no different than the intentional transmitting antenna except it is not cut to a desired length and shape, but accidental. The PC RF field(s) will sum with the field from the transmitting antenna thus producing a slightly modified field - I'll call the "Sum-Field". The actual "Sum_Field" amplitude and phase depends on the relative strength and phase of the two fields at any point and is therefore complex. These fields sum in a vector addition manner. Sounds all pretty random up to here... However, we can say for sure that: If the current in the PC changes, the resulting "Sum-Field" will change. If the position of the PC changes, the current in the PC will change. If the size of the PC changes due to an intermittent connection with another near-by PC, the current in the PC will change. And we know that: If the PC current changes, the resulting PC field will change. And most certainly If the PC field changes, the "Sum-Field" will change. Keeping in mind that: A receiver near or far away will receive the "Sum-Field" at its location. This means that if we have a conductor near the transmitter that, due to any of the above changes, it can "modulate" the field in some way. The modulation must have some relation to the change causing it. It will indeed contain the same characteristic that causes the changing current / field. Therefore, the "modulation" will have the same characteristic as the original change, and it will most certainly contain that vibration frequency or the noise which is the intermittent contact. So, the bottom line is that the vibration (or noisy contact) will modulate the signal at the receiver. This modulation must most certainly be a combination of amplitude and phase modulation. This effect is there and usually small enough to be unnoticeable, therefore it is of little to no concern most of the time. It can be the cause of noise in a mobile instillation from things like tail pipe vibration, hood (bonnet) hinges and latch and the like. P.S. this same argument explains how directional antennas work, such as the common Yagi-Uda and all phased arrays whether parasitic or driven (phased). 73, Steve, K9DCI P.S. The Apollo recovery and communication ships had this problem due to the High power HF transmitters causing RF current in the Deck railing chains which caused noise sidebands which extended up into the microwave frequencies interfering with the radars...believe it or not - don't know if this is on the web, but I have the NASA papers somewhere. |
#6
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FM transmitter in a vehicle
Thanks for the informative explanation! If you can direct me to a copy
of the NASA papers, then that would be an interesting read. |
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