Is 3IM still around?
03-28-2004, 05:09 PM
#1
Is 3IM still around?
Had a crash at the field yesterday.....ch. 54....but there were 7 other radios 'on' at the time. One expert immediately thought (and proved?) it was 3IM! Channel 37, 54 and 20 were on along with a variety of others - rx was a JR 700 FM.
LOT of hot discussion followed.....I didn't think our current day rx. would be hampered by 3IM anymore - maybe I'm wrong.
I do have one question about the strength of the Ch 20 tx that was on....the antenna was down, the plane that got hit was directly in front of the pilot about 150 ' out. The ch 20 tx. was about 75' from that poor pilot - who donated a World Zero (.60size) to the desert floor.
Any disucssion????
Jerry
LOT of hot discussion followed.....I didn't think our current day rx. would be hampered by 3IM anymore - maybe I'm wrong.
I do have one question about the strength of the Ch 20 tx that was on....the antenna was down, the plane that got hit was directly in front of the pilot about 150 ' out. The ch 20 tx. was about 75' from that poor pilot - who donated a World Zero (.60size) to the desert floor.
Any disucssion????
Jerry
03-29-2004, 04:15 AM
#2
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RE: Is 3IM still around?
What tx had the antenna down on twenty. JR Air, Fut, Hitec?
ORIGINAL: tailskid
I do have one question about the strength of the Ch 20 tx that was on....the antenna was down, the plane that got hit was directly in front of the pilot about 150 ' out. The ch 20 tx. was about 75' from that poor pilot - who donated a World Zero (.60size) to the desert floor.
Any disucssion????
Jerry
I do have one question about the strength of the Ch 20 tx that was on....the antenna was down, the plane that got hit was directly in front of the pilot about 150 ' out. The ch 20 tx. was about 75' from that poor pilot - who donated a World Zero (.60size) to the desert floor.
Any disucssion????
Jerry
04-22-2004, 03:48 AM
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RE: Is 3IM still around?
3IM is (I'll get the exact term wrong...) 3rd order Inter-Modulation interference.
Lets say you have one radio on 72.090. One on 72.110 and one on 72.130 operating all at the same time.
The high and low TX's signals can "add up" to create an interference signal for the center frequency. This interference is strongest close to the transmitters.
Worst case condition for 3IM is having the 3 pilots standing shoulder to shoulder, and having the aircraft that is potentially affected fly close in, as in when doing a take-off, landing or a low flyby.
I have never heard of 3IM hitting an FM system before... But its theoreticly possible.
In the mid 70's to late 80's before narrow band and when most people were using AM radios... you not only checked if someone was on your frequency, you checked which other frequencies were in use and where the guys were standing. If the 2 frequencies on either side of yours were in use... you sat and waited, or you had a risk of getting hit by 3IM on takeoff.
Lets say you have one radio on 72.090. One on 72.110 and one on 72.130 operating all at the same time.
The high and low TX's signals can "add up" to create an interference signal for the center frequency. This interference is strongest close to the transmitters.
Worst case condition for 3IM is having the 3 pilots standing shoulder to shoulder, and having the aircraft that is potentially affected fly close in, as in when doing a take-off, landing or a low flyby.
I have never heard of 3IM hitting an FM system before... But its theoreticly possible.
In the mid 70's to late 80's before narrow band and when most people were using AM radios... you not only checked if someone was on your frequency, you checked which other frequencies were in use and where the guys were standing. If the 2 frequencies on either side of yours were in use... you sat and waited, or you had a risk of getting hit by 3IM on takeoff.
05-17-2004, 01:03 PM
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RE: Is 3IM still around?
We can not fly Channel 20 here (Little Rock, AR) it mixes with ABC TV (I think the audio part) and blows everything out of the air.
Doesn't effect itself.
Doesn't effect itself.
