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  #61  
Old 05-22-2018, 02:05 PM
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snopercod snopercod is offline
 
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Originally Posted by BobTurner View Post
...if they canít see you, then they canít see nearby traffic either...
That makes a lot of sense. That's probably the explanation for this wacky system. Also, like you said, in 2020 the ground stations will only be needed for weather.
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  #62  
Old 05-22-2018, 02:24 PM
BobTurner BobTurner is offline
 
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Originally Posted by snopercod View Post
That makes a lot of sense. That's probably the explanation for this wacky system. Also, like you said, in 2020 the ground stations will only be needed for weather.
I didnít say that. In 2020 you must have ADSB-out in class A,B,C, and E above 10,000í (and inside class B mode C veil). But there will be tons of guys below 10,000í who avoid those (B,C) areas, and who wonít upgrade to ADSB-out. You wonít see them without radar and the ground stations.

And of course, the faa wants the ground stations so they can see you.
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  #63  
Old 05-22-2018, 04:02 PM
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...And of course, the faa wants the ground stations so they can see you.
I have anonymous mode <evil grin>
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  #64  
Old 05-23-2018, 12:35 PM
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OK, I got my transponder/UAT recertified today. Signal strength was fine front to back, but lower (but acceptable) side to side. That's due to the figure eight radiation pattern of my half-wave dipole transponder antenna. The tech said I was broadcasting on 1090 MHz so I'm scratching my head over that. I'm guessing his equipment just wasn't set up to measure the UAT frequency. I had intended to do an A-B comparison with a standard spike antenna, but the darn thing didn't arrive in the mail until I got home. Maybe in another two years

The Performance Report for the trip had my client percentage up to 61% - probably due to the fact that a ground station was located right on my destination airport [KGYH].

I feel like I've wasted enough of everybody's time trying to figure all this out, so I'm just going to keep flying with what I've got. Thanks for all the education and suggestions.
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  #65  
Old 05-23-2018, 12:42 PM
BobTurner BobTurner is offline
 
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Originally Posted by snopercod View Post
OK, I got my transponder/UAT recertified today. Signal strength was fine front to back, but lower (but acceptable) side to side. That's due to the figure eight radiation pattern of my half-wave dipole transponder antenna. The tech said I was broadcasting on 1090 MHz so I'm scratching my head over that. I'm guessing his equipment just wasn't set up to measure the UAT frequency. I had intended to do an A-B comparison with a standard spike antenna, but the darn thing didn't arrive in the mail until I got home. Maybe in another two years

The Performance Report for the trip had my client percentage up to 61% - probably due to the fact that a ground station was located right on my destination airport [KGYH].

I feel like I've wasted enough of everybody's time trying to figure all this out, so I'm just going to keep flying with what I've got. Thanks for all the education and suggestions.
If your antenna is mounted properly, as you said it was earlier, left, right, front, back should all be the same.
The tech checks the transponder on 1090.
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  #66  
Old 05-23-2018, 04:32 PM
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... left, right, front, back should all be the same.
I really didn't state it correctly. The figure eight radiation pattern has nulls off the ends of the antenna - up and down in my installation. The problem I have is that the antenna is printed on a double-sided pc board. The elements are 2" wide in the front-to-back direction and .020" side-to-side. The wideness increases the bandwidth (lowers the "Q"...but only in the front to back direction in my installation. It's entirely possible that in the side-to-side direction, my antenna is resonant at the wrong frequency. Without the proper test equipment to investigate further, I'm just going to live with what I have.
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  #67  
Old 05-24-2018, 10:54 AM
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For the record, I measured some transponder antennas today. From the face of the ground plane to the tip of the ball was:

1090 MHz quarter wave spike antenna = 2.43" (4.86" for half wave)
978 UAT quarter wave spike antenna = 2.66" (5.32" for half-wave)
My Archer SA-005 half wave dipole = 5.4"

The common formula for length vs. frequency is f = 468/length, where
f is in MHz
length of a half-wave dipole is in feet

I'm not sure the 468 works at these frequencies. A factor of 440 seems to work better. Any antenna gurus out there?
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  #68  
Old 05-24-2018, 11:26 AM
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Quote:
Originally Posted by snopercod View Post
I really didn't state it correctly. The figure eight radiation pattern has nulls off the ends of the antenna - up and down in my installation. The problem I have is that the antenna is printed on a double-sided pc board. The elements are 2" wide in the front-to-back direction and .020" side-to-side. The wideness increases the bandwidth (lowers the "Q"...but only in the front to back direction in my installation. It's entirely possible that in the side-to-side direction, my antenna is resonant at the wrong frequency. Without the proper test equipment to investigate further, I'm just going to live with what I have.
Having rolled over under my Tiger and broken a standard Narco blade transponder antenna

I found that the metal radiating element inside is actually a flat sheet and not a rod encased in plastic. It would be similar to the PCB version picture posted earlier, just a 1/4 wave not a 1/2 wave.
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  #69  
Old 05-24-2018, 12:45 PM
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Thanks for that. I think those are called "blade" antennas and are supposed to be broadband. I wish I had the equipment to play around with these various antennas. I made up a ground plane for my UAT antenna today. I was going to have the guy as the avionics shop check it out, but I was too late. I was going to mount it (Spike down, of course) in the floor of my baggage compartment.

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Last edited by snopercod : 05-24-2018 at 12:56 PM. Reason: added photo
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  #70  
Old 05-24-2018, 05:06 PM
BobTurner BobTurner is offline
 
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Quote:
Originally Posted by snopercod View Post
For the record, I measured some transponder antennas today. From the face of the ground plane to the tip of the ball was:

1090 MHz quarter wave spike antenna = 2.43" (4.86" for half wave)
978 UAT quarter wave spike antenna = 2.66" (5.32" for half-wave)
My Archer SA-005 half wave dipole = 5.4"

The common formula for length vs. frequency is f = 468/length, where
f is in MHz
length of a half-wave dipole is in feet

I'm not sure the 468 works at these frequencies. A factor of 440 seems to work better. Any antenna gurus out there?
The little ball at the end adds some capacitance, so the antenna will resonate at a bit shorter length than given by the formula for a given frequency.
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