Can't hear Indianapolis Center.........

[wa8vzq]

Yokoshibu - "usually low altitude freqs for the area you live in are comming from an rcag near you..." If I read what you're implying, you think that there is a difference between how a low and a high altitude freq is transmitted. That's not true in any sense and is in the same vein as the signal is transmitted straight up.

There is no equipment or antenna configuration difference between low, high, super high, ultra high or any other altitude assignment. The only difference is one of designation.

Sometimes a particular frequency will have a high gain antenna or linear amp (50 watts). That is done to solve coverage problems and it has nothing to do with altitude assignment.

Dan

 

[timmer]

And, if you don't want to spend a huge amount on your antenna, try say a Grove scanner beam and just put it in your attic. Take your time pointing it in diffrent directions until you decide on a permanent install. Or a discone, (go with the diamond d-130j). Although I know others say these don't have alot of gain, they are at their "peak" around the aircraft band and seem to do real well.

 

[302HO]

I'm not sure which antenna to go with. Do you just look at the gain, bandwidth and size of the antenna?

Does the bigger antenna mean better in this case? Or will smaller antennas out perform larger ones?

There are some repeaters according to the database that are located in winchester. Winchester is around 50 miles or so from me. Less if you were able to drive in a straight line.

Thanks for all the help yall....

 

[Yokoshibu]

Yokoshibu - "usually low altitude freqs for the area you live in are comming from an rcag near you..." If I read what you're implying, you think that there is a difference between how a low and a high altitude freq is transmitted. That's not true in any sense and is in the same vein as the signal is transmitted straight up.

There is no equipment or antenna configuration difference between low, high, super high, ultra high or any other altitude assignment. The only difference is one of designation.

Sometimes a particular frequency will have a high gain antenna or linear amp (50 watts). That is done to solve coverage problems and it has nothing to do with altitude assignment.

Dan

So there is no difference between a Low freq and a high freq other than its an assignment huh? I would have tought someone would have been smart enough to actually aim the rf to the intended audience .. but hey the faa is not that bright so I shouldnt give them such credit!

 

[crayon]

Sometimes a particular frequency will have a high gain antenna or linear amp (50 watts). That is done to solve coverage problems and it has nothing to do with altitude assignment.

Hate to tell you bro .. but it does.

A center's airspace is divided into two layers .. low sectors and high sectors.

As far a "aiming" RF .. lol.

anyways ...

 

[wa8vzq]

Amazing, I've been working on these sites for several decades. You'd I think I know how they work by now ;-)

As far as aiming RF, the only signals actually aimed straight up are the marker beacons. Getting that to work exactly correct is a lot more difficult than it would seem. You need to read up a little on Fresnel nulls.

As far as straight up is concerned, if you were to look at the radiation diagrams on the webpage in my previous post, you would see that the RF near the 90 point is decreased in amplitude. If you've only talked about aiming radiation doing it rather than actually done it you'd know what I'm talking about.

As far as altitude assignments, you need to look at any ARTCC airspace charts to see that there are more than low and high. And again, there is no difference in equipment or antennas for either.

Dan

 

[crayon]

Amazing, I've been working on these sites for several decades. You'd I think I know how they work by now ;-)

And you'd think that I would know better than to post late at night!

As I read my post today, I quite honestly do not know why I typed what I did.

lol.

 

[adkad]

The question I have is I get several freqs with atc controllers but can't hear the planes. Anyone know why that would be? Thanks, Adkad

 

[timmer]

I know that around my area, especially late at night, I have found this to be the case. They transmit on several frequencies at once. I assume this is because there is not enough traffic to have a separate controller handle each individual frequency, so they combine them. One controller may be responsible for several diffrent freq's/sectors. I've heard KC center transmitting on 125.5, 125.25, and 134.5 and at least one other late at night around the southern Ill./ st.louis area.

 

[timmer]

I should have said they transmit on those freq's all simultaneously. So, it sometimes takes some searching/scanning to find the freq. that the pilot is transmitting on.

 

[Yokoshibu]

Amazing, I've been working on these sites for several decades. You'd I think I know how they work by now ;-)

As far as aiming RF, the only signals actually aimed straight up are the marker beacons. Getting that to work exactly correct is a lot more difficult than it would seem. You need to read up a little on Fresnel nulls.

As far as straight up is concerned, if you were to look at the radiation diagrams on the webpage in my previous post, you would see that the RF near the 90 point is decreased in amplitude. If you've only talked about aiming radiation doing it rather than actually done it you'd know what I'm talking about.

As far as altitude assignments, you need to look at any ARTCC airspace charts to see that there are more than low and high. And again, there is no difference in equipment or antennas for either.

Dan

yeah they aim beacon markers straight up, and the ILS and G/S are nothing more than yagi's so why not use yagi's for low freq's with power dividers? I mean if you are using a diple for low and high... at 45,000 feet above a site whats the cone of silence gonna be for a vert polarzd 1/4 wave? I need to go do the math... but then again mach .72 at fl 380 -fl 450 is about 7-8 miles per min so it can only be a min or two of concern

 

[wa8vzq]

Again, there is no such thing as aiming the RF at a particular altitude for aircraft communications.

Think about it for a minute. Airplanes are moving as they travel through the airspace, their not sitting still at some particular altitude. And for that matter, they don't stay necessarily stay at any particular altitude in a sector. Exxample: low alititude is from the ground to FL230.

The lowest radiation angle used is always going to near 0 degrees as the aircraft approaches its line of sight limit. The highest radiation angle is always going to be 90 degrees as the aircraft flys directly overhead. That's true regardless of whether you're talking about a low, high or super high altitude airplane. Each one just has a different volume of airsapce to travel through but they all use the same range of angles 0-90 degrees. So there is no "magic" or optimum angle to set for a specific altitude aircraft.

And sorry, neither the GS or the LOC antennas are yagi's. The GS antenna sets are each made of 3 phased dipoles with a reflector. Depending upon the type of GS, there will either be 2 or 3 antenna sets. The most common LOC antennas are log periodics. Depending upon the system, there are anywhere from 8 to 20 LP's in an array.

There are a lot of power dividers in each system - you should try doing the math for those to make everything come out with the correct power ratio AND within a few degrees of electrical phase error. Then try cutting all of the coaxial cables to exact electrical length to put the LOC signal within a few inches of the runway centerline. It takes quite a bit of finesse.

 

[adkad]

Well, you guys know a lot more than I do about designing antennas. All I know is that with a 30ft mounted dedicated airband antenna I can follow a plane through a series of frequencies for as far as a hundred miles in any direction. I also can pick up most atc controllers within a 50 mile radius, which for me means 6 different airports. I spent a lot of money on my radio but still I think one can certainly enjoy this hobby without too much exactitude and finesse. I enjoy learning about the hobby though, even as I recognize my own limits. Adkad

 

[Yokoshibu]

uhm You can aim RF period. now, why not aim it at a particular altitude with several yagis?

what is a log periodic? nothing more than a bastardized/ broadbanded yagi correct?

there is no magic angle but the gain has to help with both tx/rx I am sure, unless you are going to tell me there is no gain added from a yagi.

 

[wa8vzq]

You apparently didn't fully comprehend my previous post. There is no angle or direction to point a yagi. Regardless of whether we are talking about a low altitude, high altitude or super high altitude sector all of the angles from 0 through 90 degrees are used to communicate. So there is no one particular angle that you can point a yagi for low altitude aircraft as example. Since airplanes are moving objects, it doesn't work the same as pointing your satellite dish.

The maximum path length for a superhigh sector is about 268 NMi. Propagation loss equation says that the path loss @ 126 MHz is about 128 dB. A 10 watt transmitter will deliver approximately a 5.5 microvolt signal to the aircrafts antenna (ignoring cable and obstruction losses). If additional signal level is needed then the transmitting site can raise the power or add an omnidirectional gain antenna. These provide an additional 4 dBi. Gain is not free and any gain antena sacrifices radiation in some direction.

http://www.antennaproducts.com/40detail.htm

While a yagi and a log periodic may look similar, they aren't. They work on entirely different principles. The yagi is a parasite array and usually only has one driven element. The LP has all the elements driven and the theory of operation is much more complex. But those are topics for the antenna forum.

Dan

 

[302HO]

Well guys, i can hear planes talk to center. After the quits txing, i open my squelch and i can hear a little reception. I dont hear voice, but can tell i am getting something.

I am a newby, but i can almost bet it i either put an antenna in the attic or install a preamp on my R20 i just might be able to get center.

hopefully anyway.

thanks for all the info guys. I enjoy reading your replies.

thanks again.

 

[DickH]

Does the bigger antenna mean better in this case? Or will smaller antennas out perform larger ones?

After about a dozen more answers, no one has bothered to answer your question, so I'll try.

Not sure what you mean by "bigger". If you mean simply longer, the answer is NO.
The standard 1/4 wavelength antenna's length depends on the freq. For example, At 860MHz it is about 3-1/4". At 460MHz it is about 6". At 154MHz it is about 18". At 120MHz (your airband) it is about 23".

 

[wa8vzq]

Dick

I agree with you. I've gotten way off track trying to clear up a lot of misconceptions about how the radio sites work and had forgotten that those weren't the questions asked.

Originally I had suggested a Moxon rectangle. But after doing a little modeling with EZNEC, it looks like a Moxon really isn't suited to this band because it is a fairly narrow bandwidth antenna. I was thinking cheap with some gain but obviously it's not a wide band antenna. So I'm backing down from that recommendation unless we're talking about using it for a very narrow slice of the band.

I'd go with the idea that an antenna in the attic may help a lot. Especially if his current antenna is significantly lower. I'd try a simple ground plane for starters with some low loss coax. And as mentioned earlier, it probably wouldn't hurt to try a TV type pre-amp. They're obviously not the best but they're cheap enough that it wouldn't hurt much if it didn't help.

dan

 

[302HO]

I enjoy the talk about how center, towers and the planes communicate. Helps me understand more.


Attic antenna. I do not want to put one up outside. The attic is the only way i want to go.
Now, i dont know which antenna to go with. I have a catalog from universal radio that i have been looking thru.

My radio is an Icom R20. Would like to experiment with my Maldol 500 antenna and a nice preamp. Am considering an antenna in the attic though. I am mainly interested in the Airbands but will listen to anything. Think i need a wideband antenna.

Antennas that i have seen in my catalog.

1) AOR SA7000, DA3000
2) Icom AH7000


The info given on these antennas dont give a gain figure. I realize not all antennas give a gain.

I Have searched for this stuff in the forums, but really havent found what i am looking for. Maybe i need to post this in the antenna forum.

I greatly appreciate all the info that has been typed so far......

thanks again guys.
steve

 

[DickH]

Since you are mainly interested in the airport, a beam antenna should do well, since beams are highly directional.
Radio Shack has (used to have?) a beam antenna for the FM band (88-108) for only $20 a few years ago. It's even pre-assembled, with fold-out elements. Since the elements are longer for that slightly lower freq., you could cut off a little from each element for optimum reception. How much to cut off? I have no idea, but 1/4 wave at 100MHz is about 27". At 120MHz (your band) it is 23".
Radio Shack number is 15-2163. It is described as a 6-element, triple-drive (whatever that is) antenna. In the attic, it should also pick up anything else you want to monitor, too.
Dick