Pointing A Directional Antenna EXACTLY At A Tower

[BinaryMode]

I have a scenario where I will be needing to point a Yagi directional antenna at a tower that's part of a phase II P25 system using simulcast. That way I can hopefully help mitigate simulcast distortion from the rest of the towers. I do not live in the simulcast affected area, only outside of it. But the use of multiple towers are distorting the digital audio from this simulcast area towards me.

To accomplish this I want to point the directional antenna EXACTLY at the closest tower to me right down to the magnetic degree. So, I took to ChatGPT and through some trial and error, and a little bit of editing myself, I created this standalone web-based application to allow me to enter a home location and a target location then hit "calculate" telling me what the exact magnetic bearing is for the tower I'm interested in feeding from. Pretty cool, huh?

Watch the video and hear my dumb voice here.

Download here or on this website.

Simulcast Distortion - The RadioReference Wiki

wiki.radioreference.com

Feel free to edit the code if you want. I have added a code comment with instructions on how to change the background image.

Edit-

This html document should work on a tablet or phone.

 

[trentbob]

I have a scenario where I will be needing to point a Yagi directional antenna at a tower that's part of a phase II P25 system using simulcast. That way I can hopefully help mitigate simulcast distortion from the rest of the towers. I do not live in the simulcast affected area, only outside of it. But the use of multiple towers are distorting the digital audio from this simulcast area towards me.

To accomplish this I want to point the directional antenna EXACTLY at the closest tower to me right down to the magnetic degree. So, I took to ChatGPT and through some trial and error, and a little bit of editing myself, I created this standalone web-based application to allow me to enter a home location and a target location then hit "calculate" telling me what the exact magnetic bearing is for the tower I'm interested in feeding from. Pretty cool, huh?

Watch the video and hear my dumb voice here.

Download here or on this website.

Simulcast Distortion - The RadioReference Wiki

wiki.radioreference.com

Feel free to edit the code if you want. I have added a code comment with instructions on how to change the background image.

Edit-

This html document should work on a tablet or phone.

Interesting, back 10 years ago when the Uniden 436 and 536 were introduced and were used on Phase 2 simulcast trying to isolate one tower using a Yagi was one of the gimmicks used along with, paper clips, drilling holes in empty paint cans and sticking the antenna in the hole, ATT and a few others.

Unfortunately getting a good connection with one tower can be affected by many different things. It's not an exact science so I used to use a yagi mounted on a cheap floor lamp from Walmart with low loss coax. I would rotate the antenna while looking at reception indicators like error rate and using my ear.

Wasn't always in the same direction when good reception resulted. Always had the issue of another tower directly behind the target tower. You also had a teardrop configuration receiving behind the yagi.

Again so many other factors involved such as topography, propagation, obstructions, reflection and time of year with foliage.

In the newspaper business we could not have missed, broken transmissions or completely missed calls so we ended up just getting NAS professional radios.

Very interesting theory, looks like you've put a lot of time and thought into this. Cool.

 

[prcguy]

Probably better to use an accurate S meter then detune off one side until it’s degraded about 6dB or 1 S unit, note that direction, then go through the peak to the other side until it’s degraded the exact same amount then park it in the middle of those two readings. This is basically how big satellite dishes auto peak themselves and it’s very accurate.

When DirecTV launched Ka band satellites at 2 degree spacing about 15yrs ago (the original Ku sats were 9 deg spacing) they needed a new alignment procedure to aim the new consumer dish so it would see 5 different satellites at the same time and be accurate to less than about 1/10th of a degree, I forget the exact spec but it’s small. The only procedure that would work is what I described above and that’s how all the installers are required to do it. Don’t ask me why I know all this…..

 

[dlwtrunked]

This html document should work on a tablet or phone.

You may want to tell people where to get the magnetic declination. I get it from the NGS program but that is over-kill. Also, a real nice program program that will give bearings, distances, and even where bearings cross is compsys21. Although no longer maintained (why does it need to be), it might be found at

Geodetic Calculator Software Informer: COMPSYS 21 is a free download designed to perform geodetic calculations. It allows the adjustment and quality control of 3D, 2D and 1D geodetic networks.

Geodetic Calculator Software Informer. Featured Geodetic Calculator free downloads and reviews.

geodetic-calculator.software.informer.com

 

[mmckenna]

Google Earth is what I use. Easy enough to draw a line between antennas and it'll give you the bearing, either magnetic or true.

But unless you have a seriously long Yagi, a few degrees one way or the other isn't going to make a noticeable difference. The beamwidth on most of them is measured in tens of degrees.

 

[KevinC]

What if the site uses panel antennas? Aiming at the tower may not help if they are mounted on the opposite side of the tower or the azimuth and beamwidth don't point any energy toward you. I've implemented numerous P25 trunked sites that use them.

 

[N9JIG]

Don't spend too much time getting a yagi pointed perfectly by math, do it by ear. It will give better performance that way. It is more important to null out the unwanted towers than key directly to the desired tower.

 

[WB5UOM]

I think its also going to depend where the other tiwers relative to your location...with the yagis beamwidth..it may or may not be possible to isolate to only one, unless maybe you could aim well to one side of a tower that is on the edge relative to the other towers..
not too sure this plan is gonna play
my $0.02 worth adjusted for inflation

 

[pb_lonny]

How has it worked for you? Did it help with the issue?

 

[BinaryMode]

Wow, so many comments. I'll address each as best I can.

Probably better to use an accurate S meter then detune off one side until it’s degraded about 6dB or 1 S unit, note that direction, then go through the peak to the other side until it’s degraded the exact same amount then park it in the middle of those two readings. This is basically how big satellite dishes auto peak themselves and it’s very accurate.

This sounds very prudent and I may just do that. Though, I don't have an accurate S meter per say other than what's in the scanner.

When DirecTV launched Ka band satellites at 2 degree spacing about 15yrs ago (the original Ku sats were 9 deg spacing) they needed a new alignment procedure to aim the new consumer dish so it would see 5 different satellites at the same time and be accurate to less than about 1/10th of a degree, I forget the exact spec but it’s small. The only procedure that would work is what I described above and that’s how all the installers are required to do it. Don’t ask me why I know all this…..

HAHA I won't then. Yeah, I know loads of "useless" Info. as well.

You may want to tell people where to get the magnetic declination.

Watch the video and look at the script. I linked to a NOAA resource and in the video I explain that as well as how to pull the declination from an aeronautical chart.

Google Earth is what I use. Easy enough to draw a line between antennas and it'll give you the bearing, either magnetic or true.

But unless you have a seriously long Yagi, a few degrees one way or the other isn't going to make a noticeable difference. The beamwidth on most of them is measured in tens of degrees.

Google Earth would certainly do it I suppose, but I don't care for Google and try to stay away from most of their offerings as best I can. My smartphone even runs CalyxOS rather than Android. LOL Though, the phone happens to be a Google Pixel, but those phones are the most compatible when it comes to third-party OSs using the AOSP (Android Open Source Project).

I had no idea the beamwidth of most Yagi antennas was in the tens of degrees. I thought it was more narrower than that. Good information, thanks.

What if the site uses panel antennas? Aiming at the tower may not help if they are mounted on the opposite side of the tower or the azimuth and beamwidth don't point any energy toward you. I've implemented numerous P25 trunked sites that use them.

Didn't know about this type of antenna and suppose that could be an issue. Would it change anything if I told you the signal I hear from this system is a full 5 bars on the RSSI of the scanner, but the audio is distorted? Yes, I have set the threshold according to what I saw in auto mode monitoring a voice frequency, but that didn't change anything.

Don't spend too much time getting a yagi pointed perfectly by math, do it by ear. It will give better performance that way. It is more important to null out the unwanted towers than key directly to the desired tower.

Yeah, that's kinda what the Wiki page was alluding to.

How has it worked for you? Did it help with the issue?

Don't know yet as I haven't tried it. I'm debating now how best to go about it based on what I have read here.


Thanks for the comments, will take everything into consideration.

 

[KevinC]

I see you mention “threshold”, so you are using a non-SDS Uniden scanner. Many times with those it doesn’t matter what type of tricks you use you just won’t get good results with simulcast P25.

 

[G7RUX]

Probably better to use an accurate S meter then detune off one side until it’s degraded about 6dB or 1 S unit, note that direction, then go through the peak to the other side until it’s degraded the exact same amount then park it in the middle of those two readings. This is basically how big satellite dishes auto peak themselves and it’s very accurate.

When DirecTV launched Ka band satellites at 2 degree spacing about 15yrs ago (the original Ku sats were 9 deg spacing) they needed a new alignment procedure to aim the new consumer dish so it would see 5 different satellites at the same time and be accurate to less than about 1/10th of a degree, I forget the exact spec but it’s small. The only procedure that would work is what I described above and that’s how all the installers are required to do it. Don’t ask me why I know all this…..

Indeed they do and this also takes into account the antenna squint which lining the boom up with a compass probably won't.

 

[prcguy]

Indeed they do and this also takes into account the antenna squint which lining the boom up with a compass probably won't.

Squint is usually a very small offset, sometimes needed on a satellite dish with very narrow beamwidth but probably not on an 800MHz Yagi.

 

[prcguy]

HAHA I won't then. Yeah, I know loads of "useless" Info. as well.

It’s not useless info, the new at the time Ka band satellite service could not have been launched without the alignment procedure and the patent for the process was voted one of the most important to the company at the time. I wrote the procedure and the patent application and my name is on the patent.

 

[G7RUX]

Squint is usually a very small offset, sometimes needed on a satellite dish with very narrow beamwidth but probably not on an 800MHz Yagi.

It does depend somewhat on the antenna; I have seen UHF yagis with ~10deg of squint but it usually occurs where the frequency in use is right at the edge of the usable range. Granted though it’s normally small unless something odd is going on.

 

[BinaryMode]

It’s not useless info, the new at the time Ka band satellite service could not have been launched without the alignment procedure and the patent for the process was voted one of the most important to the company at the time. I wrote the procedure and the patent application and my name is on the patent.

I had a felling it wasn't "useless" information per say, that's why I put it in quotes.

I have to laugh when people say "useless information" in that the information is really not useless. Like with history. The thing with history is even though it happened in the past, I have read time and time again the same thing repeat its self in the future. Humanity needs to be a better student of history...

Anyway...

 

[trentbob]

I had a felling it wasn't "useless" information per say, that's why I put it in quotes.

I have to laugh when people say "useless information" in that the information is really not useless. Like with history. The thing with history is even though it happened in the past, I have read time and time again the same thing repeat its self in the future. Humanity needs to be a better student of history...

Anyway...

LOL, that's why I replied the way I did in post # 2.. I was going by past experience and actually doing what you're trying to do in a much, much simpler way after extensive experience trying..

You didn't acknowledge my reply, but I felt it was pretty accurate. Then you got the responses that you did.. I called your theory interesting and cool.

That's after actually trying to do it myself a decade ago, very, very simply with the Walmart floor lamp.

Kind of basic 101 stuff, after someone repeated what I said after I already said it.. "use your ear." 😄

 

[dlwtrunked]

"Watch the video and look at the script. I linked to a NOAA resource and in the video I explain that as well as how to pull the declination from an aeronautical chart."

I admit I did not watch the video or run the program as I did not need it. Using an aeronautical chart is of course commonly done but requires having the chart and an airport reasonable close. (By the way I download all the FAA chart every couple months for other reasons.) Personally I like the FAA magnetic model program as it even estimates the correction between its database/formulas derived on one date and the date desired. Accuracy like that is not needed but I like it. The new updated model (it is updated every 5 years) will be released at the end of this year.

World Magnetic Model (WMM)

The World Magnetic Model (WMM) is the standard model for navigation, attitude, and heading referencing systems using the geomagnetic field. Additional WMM uses include civilian applications, including navigation and heading systems.

www.ncei.noaa.gov

 

[BinaryMode]

LOL, that's why I replied the way I did in post # 2.. I was going by past experience and actually doing what you're trying to do in a much, much simpler way after extensive experience trying..

You didn't acknowledge my reply, but I felt it was pretty accurate. Then you got the responses that you did.. I called your theory interesting and cool.

That's after actually trying to do it myself a decade ago, very, very simply with the Walmart floor lamp.

Kind of basic 101 stuff, after someone repeated what I said after I already said it.. "use your ear." 😄

Yep, read your post and between yours and others I think this may be one marvelous crapshoot. LOL!

I can always try I guess, and it is relatively flat in the direction I'm wanting to monitor.

 

[RFI-EMI-GUY]

Wow, so many comments. I'll address each as best I can.



This sounds very prudent and I may just do that. Though, I don't have an accurate S meter per say other than what's in the scanner.




HAHA I won't then. Yeah, I know loads of "useless" Info. as well.





Watch the video and look at the script. I linked to a NOAA resource and in the video I explain that as well as how to pull the declination from an aeronautical chart.




Google Earth would certainly do it I suppose, but I don't care for Google and try to stay away from most of their offerings as best I can. My smartphone even runs CalyxOS rather than Android. LOL Though, the phone happens to be a Google Pixel, but those phones are the most compatible when it comes to third-party OSs using the AOSP (Android Open Source Project).

I had no idea the beamwidth of most Yagi antennas was in the tens of degrees. I thought it was more narrower than that. Good information, thanks.




Didn't know about this type of antenna and suppose that could be an issue. Would it change anything if I told you the signal I hear from this system is a full 5 bars on the RSSI of the scanner, but the audio is distorted? Yes, I have set the threshold according to what I saw in auto mode monitoring a voice frequency, but that didn't change anything.





Yeah, that's kinda what the Wiki page was alluding to.




Don't know yet as I haven't tried it. I'm debating now how best to go about it based on what I have read here.


Thanks for the comments, will take everything into consideration.

I think both techniques are required.

1) If you swing a yagi looking for a peak you are likely to get a reflection from a water tower or building.
2) Calculating the expected direction informs you that you are "on the mark" as far as the peak you find. If you have a scanne like the BCD536HP, the bar graph is rather tiny and not intuitive.

If anyone knows different way to skew the 6 dB points accurately with that scanner I would love to know. I guess I could insert a 3, 6 and 9 dB pad and figure out the actual bar that responds.

There will be cases, for those inside the simulcast footprint where the F/B or a side null will be be useful to help reject an interfering site. In that case the nose of the yagi might be off center with the direction. In other words trading 3 dB signal for 10 dB interference rejection.