PtP400 and Ptp600 Antenna Alignment - Is it crucial?

Especially regarding short links 1/2 mile and less. With these radios how critical is it that you align the antennas perfectly? What kinds of problems could arise from not doing it? does it matter even? How much difference between signal levels on each side of the link can there be for the link to be considered effectively installed? Does it matter on short links like this other than as a professional level?

On the same note, as long as signals look decent, does it matter on longer links?

It has been my experience with wireless to have the best signal and alignment possible to have the best end user experience.

I have to agree with along5664.

However the antenna’s you use play a large role in the alignment process. If your using 2ft and 3ft dishs, the beam width on those is only 4-6 degrees so you need to make sure you have pretty bang on or you signal, bandwidth and reliabilty will suffer greatly.

It’s worth the time and money to get it aligned right the first time.

My philosophy is that the RF spectrum is not unlimited. I treat the RF space as part of the network keeping the available spectrum as clean as possible and using best practices on every link.

For me this means:
- narrower beams
- accurate alignment
- minimal power required to achieve desired link quality
- quality radios

This approach ensures maximum RF spectrum efficiency and will allow me to have the most number of links and clients within the spectrum.

I agree with Jerry - you should really pay attention to what is out there and plan your network links accordingly. You really shouldn NOT "throw a pair of radios in place and hope for the best."

Good alignment assures you have the maximum possible signal level coming from and going to your remote site. This maximum (for your path) with ensure that you see minimal effects from interference by keeping your C/I ratio (carrier to interference) as high as possible. This also makes sure that you aren’t sending stray RF in directions you don’t need to be, possibly affecting other links nearby.


Additionally, proper peaking will allow you to run the radios with the lowest possible Tx power to maintain the link.

Jerry, I ran this past my boss today, in an unintended public questioning of my boss ( I learned a long long time ago to never question your boss in front of others, it can turn out really really bad, lucky for me, he has thick skin and is sure hes right ) :slight_smile:

Heres the particular link that raised this question, 1/2 to 3/4 mile ptp400 4900MHz integrated link, on a highway, with visual LOS. Locked frequencies on each end of the spectrum.

Its a very short link, obviously alot of room to play, Ill give that.

My argument is 3fold

1. Do it by the book the first time (this is our first experience with ptp400)

2. Keeping the spectrum clean. a 6 degree beam isnt an issue at 3/4 miles, but the guy on the other side of the radio by 2 miles getting higher levels of interference because a radio is pointed at him unneccasarily might have a problem with it. (This is a golden rule issue, that I am quickly beginning to realize in the wireless industry is greatly ignored)

3. Quality and craftsmanship, If a boss tells the employee its ok to shortcut on alignment even on a short link, imagine how much further the employee will cut corners.

I give that performance wise, we will never see an issue with this. That was never my point.

I would even give that we could probably rotate the antennas further out of alignment at this short of a distance, and the signal strengths will still be high, probably even within the confines of a linke estimator result.

so for point 1- this particular location had issues with a much lower quality radio system, we never fully figured out what it was, but we temporarily replaced it with 5.x and it worked, so my assumption leads me to believe it was an issue with the 4900 band. all the more reason to do it by the book the first time, the elisive unknown variable.

the second point is where you come in Jerry. I mentioned your post and clean RF space. I called it fair use of the spectrum, in reference to other links in the path area. I was told to ask you if youve ever used an omni antenna, or bounced signal off a building to get around an obstacle, if so to point out that kills the spectrum. My concern though was still about other links in the RF path, and the further out we get, the further off the neccesary path we get if the radios arent alignedcausing unneccassary interference to those locations… In that respect The golden rule went out the window, and as long as we are within FCC guidelines, all is well.

the third point is just a big concern, I grew up working for my dad alot and he always did things by the book, or at least led me to believe he did, because he knew that I would be looking to give the full 90 percent. if the bar is set at 90 percent by letting shortcuts happen, after the employee only give his 90 percent of that, then end result is only 81%.

but anyhow, Im not upset with my boss, i disagree with him, but hes been doing it longer than me, and he pays me a decent wage, two very good reasons to keep my mouth shut. This is a friendly debate and in the long run im going to do what the man says, but i like to have alot of input for myself.

Am I just being anal about the need to align everything in the point to point, not point to multipoint

The question was “Is it crucial”. In the strictest sense, my answer still stands…take the time to do it right.

Is there room for slop, sure. The question is, how far out of alignment is it? 1 degree? 5 Degrees? What is acceptable slop within the company? How much additional power is being pumped out to make up for poor alignment?

We peak everything regardless of the distance. Then we turn the Tx power down to the minimum required to maintain the link.

Comparing an Omni to a licensed public safety link? I’m not going to go there.

This topic was discussed on another forum and my opinion still stands that the job must be done 100%. Workmanship and quality of product suffer when corners are cut.

I am all for using the highest gain antennas permitted for all ptp links and adjusting the power down.

This is even more so in 4.9GHz public safety. Cutting corners here means peoples lives are at risk. I have every reason to say this because I work with the 4900MHz band daily for PtP and PtMP links.

Paying you a decent wage is a good reason, but because he has been doing it longer then you is not. Just because he has been doing it longer doesn’t mean he does it right. Is there a reason why he doesn’t want to take the time to do the job properly? Or better yet maybe he really doesn’t know how to do the job right. It sounds to me like cutting corners is how he does things like bouncing signal off a building to get around an object, and in the long run it will only hurt his business.

As far as alignment and not taking the time. Here is aa example of a common occurance when just throwing up a point to point link. Take a look at some antenna radiation patterns. It is quite common to see a main lobe and a smaller lobe to either side of the main lobe. When not taking the time to tune properly a link can be established on one of these side lobes and look fine until fading, bad weather, and any number of things. A proper alignment would take the time to make sure both ends are on the main lobe. You need to sweep past the main lobe and find the side lobe to determin this.

With respect to the ptp400 or ptp600, the rx signal at the far end determins what the tx power at the near end will be along with the modulation scheme, so a misaligned radio will automatically turn up the power to try to compensate.