Connectorized 60Mbps BH antenna question

Hello everyone,

Iam thinking of buying a pair of the connectorized 60mbps BH . I have downloaded the user guide and spent some time reading it. What I still dont understand is that on page 137 of the guide it says you can install “two single-polarized external antennas in a spatially diversed configuration”. Does that mean I can plug one vertically polarized and another horizantally polarized antenna onto the same unit? Will using 2 antennas improved the range and quality of the signal? and by how much ? Please shed a light on this.


Many Thanks.

It refers to “Antenna Diversity” mechanism used in wireless links. Take a look here:
http://en.wikipedia.org/wiki/Antenna_diversity

In a few words (better explained on the link) antenna diversity is the combination of 2 or more antenas in the same unit to have a better Rx and Tx due to reflection or refraction of radio waves in the air. Some home router-access points has 2 antennas, this is “diversity”. The same concept you can apply to 60 Mbps Canopy system.

Thank you so much for the reply, now iam beginning to understand. Now I understand

I have done this on 5 out of 10 of my 60 Mbps links (the long ones). I use two antennas at one end (30 ft apart) and one at the other - it is recommended to use space diversity at only one end of a link.

The most sought after characteristic of these links is the resistance to fading due to weather and ground conditions.


Aaron

Acherman what do you consider your long link’s? and what did you gain more stability or more threwput?

acherman wrote:
I have done this on 5 out of 10 of my 60 Mbps links (the long ones). I use two antennas at one end (30 ft apart) and one at the other - it is recommended to use space diversity at only one end of a link.

The most sought after characteristic of these links is the resistance to fading due to weather and ground conditions.


Aaron



Hi,

More confusion for me :

One end of the link using 2 antennas(one horizantal and the other vertical) while the other end using 1 antennas (let's say vertical polarity), how does that work ?

If using 2 antennas on a single unit, do both the antennas send signal ?

Is there a minimum distance between antennas when using spatial diversity ?


Many Thanks
ekoswara wrote:

One end of the link using 2 antennas(one horizantal and the other vertical) while the other end using 1 antennas (let's say vertical polarity), how does that work ?


Bad, because you must have the same polarization between 2 antennas specially in long distances (more than 1 Km is consider for me as a "long distance"). If you have 2 antennas on side "A" vertical and horizontal, one antenna on side "B" vertically polarized, the radio link will only exist bewteen both vertical antennas and the horizontal one would be there for nothing, useless.

ekoswara wrote:


If using 2 antennas on a single unit, do both the antennas send signal ?


I don't know if there is a device that lets u use both antennas as Tx and Rx at once, i only know this config:
Assuming there is 2 antennas:
a) Left antenna Tx, Right Antenna Rx
b) Left antenna Tx, Left Antenna Rx
c) Right Antenna Tx, Right Antenna Rx.

ekoswara wrote:

Is there a minimum distance between antennas when using spatial diversity ?

Many Thanks


I think you should calculate the distance between antennas according to the distance of the radio link and the enviroment around the signal (such as trees, buildings or other obstructing-reflecting surfaces).


Hope it will be useful for you

Wow! Way too many people confused here.

I’ll start off by stating that the 30/60/150/300 Mbps BH units utilize two transmitters and two receivers in each radio. Hence the two connectors marked horizontal and vertical on the bottom of the connectorized units. These radios use this method to ensure that enough signal gets to the other end for an adequate link. Both polarization contribute greatly to the link. The radios even have stats for the ratio between the horizontal receive and the vertical receive making it easy to tell if your antennas are in optimal alignment and whether one path is better than the other in terms of fade, diffraction, reflections and multipath(especially important in microwave radio).

If we use one antenna at one end (dual polarized) and two antennas at the other end (in my case bottom horizontal and top vertical) you give the two RF paths slightly different angles of diffraction (?). Therefore, should the atmospheric or ground conditions be such that fade or greater diffraction loss is experienced, chances are that the fade will different at each level - anyone that has worked on microwave radio knows that effects from multipath can usually be overcome by moving an antenna as little as a couple of feet up or down (this can easily be seen in computer RF path modeling).

So, why do we use two antennas at one end? In case we get some fade, we hope that the fade will only affect one of the paths (hor/vert) and our wireless link, while slowing down a little, will still exist.

more than 1 Km is consider for me as a "long distance"

Hmmm… my longest path right now is 72.9 km (according to the radio haha). This summer I will be comissioning a path that is >85 km - both with space diversity. My shortest link with space diversity is 54.2 km. My longest path that I am not using space diversity on and have integrated antenna units is 33.3 km.

Is there a minimum distance between the radios that should be considered? I’m pretty sure you are referring to the space diversity antennas at one end since that is what we are talking about. An Alcatel document that I have states that the distance should be ~200 wavelengths. If anyone has read this far in this post I can send a copy of this document if someone would like it (Path Protection for Digital Signals). Also, if anyone thinks or knows that I am full of sh!t and said something wrong here, please correct me. I am not an RF engineer, just a guy that’s been doing this for a long time (and I don’t mean writing this post). :smiley:


Aaron

Also, if anyone thinks or knows that I am full of sh!t and said something wrong here, please correct me. I am not an RF engineer, just a guy that's been doing this for a long time (and I don't mean writing this post). Very Happy


I think you got it pretty good. The only thing I would add is that Orthogon designed those radios to work well in a multipath environment.

# Multi-Beam Space-Time Coding – minimizes signal fading due to path obstructions or atmospheric disturbances

# Intelligent Orthogonal Frequency Division Muliplexing (i-OFDM) – transmits data on multiple frequencies, resulting in higher channel bandwidth and greater resistance to interference and signal fading

# Advanced Spectrum Management with i-DFS (Intelligent Dynamic Frequency Selection) –
self-selects the frequency over which it can sustain the highest data rate at the highest availability

# Adaptive Modulation – continually optimizes modulation to transmit the maximum amount of data across the path while maintaining the highest levels of link quality

# Spatial Diversity – combats ducting and multipath fading via space-diverse antennas at one or both ends of a link

I have been running a Motorola service center for the past 10 years but by no means am I an RF engineer either. I do have alot of experiance though.

I have not used space diversity on the BH's yet that is why i curious. I have several links up and the longest two are 73km and 79km. On both links I am using Gabrial 4ft High perf Dual polerized Quickfire parabolic dish's with 34.3 dbi gain. I have also ran numerous path studies with diffarent programs. The links are right on for what the Link estimator tool indicates. [/quote]

attitude,

We have alos been a Motorola service center for around 20 years - I’ve been here 11. I use the same dishes. I find they perform wuite nicely. We do have problems with Spring fade in our area. I expereienced horrible fade on one path (>20 dB) a number of years ago. That is why I engineered this new network with lots of rundundancy in it - to cover my ass. :lol:

Any thoughts on what changes Motorola will make now that they own Orthogon?


Aaron

I misinformed you of my links they are at 73 and 79 miles not km or about 117km and 127km. They run at 64QUAM 7/8 99.90% of the time but I am down about 5Mbps either direction. At 99.90% when they do fade they drop to 64Quam 3/4 and i loose another 5Mbps that is why i was curious about your setup and results. The 117km link is pretty stable but i loose a little bandwidth from interferance at one end of the link due to too mutch 5.7 on the tower. I am in the process of eliminating some of that though. On the 127km link I could go to 6ft dishes or find or build a tower in the middle to reduce the distance, but am always open to suggestions. As far as the aquasition of Orthogon. I went to Orthogon’s school on those radios and most of the engineers came over from Western multiplex, or Lynx. I think it is a good radio and i guess so did Moto. I just hope it gets better instead worse.

acherman wrote:
Wow! Way too many people confused here.

I'll start off by stating that the 30/60/150/300 Mbps BH units utilize two transmitters and two receivers in each radio. Hence the two connectors marked horizontal and vertical on the bottom of the connectorized units. These radios use this method to ensure that enough signal gets to the other end for an adequate link. Both polarization contribute greatly to the link. The radios even have stats for the ratio between the horizontal receive and the vertical receive making it easy to tell if your antennas are in optimal alignment and whether one path is better than the other in terms of fade, diffraction, reflections and multipath(especially important in microwave radio).

If we use one antenna at one end (dual polarized) and two antennas at the other end (in my case bottom horizontal and top vertical) you give the two RF paths slightly different angles of diffraction (?). Therefore, should the atmospheric or ground conditions be such that fade or greater diffraction loss is experienced, chances are that the fade will different at each level - anyone that has worked on microwave radio knows that effects from multipath can usually be overcome by moving an antenna as little as a couple of feet up or down (this can easily be seen in computer RF path modeling).

So, why do we use two antennas at one end? In case we get some fade, we hope that the fade will only affect one of the paths (hor/vert) and our wireless link, while slowing down a little, will still exist.




Hi Again,

So let's say if I attached a single dual-polarized Antena to the BH unit, it will transmit both horizontally and vertically ?

That is correct both vert and horiz.

One last question,

If I decided to use a single dual-pol antenna on the unit, which connectors should i connect it to , the vertical or horizontal one ?


Many thanks

Both. Vertical to the vertical connector and horizontal to the horizontal connector.


Hmmm... my longest path right now is 72.9 km (according to the radio haha). This summer I will be comissioning a path that is >85 km - both with space diversity. My shortest link with space diversity is 54.2 km. My longest path that I am not using space diversity on and have integrated antenna units is 33.3 km.


Hi Aaron,

Could you share some info on how you achieved 33.3 km with integrated antenna ?

Thanks
Uli

40km could be done by using the integrated antennas if you have line of sight.

You can download a claulator from motorola which given gps-cordinates will tell you if you have LOS and also what bandwidth you will get, you can then modify the antennas to start seeing how to increase the bandwidth.

We worked with a company to gread a 95mile link over the sea (connecting 2 islands) using 8ft antennas (2 on each side) solid as a rock, we had to be high on both sides to compensate for curveture of earth, again calculator will do that for you.

let me know if you need more help in using the calculator or get me the GPS co-ordinates for both sides and I will send you the .XL files.

Exactly what vj said - you will need line of sight to get longer paths with integrated antennas. My 33.3 km path is clear RF LOS.

Site 1: El. 4777 ft AMSL, Radio 200 ft AGL.
Site 2: El. 3179 ft AMSL, RAdio 140 ft AGL.

I also recommend using the path calculator for all of your links (unless you “know” they will work).

I have one path that is 63.6 km, 2 - 8 ft dishes at one end and a single 4 ft dish at the other - I can’t get any better than -78 dbm. But I know this link is line of sight - I see it everytime I am at site. Every path calc I use says it should work better. I have tried everything I know to get this link better (hence the 8 ft dishes) but no luck. This link has frustrated me for years :? (since we put in the original dual T1 link, was flakey from the start). :frowning:


Aaron

Acherman you definitely got an issue. I have a 117km shot using 1 4ft dual polerized dishes at each end with a -65 and a 128KM shot with 1 4ft dish at each end at -61.9. Is the spectrum clear?

Oh don’t worry, I know I have an issues!! :shock: haha

The spectrum is very clear. I also have a 72.9 km shot going into that site - dual pol. 4 ft dish at each end, near LOS (visual LOS, but bad fresnel encroachment near one end) and I have -66 dbm at both ends. WTF?!

As I said, I have fought with this link for 4 years now. I have changed everything, including the feed elements in the dishes (maybe I should paint the face of the dishes with chrome paint :lol: )

It’s like there is a blacj hole in the middle that eats the RF. It makes me want to cry. :evil:


Aaron