Having trouble initiating a link?

I'd like to start this post by asking for forgiveness in any ignorance I may be about to display. This is my first PTP820 link and there are still many things I have to learn about the platform as it is vastly different than anything I've dealt with in the past. 

We have two PTP820S radios that operate in the 11 Gig band. I got them to link on our bench without any antennas so I feel that I have most likely programmed the radios properly, but I am open to the idea that I have overlooked some detail. The only thing that was changed after I had them linked on the bench is the license key was applied. 

We attached the radios to the antennas and mounted them on their two respective towers. One has a radio waves 2' dish, one has a Commscope Andrews 2' dish. 

Site A is a free standing tower. Site B is a water tower. Pointing to site B from site A is very easy as the water tower is clearly visible. 

However, pointing from site B to site A is very difficult. The tower just barely peeks above some trees, but not up above the horizon behind it. We have had very humid days, and very foggy mornings. and the haze is too heavy for me to see the Site A from Site B even with good binoculars. To clearify, we do have LOS. I am just not able to find the tower with my eyes due to weather conditions, and the size of it that is visible in coorelation to the vast expanse it's hiding in. It's like the most intense game of Where's Waldo I've ever taken part in. 

I've climbed the water tower 8 or so times this week and several hours at the top trying to point this thing. We've been doing very slow long sweeps at varying elevations, but still the radios do not link. I realize this is probably the most amature way to try and do this, but I am just that; an amature when it comes to these radios. 

The only other PTP links that I have set up have been rocket Dishes that link whe n you get within about 20 degrees of your heading and fine tuning from there is fairly easy. I would assume the licensed link dishes have a much more narrow focal point, but that is an assumption. 

It's obviously entirely possible the issue we have here is a pointing problem. BUT I am beginning to think that it may be something else because as mentioned, I have now spent hours at the top of the tower planing back and forth a degree or two at a time with a long pause in between awaiting a link initiation. 

I guess I'm just looking for any pointers, advice, or other input. 

Other notes:

Radios are set to lowest modulation, and highest transmit power. 

They have ATPC disabled.

Link is 8.5 Miles. 

Link calculator says we should be at -43.

Have you run a path in Link Planner? Do you know the Azimuth each antenna should point to and their respective tilt angle? If you know them then you can try that (even if you cant visually see the other site). A 2 ft 11GHz dish like Radiowaves HP2-11 have 3.4 degrees half power beamwidth (according to their spec sheet). Your antennas arent cross polarized are they?

One set of installers I have worked with was incredibly fast--I asked them how they aligned so quickly.

They write the bearing (from the LINKPlanner installation report, taking the magnetic declination into account) with a  permanent marker on the antenna, and then when they are on the tower, they point the antenna in that direction with their compass. (Suunto makes a good compass/clinometer: http://www.suunto.com/en-US/Products/Compasses/Suunto-Tandem/Suunto-Tandem-360PC360RD1/

The guy at the top uses a volt ohm meter plugged into the BNC connector to measure the RSL (remember that the lower the voltage, the stronger the signal), and the guy at the bottom logs into the web page to confirm the RSL.

Be sure that both radios are unmuted, running identical scripts, set to lowest modulation mode and highest allowed transmit power, have ATPC disabled, have identical link ids, and the link should come up.

I hope this helps!


We have used the linkplanner to get an Azmith and use a Suunto compass to point many of our radios but I've found it to be wildly innacurate when atop a tower or other large metal structure so as of now, that hasn't been used. We did have someone on the ground walk out from the tower, find the heading with the compass on the ground, and position themselves between the heading and the tower giving us a marker to shoot for but of course that has a high margin for error, and is probably not very accurate. 

We haven't yet been able to get the radios to link so as of now using the volt meter on the BNC connector is a moot point. Many I have talked to that have set these links up in the past report the Volt meter method to be a bit troublesome and most have reported using the GUI to watch the signal. Either way, we haven't gotten far enough for that to be a problem.

Both radios are unmuted and as mentioned running the same scripts, with max transmit power. I'm 99% sure I have them both oriented Vertically.

We did find the radio on the tower was pointed down a bit, have adjusted that to the elevation LINKPlanner suggests. And are now waiting to climb the other tower and try to repoint again. We've had consistent days in the 90's with insane humidity the last few days so the climb has been put off. We're hoping for a temp drop on Thursday to try again. Luckily this project isn't super time sensative. Though, after all the money spent on radios, dishes, mounting equipment, and licensing, coupled with the intense effort we've put forth to get both of these radios mounted in their respective locations (you wouldn't believe how we got the Radio waves dish and the 10' mast it's on to the top of our tower) I'm eager to get the link dialed in and do some testing with it. 

Thanks for the pointers guys! I'll do my best to update the post when we get a link.

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These are excellent observations!

We wish you all the best.

If you like, I can review your LINKPlanner file and provide additional feedback (if needed).

The forum has a private message capability--feel free to send it on.


Update: The cold front moved in a day early and I went and climbed both towers and repointed. It was a nice clear day and with good binoculars the Difficult to see tower was slightly visable.

For the first time since hanging these bad boys I feel confident that they are pointed about as well as they can be until a link has been initiated, however we are still not established. :(

Which leads me to ask two questions;

A) Do these radios need to be affixed to absolutely still standing objects? The water tower is a mono pole and sits empty. It does have a fair bit of sway to it when the wind is moving. The free standing tower also has some sway to it. Hitting a 3 degree target at 8.5 miles is difficult enough, let alone if both objects are moving... Is this a deal breaker? Does it add an extra layer of difficulty? Or does it have a minimal and negligable impact?

B) In the 11gig spectrum what kind of impact does fresnal zone obstacles have? I do have LOS to from either tower, BUT just barely. There's a hill with tall trees between us and the tower, and while I can clearly see the top portion of it, it's just barely peeking up over those trees. We've had great performance out of our current 5.8 ePMP Backhaul that currently  bridges this gap, so I assumed the 11 gig would be no problem... Perhaps that was a poorly formed conclusion to draw.

A) A typical maximum allowable sway, in degrees, is given by 18 / fD, where D is the antenna diameter in meters, and f is the frequency in GHz.

(Please see Microwave Transmission Networks, 2nd Edition, Lehpamer, page 326, and Digital Microwave Communication, Kizer, page 169. Both of these books reference ANSI/TIA/EIA-222, which allows a 10 dB loss of received signal level due to antenna structure twist or tilt under standardized wind and ice loading.)

If you scour the internet, you can find additional information about ANSI/TIA/EIA-222 and its recommendations.

B) At least 60% of the first Fresnel zone must be clear. You can use Google earth to see if there are any obvious obstructions: trees, buildings, mountains, etc., but nothing is a substitute for a good path survey. You need to know how wide the first Fresnel zone is at its maximum, and whether or not anything encroaches into that zone.

(The LINKPlanner User guide has excellent information about the Fresnel zone. For a thorough understanding of the Fresnel Zone, refer to ITU-R P.526.9. You can also see Microwave Transmission Networks, 2nd Edition, Lehpamer, pages 58-61 and this link for more information: https://en.wikipedia.org/wiki/Fresnel_zone.)

If you scour the internet, you can find additional information about the relationships between licensed microwave and the first Fresnel zone!

I hope this helps!


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A little update:

We employed the help of another WISP we work with that's set up quite a few of these links. They came out, checked orientation, pointed, and finally tried a loopback test.

One radio is showing an RX Level of (-40) and a Modem MSE of (37~37.3)

The other radio is showing RX Level of (-40) and a Modem MSE of (-99) (screenshot attached)

He informed me this indicates a radio that is unable to hear and would explain why we weren't getting a link.

So we took the radio down, I brought it to the office with the intent to pack it up and start an RMA proccess.

Out of sheer curiosity I decided to do some testing on the bench first. Low and behold when I run a loopback test at the office (with the same PSU we had at the base of the tower) it's showing an MSE nearly identical to the other radio. 

We thought maybe it was an intermittent problem. I left it on repeatedly testing the Loopback. All showing good numbers. 

Problem solved right?

So I climb the tower and remount the darn thing and still no link. So we run a Loopback which is showing -99 on MSE?!?! 

I cannot make heads or tails of it. We used the exact same cable at this tower as our other site, the site with the issue is about 50' or so more of cable. The radio is grounded in the same method as the other one.

I'm at a bit of a loss. I tried the loopback test with the radio off of the  antenna as well with no luck, not that I thought it would make a difference. 

An y ideas? We're almost out of our 30 day warranty and am not realy sure what to do.

Contact customer support for an RMA!

I’m sorry this has been so difficult!