Transparent Pressure WIndow

Hello, on the PTP820 installation guide ( ), Section 7-2 for a 1+0 installation direct mount, there is a caution not to remove the transparent Pressure window from the antenna interface.  Is this the light-blue tinted plastic peice?  IF so then I think my installation crew on a recently installed link remove it on the interface from both ends of the link.

I've been battling a slowly degrading 23GHz link for the past month (was installed 30 days ago) and many people are suggesting either moisture ingress, or the crew out in the Texas summer heat had some sweat drip into the areas that are sealed up.  However, the link didn't start out bad, it just got progresively worse to the point where now the link is dropping. The relative humidity in this area is generally always between 50% an 100%, and ambient temperatures generally are typically mid 70s (Fahrenheit) for nighttime lows and mid 90s for highs.  I'm wondering if there is moisutre getting inside and then when it cools off at night, the vapors condense inside, gradually, and degrade the signals.Then when it has heated up the next day, it gradually vaporizes again, improving the signal.

IT's also possible that they did not mount the radio to the dish correctly, didn't seal correctly, etc.



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Heya LG,

The light blue tinted piece of tape came off the annenna wave guide, not the radio. The radio itself has a clear mylar cover over the waveguide. This is the pressure window. I cant imagine an installer removing this, but than again I don't know your installers.

As for moisture ingress... IDK. I can't imagine sweating into a radio, the connectors are all facing downwards.

Are you familiar with how to perform a loopback test? I would start there. There are some other threads on this community on how to perform the test.

Best of luck, and let us know the outcome. It help us all out.

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Thank you for the reply.  I went back and found pre-installation photos of the parts I had and now recall the pressure window being in the radio.  It came shipped ready for vertical polarization, which is what the license/design called for, so they did not even have a need to remove the screws to get to the pressure window.

I was present with the installers when the assembled one end of the link, they did not remove the pressure window on that end, I doubt they did on the other end either.

I did perform a loopback test this morning a couple of times from one end (other end is unreachable and did not have anyone to drive to the other end and test for me.

So for one end of the link here are the results of teh loopback test:

Operational Tx Power: 17 dBm

Rx Level: -45 dBm

MSE: -39.12 dB to -39.11 dB on first test -39.27 dB to -39.20 dB on second test.  Tests were performed a couple of hours apart.

No deffective blocks.

Note that the far end transmitter was NOT muted during these tests as I was not able to get someone to physically go out and mute/power it down, and also the link was not reliable enough for me to remotely access it and mute it.



Well that looks acceptable LG for one end. Hard to say with all certainty without having the other end muted.

Get someone at the other end and run the full swag of testing loopback with mutes on each end and let us know.

Out of curiosity, when the link was installed, did you get the signal levels the link planner doc predicted?

I believe LinkPlanner predicted during path alignment to see -34 +/- 4dB, and at installation time both were at -38 dB.  Although within spec, I'd have liked it to be a little better.  But a lot of things about this link were less than ideal.  We were given a pair of wood utility poles to mount to and it was questionable as to whether or not there would be line of sight.  Once we got up on the lifts we determined there was indeed line of sight, but the path goes right over a large-diameter tank and some trees, both of which may be fresnel encroachers.  

Having very little experience with these, I started watching signal strenghts every day just to keep an eye on it, expecing the utility poles to blow around in the wind or otherwise shift in soft ground.  What I actually ended up seeing was receive signals seemed to correllate directly with ambient air temps.  I only had public weather data to go by as opposed to data at my exact location, but as ambient air temps dropped towards the end of teh day, signal strengths started to drop as well.  Not a sudden drop, but a smooth drop, the difference between the highest and lowest signal strengths for the day being easily 5-7 dB.  Once the sun came up and everything started getting warm the next morning, signal stregnths would improve. In all of the weather data I looked at for 10 days solid, the relative humidity was 50% at the lowest, 100% at the highest.

I expected wind would have been my biggest enemy but may not be the case.

It was just installed about a month ago, but every day, that range would drop around 1dB.  Meaning day 1 my range was (example, don't have all the real data) -38 to -43 dB, day 2 my range was -39 to -44 dB, day 3 my range was -40 to -45 dB.

One end of the link seemed to be dropping a little faster/worse than the other, and it also seemed to have the range grow quite a bit.

Along with the decreasing signal strengths was increasing MSE at both ends.  

The last time the link was reliable enough to see the far end, the the far end RSSI was more around 

Several folks have told me to check for moisture ingress.  I'm puzzled as to how the seals could be installed wrong or radio mated to the dish incorrectly, but I guess it's possible.  

Tomorrow I have a crew going out to inspect both ends, and take a can of compressed air with them among other things.  I plan to be there and can redo loopback tests with appropraite transmitters muted.



Mother nature got in the way of deploying a crew today.  It may be several more days before I'm able to get this done.

In the meantime, for those who like graphs, I have several days worth of RSL data from radios at both ends of the link.  The data is from a few weeks back, when the link was still functional.

Notes on the chart:

  • I'm not very good with Excel Charts, so please excuse the amatuerness of it
  • There are a couple of places where I somehow didn't pull the data for one or both radios:
    • 8/23/2019 - 9:30 to 23:00 there is zero data
    • 8/29/2019 - 16:00 to 8/30/2019 - 10:45 there is only data for one of the radios
  • 8/28/2019 at approximately 13:30 was a utility power failure at one end of the link.  The outage occured just before 13:30 and resolved just after 13:30, which is why both datapoints show the lowest RSL is in the noise.
  • Light green trace = Radio 2 - Max RSL
  • Dark Green Trace = Radio 2 - Min RSL
  • Light Red trace = Radio 1 Max RSL
  • Dark Red trace = Radio 1 Min RSL




This issue has been resolved.

Drumroll:  The alignment was bad. 

Fix action: completed a path alignment.

Result: Recieve signals at both ends of the link were improved to a state better than the original installation, and have been stable for three (3) full days. Stable means strong enough that the transmitters have not had to automatically increase the power at either end.

Notes for others to learn from:

Both ends of the link were installed on wood utility poles.  I knew going into it that they would wobble and wind would blow them around.  However, I do not beleieve the wind directly caused the dishes to change azimuth.  I beleive the wind provided enough load on the the dish and pole that the pole oscilated (wobbled) with a high enough magnitude that the dish mount, which was off-center (unbalanced) on the mounting pipe, gradually changed azimuth.  This occured in teh dishes at both ends of the link.  After the crew re-aligned, they made sure to apply a lot more torque to the fasteners on the mounting clamps.  The wind will continue to cause temporary misalginment, but so far the receive levels have been between -37 dBm and -45 dBm, and MSE have been between -38.8 dB and -40.4 dB.  At original installation time, my RSL and MSE had already become worse within 3 days of installation.

Long story short: If you can avoid installing these on wood poles or anything else that behaves like a spaghetti noodle, then avoid it.  If you have to, be prepared to have a lot of clamping force, or come up with a way to stabilize the dish mounts.

We did not even remove the radios from teh dishes to check for moisture as realigning quickly brought everything back to a better-than-new state.

Thanks for everyone's considaration and help viewing.