Yes there is interference on these towers (FM and TV) but nothing more than usual so, what is different
Long story short, if you are using good double shielded ethernet cable (braid and foil) with grounded connectors (as already mentioned), and still have this issue on towers that also have FM broadcast antennas, you will need ferrite cores installed at the radio ethernet ports.
Two weeks ago, we mounted an FM broadcast on a tower we use for the owner of said tower, and when it rains, we are seeing this with the 300 CSM and PTP550 (both do not have the "Smart Speed" option available, but not sure if Smart Speed would help). The 1000 AP's on this tower are not experiencing any issues.
This is a 240' AM tower that has been convertered to FM broadcast use (FM translators).
235'; Our 1000's
220' First FM antenna
205'; Second FM antenna
180'; PTP 550
140'; F300 CSM
130'; 900Mhz STL dish
All our equipment is using Cat5e with braid and foil tape (double shielded). Shielded/grounded RJ45's. Radios are bonded to tower. Ethernet surge protectors inside radio shack are bonded to copper ground bus which is ground to tower/electrical ground ring. This equipment, besides the CSM 300 has been up for at quite some time with absolutely no sync issues or even any real amount of ethernet errors. The 300 CSM has been up about 3 months with drops from 1G to 100M once or twice.
A few weeks ago, we installed the FM antenna at 220' and put in a 1400w FM translator running at 700w (purposely designed so transmitter can run for years with no stress). We installed FM antenna, with proper grounds at top, bottom, and in shack for hardline coax. We swept antenna and hardline before and after installation. Basicaly no reflected power, so we know a mismatch is not the issue. I know what RF at 150Mhz and below can do to ethernet data from experience over the years. I had the Netonix GUI open when we fired up the FM transmitter. Everything looked good as far as ethernet sync, and stayed that way for the rest of the day. The next morning I found the 300 CSM was at 100Mbps. I peformed "Port Bounce Link" in the Netonix GUI, which put it back at 1Gbps, only for it to fail back to 100Mbps later, and continue to do so every time I put it back at 1Gbps. This was not a huge deal as this 300 CSM is for back up. I figured we could dig into issue when we had more time to do so.
Fast forward to early this past week. It was raining, we get calls that evening from customers on this tower that video was buffering, slow loads, etc. Go to Netonix GUI for this tower (it was already up) and see the PTP 550 is now at 100Mbps and the 300 CSM is at 10Mbps, yes 10Mbps. The 550 is saturating the 100Mbps ethernet, hence the phone calls. I try a few times to 'Port Bounce Link" for the 550 as well, and it keeps going to 100Mbps. Try the same with the 300 CSM, and it keeps going to 10Mbps.
I ride out to tower that same night to verify it is the new FM translator. There is also a 900Mhz STL link on this tower to an AM array 5.5 miles away (same broadcasting format as the FM translator we also installed). We installed the 900Mhz STL the same time as the FM transmitter. I flip the STL off, attemp "port bounce" on both the 550 and 300, and no luck, both go back to 100Mbps and 10Mbps respectively. Drop power on FM transmitter down to 250w and boom, 550 will sync back to 1Gbps and hold. I can not remember if the 300 went to 100Mbps or not, my main concern then was keeping the FM transmitter on air and getting our 550 back to 1Gbps. I do know the next morning after rain had stopped and everything was semi-dry, the 300 would sycn back to 100Mbps. I go back to tower and by this time the 300 will sync to 1Gbps. I turn FM transmitter power back to 700w and the 300 immediately synced back to 100Mbps.
I come back to office and look through different ferrite core makers (Palomar, Fair-Rite, etc). There are formulas you can use to find cores that are just for the frequency of the FM transmitter (92.5, 101.3, etc). Those cores are special order many times. This FM transmitter is not a high powered station so I ordered these cores. They cover up to 250Mhz with the sweet spot around 100Mhz (FM broadcast band).
Cores came in Thursday afternoon. Was pouring rain all day (both units downgraded their sync once again). Yesterday we had damaging winds, so no go up the tower. Will go up Monday and get these installed as more rain expected next week. You can wind Cat5e with braid and foil 5 times around these cores (will need to file down some plastic tabs sticking into core hole). We plan to use 2 cores at ethernet input of 550 and 300.
I am 99% sure this will fix our issues. I have been in the communications field for over 20 years. We have had to use ferrite cores at 911 centers, communications towers, CCTV ,and SCADA systems, solar systems with solar controller inside radio shack. We have used them in police cruisers to stop two-way radio from ripping analog dash cam video a new one, to turning on warning lights on/off, changing lights pattern, etc. We have used these anywhere cabling ran near two-way radio antennas and we had issue with RF getting into other equipment. These baby's nearly always fixed our issues with RF bleeding into cabling of other systems. Sometimes we had to also upgrade grounding of effected equipment, wrap HVAC tape (foil tape) on sections of unshielded cabling of effected equipment to act as a shield, and add ferrite cores.
The 300 CSM at the other end of this link has no issues wth sync at all. But, it is on the catwalk of a water tower, connected to a Netonix switch with 20' of ethernet cable. We also have many 300-16/25's at customer locations with no sync issues.
I would almost bet money that if everything is properly installed and grounded (both yours and the broadcast equipment), that if you add some ferrite cores at input of radio RJ45 jacks, it will fix your problem.