Powerline Interference?

[Captain Midnight]

Has anyone here noticed interference from nearby powerlines? I had my antenna up around 32ft and my local NBC on RF32 barely locks with around 16dB C/N. My CBS on RF12 is stable at around 25dB. My ABC on RF22 runs around 27-28dB at ~32ft. Antenna looks thru the powerlines around 45ft away.

When I lowered the antenna to check my connections, the signal on RF32 went up to 28dB, but RF22 dropped to 21dB and RF 12 dropped to 18dB...

I will attach my RabbitEars Report, but anyone here dealt with a similar issue? I guess I may need to just find the sweet spot for everything?

RabbitEars.Info

RabbitEars, where you can learn all about local, over-the-air TV channels.

rabbitears.info

 

[primestar31]

and my local NBC on RF32 barely locks with around 16dB C/N. My

IF that's really on RF32, it's far more likely your issue is with local LTE/5G towers. Try one of these as close to the antenna as you can get it, it works for me: LTE/5G Filter

Of course, looking at your report, the fact that there's mountain ridges in-between you and the towers doesn't help. That means most of your signals are diffracted, which means anything goes. Best signal could be on the ground, or anywhere.

 

[Captain Midnight]

IF that's really on RF32, it's far more likely your issue is with local LTE/5G towers.

Try one of these as close to the antenna as you can get it, it works for me: LTE/5G Filter

I'm using a Televes preamp with a 5G filter. I hope it is not dropping the ball

 

[primestar31]

I'm using a Televes preamp with a 5G filter. I hope it is not dropping the ball

IF your LTE/5G towers are close enough, that may need help, because the signals might be too strong. I'm using the same and also need that filter. It's power-passing also.

 

[Cham]

If your LTE filter is between the preamp and antenna would it have to be power-passing?

 

[Captain Midnight]

IF that's really on RF32, it's far more likely your issue is with local LTE/5G towers. Try one of these as close to the antenna as you can get it, it works for me: LTE/5G Filter

Of course, looking at your report, the fact that there's mountain ridges in-between you and the towers doesn't help. That means most of your signals are diffracted, which means anything goes. Best signal could be on the ground, or anywhere.

I have that filter and I will try it. Oddly enough, when my antenna is directly toward RF34, it's my best signal. I think it is likely the diffraction. My network signals have to bounce over a ridge. RF34 is coming over different terrain.

 

[primestar31]

If your LTE filter is between the preamp and antenna would it have to be power-passing?

No, unless the preamp is built into the antenna, and you couldn't put this in-between. In that case, it needs to be power-passing.

 

[Tower Guy]

I agree with your final assessment, you should look for a height that picks up everything. To understand what you’re seeing, read this and skim down to ground reflections. Siting the antenna
The trick is to try and find a single antenna height where none of your UHF signals are weak.

On your case I rule out power line interference because power line problems bother VHF more than UHF, and your VHF signal is working very well.

 

[Captain Midnight]

No, unless the preamp is built into the antenna, and you couldn't put this in-between. In that case, it needs to be power-passing.

I agree with your final assessment, you should look for a height that picks up everything. To understand what you’re seeing, read this and skim down to ground reflections. Siting the antenna
The trick is to try and find a single antenna height where none of your UHF signals are weak.

On your case I rule out power line interference because power line problems bother VHF more than UHF, and your VHF signal is working very well.

Thanks. I was under the impression that VHF suffered EMI more than UHF. I am also setting up a dual antenna system to cover VHF-Hi with a Stellar Labs 30-2476 yagi and UHF with a Televes DAT Boss LR. My current Channel Master Masterpiece 100 is just not cutting it for my situation. It was more than fine when I lived on a rural hilltop, but my location now is trickier.

So I have a lot of experimentation to look forward towards. I ordered one of those handheld spectrum analyzers from Amazon to really monitor my signals as I decide on the best height for best coverage.

 

[Tower Guy]

Your two antenna plan makes sense. Just use a UVSJ to combine them.

 

[Captain Midnight]

Your two antenna plan makes sense. Just use a UVSJ to combine them.

Got it covered. Lucky I found these for $2.49 each back in 2019. The ebay prices are ridiculous.

 

[Radioguy41]

I have a similar issue with mountains between me and the towers. What works for me is to angle the antenna upwards until it is pointing directly at the ridgeline. A ridgeline creates something called knife edge refraction. It bends the signals downward. I know a couple of people who actually installed an actuator motor to angle the antenna up and down remotely to find the sweet spot for each channel.

 

[Captain Midnight]

I have a similar issue with mountains between me and the towers. What works for me is to angle the antenna upwards until it is pointing directly at the ridgeline. A ridgeline creates something called knife edge refraction. It bends the signals downward. I know a couple of people who actually installed an actuator motor to angle the antenna up and down remotely to find the sweet spot for each channel.

I might try a slight upward angle. Both antennas allow it with the mounting hardware included. Thanks.

 

[Tower Guy]

Tilting an antenna upwards can improve signal strengths if the antenna is mounted either too high or too low. But, it’s better to aim the antenna horizontally and find the heights that get the strongest signal. Note that an antenna tilted upwards has less ground gain than an antenna not tilted and mounted at the optimum height. However, I’d suggest that tilting may be used effectively as a way to get good reception on multiple channels when the optimum heights for reception of each channel is significantly different.

 

[Captain Midnight]

I had to install directly on the mast. My pillow block bearing needs a mount bracket welded to try this on my rotor. (Shame you can't easily get a TV rotor support bearing...)

But the signals are booming in!

 

[Captain Midnight]

Signal Meter pictures for RF7, 12, 22, 24, 30, 32, 34, and 36...

24 and 36 come in and out, but no issue. I don't watch them.

All in all, everything is great. I'm just a little surprised that my ABC on RF22 is 15% lower than before.

 

[Captain Midnight]

Tilting an antenna upwards can improve signal strengths if the antenna is mounted either too high or too low. But, it’s better to aim the antenna horizontally and find the heights that get the strongest signal. Note that an antenna tilted upwards has less ground gain than an antenna not tilted and mounted at the optimum height. However, I’d suggest that tilting may be used effectively as a way to get good reception on multiple channels when the optimum heights for reception of each channel is significantly different.

Thanks for that info. I did a slight tilt. Results are fairly good. I am not comfortable on my ladder enough to tweak the tilt setting 3 or 4 times to find the sweet spot.

 

[Inclined Orbit]

A good way to diagnose your problem is with a spectrum analyzer and a cheap SDR with spectral display may work. You can usually see powerline zap noise as dancing spikes on a spectrum analyzer around your channels of interest which can confirm the problem or point you in another direction. Power line noise usually affects lower frequencies worse so RF ch 2 through 6 would be most susceptible with 7 through 13 to a lesser extent and ch 14 on up not so much. If its 700MHz 5G stuff the spectrum analyzer can point that out also by measuring the levels.

 

[Captain Midnight]

A good way to diagnose your problem is with a spectrum analyzer and a cheap SDR with spectral display may work. You can usually see powerline zap noise as dancing spikes on a spectrum analyzer around your channels of interest which can confirm the problem or point you in another direction. Power line noise usually affects lower frequencies worse so RF ch 2 through 6 would be most susceptible with 7 through 13 to a lesser extent and ch 14 on up not so much. If its 700MHz 5G stuff the spectrum analyzer can point that out also by measuring the levels.

My analyzer is coming tomorrow. Hopefully everything checks out fairly clean. I did a cell tower search. My closest one to my south happens to be on the same ridge my OTA signals are bounced off.

 

[Inclined Orbit]

I might add that the 200MHz range is common for power distribution companies to receive with directional antennas when sniffing for power line zap and its very effective. Several years ago I got hired to find interference to a C-band satellite downlink at a satellite uplink site in Marina Del Rey, CA. It started and stopped about the same time every night taking out a satellite receive feed. The first night of the exercise I was looking at the C-band feed inside the facility and at start time I instantly recognized the dancing spikes all through the C-band downlink range. Didn't have quite enough time that night to search outside but the next night we were armed with a C-band LNB with horn antenna up in a man lift and a 220MHz 4 element Yagi and spectrum analyzer that covered the 220MHz range.

At the typical interference start time we saw lots of interference out in the dish area with the C-band LNB/horn but it was difficult to pinpoint the source, but at least it appeared to be within the confines of the uplink site. Switching to the 220MHz Yagi and spectrum analyzer I quickly found a spot right above my head that was the hot spot for dancing noise spikes on the analyzer. It didn't make sense at first but someone with better eyesight than me pointed out the tall parking lot sodium type lamp right above me was dark but had an occasional little blue flicker inside. I grabbed something to beat the pole with, I think it was a long 2X4 and whacked the lamp pole while watching the 220MHz analyzer and the C-band setup and they both went off the screen with interference every time I whacked the lamp pole.

A quick call to the facility maintenance dept got a guy outside to disconnect power to the lamp post and problem was verified and solved. They scheduled a lamp replacement during the next maintenance window. Bottom line with my rambling story is don't overlook the range just above the 220MHz amateur band like 225-227MHz where a 220MHz amateur Yagi is still resonant with good directivity. This frequency range typically has no radio users with a quiet noise floor, is still within the range of power line zap and antennas are much smaller than for lower frequencies.