-106dbm noise floor. Is this the new normal for VHF?

[70cutlass442]

Put a p25 system on the air today... to my surprise, I am seeing a -106-108dbm noise floor.

Is this just the state of high band in 2022? We are the only VHF system on the tower but now share the top of the water tower tiwh two cell providers.

 

[GTR8000]

VHF High is the new VHF Low. The noise floor is terrible.

 

[KevinC]

Couple of things...

Any RXMC? Maybe the gain is too high.

A couple of years ago I did a 3 subsite VHF P25 conventional simulcast and had a horrendous noise floor at 2 subsites. Tracked both down to corroded and/or oxidated lightening arrestors on power poles. Once they cleaned up/replaced those everything was good.

 

[70cutlass442]

Couple of things...

Any RXMC? Maybe the gain is too high.

A couple of years ago I did a 3 subsite VHF P25 conventional simulcast and had a horrendous noise floor at 2 subsites. Tracked both down to corroded and/or oxidated lightening arrestors on power poles. Once they cleaned up/replaced those everything was good.

No multicoupler on this. DB224 to about 180' 1/2", duplexor then repeater.

I can move this to a tower about a half mile away with no cellular, but ill give up about 100' of overall height. I'm going to take some measurements from there and see how it works.

It's not that it performs poorly, I just know it will be better if we clean that up.

This is a multicast system with the ability to add more rx sites

 

[12dbsinad]

Deal with it everyday. VHF is becoming almost unusable in my area. Probably crap at the site. Try putting a VHF system near one of those new LED dual red/white beacons... Learned that recently. Wipes the receiver clean off the face of the earth when it's on. Also POE stuff drives VHF nuts as well as pretty much everything these days. You may be better off 100' lower on a quiet site IMO. Good luck!

 

[WB5UOM]

as do wireless internet folk- if they put their switch up on the tower- or crappy cat-5
Had to have a very verbal not so nice conversation with one that raised Noise floor up to -100

 

[KK6ZTE]

Ubiquiti WISP equipment loves to generate noise at VHF as well...

 

[70cutlass442]

Ubiquiti WISP equipment loves to generate noise at VHF as well...

There is a ubiquiti LTU 5' from us

 

[WB5UOM]

Easy test- find the Owner and get them to turn their system off for just a minute...yes they will argue...or say it has to be done at 5am (which we did on my taste of this)....I sat up spectrum analyser showing elevated noise floor. at 5am (on Thanksgiving no less)...Wisp guy shows up and says-this wont take long as it can not be us....
He about died when he killed power and noise floor dropped like a rock.
Might be worth a try...

 

[a417]

There is a ubiquiti LTU 5' from us

thoughts and prayers.

 

[70cutlass442]

Easy test- find the Owner and get them to turn their system off for just a minute...yes they will argue...or say it has to be done at 5am (which we did on my taste of this)....I sat up spectrum analyser showing elevated noise floor. at 5am (on Thanksgiving no less)...Wisp guy shows up and says-this wont take long as it can not be us....
He about died when he killed power and noise floor dropped like a rock.
Might be worth a try...

We (the village) are the owner. I will have to work with IT to get that to happen. And to think I'm the ont that turned them on to Ubiquiti gear way back 🤦

 

[a417]

Power transients can be a *****, especially if they're singular in nature...and there's a spectrum analyzer running nearby...

 

[WB5UOM]

All I can say is they finally started working with me. They turned off the AP's....the 11ghz hop...the 5ghz hop..
noise still there...
I had already talked with FCC EB....and sent pics.... the EB guy agreed with me and I knew if he showed up the WISP site would likey get turned off...
Thats when the conversation turned colorful....but I was trying to keep them on the air but I was tired of playing...I told them what the EB guy said-and
they finally said "tell us what to do"...
lol got that Switch turned off and poof no noise

 

[RFI-EMI-GUY]

Put a p25 system on the air today... to my surprise, I am seeing a -106-108dbm noise floor.

Is this just the state of high band in 2022? We are the only VHF system on the tower but now share the top of the water tower tiwh two cell providers.

Sadly yes. I use much worse numbers for coverage planning. You should probably do some spectrum analysis to see if there is a contributor that you can get fixed. But the reality is that , you have all that man made noise.

 

[WB5UOM]

oh I missed the part about water tower top with co-located cell sites...that and a WISP is a recipe for VHF noise....
but still- just for giggles turn off the WISP Stuff....it wil be easy to see if thats the issue...
that was the situation I had with my 1st experience with this stuff. only 1 cell carrier the WISP and 1 vhf analog repeater

 

[Project25_MASTR]

PoE noise sources can be a problem for VHF. Noise floors are getting higher but occasionally you still find fairly low floors in places. I was discussing with a peer the other day one of my main dislikes for the VHF MASTR III/IV's when compared to a VHF Quantar which is roughly a 10 dB lower receive sensitivity but then I actually began assessing who bought VHF MASTR III/IV's and came to the realization that my best example of where it actually made a difference was the one outlier I've come across professionally in the last decade. Most of the guys who could benefit from the more sensitive Quantars due to being extremely rural with next to no noise floor...already had them as they were Ma/Com's prime market 20 years ago.

 

[xmo]

70cutlass442 wrote: "... I am seeing a -106-108dbm noise floor. "
-----------------------------------

In order to more clearly show how bad your noise situation is, you should state the noise in terms of a specific bandwidth.

How did you make this measurement? If it was with a spectrum analyzer, what was the RBW setting?

Spectrum analyzers usually have a noise marker function that reads out in power density (dBm/Hz) which is the best way to state your noise. This allows direct comparison to the thermal noise floor.

As others have stated, the VHF band is very noisy.

On a state-wide VHF system I worked on, the vendor used the TIA guidance on noise above kTB when creating coverage maps. They also recommended that the state test every site for actual noise level

 

[xmo]

Did you measure the effective sensitivity of the station receivers?

Knowing that and the receiver reference sensitivity along with any gains or losses from the receiver antenna input to the measurement point will tell you what the noise level is (with a little math)

 

[ElroyJetson]

I blame most of the elevated noise floor on switch mode power supplies. For good reason.

I spent some time working in engineering support at an avionics manufacturer, and one of the engineers was working out some bugs on a new VHF-AM aircraft radio that was his baby. I saw the RF spectrum of it and over its entire operating bandwidth (within the bandpass filtering limits) the noise floor was -60 dBM. That was the issue at hand. BARELY made FCC acceptance, functionally did not work due to generated interference to other radios. I took one look at the spectrum analyzer and asked, "You're using a switch mode DC source, aren't you?" He said yes. I then replied, "If it were me I would try changing the SMPS oscillator frequency to see how that affects the noise floor." He said he was about to do that.

Later in the day I walked by his work area and saw the same radio running, and the noise floor was way down. I asked him how the test had worked. He said, "Great. Just by dropping the oscillator frequency a few KHz the noise floor dropped 30 dB. Changed ONE capacitor, and everything about the radio works better now."

The preponderance of cheap Chinese switch mode power supplies in every consumer product is only making the average RF noise floor worse and worse.

 

[12dbsinad]

I blame most of the elevated noise floor on switch mode power supplies. For good reason.

I spent some time working in engineering support at an avionics manufacturer, and one of the engineers was working out some bugs on a new VHF-AM aircraft radio that was his baby. I saw the RF spectrum of it and over its entire operating bandwidth (within the bandpass filtering limits) the noise floor was -60 dBM. That was the issue at hand. BARELY made FCC acceptance, functionally did not work due to generated interference to other radios. I took one look at the spectrum analyzer and asked, "You're using a switch mode DC source, aren't you?" He said yes. I then replied, "If it were me I would try changing the SMPS oscillator frequency to see how that affects the noise floor." He said he was about to do that.

Later in the day I walked by his work area and saw the same radio running, and the noise floor was way down. I asked him how the test had worked. He said, "Great. Just by dropping the oscillator frequency a few KHz the noise floor dropped 30 dB. Changed ONE capacitor, and everything about the radio works better now."

The preponderance of cheap Chinese switch mode power supplies in every consumer product is only making the average RF noise floor worse and worse.

Bingo.

Just take a look at the cheap LED drivers. Those alone will make VHF (and even approaching UHF) useless, and that is just 1 product. Of course you can make them clean, but that increases R&D costs and nobody want to do that unless you need to meet some sort of spec