Possible UHF interference in west Las Vegas?

[LVThumper]

Greetings - complete newbie here. I operate a data repeater network on a licensed frequency in the 450-460Mhz range. It's been quite stable for the past fifteen years - I didn't have to do anything so I didn't have to learn anything.

The past week or two it seems like many of my sites are having problems communicating. The problem area is around West Charleston & Buffalo. Anyone aware of something that would be affecting me? I took a handheld out there, a real high end unit...Baofeng UV-5R... , and all I initially heard were the intermittent packet bursts from my radios as normal. The masters they're communicating to are primarily in Summerlin, a little west of the Summerlin hospital.

And...actually I've got other units on the west side, both north and south, also having problems communicating with my Summerlin masters - yet units on the east side (with higher gain antennas) are still able to reach Summerlin. It's like there's a bubble blocking communication within a local area yet signals are able to leave that area

I don't know how to identify the source of the interference - if there is interference. Since about 12 radios suddenly all have problems communicating at the same time I doubt it's equipment failure - I'm assuming there's something environmental about it even if it's just construction. I'm just not seeing anything obvious yet.

 

[prcguy]

Get a spectrum analyzer or SDR with spectrum display and see if you have any signals on your operating frequency or repeater input. If you see anything then use a directional antenna to locate the source.

 

[rr60]

Another consideration. Events. Any special events visiting that use allot of spectrum? Like the F1 race?. Sometimes these problems can arrive and then depart. I have seen this in the past with NYC Fleet Week. Also perhaps check the FCC database for any STA’s that may have been granted that could impact you. Good luck!

 

[Rozie45]

I'm sure it's the race. I'm a former (retired) freq coordinator (primarily broadcast). I have zero direct knowledge of what freqs are being used for the race, but I'd bet the pension on the fact there are thousands. This includes two way, wireless mics, telemetry, microwave, etc... Needless to say that the mixing of the freqs generate harmonics. Yet another cause of interference...

If it's still there after the race people have left, find out who the local freq coordinator is for two way operation and let him/her know what's going on.

Good Luck.

 

[Rozie45]

Forgot to mention...My guess is that the NAB (National Association of Broadcasters) provides for the frequency coordination of large broadcast events (The race being exactly that). With a little research you should be able to find out who that person is. They may be able to help as well.

 

[LVThumper]

Appreciation to all who replied. It's quite possible it's race related - though I'm confused as to why a section of Summerlin would be affected given the race area.

Practically speaking I probably do need to start playing with a spectrum analyzer. Suggestions? Should I start with a USB dongle and SDR#? Or is there an inexpensive one I should explore on eBay or elsewhere? This isn't a tool I *hope* I'll need to use often.

 

[Rozie45]

When I did freq coordination for the NFL, they, (NFL) gave us a Rhode and Schwartz spectrum analyzer. I forgot the model, but it was portable and excellent for what we used it for. It was about the size of a fat tablet.

I own an analyzer made by RF Explorer (Official RF Explorer home). They have some very moderately priced units. Clearly not of the caliber of a Rhode and Schwartz, but still can be helpful. IF you do get one from rf explorer, download the software package for that model (much better). Google something like "portable RF analyzer." There are quite a few out there now-a days. If you're innovative enough, you can craft, or purchase a hand held yagi, or some kind of directional antenna too. Analyzers are always a good investment. They're a tool...if you have the tool you'll use it more often. Pretty much, this is all about budget, and what's it all worth to you.

As far as location vs interference, keep in mind that your repeater(s) may have very good hearing, and can pick up signals from a pretty fair distance...not to mention all the mixing and harmonics associated.

 

[LVThumper]

Well - still not finding any obvious interference. Don't hear anything at my sites with receiver - and don't see anything on the spectrum analyzer (I got a TinySA Ultra). Sigh. Maybe there's new building somewhere affecting LoS but I'm just not seeing it. Next step might be to play with a Yagi antenna.

 

[devicelab]

Did you check the 150-155 Mhz range? Specifically the pager freqs around 152? A high power transmitter may be screwing with your signals... and since they're usually intermittent, they can be a pain to track down.

 

[LVThumper]

No I didn't - since my target freq is 450Mhz I was watching from 440-480. I didn't think other freqs could affect me. Is that likely?

 

[737mech]

Seems weird but yes, that why many scanner users install fm trap filters to notch out the powerful FM radio stuff. You need to find the problem freq and then filter it out. There are many notch filters and also band pass filters you can try. Notch cut it out band pass only listen to the band you want.

 

[devicelab]

Seems weird but yes, that why many scanner users install fm trap filters to notch out the powerful FM radio stuff. You need to find the problem freq and then filter it out. There are many notch filters and also band pass filters you can try. Notch cut it out band pass only listen to the band you want.

Yeah that's where I'd start too. I don't think it'll be a FM BCB issue but you never know. Tight UHF bandpass filters are somewhat hard to find but every once in a while they show up on E-Bay. I got lucky and found one earlier this year -- K&L Microwave. Its CF is 460 mhz and is usable from 448-472 Mhz. Works great. Do a search for "tubular bandpass filter 460" and you might find one.

You can try Minicircuits and see if they have something similar.

Here's a decent bandpass filter: Lumped LC Band Pass Filter, 410 - 470 MHz, 50Ω | ZX75BP-440-S+ | Mini-Circuits

This HP filter is really wide but it be worth a test: Lumped LC High Pass Filter, 395 - 3200 MHz | BHP-400+ | Mini-Circuits

PS. How much DMR do you have in the area? You might be just seeing an increase in digital traffic and that can easily stomp on your RF signals.

 

[WB5UOM]

2nd and 3rd harmonics from a VHF paging transmitter can be nasty.
The 3rd puts it in 450 range. And the 2nd can couple with another vhf to put it in 450-460.
not saying this is your problem, but it can happen

 

[devicelab]

2nd and 3rd harmonics from a VHF paging transmitter can be nasty.
The 3rd puts it in 450 range. And the 2nd can couple with another vhf to put it in 450-460.
not saying this is your problem, but it can happen

152x3 == hmmm

Yeah a dirty paging transmitter could be causing these issues but (usually) those [bad transmitters] stand out and are not around very long. I think it's more likely just an increase in digital noise -- DMR/NXDN, and the traffic is stomping on his channels. Business band UHF is often shared among multiple parties.

 

[LVThumper]

Hmm...I'm still floundering trying to find something. Would posting an image of my spectrum analyzer show anything to you?

What's weird is the interference is basically constant - units that used to be rock-solid reliable no longer communicate. Doesn't matter time of day. I would think that if my problem is a 3rd party transmitter there would be bursts of interference and windows of open communication - unless there's something that's a constant digital signal? But I didn't think that existed in this freq range (or wasn't supposed to).

 

[devicelab]

What's weird is the interference is basically constant - units that used to be rock-solid reliable no longer communicate. Doesn't matter time of day. I would think that if my problem is a 3rd party transmitter there would be bursts of interference and windows of open communication - unless there's something that's a constant digital signal? But I didn't think that existed in this freq range (or wasn't supposed to).

Sorry there are so many possibilities here and without knowing your exact configuration it's impossible to say.

 

[bryan_herbert]

Did you check the 150-155 Mhz range? Specifically the pager freqs around 152? A high power transmitter may be screwing with your signals... and since they're usually intermittent, they can be a pain to track down.

I dont think theres any VHF/UHF pagers left in the country except for a select few 155, 157, 158, 454 and 459 MHz on-site hospital pagers. I also found a medical paging system near the medradio freqs (462 MHz) a couple years ago. Other than that, all paging systems were migrated to 900 MHz over a decade ago before being made obsolete by smartphones.

Still, a dirty or high powered paging system wouldnt account for constant interference when paging transmitters arent constant especially these days when theyre almost nonexistent.

 

[RFI-EMI-GUY]

Hmm...I'm still floundering trying to find something. Would posting an image of my spectrum analyzer show anything to you?

What's weird is the interference is basically constant - units that used to be rock-solid reliable no longer communicate. Doesn't matter time of day. I would think that if my problem is a 3rd party transmitter there would be bursts of interference and windows of open communication - unless there's something that's a constant digital signal? But I didn't think that existed in this freq range (or wasn't supposed to).

Have you checked your own terminals? Years ago I was grabbed to look at a transit data system, Motorola MetroCom. The system was just being turned up and worked fine one train at a time.But when they loaded it up, the polling failed. I found one train was sending a dead carrier for a few hundred milliseconds after it had responded to a poll. Whatever train followed was stepped on and data garbled. The fix was rather simple.

 

[LVThumper]

My thanks to all who replied here. The site in question has gone with another vendor - so now it's Somebody Else's Problem. None of my other sites around the valley are experiencing problems - so it is indeed possible one or more of the site transmitters were the culprit.

This stuff is so weird. I have some units with paths of over 15 miles with their line-of-sight literally blocked by a mountain range - and somehow the signal gets through/over/around perfectly fine. Other units that should have short clear transmission paths need all kinds of mystical prayers and spiritual intervention to get a signal through. I'd like to actually understand, at least partially, some of the hows and whys this stuff works or doesn't - but at the moment what's important is that those units my customers are paying for are working correctly.

 

[vagrant]

knife-edge effect - TIA's Glossary of Telecommunication Terms