VHF High (2-meter) Modern Day Noise Floor

[n4dbm]

Is it just me, or does the 2-meter ham band seem to have less mobile-to-repeater coverage than it used to? I received my ham ticket in 1988, upgraded to Technician in 1991 so I could use the 2-meter band. Even as late as the mid-90's, driving to and from college with a 1/4 wave magnetic mount and a Yaesu FT-2400 mobile, it seems I could work much father distances to numerous high-profile repeaters in the mobile than I can now. Even in rural Eastern NC, it seems as if the noise floor has crept up until there's nearly a microvolt of noise just about everywhere.

I operate quite a few UHF FM ham repeaters and GMRS repeaters. I have three 2-meter machines, one is an MTR-2000 and the other two are Kenwood TKR-750's. Naturally, on the bench they receive extremely well with factory equipment (no preamps, etc) so we're talking 0.35 uV for a 20 dB quieting signal on the MTR-2000, and maybe 0.45 uV for the Kenwoods. With the duplexer attached and into a dummy load, I get a relative signal reference with a 30 dB directional coupler. Then, removing the dummy load and attaching to the antenna, an instant 8 to 10 dB degradation in receive performance due to the noise floor of the "outside world." Even at my quiet sites, the noise floor is around a -110. Maybe I'm wrong, but 25 years ago I don't remember the noise being this bad on 2-meters. 220 MHz is OK, and UHF is extremely quiet in my area.

Has anyone experienced or noticed this? I guess the sheer amount of wireless "garbage" out there where everything has a microprocessor running, it has caused the entire noise floor to rise as a whole, and it doesn't seem like much can be done to help it.

Your thoughts?
73, N4DBM.

 

[mmckenna]

I hear a lot of random crap on VHF in my travels.
Big offenders I've found:
Cable TV leakage
Fiber <-> copper conversion equipment run by the phone company.
I can drive down rural roads and I can hear where some of the service cabinets are before I see them.

I'm sure there's a ton more, but those are the big ones I notice. With all the cable TV systems and phone company equipment out there, it's probably part of the issue. Consumer electronics probably don't help.

 

[a417]

There was a thread on here in the past several years (damned if I'll find it now) that discussed how the relative noise floor has been rising over time. I would agree with you that it used to be much quieter many years ago.

 

[OpSec]

It's not your imagination.

 

[n4dbm]

35 years ago, our club ran a Yaesu 10-watt 2-meter machine with a Wacom WP-639 and a Hustler G7 in a relatively good HAAT location. Figuring that the (maybe) 5 watts reaching the antenna covered a tremendous area in the mobile now seems borderline unbelievable. It was also very typical for many hams in this area to run Icom 2AT's to 1/4 wave mag mounts running 2 or 3 watts and getting back into the machine just fine. A 10-watt mobile (Yaesu "Memorizer") worked exceptionally well. During that time, though, the amount of noise-generating devices in "open air" was minimal.

I did a very basic experiment, which was to run a signal generator into an "iso-tee" coupled to my 2-meter radio and vehicle antenna. The radio is a Motorola APX-8500. The signal generator was set to simulate around a 1-microvolt signal into the radio with first, the dummy load attached to the antenna port. After the reference was marked, the mobile antenna was attached, and the otherwise full-quieting signal diminished into a sea of hash just sitting in the driveway. I played with this for a few days and as I traveled around, the one-microvolt signal would many times drop completely out, and other times get relatively quiet for a short minute.

The noise floor at my main repeater site varies from day to day. Dry, windy conditions are always noticeable, because there's a 3-phase power pole close by that generates noise. During those times, it takes a comparable 2-microvolt signal to sound "good" into the machine. I've never seen it get any better than 0.5 uV on its best day. This is the MTR-2000 RX, DB224 antenna out the top of a 410 foot stick.

My well-meaning friends make suggestions of sharp pass filters and such, but I keep trying to explain, it isn't overload or desense from nearby transmitters. It's an elevated noise floor. You can't filter out broadband noise when it's on your own desired RX frequency.

Repeater is running 180 watts ERP at 410 feet HAAT on flat, flat terrain. Mobile coverage with a 1/4 wave roof mounted antenna is 35 to 40 miles in all directions. Seems like it should reach out a little further, and probably would, if the noise floor was diminished 10 dB.

 

[AB4BF]

35 years ago, our club ran a Yaesu 10-watt 2-meter machine with a Wacom WP-639 and a Hustler G7 in a relatively good HAAT location. Figuring that the (maybe) 5 watts reaching the antenna covered a tremendous area in the mobile now seems borderline unbelievable. It was also very typical for many hams in this area to run Icom 2AT's to 1/4 wave mag mounts running 2 or 3 watts and getting back into the machine just fine. A 10-watt mobile (Yaesu "Memorizer") worked exceptionally well. During that time, though, the amount of noise-generating devices in "open air" was minimal.

I did a very basic experiment, which was to run a signal generator into an "iso-tee" coupled to my 2-meter radio and vehicle antenna. The radio is a Motorola APX-8500. The signal generator was set to simulate around a 1-microvolt signal into the radio with first, the dummy load attached to the antenna port. After the reference was marked, the mobile antenna was attached, and the otherwise full-quieting signal diminished into a sea of hash just sitting in the driveway. I played with this for a few days and as I traveled around, the one-microvolt signal would many times drop completely out, and other times get relatively quiet for a short minute.

The noise floor at my main repeater site varies from day to day. Dry, windy conditions are always noticeable, because there's a 3-phase power pole close by that generates noise. During those times, it takes a comparable 2-microvolt signal to sound "good" into the machine. I've never seen it get any better than 0.5 uV on its best day. This is the MTR-2000 RX, DB224 antenna out the top of a 410 foot stick.

My well-meaning friends make suggestions of sharp pass filters and such, but I keep trying to explain, it isn't overload or desense from nearby transmitters. It's an elevated noise floor. You can't filter out broadband noise when it's on your own desired RX frequency.

Repeater is running 180 watts ERP at 410 feet HAAT on flat, flat terrain. Mobile coverage with a 1/4 wave roof mounted antenna is 35 to 40 miles in all directions. Seems like it should reach out a little further, and probably would, if the noise floor was diminished 10 dB.

Not knowing anything about the antenna farm layout, might I suggest that the 3 phase transformers be relegated to an enclosure on a ground pad or, even below ground if proper drainage could be achieved. On top of the ground, mount the transformer as close to a chain link enclosure as possible for a semi faraday effect (shield if you will). Running the primary line underground to the transformers will help, too.
I guess maybe these things would be possible depending how well you know and get along with the power company, although, 9 times out of 10 they want to reduce line noise also.

 

[n4dbm]

Not knowing anything about the antenna farm layout, might I suggest that the 3 phase transformers be relegated to an enclosure on a ground pad or, even below ground if proper drainage could be achieved. On top of the ground, mount the transformer as close to a chain link enclosure as possible for a semi faraday effect (shield if you will). Running the primary line underground to the transformers will help, too.
I guess maybe these things would be possible depending how well you know and get along with the power company, although, 9 times out of 10 they want to reduce line noise also.

I would love to get rid of all the aerial transformers in this area, but that's likely not going to happen. The power company did replace several cracked insulators a couple of years ago. The noise was so bad that it was actually interfering with 700/800 MHz public safety stuff at the same site. It's nowhere near as bad as it was before the repair, but line noise is still there.

It's natural "ham" behavior to want to be out the very top of the tower. I have since learned after much reading and my own trials that being the absolute highest antenna out the very top of the tower is also the noisiest place to be. I have access to a DB224 down the tower a little way, but the trade-off in omni-directional coverage versus noise is not worth the swap.

 

[ladn]

I've noticed a noise floor upward creep here in the Los Angeles area, but it's not easy to quantify because of the gradual decrease in 2-M repeater and simplex traffic. Leaky cable systems seem to be the worst offenders, followed by power distribution infrastructure.

When I'm in the Owens Valley, the noise floor is a lot quieter (as would be expected), except in towns like Lone Pine or Bishop where the greatest offenders are leaky motel CATV systems.

 

[MTS2000des]

Get a good spec-an with logging capability, and connect it to your RX antenna port and "see" what your repeater is seeing. VHF has become a hash and trash band thanks to Chinese switching power supplies, Ethernet, cable TV, fiber ONTs, in short, just about everything poorly shielded with a CPU base clock of 150MHz. Since the FCC dba Radio Spectrum Sales and Leasing LLC doesn't give a rats' tail about "intentional radiators" and other part 15 rules, it's gonna be an uphill battle.
What a shame no one is really looking out for radio spectrum anymore except us hams.

 

[n4dbm]

Get a good spec-an with logging capability, and connect it to your RX antenna port and "see" what your repeater is seeing. VHF has become a hash and trash band thanks to Chinese switching power supplies, Ethernet, cable TV, fiber ONTs, in short, just about everything poorly shielded with a CPU base clock of 150MHz. Since the FCC dba Radio Spectrum Sales and Leasing LLC doesn't give a rats' tail about "intentional radiators" and other part 15 rules, it's gonna be an uphill battle.
What a shame no one is really looking out for radio spectrum anymore except us hams.

I've done that with an Aeroflex spec-an that has peak-hold logging (and other snap-shot abilities, too). It doesn't appear to be one particular thing, it's the entire noise floor spanning 130-180 MHz. It does taper off quite a bit, with only a few dB of degradation on the 220 MHz band, and no degradation detectable on 440 MHz up.

I have installed a permanent 30 dB tap in line with the repeater's receiver. I am fortunate enough to be at the site almost daily with an older signal generator that stays at the site and can remain hooked up to the 30 dB tap all the time. Quite often, I'll disconnect the receive line going to the repeater and put a 50-ohm termination where the receive line normally goes, inject a -90 dBm signal into the 30 dB tap (simulating a -120 into the receiver) and get an audible reference. The signal is just "full quieting" at that level. Then, removing the 50-ohm termination and attaching the antenna line to the receiver, the signal is immediately degraded 10 dB. To get the same "quieting" effect on the repeater, I now have to dial the generator up to -80 dBm. This is usually when real-world conditions are their worst. After a good soaking rain, the air is still and the humidity is high, sometimes I only see 3 dB of degradation.

On a dry, windy day, the lower DB224 is quieter. There doesn't seem to be much I can do about it, so I'll accept the fact that I can live with it.

 

[mmckenna]

What a shame no one is really looking out for radio spectrum anymore except us hams.

Too much money to be made by the FCC and everyone else. Like most other natural resources, some feel the need to burn through them as fast as they can simply to make sure no one else beats them to it.

 

[MTS2000des]

This is why we abandoned VHF high band decades ago, even in the mid 2000s, it started to become untenable in suburban areas filling up with homes chock full of China pride hash and trash generators. Then came plasma TVs in the late oughts. Even with remote receivers, just not reliable for body worn portable coverage. Then narrowbanding came. Noise causes you more problems the narrower you go in an analog world.

One agency around here tried to VHF P25 trunking, at the insistence of their fire chief who thought the sun rose and sets on VHF because "that's what we've always done" despite their consultant telling them to go 700, and they learned an expensive lesson along with making the news, only to have to tear out all the VHF infrastructure and subscribers, and replace them with 700MHz stuff. At another 12 million dollars they weren't planning on spending.

Their choice to stay on VHF was poor, as co-channel interference, extremely high ambient noise floor, resulted in constant illegal carriers detected, sites voted out, and non-existent portable coverage. Pre-selectors are useless when the noise floor is at -80dbm of on frequency feces pieces.

 

[n4dbm]

440 MHz has always been my go-to FM base-to-mobile band. I am actually getting surprisingly close coverage on the co-located 440 machine as I am the 2-Meter. I guess I am just lucky that the 440 MHz band around here is (for now) super quiet. The noise floor is low enough that running properly padded low-noise RX amplifiers actually benefit real-world receive performance on ALL my duplexed UHF repeaters.

The only thing that VHF high band is used for around here (public safety-wise) is paging. Most of the agencies in my area are on 700/800 MHz P25 trunked, but their dispatch simulcasts on 155.xxx MHz with two-tone paging, mostly running 500 watts ERP at lofty heights.

I guess I was borderline insane when I thought 6-Meters would be a fun band to play FM repeater on. 25 years ago, I had modified a Mastr Exec II to run on 53.51/52.51 with a TX/RX 4-cavity duplexer. It worked pretty well but even then the noise floor was high (over a microvolt ALL the time). It appears the 2-Meter noise floor is comparable to that the 25-year-ago 6-Meter noise floor was.

I reworked a DB-201 for 6M and had it placed out the top of the 400 footer near the VHF DB224. The noise floor on 6M is more like 2 microvolts all the time. UHF with 6 dB more ERP outperforms it.

Agreed on the foreign noise crap generators. I experienced that with a Samlex 80 amp switching power supply. I eventually got aggravated enough that I replaced it with an old-school transformer Astron.

 

[Golay]

I'm going to preface this by saying I'm not much of a techie. So it may not be genetic that my eyes are brown .
But I've been pondering something since the BPL scare came out many years ago.
Hanging a low pass filter across the incoming of your house. Take anything that's on the power lines in your neighborhood above let's say 1KHz to ground . Like I said, it crossed my mind for BPL way back when that was the Big Fright. But would that work for power line noise in the 'hood?
Yeah maybe the L-C network would need to be as large as the set of cans on a 10 meter repeater.
But it's just a thought that crossed my mind back then.

 

[prcguy]

The worst offender in the VHF band I have seen in recent times is modern LED home lightning. This would be LED equivalents for incandescent light bulbs in ceiling lights, table lamps and flood types. Its not really the LED but the internal switching power supply. All the LEDs in my house trash out the VHF band at quite a distance but not much of anything at UHF or HF.

I added a ton of ferrite in my ceiling can type light fixtures and have reduced the problem enough to a tolerable level but my neighbors who certainly have similar lights don't have radios and are unaware of the RFI they cause. I can also watch the spectral display in my Icom 9700 on 2m and it wavers all over the place all day and night where the 70cm band is fairly quite.

 

[n4dbm]

I'm going to preface this by saying I'm not much of a techie. So it may not be genetic that my eyes are brown .
But I've been pondering something since the BPL scare came out many years ago.
Hanging a low pass filter across the incoming of your house. Take anything that's on the power lines in your neighborhood above let's say 1KHz to ground . Like I said, it crossed my mind for BPL way back when that was the Big Fright. But would that work for power line noise in the 'hood?
Yeah maybe the L-C network would need to be as large as the set of cans on a 10 meter repeater.
But it's just a thought that crossed my mind back then.

Most of my power line noise is due to dirty or cracked insulators on the poles. I have a higher voltage line than normal residential areas in front of my house because the lines connect two substations together. One of the insulators was so bad years ago that you could see the faulty insulator light up blue, orange and purple at night, along with it sounding like a miniature arc welder. But your theory is interesting.

 

[n4dbm]

The worst offender in the VHF band I have seen in recent times is modern LED home lightning. This would be LED equivalents for incandescent light bulbs in ceiling lights, table lamps and flood types. Its not really the LED but the internal switching power supply. All the LEDs in my house trash out the VHF band at quite a distance but not much of anything at UHF or HF.

I added a ton of ferrite in my ceiling can type light fixtures and have reduced the problem enough to a tolerable level but my neighbors who certainly have similar lights don't have radios and are unaware of the RFI they cause. I can also watch the spectral display in my Icom 9700 on 2m and it wavers all over the place all day and night where the 70cm band is fairly quite.

Some LED bulbs seem to bother me, and some don't. I've done the whole listen to a weak signal with noise and turned each breaker in the house off one at a time to find the problem, but I don't think it's a single device at my repeater site. Agreed, LED lights do produce noise and with all these new billboards turning into TV screens, no doubt this contributes to the problem as well.

 

[mmckenna]

Most of my power line noise is due to dirty or cracked insulators on the poles.

I used to work with someone who had previously worked for the local utility. At one point she had the job of working on the crew washing insulators. When I was a kid, we used to see them go through our neighbor hood every year or so washing them for a 112KV circuit that ran down a main street.

I have not seen them do that in decades. Attitude seems to be "wait for it to fail and we'll replace it". So many of the utilities have gone to that method. Increase shareholder profits at all costs, even human lives.

 

[KC3ECJ]

Get a good spec-an with logging capability, and connect it to your RX antenna port and "see" what your repeater is seeing. VHF has become a hash and trash band thanks to Chinese switching power supplies, Ethernet, cable TV, fiber ONTs, in short, just about everything poorly shielded with a CPU base clock of 150MHz. Since the FCC dba Radio Spectrum Sales and Leasing LLC doesn't give a rats' tail about "intentional radiators" and other part 15 rules, it's gonna be an uphill battle.
What a shame no one is really looking out for radio spectrum anymore except us hams.

Yeah there's some household light or transformer for such in my neighborhood likely that's causing interference on VHF airband on and off.