Posts Tagged ‘noise’
*** The following blog was originally published in 2016 but is still very applicable in 2020! ***
How often have you struggled to pull a weak signal out of the noise? "Just give me one more db", you tell yourself.
A recent posting to the Topband reflector by Frank, W3LPL, sent me to the interesting webpage of Dave, AB7E. Dave had been pondering two antenna systems, one of which would provide a 2db improvement in forward gain but at a much higher cost ... he wondered if the extra expense would be worthwhile and could he even hear the difference that 2db would make? He created a series of CW files, incrementing the signal level in 1db steps to see for himself!
Now I've always been told that you need to increase signal strength by at least 3db before your ears can detect any difference ... but listen carefully and you may be in for a surprise, as AB7E discovered.
It's probably best to listen to this signal with headphones but, even on my I-Pad's tiny speaker, the demonstration is clear. The first recording starts at "zero db", which is sent twice while the next signal is "one db", sent twice. See if you can hear the difference between each 1 db increment as he steps up to "six db":
Lastly, AB7E demonstrates the problem with sending too fast when conditions are very marginal. Here, several signals are sent at 20, 25, 30 and 35 WPM. Sending calls at high speed can often seem effective, even under poor conditions but this seems to demonstrate that slowing down just a bit would make it somewhat easier:
One of the more interesting comments posted regarding these recordings was from Bob, N6RW who cited his work in satellite communications:
"I spent part of my engineering career designing satellite command FSK
demodulators - including the deep space Pioneer Venus orbiter. To test
the performance of them, we would mix the test signal with white noise.
When you look at the FSK Bit-Error-Rate (BER) curve (bit errors versus
signal to noise ratio in a bandwidth equal to the bit rate), you can see
the BER improves by a factor of 10 to 1 for every dB in S/N ratio. In
other words, for every dB improvement, you get one tenth the errors."
Now Dave never did tell us if he bought the bigger antenna or not but I'm betting that he did ... it looks like "just one more db" may really be just enough after all.
|Utilitech Pro Soft White LED Bulb|
A recent posting by Phil, KO6BB, to Yahoo Group's ndblist, described his recent search for some LED lamps to replace the CFL's in his shack / radio workbench area. If you have been wondering how much RFI that LED lamps might be producing, you may find Phil's findings of some value.
I had a 60W equivalent CFL in the floor lamp directly over my operating position. I'd tried a 100W equiv one but it was extremely noisy! Also a couple CFLs in the ceiling lamp.
This is a floor lamp with a crookneck at the top and a triangular metal
shade reminiscent of the old style desk lamps, bulb is horiz to the
floor. I've used it for years and like it because it places the light
directly over the operating position work area (keyboard, radios etc).
The actual bulb was about 4.5 inches from the front of the Softrock SDR
receiver (in a plastic case), with the base of the lamp (where the
electronics are) about 7.5 inches (somebody asked about the distances).
This coupled a LOT of RFI directly into the SDR, visible on the
waterfall. For best results when recording and having the light on I'd
slip a 60W incandescent lamp in place of the CFL. The lamp is also
about 16 inches above the operating table, and when listening to ANY
portable radio on the table, if it was in the AM or Longwave band and
using the built in loopstick antenna, got a LOT of RFI from the lamp
(unless the lamp was off ;-)
So today I went down to Lowes (we have a Costco, but I don't have a
card) and looked at their LED lamp offerings. As I expected they had a
large variety of them, from a low cost 3 pack for ~$9.00 for 60W units
to about $18.00 or so each (Sylvania). From what I read here I wanted
to avoid the REALLY cheap ones as some reported them to be 'noisy'.
Also, I wanted to put a 75W equivalent unit in the one over the
operating position, and a pair of 100W equivalent units in the ceiling
lamp. All three had CFLs, and if I walked around the radio room with a
portable radio and the ceiling lamp on I could hear it's 'hash' anywhere
in the room. . .
The ones I settled on were a brand I'd never heard of, "UtiliTech Pro"
soft white, 75W for the bench and 2 100W ones for the ceiling. They
were what I'd call "mid-priced", $8.98 for the 75W and $9.98 for the
75 W one draws 12W and gives 1100 Lumens.
100W one draws 16.5W and gives 1600 Lumens (the pair in the ceiling
should then be 3200 Lumens if I calculated right).
How low is the RFI to my Radios?
75W one over the bench:
NO trace from the lamp electronics visible in the SDR waterfall at
all. With a portable radio on the bench-top, NO audible RFI. Put a
portable radio up to the "bulb" part (light area) and with no station
tuned in can't hear ANY RFI. Move the portable to the base area of the
lamps there is SOME RFI, but I won't be putting the radio that close to
the lamp, move it a couple inches away and the noise disappears.
100W ones in the ceiling lamp, NO audible RFI in the portable when
walking around the room, RFI just barely perceptible right next to the
light wall switch that turns the lamp on, again, audible IF I put the
radio right up to the base of the lamps, not a likely real-world scenario!
Based on the sample of three that I bought and the almost
non-existent RFI from them I'd consider the UtiliTech Pro lamps to be a
good product and suitable for use in the radio room. I consider them
good value for the ~$30.00 I spent for three."
If you have tested anything similar (other brands / models), please let me know and I will add it to Phil's helpful information.
KO6BB's website can be found here, along with some of his homebrew equipment.
Today's blog is a repost from August, 2015.
I see that the ARRL has filed three more formal complaints to the FCC concerning the bone-crushing HF emissions being produced by off-the-shelf grow light ballasts. The complaint also includes detailed lab data collected on all three devices and it is not pretty. One wonders why it is necessary at all that the ARRL be the industry watchdog instead of the FCC ... why aren't they being more diligent in filtering out these products before they hit the market? If importers and dealers are simply bypassing regulations for the sake of a quick-buck, then heavy fines must be imposed until someone 'gets the message'.
Some of the test products were ordered and purchased through Amazon and through Sears ... the ARRL's thorough report makes it obvious that rules are being ignored and amateurs are paying the price.
“The level of conducted emissions from [these devices] is so high that, as a practical matter, one RF ballast operated in a residential environment would create preclusive interference to Amateur radio HF communications throughout entire neighborhoods,” ARRL General Counsel Chris Imlay, W3KD, wrote in each complaint. The devices exceeded conducted emission limits under all test conditions, “sometimes by extreme margins, throughout most of the HF range ...”
In a similar vein as its recent complaint about marketing of certain RF lighting devices by The Home Depot, the ARRL pointed out that there were no FCC labels on two of the devices mentioned nor any FCC compliance information “anywhere in the documentation, or in or on the box, or on the device itself,” in violation of FCC Part 18 rules.
The League asked the FCC to require removal of all such illegal “grow light” devices from retail sale and marketing and the recall of those devices already sold or available for retail sale, and it said the device importers should be subject to a forfeiture proceeding.
With the proliferation of both legal and illegal 'hydroponic' operations, this kind of QRN is probably just the tip of the iceberg. It's good to see the ARRL slowly pounding away at the rule-breakers on behalf of American amateurs.
I see these same devices being sold on E-Bay, where presumably, they could be purchased worldwide and installed anywhere. As well, several of the U.S. online dealers state "We ship to Canada" ... just great.
Hopefully Industry Canada and RAC are gearing-up for the fight.
Perhaps others can help explain something odd that I have just noticed with my Perseus while comparing antennas.
I was comparing signal levels and noise between a 40m half sloper and a very high dual 40/80m pair of inverted-V dipoles fed from a common feedline. Both the sloper and the dipoles are fed with 50 ohm cable and all three antennas are well matched at the low end of the band(s).
Listening to a 6 MHz signal from China National Radio around 10 am today, the signal was around S7-8 on the Perseus, using the 40m sloper. Listening to the same signal, at the same time, on the Yaesu FT-1000mp, with the high inverted-V, it was slightly better, maybe by 5-6 db and overall lower noise. I then put the inverted-V onto the Perseus and there was not even a trace of the signal! I made this check with several signals and always with the same result.
Now I suspect that the SWR of the 7MHz inverted-V when used at 6MHz, is very high and the load presented to the Perseus antenna input is likely highly reactive and far from 50 ohms but that doesn't seem to bother the FT-1000.
I then ran the inverted-V through my antenna tuner so that it effectively produced a 50 ohm non-reactive input load for the Perseus and did the tests again...with the same results. Swapping antennas for the 40m sloper once again produced the same signal levels in both the Perseus and the FT-1000.
So what is going on here and why does the Perseus balk at the 7 MHz inverted-V while listening on 6 MHz? Is there something in the Perseus front-end analog filtering system that is overly sensitive even though the reactance was tuned out via the tuner? Is it the 80m V on the same feedline as the 40m V that is causing some still unwanted reactance that is not tuned out with the tuner?
Any ideas what is happening here as it looks like I will not be able to use the inverted-V antennas on the Perseus for general SWL out-of-band listening for some, as yet unknown, reason.
As you can see, I was completely mystified by what I was hearing, or rather not hearing, and as it turned out, completely off the mark.
I received a few replies offering some possible reasons for what I was seeing but none of them proved helpful in solving my dilemma ... until Roelof Bakker (PAØRDT) weighed-in! Roelof suggested that I look at the antenna's performance while running Perseus's built-in 'HFSpan' function.
HFSpan is a stand-alone 0-40MHz spectrum analyzer, that comes with the Perseus software. Although I was aware of it, I have only used it sparingly. I next did some screen captures with all three antennas, one at a time, and sent them to Roelof.
His analysis did not take long as he immediately identified my problem ... a very high noise floor when using the mysteriously-performing inverted-V. Roelof suggested some common mode choking to eliminate the problem.
Already having an isolating transformer in hand from a previous experiment, I inserted it directly at the Perseus antenna input and looked at the noise floor again, around 40m. The transformer was wound on a small FT87-J core with a 3 turn primary directly opposite a 3 turn secondary. I was astounded to see the background noise floor drop from -85dbm to a very quiet -110dbm!
Evidently there was a lot of noise being picked-up on the inverted-V's feedline shield. Not hearing any of this noise on the FT-1000 indicated that the noise was probably associated with the Perseus power supply, the laptop or the laptop's power supply. This immediately explained why I wasn't hearing anything with this antenna when used with the Perseus.
Roelof then suggested that a 2 turn / 2 turn transformer, offering less inter-winding capacitive coupling, might provide even more isolation ... and he was right again. A further ~4dbm lowering of the ambient noise was measured.
|It may not be pretty but it produced an astounding improvement!|
Further comparisons between the FT-1000 and the Perseus revealed that the FT-1000 was still producing a slightly better SNR than the Perseus, when using the inverted-V so evidently there was still some noise affecting the signal. I had a few very large #43 ferrite toroids and decided to wrap a few turns (5) of the RG8-X feedline around the toroid to see if there would be any improvement.
Once again, using HFSpan, I compared the noise floor both with and without the #43 choke and saw a further 6-7 dbm improvement! Going back to comparing SNRs between the FT-1000 and the Perseus, I now saw no difference between how I was hearing on both receivers, when using the troublesome inverted-V ... eureka!
|Same sweep, noise eliminated, signals now unmasked|
As of yet, I have not determined the actual noise source. I suspected it may have been coming from the Perseus power supply or from the laptop supply but that was not the case. Perhaps it is coming from the laptop's processor via the USB cable which I will also choke and see if HFSpan reveals anything further
This problem was a great learning experience for me, in more ways than one and I am most grateful to Roelof for his detective work and experience with noise issues and for taking the time to respond to my initial inquiry. Hopefully you may find something here that can help you as well.
John, VE7AOV, has been operating from his apartment, in the heart of the very large and noisy greater Vancouver, for several years now ... not simply 'operating', but thriving, from his cozy fourth-floor apartment radio station. The wallpaper shown below would not usually be expected to grace the shack walls where antennas are not permitted!
It's soon apparent that John has also overcome the usual problem of noise ingression, from every appliance and random RFI generator in the complex. This is no lucky fluke but all by design, and delivered via an all but invisible classic antenna system made of #26 wire and a few Starbuck's stir-sticks!
|600 ohm #26 balanced line|
I'll let John tell you a bit more before sending you to his fascinating website, Intuitive Electronics, where you can learn more about his system and the engineering behind his successful, low-noise installation.
When it comes to a high frequency ham station, the antenna alternative chosen by most apartment dwellers is no antenna at all. The design here is a wisp of an antenna that bothers no one and which can work Japan, Australia, France, European and Asian Russia, the Caribbean, Central America, Polynesia and South America from the Pacific coast of Canada. It is a simple solution for apartment dwellers, it is a cheap solution and it causes no t.v.i. or other r.f. problems. It is far preferable to the alternative selected by so many fellow apartment dwellers: no antenna at all.
An implication that it seems to be impossible to rid from the minds of fellows using a Marconi antenna is that they are not just pumping 100 watts of r.f. into their antenna but that they are also pumping that same 100 watts of r.f. into their ground, that is to say the building’s wiring, the safety ground wiring. R.f. in the safety ground is well coupled into the power and neutral conductors of a residence and, in North American code, is even hard connected to the neutral line at the service entrance. The house wiring becomes part of the antenna system.
The ground wiring and everything connected to it is every bit as much a part of the antenna as is the live element. Both radiate just the same amount of r.f. power, fellows. The ground wiring along with every electrical power consumer in the building is worked against the live element. Thinking of what is connected to ground in your house is thinking about one side of your antenna. It’s not just appliances that get the “benefit” of r.f. The land line telephone system, the cable television system, the garage door opener, the security lights and…you name it. They are all “feeling” that 100W of r.f. With regard to r.f., there is no distinction whatsoever to be made between “hot” and “ground”.
You know the reason why vertical antennas have gained a reputation for being noisy on receive now, too. Most verticals are Marconi antennas. Both the safety ground and the neutral serve all the houses in the neighbourhood. The receiver is wired into the electrical appliances of the entire neighbourhood.
This radio station, located four stories above grade and in a wooden building full of apartments would be a worst case for r.f. in “ground”. This station has no r.f. in the station. It has no r.f. in “ground”.
The station has no interference issues. The Building Manager, the Building Superintendent and the administrator for this building’s cablevision have been aware of the station from the beginning. There has not been a single complaint of t.v.i. or any other complaint about the station. That’s a clean record extending back to 2006. There are no red faced, spluttering tenants hammering on the door of this station! At this station, all the r.f. produced by the transmitter makes its appearance out on the antenna. The radio station’s r.f. is not referenced to station ground. Station ground “knows nothing” about the r.f. being generated.
In the present case, that is to say a station to be operated in an apartment building, it is required to have an antenna that is “invisible”. Now it’s not possible to achieve that literally but at least the antenna should be so inconsiderable that there will be no complaints from neighbours about having to look at it. The antenna here is made of #26 A.W.G. wire. That’s wire that is 0.40mm, 0.016 of an inch, in diameter. Four stories up, it’s difficult to see the antenna and that’s even when knowing where to look for it. Part of the antenna’s run is through trees and in among the tree branches it pretty much is invisible. It does not annoy neighbours by casting a shadow; there is no shadow.
In spite if the naysayers, John's small gauge antenna has survived years of winter storms, regular occurrences here on Canada's western edge ... simply because it presents such a low cross-section compared to most conventional antenna wires.
To read more about enjoying your hobby again from your new 'restricted' location and more than likely, learn something new about old fundamentals, give John's website a very close inspection ... there is much wisdom and many gems to be found, even if you don't live in an apartment!
For some reason, the FCC continues to pour money into its hell-bent roundup of FM pirate broadcasters! I suspect much of this 'tough stance' is more politically motivated than for the reasons that they state, but the FCC seems to have plenty of will-power and the necessary funding ... it's too bad that they couldn't put the same zeal into getting on top of or making a start on the huge growing noise problem throughout the radio spectrum. I guess rounding up pirates is much easier than tackling the far more important noise issues, now growing so rapidly that many radio amateurs just throw up their hands in surrender and close up shop for good. Even commercial users of the spectrum are being negatively affected by the growing noise floor, as the growing Internet of Things connected devices produce even more radio crud.
It now seems that the FCC may get a further boost in its crackdown if a new bipartisan proposed federal law becomes reality. A May 9, 2018, article in Radio World reports the tabling of the new bill in the US Congress called the PIRATE Act or "Preventing Illegal Radio Abuse Through Enforcement Act". It would also be nice to see the PAIN Act (Preventing All Illegal Noise) in the RF spectrum but I see no Washington appetite for this much-needed FCC oversight.
The continued obsession for rounding up FM pirate broadcasters is fascinating in its own right. "It is time to take these pirates off the air by hiking the penalties and working with the Federal Communication Commission on enforcement", stated Rep. Leonard Lance (R-NJ).
"As reported in Radio World, the PIRATE Act proposes to hike the fine for violations to as much as $100,000 per day, with a maximum fine of $2 million. The rules currently allow the FCC to impose a maximum daily penalty of about $19,200 per day. At a Congressional hearing on the bill in March, New York State Broadcasters Association President David Donovan told lawmakers that illegal operators are undermining the nation’s Emergency Alert System, causing invasive and insidious interference, pose potential public health problems due to overexposure to radio frequency radiation, and interfere with airport communications."
It is apparent from reading investigative reports, that each acted-upon complaint requires a substantial investment of time and money as in the April 24 Notice of Apparent Liability for a case in Paterson, New Jersey ... it seems that NJ and NY are 'pirate hotbeds'. By the end of the investigation, a team of fully-equipped FCC field agents had visited the pirate's site(s) on eight different occasions, a considerable investment in time, energy and money. In the end, a $25,000 penalty has been proposed for the offender.
I am not a fan of illegal pirate radio broadcasting in any form but the reasons stated by the FCC for the ongoing pirate purges seem somewhat shaky. In all of the investigative reports that I've read, I have yet to find any that were reported to cause "interference with airport communications" and I question the assertion that the low power levels used by most pirates are going to "pose potential public health problems due to overexposure to radio frequency radiation". One more likely reason may be the strong lobby pressure from broadcasters who see the possible loss of advertising revenue. I'm sure that many Washington electees receive healthy campaign donations from state broadcasters as well.
Although many pirate radio ops seemingly solicit advertising revenue, overall it can't be much of a threat to mainstream broadcasters. Is it just the NAB Washington lobby that is fuelling the FCC pirate craze or is it muscle-flexing from the new administration, wanting to look tough on "crime" and radio-pirates are just easy low-hanging fruit? I suspect that it may be more of the latter.
The FCC's 'Pirate Action' postings make for interesting reading as does the fascinating Westword article on pirate radio activity in Ward, Colorado, and the recent attempted FCC take-down of stations in operation since 1997!
There's no question that a lot of FCC resources are being used to eliminate unlicenced QRM. What will it take to see the same attack on unlicenced QRN as well?
It seems like the FCC's recent interest in doing an in depth study of the growing RF spectrum noise floor has taken a new twist.
The FCC's apparent lack of real action in gathering the data needed to make serious inroads into RF noise pollution has drawn the attention of the ARRL, which voiced their concerns in a recent ARRL Letter as well as in their formal response to the FCC.
In response to the FCC's Public Notice (ET Docket No. 17-340) Spectrum Management proposals.
The ARRL "took the opportunity to strongly urge the FCC to reinstate a 2016 TAC noise floor study, which, ARRL asserted, apparently was terminated before it even got started." It would seem that the proposed in-depth study never even happened and the term 'noise' has morphed into an 'interference' issue!
The FCC's paper proposed a number of guiding 'principles' in going forward with spectrum management policies, loosely based on the concept that more emphasis on eliminating 'interference' should be placed on receivers along with continued development of transmitter spectral purity and that with increased spectrum crowding, users will simply have to expect and accept certain, as yet unspecified, levels of interference!
It sounds suspiciously as if the FCC has decided that the source of any noise / interference problems have become too large to control and have passed the buck to equipment manufacturers in order to solve the growing problem for users!
“Indeed, it is difficult to imagine how the Commission can now…suggest the adoption of specific spectrum management principles, incorporating such concepts as receiver immunity, HCTs [harm claim thresholds], and interference temperature determinations without having…a firm grasp on ambient noise levels in basic RF environments and geographical areas,” the League told the FCC.
In their series of guiding principles relating to 'interference realities', the FCC has issued a number of broad, somewhat ambiguous statements, that might be interpreted in any number of odd ways ...
"Principle #1 -- Harmful interference is affected by the characteristics of both a transmitting service and a nearby receiving service in frequency, space or time;
Principle #2 – All [radio] services should plan for non-harmful interference from signals that are nearby in frequency, space or time, both now and for any changes that occur in the future;
Principle #3 – Even under ideal conditions, the electromagnetic environment is unpredictable. Operators should expect and plan for occasional service degradation or interruption. The Commission should not base its rules on exceptional events;
Principle #4 – Receivers are responsible for mitigating interference outside their assigned channels;
Principle #5 – Systems are expected to use techniques at all layers of the stack to mitigate degradation from interference;
Principle #6 – Transmitters are responsible for minimizing the amount of their transmitted energy that appears outside their assigned frequencies and licensed areas;
Principle #7 – Services under FCC jurisdiction are expected to disclose the relevant standards, guidelines and operating characteristics of their systems to the Commission if they expect protection from harmful interference;"
The ARRL response argued that:
“Requiring better performance from receivers or RF-susceptible devices is a valid, reasonable, and long overdue requirement,” ARRL said, “but the major goal of doing so should be to prevent instances of interference ..."
Specifically they argue that amateurs are unique users and able to recognize harmful interference beyond their control and should not be subjected to the same restrictions (ie. get ready to accept new levels of yet undefined interference levels) as commercial users.
"ARRL argued, however, that the Amateur Service should not be subject to receiver immunity standards, because licensees employ a wide range of propagation, emissions, bandwidths, power levels, receivers, and antennas, making any receiver performance standards arbitrary and compromising the Service’s experimental nature. They also are able to differentiate between interference from nearby spurious or out-of-band signals and that caused by receiver deficiencies. The HCT concept does not fit the Amateur Service particularly well, either, the League said; any interference hams suffer from each other is resolved cooperatively. Brute-force overload also occurs occasionally but is resolved by licensees without FCC intervention."
The ARRL seems somewhat forgetful when it comes to several long-standing complaints of inappropriate amateur-generated interference and bad behaviours which have been ignored for far too long ... problems well beyond 'cooperative resolution' by affected amateurs.
Although the ARRL does agree with many of the FCC's proposals, they doggedly insist that the FCC's apparent quashing of their original noise data investigations is critical to going forward:
“That, in ARRL’s view, is a big mistake,” the League contended. “No system of spectrum management incorporating [harm claim thresholds] and receiver immunity levels can be accurately implemented” without the noise study data.
“That study is more important now than ever before,” ARRL concluded, “and it is increasingly urgent as a prerequisite for any new spectrum management policies.”
With Washington's drastic cutbacks in FCC field-office investigators and overall budget trimming, it seems that the FCC is still relentlessly driven to eradicate all forms of illegal (pirate) broadcasting. It's a pity that they don't display the same zeal for dealing with the illegal imports and distribution of the offshore equipment that is quickly killing our ability to hear anything on the ham bands ... without selling-off and moving to several acres in the country.