Posts Tagged ‘RFI’
|Old HDMI monitor cable|
I am the kind of person that things just don't click right away and I need time to mull things over. One thing that came to mind was my monitor issue I was having. I was using an HDMI feed from my PC to the monitor as I always have in the past BUT in the past I was not faced with the RFI issue. Chameleon Loop antenna and I remembered the coax that came with the antenna had a set of RF
|Chameleon coax choke|
I replaced the HDMI cable with a DVI cable that had RF chokes at either end. This solved my monitor issues of it waking up from sleep mode on it's own and characters showing up on the screen.
I did on Friday end up ordering the Balun Designs 1115 Balun and it should be arriving within the next week or so. My positive tests using the RF choked coax tells me that the purchase of the Balun was a good choice. My next step will be to try out a counterpoise that is 25 feet long secured at the PL-259 that feeds the W1SFR Endfed antenna and see what this step produces. I am hoping with the new Balun, the counterpoise and changing the monitor cable will solve the issues I have been experiencing.
It now the next day and my experiment with the separated 25 foot counterpoise have been completed. I stripped one end of the 25 foot piece of wire and attached it to the outside of the PL-259 using a screw clamp similar to the clamps you see on automative rad hoses.....but much smaller. I checked the SWR on 40m, 30m, 20m and 18m and it really did not change much but what did change was the amount of RFI what was showing up on my waterfall on the 7610. I then removed the counterpoise and the offending RFI was gone. So that was good enough for me I am going to keep the Chameleon coax with the chokes in place until the Balun from Balun designs comes in.
This blog first appeared in February 2016 but is just as relevant today as it was then!
I admit it. I have an extraordinarily kind next door neighbour!
Ever since erecting a new, much bigger LF antenna several years ago, she has allowed me to run its large, three-wire 100' tophat, directly over the top of her house to a tree on the far edge of her property. As well, she removed her only light dimmer, knowing that it was creating a LOT of nasty RF 'hash' throughout the LF / MF spectrum, seriously degrading my LF reception. To hear the RF noise-signature of a typical light dimmer, listen here, on the ARRL's helpful page of 'household' RFI recordings ... that's just how it sounded here as well!
She recently did a major renovation, which included a new multi-light dining-room fixture and expressed to me a desire to be able to dim it ... oh-oh, I was definitely not looking forward to this.
I did a little web-research and soon learned that some of the most RF-quiet dimmers were being produced by Lutron. One model in particular, claimed to pay special attention to RF noise-filtering and that was the "Centurion", whose smallest model is a 600 watt-capable unit, with a large finned heatsink front plate ... model #C-600P-WH.
I decided to order one from the only dealer I could find in Vancouver that seemed to carry this line of dimmers. The cost was just a little over $40 Canadian (sells for about $25 in the U.S.A.) ... cheap enough if it would do the job!
When the unit came in, I picked it up on my next ferry trip to the city and upon my return, installed it the following afternoon. Before doing the installation, I fired-up the receiving system, tuned to 300kHz, and with the baby monitor set up beside the speaker, took the portable monitor with me.
After installing the new dimmer, I turned on the baby monitor, held my breath ... and turned on the light fixture. Wow ... not a trace of hash could be heard! Adjusting the dimmer from high to low produced no difference in the noise level. I later did a more thorough bandscan and could find no evidence of RFI, on any frequency. The only RFI that I could detect was when placing my Sony ICF-2010 close to the actual dimmer. I was unable to detect any noise further than 6" away from the lights or the dimmer!
So it seems that this model can be highly recommended, for your own home or if you have a next door neighbour 'light-dimmer problem'.
In my previous blog post, I listed four barriers to getting on HF:
- antenna restrictions
- radio frequency interference (RFI)
- the fiddle factor.
Fiddle Factor really represents how multiple issues can come together to dramatically increase the complexity of an HF installation.
Now I’d like to propose some ways of dealing with these barriers.
A lot has been written about this problem and there’s enough material to write a dozen books about this topic. The remedies that come to mind fall into two main categories:
- Hide your antenna
- Change your location (temporarily or permanently)
Common strategies for hiding an HF antenna include: attic antenna, low profile wire antenna, flagpole antenna and temporary antenna. I recently came across this fabulous guide to stealth antennas from The Villages Amateur Radio Club. It was developed based on practical experience in an HOA-controlled community. One interesting point they stress is that the mode you use interacts with the capability of the antenna. Simply put, if you are using a compromised antenna then it really helps to use a more efficient mode such as CW, PSK31, JT65 or FT8. Good advice!
I received quite a bit of feedback via twitter that a solution to antenna restrictions is change your location. One answer is to permanently move your home to a new location, typically out in the country with wide open spaces and no restrictive covenants. This is easy to say and often difficult to do. I am going to assume that for the most part you are stuck with your home location (for whatever reason) and not spend much time on it here. But keep this in mind when the opportunity to move happens. Every time I’ve purchased a house, I always evaluated the property for antenna options.
Another option is to change your location temporarily, as in portable operation (can you say Summits On The Air?) I like portable HF operating and have operated from a number of islands while on vacation. You don’t have to do a DXpedition, you can always just go to a local park and set up a station there. Heck, you can always “go portable” in your backyard. Set up a temporary antenna, operate and take it down before anyone has a chance to complain.
Another “change your location” strategy is to use a remote ham radio station. Many clubs have established a remotely-controlled station (usually controlled via the internet) for their members to use. Or you could use one of the commercial remote radio systems (such as Remote Ham Radio).
Radio Frequency Interference (RFI)
RFI generally occurs when a device creates radio frequency energy on frequencies that you want to use. One very discouraging experience is to turn on your newly-installed HF station to find the ambient noise at S5 across your favorite operating band. Frankly, this can be a really difficult problem to solve. Many books have been written on this topic, too. One of the best is The ARRL RFI Book. The ARRL RFI web page may be helpful, too.
The source of interference is either under your control (something in your residence) or it can be from external sources (your neighbor’s house, the AC power lines, …) RFI sources are easier to find in your own home. A good first move is to go around and unplug everything electronic in the house to see if the problem goes away. Or you can go through your circuit breaker box flipping all circuits off until the problem disappears. (Of course, you need to keep you HF radio powered up so you can listen for the noise.)
If the problem is outside your home, things get a lot more difficult. You’ll have to track down the source and engage the owner of the device in a conversation about correcting the problem.
If the problem is power line noise, the electric utility is supposed to be able to correct it. However, the technical capability on RFI issues at electric companies ranges from none to quite competent.
What can we do about the cost of getting on HF? I’d say, not a lot. Your best strategy is to look for used equipment which can be less than half the price of new. However, if you are comparing an HF station to the cost of a $30 Baofeng handheld transceiver, you will probably be disappointed. In my previous blog post, I estimated that a used HF station could be on the air for ~$500.
One comment I received via twitter is that the cost alone may not be the issue. For some folks, the issue is spending that much money and not knowing how much success they will have on HF and whether they will truly enjoy it. Good point. One way to deal with this issue is to operate from someone else’s station to try out HF or to borrow some equipment. This will defer the cost until you know more about HF operating and judge whether it’s right for you.
One idea that might look attractive for saving cost is to buy an inexpensive, low-power (QRP) transceiver. I would avoid that option as it increases the fiddle factor.
The Fiddle Factor
The fiddle factor represents how multiple issues can come together to dramatically increase the complexity of an HF installation. When the complexity increases, the probably of success decreases because there are just more things to go wrong.
So the remedy is to avoid a high-fiddle-factor installation. Ideally, you would use a simple antenna (dipole, end-fed halfwave, etc.) hung in the clear with no obstacles around. Real world constraints may come into play here and require you to make other choices. Just be aware that each complication drives complexity.
Find a Mentor (Elmer)
The one universal strategy for success with ham radio is find a mentor, also called an Elmer. Having an experienced radio ham to answere questions and bounce ideas off of is extremely valuable.
How do you find a mentor? See Dan/KB6NU’s suggestions on the topic. You may have to settle for mentoring via the internet but it is way better to have someone local that can actually see your house and antenna installation options.
Those are my suggestions for how to deal with the barriers of getting on HF. I am sure there are more ideas out there.
What do you think?
73 Bob K0NR
We’ve had a steady stream of new licensees come into our radio club driven mostly by our highly-successful Technician license class. Many of these licensees have gone on to get their General license so they can have fun on the HF bands. I’ve given advice and aid to a variety of people as they get their HF station set up and I’ve come to appreciate that for Average Joe Ham this is a big step. I’ve also noted some recurring problems that get in the way of success on the HF bands, which I’d like to explore here. Recently, I asked my twitter followers for input and got some great ideas from them, too. Thanks!
Here’s what I came up with as the four main barriers to success on HF.
The first barrier that pops up are antenna restrictions which can come in the form of zoning regulations, protective covenants (homeowners associations), spouse’s opinion, potential objections from neighbors and your own sense of aesthetics. Any of these can limit the type and size of antennas you can or will install. More to the point, this can be a showstopper for some folks. They may decide that they simply can’t have an HF antenna on their property.
Of course, HF antennas tend to be large due to the longer wavelengths used (compared to simple VHF antennas). But there are some compact antenna designs that use magnetic loops, loading coils, etc.
The second issue that often pops up is radio frequency interference (RFI) from sources such as power lines and consumer devices. These issues can be very frustrating because you have to do two things: identify the source of the noise and eliminate it. If the problem is power line noise, your local utility is supposed to be capable of finding and correcting the problem. Some are better than others. Consumer devices are a huge problem due to the common use of high-speed digital circuits. If the interfering device is in your home, that makes it a bit easier to deal with…if it’s somewhere in the neighborhood, then its harder to diagnose and fix.
My twitter followers mentioned that solar electric systems often radiate RF energy (and they are a growing trend). Here in Colorado, we are seeing more problems with cannabis grow operations that use RF-ugly industrial grow lights. But Part 15 consumer electronics are a big and growing problem…too often they are little RFI generators.
I hesitate to add cost to the list but I do think it’s a factor. A starter HF station costs something like this (your mileage may vary): $750 for a new transceiver (think Yaesu FT-450 class), $100 for a power supply, $100 for wire antenna (homebrew) and coax => ~$1000. Yes, you can buy used gear and get this cost down…maybe to half ($500)?
Comparing this to a Baofeng HT purchase ($30), it is a lot more money. However, it is on the same level as other significant consumer electronics purchases such as a high end smartphone or mid-range notebook PC. As someone correctly pointed out to me, the utility of a notebook PC is very clear…you will get value out of it…but success with HF is still a gamble. What if you spend $1k on an HF station and never have any success with it?
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!
Many small electronic devices have switching regulators in them that can generate a bunch of Radio Frequency Interference (RFI). This is not my first encounter with RFI-spewing devices. See this article about a automotive 12V-to-USB adapter giving me trouble: This Interference Seems To Follow Me Everywhere
I recently bought a couple of adapters that are physically larger than the one I wrote about. I was thinking that a larger size might allow for a little more filtering and a design that does not radiate. I was half right: one of them works pretty well, the other is an RFI Bad Boy.
Take a look at this short video where I check them out.
This is an Amazon link to the adapter that works pretty well.
Enercell® 2-Port USB CLA Car Charger
73, Bob K0NR
The post Radio Frequency Interference From 12V-to-USB Adapters appeared first on The KØNR Radio Site.