Category Archives: RFI

Broken Links

I survey what folks that read this blog are clicking on from time to time. Lately I am seeing lots of clicks on a post that migrated here from my old W7MAP Blog  and somehow in the transfer were broken. Specifically the photos of my transmitting common mode chokes article has lost its pictures. Inasmuch as someone is searching for the photos I thought I should re post them here on this blog and attempt to repair the links. Should I fail at fixing that old post Ill re post here later today.  Just a warning for those that have seen it before that some redundant material may show up again.

Okay a late edit. I was successful in re attaching the photos to the blog entry and so, should you be interested, it can be found here. There have been some changes over the three years this feedline has been in place but none WRT to the feedline itself. The big change was the antenna going from fiberglass fishing poles to aluminum when my tree branches fell in a windstorm.

Thanks for reading my Blog. Best, Chas W5PG

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Posted by on October 28, 2011 in Radio, RFI, Stuff


Hey hey hey!

10 Meters is BACK! I may be late to the game but at least I’m now there on 10. Ive spent my hamming hours listening to the CW portion of the band and it is sounding a lot like days of yore. Yesterday I was sitting in on the T32 boys pile up and even attempted a call of two but didn’t get any responses. Just now listening to F8 station carrying on with a W2. EU has been in like gangbusters almost any morning I listen. It is now 1850 Z and still the EU stations are loud here in Texas. I have not taken a look at WSPR for spots but I bet it is loaded with DX these days. Before this past week the highest I have ventured in a very long time has been 18 Mhz.

My CW practice buddy is on holiday so I have had to root around and find things to keep me entertained as no practice of late. I finished my two snap it common mode choke data and put that to bed. I was attempting to find the best (most impedance over widest band of frequencies) while only using two snap its of ferrite. The results are posted in a previous posting here in pdf format.

While I am on the subject of ferrite again let me say something that may seem obvious but perhaps not so much if your not as persistent as I am with the stuff. For interconnecting station cables I apply a binocular choke at each end of any interconnect around my station. For example at both ends of my paddle line; or both ends of speaker connection weather it be PC to speaker or radio to speaker.  For signal sources (noise sources within your home), I apply a single choke (in most cases) at the appliance end to keep the offending noise source off of the homes power lines. Power lines are antennas and if you manage to keep it out of your AC wiring you can expect good results generally. Of course WRT noise sources some are so pervasive that more is necessary. Recall my bout with the Verizon FIOs battery charger that trashed the whole house with RFI….that took a lot of ferrites and an AC line filter too!

Well the weekend is finished and all the Aggies have returned to College Station and my daughter and her family just passed through on the way back from Colorado to Walt Disney World and return. They stopped by for a nights sleep and to pick up their dog which we were taking for the duration of the trip on the way home. Me and my dog get to sleep now!

Thanks for reading my Blog. Best, Cash W5PG

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Posted by on October 4, 2011 in Family, Radio, RFI


Some Notes on RFI

The PDF that this article points to has been removed as I had an error in my data. In actual fact I miscounted turns in the series chokes (Not the Binocular one). Inasmuch as the miscount is propagated into captured screen shots from my AIM 4170 I will need to rerun the data to insure it is correct. This may take some time. I apologize for the error and any inconvenience.


I recently attended a club meeting where a fellow asked about making a choke for his 20 Meter antenna. During that conversation I focused mostly on a two snap-it constructed choke as it is simple, works for the general 1-30 MHz range that HF ops are mostly interested in and can be repeated along a transmission line or interconnect cable to great advantage. In my case I use four such chokes along my transmission line between my amp and antenna.

The subject of how to wind these chokes came up and so I found that intuitively, I thought I knew the correct answer but I had not done the physical construction and measures to cement my thoughts. Therefore I undertook to make the measures and so have collected a lot of data that I would like to make available here. To that end Ive made a PDF and included some links to other data set pdfs so that you can manually go through the information should the graph provide  insufficient detail.

Anyway, I trust this may be of some use to Hams with RFI issues.

The document can be found here.

Thanks for reading my Blog. Best, Chas W5PG

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Posted by on September 21, 2011 in Radio, RFI


RFI Experiment

I had a few minutes to experiment this week and wanted to try something involving my 100 Mhz O’scope and a hank of wire. Impetus for this came from the fact that my wife informed me that the HDTV had its’ menu appearing intermittently while I was transmitting. I knew of course, what the issue was- I recently hooked up a new HDTV Blu Ray DVD player and failed to choke both power line to the player and its HDTV HDMI connector. The HDMI connector was but 1.5 meters long and so (I thought) it should not be coupled sufficiently to carry a lot of RF into the HDMI port. Not so fast.

My experiment entailed hooking a one meter long bare wire to channel one of the O’scope and hanging said wire as vertically as possible about 20 feet from the rig and by shortest distance from the antenna of about 45 feet. After setting up the O’scope I went into the radio and began sending dits or dahs (I forget which) and running out to the O’scope to measure my received RF Envelope before my keyer timed out. I did this on 18 Mhz.

After doing this several times I averaged my readings on the scope and found that while transmitting 500 W output to an antenna 27 feet up and 45 feet away from the one meter sensing wire I could measure 3.5 volts RF peak to peak.  If you consider it takes but 1.4 volts to turn on a transistor junction, you can readily see why RFI is so prevalent. Most devices are connected via wires much longer than one meter.

And so, after I measured the RF Envelope, I returned to the new DVD player and choked off both power and HDMI with binocular Mix 31 snap its and as if by magic no more intermittent menu’s popping up on the TV set.

There is never enough ferrite.

Thanks for reading my Blog. Best, Chas W5PG


Posted by on September 10, 2011 in RFI


It’s Been a Long Hot Summer in Texas

I cannot recall a summer so hot. Not warm, not sweltering but just plain hot. Haydes hot. I mean cooking eggs on sidewalk hot. The pool felt like a bath tub mostly throughout the summer which is a less than a desirable way to enjoy a place designed to help cool you off. Finally, it seems as though the back of this oppressive heat is broken. None to soon methinks.

Radio activity has been consistently minimal throughout this period. Daily code practice is about all I could muster energy to get done. I continue my morning walks and attempt to keep my eating regimen up but Ive failed miserably at weight loss since June 19th when I hit my modern day low in that category. But life is generally good and I have time to catch back up with the weight goals. Rome wasn’t built in a year.

The amp continues to work well and my battery backup system for the little rig on the shelf (IC-735) seems to be working well although I still need to find a good GSM cell to add a little more hours to its discharge life. I managed to find a little Fair Rite Mix 31 surplus the other day so I snatched it up quickly to add to my RFI fighting tool kit. I fight precious little RFI these days as I have deployed a lot of ferrite material around but one never knows when someone will have a problem that needs fixing, and Mix 31 is almost never found surplus so I grabbed it.

My son is back at A&M again with a new set of wheels provided by his sister. A 2000 Jeep Cherokee that was extra to their needs and since Matt sold his car to help defray expenses with school it came in very handy and was a timely addition to the family. This semester should prove or disprove his desire to proceed with a degree in Meteorology. I admire his tenacity, but Calculus 3 and Calc based Physics in a single semester seems daunting to me. So we shall see. I only hope that Corps activities don’t manage to divert all his time away from school work. News at eleven as they say on TV.

Ive been getting excited about taking my little Questar 90mm cat out to look at the stars again this fall. Our city sky is too light polluted to see much in summer as the atmosphere seems full of debris and particles. The sky gets darker in Fall and Winter as the air clears out a lot. This summer must be the summer of re-reads as I have been plowing through some old shelf books long forgotten. For read number five or six now I finished Starlight Nights, while later this summer I am enjoying all over again some John Graves Texana writings and also finished up the road book series written by Edwin Way Teale; a set of four books describing  America during each of the four seasons. I may yet find some long forgotten tome that I will like to read again but in the meantime Ive got a book from the local library by David McCulloch called the Greater Journey, a story of Americans in Paris during the early nineteenth century. So far it is a good read. I think I have read all but one of his historical books and the last is in process now.

A few years ago I posted some nonsense here about Anole Lizards taking up the challenge of replacing the Palos Verdes Sundancers….this in response to our long drought of spots. Well I am glad I got that inspiration when I did as this summer has been so hot and doughty that the erstwhile Anole has all but disappeared from our yard. No help for the sun this year! No more bivouacs of Anoles dancing to the beat of modern jazz or god help us Rap!. Only blistering, searing Texas styled heat and zero rain. Perhaps they will return for another try in Fall.

Thanks for reading my Blog. Best, Chas W5PG

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Posted by on September 3, 2011 in Radio, RFI


Ham Radio and the “New Normal”.

Traditionally, ham radio becomes more interesting and engaging with the addition of tall towers, larger antennas or more flexible and better performing radios. Every hobbyist longs for that new rig or improvements in station  design for capturing that new and rare DX station, accumulating more contacts in a shorter period or working more stations with less power in less than ideal conditions, whether it be trail side or at home. Increasingly though, we are being masked from capturing the utility of these ever expanding improvements in technology by living in a cloud of RFI. In my experience, most enthusiasts do not recognize the encroachment as it comes in small steps, and then one day,  with a new source added,  you find yourself overwhelmed by noise.

Ham Radios “New Normal” is increasingly akin to a bird watching experience in a wet and dense foggy morning. Only with bird watching one can wait until the fog burns off with the advance of the light of day, while in our hobby we can never rid ourselves of the local “cloud” of RFI. Each and every time we, in our own home, or one of our ever closer neighbors purchases a new gadget or appliance we add to an already thick blanket of interference surrounding our radios. Most of this mist violates current good practice and perhaps FCC Rules but it matters little as there is no enforcement. It comes to us then to police our environs and track our quarry while exercising our best community citizen face forward. It used to be simpler. A faulty electric fence, a leaky power pole or some easily tracked arcing switch that ofttimes gave off as much light  as RFI to telegraph its presence. Nowadays, to meet Green Power and efficiency standards we see ever more small switching power sources, each with less and less RFI filtering and adherence to good design practice. Economics rule the day in this arena and not good engineering.

This “New Normal” requires a change in thinking. It becomes our own economic war to wage. Where to best spend our scarce hobby dollars? A new tower? A new radio? Or better spent in noise abatement? Over the last three or four years I have become increasingly convinced that unless and until my local environs are cleaned of every bit of RFI in my control, that adding more sensitivity, a new higher tower or support or other accoutrement to my radio ensemble is money wasted, and would be better spent in reducing my local noise. Adding a new tower or larger antenna and keeping a local noise environment intact is an invitation to being heard better but not getting any advantage on receive. It becomes an advantage divided by two. One may say that engaging in noise abatement is also an advantage divided by two as it contributes nothing on transmit. Granted, that is true to a degree. However, there remains one overriding caveat with that equation, and it tilts toward noise abatement first: You cannot work them if you cannot hear them. Additionally, that cash spent on noise abatement can mightily contribute to lower TVI/RFI while on transmit. Transmission line chokes prevent, to a large degree, this phenom.

Noise abatement is a change in thinking. It is a skill that needs to be acquired and that requires some work. It isn’t as simple as plunking down some cash or a credit card and installing a new tower or purchasing a new radio. Gaining those skills in noise abatement may not solve the noise problem forever: things change and so do home appliances and gadgets, so it is an ongoing challenge.  Someone once wrote me a note suggesting that noise abatement equipment was expensive. I would ask which is more expensive, a new radio that provides no advantage, a tower or antenna that “hears” no better than an older model, or, flipping the question, perhaps you can make do with a dipole and forgo the tower/beam and work everything you wish? There are advantages outside those that may immediately come to mind, such as ones age and how much longer we can climb said tower, or perhaps neighbors and the increasing visual standards that are acceptable or perhaps new covenants and restrictions.

This local noise problem is encroaching more every day. On one hand Hams are getting squeezed by the aforementioned proximity to neighbors and increased restrictions while on the other hand, we lose ground to ever more populous small switching supplies to meet efficiency standards. Each trip to the department store produces more challenges and opportunities. We as a community should become more proficient at dealing with this issue or it may well become our undoing.

Thanks for reading my Blog. Best, Chas W5PG

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Posted by on October 23, 2010 in Radio, RFI


A Few Feet Short of Amazing

The last few days following our effort in the Cal QSO Party has been pretty interesting from a noise redux perspective. With Chuck here we managed to further quiet my nasty 60 Hz buzz from the FIOS battery backup charger. That alone resulted in a 2 S Unit reduction of my noise level on 20 Meters. The messing about with Gas Meter and AC cooling copper lines took out a nasty intermittent that really wiped out 30 Meters.

This afternoon on our regular CW Practice Sked, Chuck asked me how much the total effort had yielded to date all up and in WRT to noise reduction? To begin with, when I first started noise hunting I had no transmit feedline chokes, no ferrite around anywhere and I was using an inherently noisy antenna -a vertical. From that setup to current has seen a vast improvement. Just examining 20 Meters, I started with an S Meter reading of S-9 plus 10 DB. This measured in AM mode at 9 Khz bandwidth with Preamp 1 set to “On”.  Today that reading is S-5 with the same set of measuring parameters. Along the way I calibrated my S Meter by building an Elecraft Xtal Calibrator and a Step Attenuator kit, also from Elecraft. I measured my S Units at 3 DB per step or 3 DB between S-1 and S-2 etc all the way to S 9. Above S-9 the DB measure on the S Meter compared favorably with the Elecraft Step Attenuator.  Using 3 DB per S Unit I come up with a  measured difference of 22 DB change in noise levels here based  on active noise searching and antenna changes. Unfortunately, I did not note how much change the Vertical to Horizontal antenna switch made.  All in all a respectable change up in received noise hereabouts.

When running a station with low power or low antennas it is doubly important to reduce the local noise cloud-that is whatever is in your control. I find that it has been well worth the effort.

Thanks for reading my Blog. Best, Chas W5PG

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Posted by on October 12, 2010 in Radio, RFI


Heater and Water Heater RFI Proofing

The other day I mentioned having RF Hot plumbing. I thought I would post a picture of some of my RFI prevention ideas. It is important to remember that I worked on both ends of this natural gas and copper run. When I sniffed the closet on the first day it had Hot RF on both Natty gas and AC copper tubing to the AC air handler mounted above the Trane Heating unit. It was also hot outdoors where the copper entered the AC Condenser unit as well as the Natural Gas entry into the house. I first clamped ferrites all along the copper AC plumbing and also the NG flexi tubing in this closet. Then I went outdoors to the AC unit and it was quiet-a lot quieter than on the previous day, however the Gas Meter end of things was still very RF Hot. Lastly I reattached the loose ground at the Gas Meter end outdoors. I am not sure which element fixed the noise but it has been gone for 2 full days now. I should pull my snap its and see if the noise comes back and may yet do that, but for now I will leave them in place. The RFI problem could have been caused by a rusty bolt or some rusty hardware that I disturbed when putting the ground wire in place. We have a commercial radio broadcast station within a thousand feet of my house and the Gas Meter hardware is rusty. Rusty hardware in the presence of a strong RF Field is essentially a back biased diode and gens up severe RFI broad banded. Strength depends on multiple factors but field strength is pretty important. My sense is that the rusty hardware was not the primary cause as the nature of the RFI was modulated by 60 Hz and had the normal buzzy character. The noise could have been a composite of all of these things as well. The point again is that just because it runs to ground or through ground does not mean it is incapable of carrying RFI. Test everything.

I test for RFI (sniffing) with a cheap shortwave (Yachtboy) and a homemade B Field RF Sniffing loop that has been detailed on this blog several times. Here then is a photo:


Snap its applied to metal plumbing.


Thanks for reading my Blog. Best, Chas W5PG

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Posted by on October 7, 2010 in Radio, RFI


RFI and Verizon FIOS Installations

One of the things I accomplished while Chuck, W1HIS was here is to address the FIOS battery backup charger RFI that was present in my background noise. Without a doubt, this single device puts out more RFI than any other device I have encountered. The Direct TV HDDVR was bad enough but this one takes the cake. I had it RFI’ed but certainly not well enough. I had put several binocular Mix 31 chokes on both input and output but felt I was in need a a differential line filter for the unit plus much more ferrite on the output side of things. Inasmuch as this unit is owned by the utility I also believed that to cut and splice their AC Line cable should be approached with caution-hence I never did it. However, while Chuck was here he suggested applying more ferrite to all cables surrounding the unit and all associated cables to lamps, telephones etc as these were all coupled to the FIOS battery charger through E Field coupling due to proximity. I was unable to apply more ferrite to the output side but did manage to apply much more to the input (117VAC) side of the unit. This application, together with the ferriting of the associated close proximity cables took 2 S Units of background noise out of my received noise level on 20 Meters. It also reduced my noise level on 17 Meters to almost zero. The way we check noise levels is to open up my bandwidth to 9 Khz and place the receiver in AM mode. Any S Meter readings I refer to will be done in this manner. For several years my received 20 Meter noise level has varied between S-5 and S-7 and now it has been routinely at about S 3 to S4. A rather nice improvement.

In the following picture you will see the power strip covered with ferrites. I had them on the shelf and so I just went whole hog so to speak and maxed out the coverage. I have done similar installations to all of my computer monitors in or close to the shack. Tracking local noise sources seems like a never ending chore.

Verizon Fios Battery Charge Switching Supply (48 VDC)

Thanks for reading my Blog. Best, Chas W5PG


Posted by on October 7, 2010 in Radio, RFI


Some Pix of the Completed Feedline Project

I wanted to add a few pictures of my feedline project. I will describe it with words then with some photos. I am not sure if I can retain all of these pictures because of space limitations. However, I will wing it initially and see how it goes.

It should be noted that this is a joint project of two Hams and, with deference to privacy, I acknowledge his contributions and would like to say publicly that I would never have arrived at this place without his instruction and patience.

Since this antenna is intended to be used on all bands from 40 meters to 10 meters at legal power, certain performance criteria need to be maintained. Physical and electrical integrity is paramount due to high voltages present along its route. This balanced feedline was constructed to accomplish two goals. One goal was to fabricate a balanced feedline system that would allow legal limit use with no failures due to high swr induced voltages. The second goal was to marry the well constructed physical line with a set of balanced chokes capable of handling legal limit power levels while maintaining electrical integrity. After 4 weeks of service I can safely say both design goals have been met.

Balanced common mode choking in a feedline such as mine is used to reduce common mode RFI from propagating in both directions along the feedline. Balanced common mode choking accomplishes this while having little to no effects on transmission line signaling. Common mode chokes suppress near field RFI from being conducted back along its length into the shack and it also suppresses ac switching and locally generated household noise from propagating up the feedline in common mode to the antenna and then back into the transceiver in transmission line mode. In doing this exercise I have minimized the RFI into my home in the form of TVI and RFI and reduced my noise floor in my receiver to a very low level. The feedline is not doing all of the noise mitigation, but it goes a long way toward dropping my received noise levels. Each choke box contains one choke with a common mode impedance of 2700 ohms at 14 MHz. The impedance curves are presented elsewhere on this Blog. The feedline is constructed of one eighth inch phosphor bronze wire rope. The insulators are fiberglass rod stock cut and drilled and then epoxied to the PB wire rope. The sources were Surplus Sales of Nebraska and U.S. Plastics Corp. The Boxes contain a single choke constructed with Mix 43 Fair Rite toroids and the center conductor of RG-393 coax which is made from teflon. I removed the shields.

The common mode chokes are impedance potholes. No regard is payed to the impedance bumps that they present to the feedline. Choking impedance is 2700 ohms at 14 MHz. Through impedance is about 110 ohms at almost all frequencies between 1.8 and 30 MHz. There are 4 chokes along the feedline. Two at the feedpoint of the antenna separated by 6 feet and two at the exit to my shack, also separated by 6 feet with the first choke located at the tuner output.

Here then are a few pictures. All hardware is stainless steel save the crimp on lugs and swage’s which are standard metal hardware.

Feedline Curing Epoxy

Prepackaged Common Mode Choke.

Choke fitted into its outdoor box

Swaging completed choke onto completed feedline.

Completed feedline with chokes swaged in place

Antenna Mast with Antenna, Feedline and Choke Boxes in place

An interesting aside. While I was redoing my antenna feedlines, I changed the dipole wire from AWG 22 stranded to AWG 10 (105 strand) which modified the antenna efficiency as modeled in NEC 4 from 91% to 99.X %. Wire size alone bumped efficiency 8 %.

I hope this describes in sufficient detail the whole of my feedline project. Should anyone wish to duplicate this project or ask questions I can be reached at the email address noted at QRZ.Com.

Thanks for reading. Best, Chas W7MAP/5

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Posted by on August 3, 2008 in Radio, RFI, Stuff




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