Minimizing RFI and Noise

Or….

How to enjoy radio while living in the Burbs...

Disclaimer

I will refer to others work in this presentation. If I misrepresent or corrupt their ideas it is solely my

failure.

Why Do This?...Reasons Du Jour

• Subdivisions allow smaller antenna footprints-More RFI

• Houses closer together-More RFI and Noise

• Antenna closer to many neighbors

• Modern life is replete with new devices

• Want to work DX or weak signals with low or compromise antennas

I believe that:

• The single biggest reason for HF Dropouts is RFI and its affects on families/neighbors.

• How can a Ham enjoy doing radio if the family cannot watch TV?

• How can one operate in good conscience if the computer speakers are screaming while operating?

• How much info is available to help?

Natural Organization

• 1st Eliminate effects of transmitters on appliances in your home and the neighbors while simultaneously reducing CM noise propagating to your receiver

• Then improve your receiving environment by reducing or eliminating local sources

What is Common Mode?

Is there a perfect Common Mode Choke?

RFI Elimination

• Antenna Placement

• Transmission line treatment

• Station Interconnects

• Other Household devices-what to do if the above treatments don’t cure everything

Antenna Placement

• The farther the better

• At least 50 feet from your home

• Barring remote installation: choke everything

• Even if you can get 50 feet-choke everything (Received noise redux)

• By everything I mean everything

Complete Cookbook Treatment

http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf

Transmission line treatments

• Noise from your home travels by common mode to your antenna and then by transmission line mode into your receiver

• This creates increased noise in your receiver

• RFI caused by the antennas near field travels to your home via common mode

• This makes TVI/RFI

2nd Generation Feedline

More 2nd Gen

QRO Choke Impedance Sweep

Some early examples of feedline chokes

More Examples

More Early Experiments

Cable Treatments

• Common Mode impedance is difficult to anticipate-average impedance seen by a conductor may be in the range of 400-700 ohms

• Chuck recommends a minimum impedance of 1000 ohms for any CM choke (see his write-up)

Cable Treatments

• All lines running to and from the antenna must be choked

• This includes rotor, switching, secondary coax runs (like to vhf) etc.

• All cables MUST be choked at multiple places along the run

• I choke every 12 feet with at least a 1K ohm choke

A Word about Ferrite Material

• I have been using Mix 43

• Since the material in W1HIS paper was written a new Mix 31 material is available with a better low frequency performance

• I have begun using Mix 31 wherever I can

• Loads of surplus outlets for mix 43-Mix 31 not so much

Station Interconnects

• Same rules apply: 1 K ohm on all cables

• I tend to err on the conservative side: more is better with ferrite material

Other “Inside” RFI-From Xmit to device

• TV Sets• Stereo• Internet Appliances• STB/DVR etc.

• Ferrite at 1K ohm per line and cover all lines to and from the affected device. In the case of speaker leads I do both ends

So Far we have discussed:

RFI from your transmitting device into your appliances and to some

degree, reduction of received noise

Part Two: How to find and eliminate noise from your home

First Steps

• I know-resetting all of those digital clocks is a pain! But if you want to know how good it can be you must shut down your main breakers

• It helps to have a battery rig but if you don’t then leave a single branch on and CM Choke an extension cord from the wall outlet to your rig

How Bad is your environment?

• Set radio to AM Mode, Wide as it goes, pick a band and read S Meter

• Turn off house power

• Repeat tests

• The noise that is in your control is the difference in S Meter results

• Switching noise shows up as birdie like signals-it add to background but is discrete

Self generated noise is loud!

• Most modern homes have a plethora of switching supplies and other noise makers

• DVR, STB, Routers, Toothbrush chargers, water bed heaters, DC Drive appliances like washers and dryers, almost anything using a wall wart, low voltage lighting are all major contributors.

So how do I find it?

• Shut down AC to see and hear what is possible

• Re-power your home and use a B Field Receiving Loop to hunt each noisy device and quell them one at a time

• Remember-1K Ohm minimum

• Retest with B Field Loop

Some Ferrite Winding Guidelines

• When winding chokes; more is not always better

Drastic Measures

• Sometimes both transmission line filtering and common mode chokes are required

• In my home I found that direct connect switching supplies as are found in DVR’s, STB’s and FIOS battery chargers, as well as low voltage lamps required line filtering and CM choking

Line Filter Source

• http://www.hosfelt.com/en-us/dept_572.html#item_1706 (35 cents each)

• 3 Amp units

To Summarize

• Eliminate RFI by CM Choking Transmission Lines-also reduces Rcvd Noise

• CM your interconnects at the station

• Eliminate any appliance RFI by CM Choking

• ID and eliminate local sources

Some Interesting Notes

All is not what it seems...

My Hardest Lessons Learned

• RF is a lot like bugs. If you see one it is likely to be EVERYWHERE!

• Difficulty in making balanced measures with a unbalanced tool

• Taking proper care with test setups

• Repeating tests to insure consistent results

My Testing Setup

Front View of Test Setup

Recognize this?

That was a pretty good choke

Before it was put into a metal box

Back to my hardest lessons

• For anyone doubting the effects of stray capacitance-have a look at the common mode measurement of that commercial choke

• The effects of stray capacitance and what it does to high frequencies is awesome

Bad Commercial Choke

Better Home Made Choke

Better Home Made Choke

Dispelling a Myth

• Intelligent sounding documents floating around the internet and presented at DX Conventions suggest CM Chokes are bad in Balanced Line Environments

• Nonsense!

• I undertook to measure Balanced CM Chokes under stress

Testing Balanced Chokes

• If a choke is going to fail due to the balanced fields leakage into ferrite material they would fail by increased temperatures

• Did my temps go up? Yes a little but only after pumping 500 watts continuous through a choke sized for 200 watts and then only a little

Temperature Measures

Making a B Field Loop

B Field Sniffing Loop

• It should be noted that Chuck uses his loop with a receiver that has an S Meter.

• I could not find one but have found it to be very useful in spite of the lack of a meter

Thanks!

Questions?