As Jamie, WW3S pointed out with the Telephone/cable-modem UPS as RFI Sources
even when AC power is turned off at the main breaker panel, some other home UPS
units for computers or any smart appliances are also possible sources as they
have back-up batteries converting DC to AC power. Just killing AC power may no
longer eliminate our homes as a possible RFI source.
73, de ed -K0iL
-----Original Message-----
From: RFI <rfi-bounces+eddieedwards=centurylink.net@contesting.com> On Behalf
Of WW3S
Sent: Tuesday, December 22, 2020 17:00
To: donovanf@erols.com
Cc: rfi@contesting.com
Subject: Re: [RFI] QUESTION
One caveat to kill all the breakers....if you have phone service along with
cable tv, you probably have a battery backup in your modem to provide phone
service in the event of a power outage....that may be one of your sources of
local rfi, and you may spend weeks trying to track it down outside your home,
when it really is just sitting on a desk in the home office .....cable company
changed out old modem for new one....at least for now, the rfi from my home is
gone, but the other 110+ homes in the subdivision, that’s a different story....
Sent from my iPad
> On Dec 22, 2020, at 4:53 PM, donovanf@erols.com wrote:
>
> Hi Gary,
>
>
> The process for identifying this type of RFI is the same as for any
> other RFI, except you need to use your transmitter to excite the RFI
> generating source.
>
>
>
> First verify that the RFI is not coming from your own home
>
>
> - kill all of the circuit breakers in your home and power up ONLY your
> transmitter. All accessories should be DISCONNECTED from AC power. You
> may need to use your amplifier to produce enough RF to trigger raspy
> harmonics from RFI generating source.
>
>
> - Put your transmitter on the air, keying it from a memory keyer is a
> good approach
>
> - if the raspy harmonics have gone away, start turning on the circuit
> breakers in your home, one by one, until the raspy harmonics reappear.
>
>
> If you determine that the RFI is not being generated in your own home,
> turn your directive antenna in the direction that produces the
> strongest raspy harmonics. A sensitive spectrum display such as the
> Elecraft P3 helps immensely.
>
>
> Then use a portable receiver to hunt for the RFI source along the line
> of bearing identified by the previous step.
>
>
> Good luck
>
>
> 73
> Frank
> W3LPL
>
> ----- Original Message -----
>
> From: "Gary Johnson" <gwj@wb9jps.com>
> To: rfi@contesting.com
> Sent: Tuesday, December 22, 2020 12:48:16 AM
> Subject: [RFI] QUESTION
>
> That’s easy. RF is picked up on the AC lines then enters any nonlinear device
> plugged into those lines, such as a walk wart. There, RF is rectified,
> harmonics are generated, and that’s mixed with all the garbage on the power
> line, then re-radiated via conducted emissions. Many harmonics are normally
> expected. This is the classic problem for any SO2R or M/M station.
>
> Case study: At 8P5A, Tom has very little ancillary stuff plugged in and yet
> he had your problem. He traced it to a single LED light. Once removed, the
> harmonic garbage disappeared.
>
> Gary Johnson NA6O
> gwj@wb9jps.com
>
>> On Dec 21, 2020, at 4:06 PM, rfi-request@contesting.com wrote:
>>
>> From: David Eckhardt <davearea51a@gmail.com>
>> Subject: [RFI] QUESTION
>>
>> I'm out of ideas on this one! Where does the raspy modulation come
>> from on the harmonics which changes with position in my radio room on
>> a battery operated receiver?
>>
>> Situation:
>>
>> transmit on 7.010 MHz
>> receive on second harmonic, 14.020
>>
>> transmitter: IC-7300
>> receiver: IC-7610
>> and reversed
>> Demod: CW or SSB (or AM, for that matter)
>>
>> Fundamental sounds clean. Second harmonic sounds modulated by 120-Hz
>> (and a few harmonics of the line) and quite raspy - pretty awful.
>>
>> Receiver: portable battery operated receiver (Grundig G3) with same
>> transmitters: I can walk around the room tuned to the second harmonic
>> and find places in the room where things are clean and other
>> positions where the second harmonic (and third) sound awful with 120
>> Hz raspy 'modulation'. Any idea how I can account for this localized
>> behavior? I'm out of theories.
>>
>> Dave - W?LEV
>
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