I would also disconnect the 75-ohm coax that connects up to the modem if
you have BB service as that line is hot with all kinds of RF.
Gedas, W8BYA EN70JT
Gallery at http://w8bya.com
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 12/23/2020 1:28 PM, Eddie Edwards wrote:
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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