On 7/27/2018 10:49 AM, Stan Zawrotny wrote:
I have been troubled for quite some time with our smoke detectors
frequently beeping (two beeps) when I am working HF. It is worst on 80 and
40, but also occurs frequently when I am on 15 and 20 meters. The beeping
will be intermittent at intervals of 1-3 minutes and will last for a couple
of minutes after I am through transmitting.
Describe these units -- are they "free-standing," with no connected
wires, or are they wired to a central unit?
I has happened with several rigs. Yaesu FTdx5000, Flex-6600M and Icom
IC-7300, at power ranging normally from 50-100 watts.
Of course, the antenna system is likely the culprit. It consists of several
OCF dipoles: one 160-10 M and two 80-10 M. (I know OCF dipoles are bad for
RFI). All have 1:1 baluns at the antenna and at the shack.
I have tried clip-on ferrite beads on the power leads of the smoke
detectors without luck.
Of course they don't work. Study k9yc.com/RFI-Ham.pdf
I just bought a DX Engineering Feedline Current Choke (DXE-FCC050H05-B)
that is supposed to suppress RFI on antenna leads. That is ineffective.
Where is it installed? To be effective it MUST be at the feedpoint
(that is, where the feedline connect to the horizontal part of the antenna.
I am now considering replacing the entire smoke detector system. We share a
house with my daughter and there are 9 units tied together in the system,
so the cost will not be small.
AH! Now we see the problem -- all that interconnect wiring is a receive
antenna, picking up your transmitted RF FROM THE ANTENNA and getting
detected in those units. In general, alarm and security systems of all
types are notorious for poor design and construction that CAUSES RFI to
their system. Likewise, the power line (via the power supplies to the
unit). At a minimum, ALL of that wiring should be twisted pair, and ALL
of that wiring should have a GOOD common mode choke at each end. By
"good" I mean follow the guidelines in k9yc.com/RFI-Ham.pdf CAT5/6
cables consist of four excellent twisted pairs.
Are there other solutions?
Are there brands of smoke detectors that are less susceptible to RFI than
others.
I can't help with that.
73, Jim K9YC
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