Hello Don,
Thanks again, I am learning a lot from this thread. The 1" sniffing loop
trick looks great! I am surely going to build it. I am sure this is not
the last RFI I am going to encounter. I have started collecting parts
for the pre-amp.
The main breaker is outside the house but inside his gate and I have
access to it. The individual breakers are inside. There is a big box
that has fuses to individual houses. I have access to that as well. I
think it will come handy to have a sniffing loop. Thanks again.
73
Ram VU3RDD
On 21/07/2021 14:25, Don Kirk wrote:
Hi Ram,
I don't know if you can get access to your neighbors circuit breaker box
or what his circuit breakers even looks like, but I have had great
success using a simple 1 inch loop to sniff circuit breakers to find
what circuit the device is located on that's causing RFI (you can
consider this 1 inch loop an H probe). Typically the RFI from the
faulty device is conducted onto the electrical house wiring and then
radiated from the house wiring versus being radiated directly from the
device.
I recently found my own microwave oven control panel was generating RFI
using this simple circuit breaker sniffing technique. The sniffing
method said my microwave oven circuit was causing the RFI and then I
sniffed around my microwave oven and found its control panel/display
unit was generating the RFI. I have also used this simple sniffing
method on circuit breakers at a large apartment complex to find the
circuit that the device generating RFI was located on without the need
to shut power down to the entire apartment complex as an example.
Here is the link to a video showing the small 1 inch loop I use for
sniffing circuit breakers after I had identified the suspect circuit
https://youtu.be/UqLQ-mmUrVA <https://youtu.be/UqLQ-mmUrVA>. I just
pass the 1 inch loop over the top of each circuit breaker listening for
which circuit breaker produces the strongest interference, and this
typically allows me to identify the suspect circuit.
My 1 inch sniffer loop is just a short piece of coax (like 2 feet long)
where I expose the last part of the center conductor and make a 1 inch
diameter loop out of it and connect it's free end to the shield (very
simple).
Just another trick you might be able to use if you think you have
identified the correct property generating the RFI, but please be
careful (remember safety first).
73,
Don (wd8dsb)
On Wed, Jul 21, 2021 at 3:31 AM Ramakrishnan Muthukrishnan
<ram@rkrishnan.org <mailto:ram@rkrishnan.org>> wrote:
Hello Don, Dave, Jim and others:
Thanks so much for all the wonderful information. I have started
reading
the articles mentioned in order to build a DF loop. I think I am going
to try Don's design along with a pre-amp.
Apparently the next door neighbour (the houses are densely packed here,
so next door is "literally" 5-6 ft away) has a 4kVA inverter. Last
night
when everyone is asleep, I stepped out with a shortwave receiver
(sangean radio which I borrowed from another friend) and could zero in
on the neighbour's house more or less. I initially suspected his fridge
and politely asked him to turn off the fridge for a few minutes while I
am looking at the spectrum. The birdies remained (assuming he actually
turned it off). He did mention that he has a 4kVA inverter powering
everything from refrigerator to other devices. That is the prime
suspect
now because these birdies are present 24x7.
Going to do an on/off test of the inverter (if the neighbour is
willing)
this weekend. Here in the India, there is very little one can do about
flagging violations. So, perhaps installing an x-phase based canceller
is probably going to be the only workable solution for my shack. :-( I
feel bad about letting a known source pollute the RF spectrum and I am
going to try my best to fix it somehow. May be buy toroids and wrap the
outgoing mains from his inverter or see if the chassis is properly
grounded on the outside.
73
Ram VU3RDD
On 21/07/2021 06:03, Don Kirk wrote:
> Hi Ram,
>
> I recently built and tested side by side numerous direction finding
> tuned loops, untuned unshielded loops, untuned non shielded
loops, loops
> with chokes, loops with transformers, terminated loops, etc.
>
> Based on all my testing the simplest but still reliable
bi-directional
> antenna for MF and HF portable direction finding that you can go
with
> would be a simple single loop of wire similar in size that Dave
(W0LEV)
> mentioned (12 to 17 inches in diameter) fed directly with coax,
but you
> need to use a choke right at the antenna feedpoint consisting of 14
> turns of coax (RG58 or RG174, etc.) wound on an FT240-31 toroid core
> (this choke is based on the K9YC choke design). I would use
enough coax
> to get the 14 turns of coax wound on the toroid core plus another 36
> inches for running to your preamp or receiver input. The output
> impedance of this single turn loop is reasonably low, and you can
> therefore connect it direct to the 50 ohm input on your preamp or
> receiver, etc (no transformer required). If you omit the choke, the
> antenna balance is not reliable depending on what frequency you
use the
> antenna on (the feedline becomes part of the antenna which then
alters
> the pattern and you will find big differences in the depth of the
nulls
> and even experience only one null depending on how high in
frequency you
> go). This antenna will be bi-directional if built properly.
>
> The other simple option that I prefer is a untuned shielded loop
like
> Dave mentioned made with a piece of coax. I tested numerous
designs,
> and the most reliable and easy to build untuned shielded loop for
full
> MF and HF coverage is what I call a traditional untuned shielded
loop in
> which the shield of the coax that makes up the antenna has its
shield
> exposed (jacket removed) near the antennas connector and the far
end of
> the coax (coax that makes up the antenna) shield and center
conductor
> connect to each other and they are then soldered to the shield
that was
> exposed near the antennas coax connector. Then about 1 inch of
shield
> on the coax that makes up the antenna is removed at the center of
the
> loop which was formed by the coax. You can then feed this simple
> untuned shielded loop directly into your preamp or receiver since
once
> again the impedance of this untuned shielded loop is reasonably
low (no
> transformer needed). A choke is not needed because the shielded
loop
> has a built in balun based on the geometry of the design. This
antenna
> is really my favorite portable untuned bi-directional loop. Once
again
> I would make it about 12 to 17 inches in diameter (the larger it
is, the
> more sensitive it will be but you need to stay 0.1 wavelengths in
> circumference or smaller).
>
> The signal strength of the interference will dictate if you need a
> preamp or not regardless of what portable MF/HF direction finding
> antenna you use. A 20 dB preamp will normally be adequate in all
but
> the weakest levels of RFI. My favorite preamp is the DX Engineering
> preamp that was designed for use with my portable flag, but I
also like
> the W7IUV preamp which you can power with a 9 volt battery for
portable use.
>
> My favorite antenna for direction finding is the portable flag I
> designed for radio direction finding that Jim (K9YC) mentioned since
> it's unidirectional and this antenna saves me an enormous amount
of time
> since I instantly know what direction the RFI is coming from (no
need to
> triangulate like you have to do with a bi-directional antenna in
order
> to determine what direction the signal is coming from). Here is my
> simple website that describes the portable flag, and it really is an
> easy antenna to build, but once again you will likely need a preamp.
> https://sites.google.com/site/portableflagantenna/
<https://sites.google.com/site/portableflagantenna/>
> <https://sites.google.com/site/portableflagantenna/
<https://sites.google.com/site/portableflagantenna/>>
>
> You could also just go walking around with a portable shortwave
receiver
> and whip antenna looking for the strongest signal, but that's
really a
> process that can cause a lot of indecision and guessing.
>
> P.S. it does you no good guessing what device is generating the
RFI as
> long as you understand its behavior (example: on 24 hours a day, not
> drifting, what frequencies you hear it on, etc). You first must
locate
> the property where the RFI is coming from using radio direction
finding
> gear, and then you can figure out what the device is.
>
> 73, and let me know if you need more details on the antennas I
mentioned
> above. I have lots of pictures and diagrams I can share with
you, and
> they really are simple to build.
>
> Don (wd8dsb)
>
--
Ramakrishnan
--
Ramakrishnan
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