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Author Topic: electrical interference  (Read 750 times)
KE8MCR
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Posts: 27




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« on: July 12, 2019, 10:23:37 AM »

New to the hobby. I purchased an ICOM 7300 and have an MFJ 6-40 cobweb antenna. On the waterfall screen the 40 meter band shows little interference. However, the 20 meter band shows quite a bit. Any suggestions?
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KE6EE
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Posts: 2794




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« Reply #1 on: July 12, 2019, 11:50:55 AM »

A huge topic. There is a forum right here on eham devoted to interference/EMI/RFI problems.

Go to that forum. Look at the subject areas which are directly or may be indirectly related to yours.

You will learn a lot by doing an hour's worth of reading. Some of the primary things you will learn
have to do with understanding the sources of RFI/EMI and how to identify such sources.
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WA3SKN
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Posts: 6991




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« Reply #2 on: July 12, 2019, 02:44:44 PM »

Do you hear/see any interference when connected to a known good dummy load?

-Mike.
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SIMON123
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Posts: 128




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« Reply #3 on: July 12, 2019, 04:09:06 PM »

"the 20 meter band shows quite a bit", seem noise level at S3 to S5 is normal, at "lower HF" frequency. Conditions and results vary largely.

Try compare your site receive condition with websdr remote receivers, best in near by area. Try 9V1RM and PI4THT

A few months ago, the SDRPlay sdr receiver company official forum (not here) has a formal detail analysis discussion on how low noise can a site get, under best conditions. ITU-R has formal report / handbook guide, if you want details.
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K0UA
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Posts: 4364




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« Reply #4 on: July 12, 2019, 04:30:33 PM »

Take a screen shot with the 7300 (its in the manual) but just momentary press the power button, not long enough to turn the rig off.  It will take a picture of the screen itself.  Then take the SD card out and shove it into your pc so you can post the image to a site like postimage or other photo sharing site. Then post the URL for forum size into a response here so we can see the photo. We might be able to help.
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73  James K0UA
ARRL Missouri Technical Specialist
KE8MCR
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« Reply #5 on: July 13, 2019, 05:15:32 AM »

Good thoughts
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G4AON
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Posts: 1382




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« Reply #6 on: July 13, 2019, 05:52:34 AM »

While the antenna has a “matching box” and a few ferrites slipped over the feeder, it might benefit from an effective feedline choke to reduce electrical noise from house wiring reaching the antenna. For 20m you could try coiling the coax, 11 to 16 turns of RG213 as per the chart here: http://karinya.net/g3txq/chokes/ is worth a try.

73 Dave
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WA7ARK
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Posts: 621




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« Reply #7 on: July 14, 2019, 12:12:53 PM »

My take on how to minimize receiving QRM from stuff inside your own house.
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Mike, WA7ARK
K6BRN
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Posts: 1269




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« Reply #8 on: July 14, 2019, 01:01:48 PM »

Mike (WA7ARK): 

Good advice...

Quote
The secret is common-mode choking and grounding on all the coaxes that come into the hamshack.
If your antenna has common mode current flowing on the coax toward the shack, put the CMC on the outside of entry panel

This is exactly what I do.  This and a few other steps (toroids with several loops through them for all control lines) pretty much eliminates RF problems in the "shack".

But in two QTHs, a lot of noise was being coupled into the station via the house (plug) ground from inverter driven appliances.  So I've run dedicated power and ground lines directly from the electrical entrance panels to the rooms housing my radio equipment and that ground is further bonded to a cluster of ground rods that have my coax ground blocks directly connected to them and to my station "single point" ground.  Pretty much killed the noise from the iA/C, washer and dryer.  No RF problems, either.

ALSO....

Just came from a club meeting.  One ham has his antenna 6 feet away from his operating station and gets quite a bit of upsets on his USB interface doing so.  He runs 100 watts and want to move up to 500W+.  XYL will not let him move the station, HOA will not let him move the antenna.  Basically... a social engineering problem.  Not all problems ae technical!

Brian - K6BRN
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K6AER
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Posts: 5690




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« Reply #9 on: July 14, 2019, 04:25:35 PM »

My first wife did not like ham radio.
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WA7ARK
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Posts: 621




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« Reply #10 on: July 14, 2019, 06:32:58 PM »

My first wife did not like ham radio.
My first wife didn't like light aircraft; my second wife is a pilot...
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Mike, WA7ARK
K6BRN
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Posts: 1269




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« Reply #11 on: July 14, 2019, 07:54:52 PM »

Wow!  I really lucked out.

My 1st (and only) XYL makes suggestions, but pretty much tolerates all of the goofy stuff I've done and do.  And... it's very much a two way street.  She is a formidable but very tolerant lady.
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NK7Z
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Posts: 2504


WWW

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« Reply #12 on: July 14, 2019, 08:49:54 PM »

New to the hobby. I purchased an ICOM 7300 and have an MFJ 6-40 cobweb antenna. On the waterfall screen the 40 meter band shows little interference. However, the 20 meter band shows quite a bit. Any suggestions?
I have an extensive RFI location and mitigation section on my web page at:

https://www.nk7z.net/category/info/rfi-mitigation/

Also there is a handy RFI location flow chart at:

https://www.nk7z.net/i-have-rfi-now-what-locating-it/

Take a read, and do a few tests as outlined there, you may be lucky and find it is within your own home...
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Thanks,
Dave
Amateur Radio: RFI help, Reviews, Setup information, and more...
https://www.nk7z.net
KA4WJA
Member

Posts: 1098




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« Reply #13 on: July 17, 2019, 09:22:16 AM »

Brian.
My HF set-up on the boat has my HF antenna (remote-tuner fed ~60' vertical) just couple inches from my solar array, and with the base just a foot or so from other electronics wiring (not running parallel)....and with HF Radio (Icom M-802) and mic wiring, etc. just a few feet away...and with all sorts of sensitive electronics on-board, all within just a few feet of the antenna, and all with their own wiring (acting as their antennas)....I have a bit of experience mitigating RFI...

The good news is, I have NO transmit RFI...I don't "get into" anything on-board, no computer issues, USB issues, etc...(although many years ago, when using a remote-mounted USB-based ext Wi-Fi radio, and some "active" 15' long USB cables, I did have some occasional internet drops...but the USB cable ran within 1 foot of the base of the HF antenna, and the ext Wi-Fi radio itself was just 2.5 feet away from the HF antenna)

And, no issues with receive RFI either....except for a couple low-level birdies from the solar charge controllers, that don't move the S-meter and never cause any issue, and some low-level birdies from a refrigeration compressor controller (a Danfos DC-to-3-phase AC inverter/controller, that is just a few feet away from the HF antenna), I have NO receive RFI at all!

An excellent antenna ground;  "line isolators" and common-mode chokes at both ends of the radio-to-tuner coax and control cables;  judicious use of ferrites on all other electronics wiring, etc....and you can operate an HF 100 - 150 watt HF station (I also used to have a 500 watt SGC amp on-board, and no RFI issues when running 500 watts, either) right next to lots of gear, without issue....
(and remember I'm running an end-fed vertical, not some balun-fed 1/2-wave dipole)


As I'm sure you know, a good antenna ground and lots of common-mode chokes (half-dozen turns thru a Mix 31 core, etc. on ALL USB wiring, ALL Ethernet wiring, and ALL radio, ALL computer, and ALL USB-peripheral power wiring, will help your friend...but, also...

ALSO....

Just came from a club meeting.  One ham has his antenna 6 feet away from his operating station and gets quite a bit of upsets on his USB interface doing so.  He runs 100 watts and want to move up to 500W+.  XYL will not let him move the station, HOA will not let him move the antenna.  Basically... a social engineering problem.  Not all problems ae technical!

Brian - K6BRN

But, also thought you may wish to point him to some useful "ham accessories" that should be of great help as well...

For Ethernet RFI issues:
https://www.dxengineering.com/parts/dxe-iso-plus-2


For USB / Serial Port issues:
https://www.kkn.net/~n6tv/S-BOX/index.html

https://store.djtechtools.com/collections/chroma-caps-cables/products/chroma-cables-usb-c
(great USB cables)

https://www.usbfirewire.com/parts/rr-usb2-hub7.html#RR-USB2-HUB7
https://www.usbfirewire.com/parts/rr-usb3-hub7.html#RR-USB3-HUB7
(great USB hubs)


And, of course there are Jim, K9YC's pages...
http://audiosystemsgroup.com/RFI-Ham.pdf

http://audiosystemsgroup.com/NCDXACoaxChokesPPT.pdf

http://audiosystemsgroup.com/2018Cookbook.pdf


And, also this:
https://www.aa5au.com/rtty/rfi/


Pass this onto your friend at the club meeting, and he mat find some peace.  Smiley

73,
John, KA4WJA


P.S.  You see, I do actually contribute more than just an occasional rant about IMD... Smiley  hi hi...
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W8JJI
Member

Posts: 358




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« Reply #14 on: July 18, 2019, 12:30:25 PM »

Is your receive preamp activated on 20 meters ? Maybe you overlooked its setting.

How is your swr on 40 meters ? Maybe 40 is quiet because of an antenna issue. ?

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