Finally own an HF rig: 20m Noise!!

Discussion in 'General Technical Questions and Answers' started by K3RLD, May 10, 2018.

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  1. K3RLD

    K3RLD Ham Member QRZ Page

    Licensed as a general for about a year, finally bought a used HF Rig (706MKIIG - doubles for half a linear sat station, too). Made an el-cheapo 20m antenna and hung it outside a window. Checked SWR, and it ranges from 1.5 to 2.0 across the band, so I figured I'd give it a shot (don't own a tuner yet). The band is trashed with S7 noise.

    So, I switched off the main house breaker and the noise is gone. Good.
    Switched on the main breaker, and running up and down the stairs between the breaker box and the radio, finally narrowed it down to one circuit, of which the only significant appliance (or anything at all, I think) on it is the refrigerator.

    Stuck an RTL-SDR on the end of a 6 foot usb cable, and stuck a 2m antenna on the SMA connector, and started walking around the house pointing the antenna (touching it, actually) to everything electrical (lugging laptop around with me running GQRX). I'm sure I looked like Peter Venkman when he visited Dana Barrett's house for the first time. I didn't flip any fried eggs with my sniffer, though.

    Anyhoo, sure enough the ONLY thing that lit up the FFT in GQRX was the capacitive touch panel on the refrigerator.... And I sniffed all the electronics, all the power supplies, all the digital light controls, everything.... only the fridge sets off my budget sniffer.

    So, assuming I've found the culprit, what can I do to kill the fridge noise?

    [edit] a new fridge probably isn't an option right now....
     
  2. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Tough one as capacitive touch panels are RF generators by design. I struggled with some capacitive touch lamps and after many attempts to kill the RFI they produced I finally replaced the lamps themselves.

    I'd try the usual things, ferrite chokes on the fridge power cord, something like a large mix 31 choke with the power cord wrapped through a few turns may help. If you can access the wiring to the capacitive touch panel itself you might also try some choking on its supply and control lines though that may not be possible.

    Getting your antenna further from the house may help more than anything else. It's likely the noise from the fridge is radiated and being picked up by your antenna so getting it away from the house and up in the clear should both increase strength of signals of interest as well as decrease noise coupled from your fridge. If the noise from your fridge is indeed radiating from your household AC lines then choking it as mentioned above may help a lot so it's worth a try but to improve Signal to Noise ratio (S/N) for radiated noise sources your best bet is to get the antenna away from those noise sources.
     
  3. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    First, I'd say if an "S7" noise level prohibits you from hearing stations on 20 meters, that's a strange problem because lots of 20m signals are in the "20+dB over S9" strength range.

    My "normal" noise level on 20m varies, but can be S7 sometimes. I still hear hundreds of stations just fine.

    "Hanging it outside a window" is likely the real problem. Get the antenna farther away (K7TRF said the same thing), and preferably higher if possible.

    IMO, ferrites on the refrigerator power cord "might" help, but may be too far away from the panel to really do any good. It may be much better to open the fridge interior door panel (should be a way to do that), find the small wiring to the panel itself, and use ferrites on that wiring -- much closer to the noise source, and a much lower-current path, which is much easier to filter than a high-current path like the AC power cord.

    But "antenna separation" is king.
     
    NH7RO likes this.
  4. AG6QR

    AG6QR Subscriber QRZ Page

    Before you put too much effort into the refrigerator, at least try unplugging only the refrigerator to see if that makes the noise go away, and plug it in again to see if the noise comes back. That would conclusively rule out anything else that might be on the circuit (sometimes non-obvious loads are wired into non-obvious circuits). It sounds like it is the refrigerator, but I'd just want to be sure.

    Ferrites are your friend. You might look for a wiring diagram for your refrigerator (with any luck, it's in the fridge, hidden behind the back panel or something), and see if you can get to the wires at the touch panel, and put ferrites on them.
     
    NH7RO likes this.
  5. N7WR

    N7WR Subscriber QRZ Page

    Many years ago (late 1970's/early 1980's) we were plagued by noise at the NK7U contest station during the CQWW DX contest. Joe and I did some testing and DFing. It was the refrigerator in the kitchen maybe 40 feet from the radio room. Shut it down, moved the perishables to another refrig in the garage which was not generating noise, and finished the contest in peace.
     
    WD0BCT and NH7RO like this.
  6. KC8VWM

    KC8VWM Moderator Volunteer Moderator QRZ Page

    ^^^
    This.
     
    NH7RO likes this.
  7. NU4Y

    NU4Y Ham Member QRZ Page

    At VP5DX in 2016, new refrig was delivered Thursday before CQWW. Noise was S7 on 20 meters.
    We tried chokes, ferrites, all kinds of stuff. Refer was upstairs, we finally ran an extension cord from shack
    up to refer. When on 20 meters, unplugged the thing. Yes also had a another refer in the shack to keep
    the Drinks cold.
    Jim
     
  8. K3RLD

    K3RLD Ham Member QRZ Page

    The window antenna is literally a couple of pieces of automotive power wire soldered to an SO-239, and is only being used to try out the radio (I ordered a 20/40m dipole that should ship in a few days - more on that below). I just wanted to play with the thing.

    Having said that, the plan was to put the new antenna in the attic. It would be 10 to 15 feet higher than the existing homebrew, but the overall distance from the fridge is probably going to remain the same. Any rule of thumb as to how far (straight line distance) from a noise source such as this fridge I'll need to be? I could string the antenna up from some trees, but I'd probably want to get a better antenna (balanced feedline, usable on more than just 20/40m, +tuner/balun etc) if I have to go through the work of hanging from the trees.

    Not opposed to doing that, I just don't want to do it twice. And I DO realize that the "how far" question is practically impossible to answer by anybody other than myself.... and then only after actually trying it.
     
  9. KI4AX

    KI4AX Ham Member QRZ Page

    Dumb question.... Have you engaged your Noise Blanker (I am assuming your rig has one)?

    Dan KI4AX
     
  10. K3RLD

    K3RLD Ham Member QRZ Page

    Not a dumb question. Yes, it does have one. And I THINK I successfully turned it on, and I also believe it didn't do anything.

    The 20db attenuator, on the other hand, certainly helped - dropped ALL signals to S0! :)

    It's a 706MKIIG.
     

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