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High noise floor mitigation

I realize this probably not a flex problem, but the receiver is so good, take a look at this noise ramp up on 40m...I have RF gain about half, and even turned all the way down it's very high. Any ideas on what it could be or how to at least control it better with flex? See picture.


  • Larry _ NY8T
    Larry _ NY8T Member ✭✭✭
    edited April 2022

    You have +16 DB of preamp turned on, set it back to zero preamp and also turn off Wide Noise Blanker and see it it helps, Wide Noise Blanker works wonders for the correct type of noise but can cause all kinds of overload issues if you have close by signals on another frequency. Depending on which radio you have, yours may look a little differant but the image shows the zero DB preamp position, a setting below that is RF Gain, any setting above that is levels of Preamp and you can see it on your screen that you have 16 DB of preamp turned on. Also you are seeing the noise ramp up because its where your antenna is tuned to, but you do have a high noise level, I have roughly 110 dbm noise floor on 40 meters right now.

  • PaulB
    PaulB Member ✭✭

    Thanks Larry. I was reading that as RF gain, not a preamp but guess in this instance it's the same. Nevertheless both are disabled now and not much change. See attached.

  • Stan VA7NF
    Stan VA7NF President Surrey Amateur Radio Communications Member ✭✭✭

    There will always be signal level increases as you pass through antenna resonances; your antenna seems to be resonant around 7.250

    The pattern shown is typical, and a good thing, when you have a 40M dipole or vertical connected.

  • PaulB
    PaulB Member ✭✭

    Yes, it is resonant around there. It is a 40m 2 element beam at 75'. My EFHW 10-80M by contrast is much quieter. S9 Noise seems awefully high. With my 7300 there were times at night and day where it crept up to S7, but usually was around s5-s6.

    I'll add a slice with my EFHW for comparison.

  • WX7Y
    WX7Y Eastern Utah, USAMember ✭✭✭

    Does your Beam rotate, if it does check the noise level in different directions, You may have some local noise from a neighbor and the beam's direction will change the noise level a lot.

    This may be why your noise is much lower on the End fed then the Beam.

    Also it doesn't hurt to run the WBN level up to 10, above that it will distort the Audio in some situations.

  • Mike Steventon
    Mike Steventon Member ✭✭✭

    A **** question, I imagine, but do you have a decent toroidal common-mode choke immediately before the co-ax enters the Flex? It might help?? I am just clutching at straws to suggest anything..........


  • Mike Steventon
    Mike Steventon Member ✭✭✭

    Read silly for the XXXX!!

  • PaulB
    PaulB Member ✭✭

    I have a balun designs current balun at the feed point, and a torroid where it enters shack (only with a couple turns)

    See attached. I have a bunch of noise from an AC that kicks on so the test is a little polluted now. But the EFHW is picking it up too. Doh! I guess I should get the offender out of the way before I continue now. I'm working from around the world so can't do real time testing at home unless I get someone to turn off the AC in the shack:)

  • Stan VA7NF
    Stan VA7NF President Surrey Amateur Radio Communications Member ✭✭✭

    Actually with 40M up 75' there should be a toroid at the antenna feed point to prevent coax shield pickup from transferring to the inner conductor. That should present over 1K ohm at 7Mhz; 2" type 31 with 6 turns of coax (or some RG142 with 8 turns which is good at 3KW on HF)

    Also according to most codes your tower must be grounded, optionally for lightning (and RF) at the tower and bonded to your electrical ground (unless 200' away).

    In practice the best noise mitigation process is to have a good RF ground (I like 3 x 4 foot deep holes dug with 4" copper strap surrounded with earth and bentonite clay) then have the feed line be grounded at the foot of the tower to that ground system. This will prevent much noise pickup being routed to ground rather than the shack. I have seen this reduce noise pickup by over 4 S units on 160 and 80M. A good place for a lightning protector as well as at entry to the shack.

    A deep inspection of your latest panadapter shows a repeating pattern, including between the big birdies of two smaller peaks, that indicates to me that your ~18Khz noise carries a lot of mixing products creating the high hash level. Fix that if it is your source and/or follow the feed-line suppression methods. A 40M beam at 75' should not pick up that level of local noise; atmospherics yes, local birdies - no.

  • PaulB
    PaulB Member ✭✭

    There is a current balun at the feedpoint. https://www.balundesigns.com/model-1115-1-1-balun-1-5-54-mhz-3kw/

    Tower is grounded, all three legs, to 8 ground rods in series. Those 8 ground rods go to the shack, and the shack RF ground is part of that. Perhaps the RF ground connected to Tower ground system is a bad thing? Saw it on youtube at one point.

    I have a ground plate with polyphasers mounted to copper plate that is about 15' up from the ground, but has a solid copper wire going to the ground system. The reason it is 15' up is the coax departs the tower at about 10' to run along the roof and into the shack.

    The only thing I have thought about is that the tower ground is connected to the same ground system as the RF ground from the shack.

  • PaulB
    PaulB Member ✭✭
  • Stan VA7NF
    Stan VA7NF President Surrey Amateur Radio Communications Member ✭✭✭

    Paul, with that grounding it is indeed unusual to see that much noise unless it is locally generated. Do rely more on the Flex panadapter signal strength than a Japanese S-meter.

    I'm assuming your RF ground continues to inside the shack, it just isn't shown quite extended in your diagram. I'm lost for suggestions other than your already suggested running on battery and chasing in-home noise.

    Although you do not show any toroid before your shack entry with the outside part grounded; to introduce 1K impedance that forces any coax noise pickup into ground before routing to the radio.

    Good Luck when you return.

  • John KB4DU
    John KB4DU Member ✭✭✭✭

    A note on s meters. The flex S meter accurately measures signal strength at the antenna terminals though not to lab standard but pretty close. Not sure about the 7300 since it is promoted as being direct sampling. Analog superhet rigs usually derive S meter info from the if avc. For these rigs varying the rf gain will vary the S meter reading, so it is not measuring the signal at the antenna terminals. If the 7300 shows the same behavior, the S meter is not calibrated.

    Also, set the bandwidth to 500 hz, which is the ham radio convention for measuring noise level.

    Another trouble shooting technique would be to operate the flex from a battery and turn off the incoming ac at the main breaker to see if the noise is local to the radio.

  • David Decoons, wo2x
    David Decoons, wo2x Member, Super Elmer Moderator

    Does the noise floor change at different times of day or night? That might help give a clue.

    Also can you power up either radio on battery and turn off your main breaker? That would tell if it is coming from your house or somewhere else.

    Dave wo2x

  • PaulB
    PaulB Member ✭✭

    Thank you for all the suggestions! To answer a couple of the questions.

    My shack is on batteries. It is off grid with a high quality solar system that is RF quiet. I realize once I say solar chargers, it is an immediate concern. But when I installed them I have disconnected them and run strictly off battery to ensure they were not noisy.

    Day or night is not the same for sure. Different noise after the sun is down (and subsequently the solar is not charging)

    I will add a toroid at the house when I get back later this year. I thought about interrupting that chain of ground between the shack and the tower. Any ideas there?

  • Stan VA7NF
    Stan VA7NF President Surrey Amateur Radio Communications Member ✭✭✭

    Your local code probably says something like "tower bonded to service panel except if over 200 feet". Your diagram should be lower noise but may not be according to electrical code.

    If your 18Khz birdies do not disappear with the solar then solar isn't your problem unless your dc to ac converter is in the game, but you seem to have been thorough in that testing.

    I agree with others, when you get back start a noise hunt, unless you have a friend that can do that in your absence. I have found vacuum cleaner transformers, lights, network switches, UPS devices, power outlet cord extenders, security camera power supplies, door bell transformers, cycling battery chargers, and especially VFD drivers (now often found in appliances ) but these cycle with load. You didn't indicate if your birdies are constant or intermittent. and of course the famous wall-wart.

  • PaulB
    PaulB Member ✭✭

    Yeah, I've eliminated most wal warts with BUC converters so I can run just about everything on DC (even computer routers, etc. I did NOT think about my UPS though. That's a good point. Thanks for all the tips. I realize this is more of a flex forum for those concerns, which is why I was wondering how much flex could help out, but it can only do so much!

    Thanks again.

  • VE7ATJ_Don
    VE7ATJ_Don British ColumbiaMember ✭✭✭

    Hi Paul... I had a problem with an LG Fridge at my previous abode. Even with choke/RF filters on all the AC lines (fridge and rig) and the coax, the only 'solution' was to turn off the fridge when I wanted to work 40m DX (had to be carefully timed when the wife wasn't home :-))

    If it's any consolation, my new locale has a -85dbm (~S7) noise level most of the time -- and I'm in a somewhat 'rural' area, but there's lots of new homes around me with lots of potential noise sources. Occassionally it will drop down to S5, but 40m is somewhat lost to me. Sages said it was due to my 43' vertical in the back yard, but the fan dipole in the attic seems to reduce the noise slightly (and it's not nearly as sensitive to signals!) 80m is pretty noisy around here too.

    Bottom line -- it could just be the environment....

  • ka9ees
    ka9ees Fithian IL USAMember ✭✭✭

    I have been watching this thread closely. I have been dealing with a noise that has kept me from running the "Wolverine Single Sideband Net" at 3935 for a couple months now. I got Ameren Illinois involved about a month ago. They found the location of the noise this morning, but not the source. They pulled the power to a house where they said it was coming from. Bingo! Gone it was. When power was restored the noise did not return. I'm thinking it was a computer that didn't reboot. I will contact the owner of the home this evening. Which hopefully will work out okay as they live next door to my daughter and her husband. Ameren still has some things to do on their part. I sure hope it is solved for good.

    I have nothing but praise for the people involved in this search. The power company (Ameren) people have gone way beyond what I expected. K2ZSD, and K8CGS for lending the equipment to help in the search. It wouldn't have been possible without them.

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