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Base antenna, High noise floor tips..

Discussion in 'CB Antennas' started by CB590, Mar 29, 2020.

  1. CB590

    CB590 W9WDX Member

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    I'm running the lovely A99. Feed point is 20'. Houses are close (row home).

    61E1D123-E845-45AE-AD27-B249EF2C6906.jpeg

    During the day the noise floor is like S5-7. At night about S4.

    Also when running some power like 90w dk (4 pill amp) I do notice my SWR is like 1.5-1.6 vs being say 9w dk with amp off (with RF power knob turned up on the radio for testing, I don't run it that way)

    I don't want to drag the antenna down off the mast as lifting the top rail with the A99 while standing on a slant roof is tedious.

    I'm thinking snap on chokes about 9' down from the feed point. Someone said to give the A99 some counterpoise room, but not the entire feed line.



    Would this help?? (And no I'm not putting up an entire new antenna) :rolleyes:

    My main concern is trying to knock down the noise floor at lease 1-2 points.

    Thinking ground rod as well to help (and for safety), once I can figure out how to drive it thru concrete or find a crack in the walkway near the antenna.
     

  2. sp5it

    sp5it Master of puppets

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    Switch off circuit breaker powering your house, run radio from battery, check noise.
    Do the same with neighbours house.
    Do you have cylindrical transformer on power pole nearby? Might be a noise source too.
    Mike
     
  3. BammBamm

    BammBamm Instigators ...173 on the southside.

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    Ok after looking at pic this is just my thought..a choke at the feedline at antenna. Also unplug electronics in the room and check for any difference. Does that AC unit run during the day? A ground wouldn't hurt but may not help either. Possible to raise the antenna a bit?
     
  4. sp5it

    sp5it Master of puppets

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    A99 is very problematic, noise picking antenna. Why? Because mast pipe and coax is active part of the antenna.
    Solution is: insulate antenna from pole. Right under antenna put 1:1 balun like in attachment.
    Same balun where coax enters your house.
    You could make balun by yourself. FT240-43 core and RG-142 coax.
    Mike
     

    Attached Files:

  5. CB590

    CB590 W9WDX Member

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    I used some 5" or so PVC standoffs when running the coax up the pipe to try and avoids the mast acting like part of the rig. Learned in NY and that helped abit.

    DB41B967-8178-4480-819D-B07BDDDFE5B6.jpeg

    I do have a MFJ915 1:1 choke laying here. I can try and install that possibly too. I used to use that on the endfed for HF. The issue is dragging the antenna and mast off as one unit.
     
  6. sp5it

    sp5it Master of puppets

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    Insulate antenna from pipe.
    MIke
     
  7. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    Just a thought...

    This is only a thought... So you have been warned...

    That downpipe...can you slide that mast and any extra mast length sections down INSIDE the pipe to offer support as well as a ground?

    At least that downspout would offer a counterpoise and a means to "hide" the antenna, mast mount as a more effective radiator and well as conductive path to ground if ever a lightning strike - at least the flashover would use the downspout anyways due to the easier-to-earth, earth ground.

    I've known of people that lived in NY that in hi-rise buildings, they'd stick out the radiator and flush a ground wire with sinkers down the toilet or even fish it down in the shower stall to offer counterpoise and an extra radiative length thru the buildings plumbing. Crazy I know, but they did and it worked .I know of a guy that ran a HR2510 with a Francis 5' Hot-Rod this way...
     
  8. CB590

    CB590 W9WDX Member

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    I added another wall bracket just above that joint you see in the pic for extra support. After the pic was taken. This is when the install first went up.

    Mike. As far as insulating the antenna from the mast many (on here) run the same setup and have no issue with metal mast. I really have no good way to do that as that I'm sure would create an added weak point.
     
  9. sp5it

    sp5it Master of puppets

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    Insulating antenna from mast is simple.
    Use PVC pipe. Put in on mast between antenna and mounting brackets.
    If too tight cut it along and slide onto mast than mount antenna. No weak points, antenna insulated from a mast.
    Mike
     
    CB590 likes this.
  10. HomerBB

    HomerBB Sr. Member

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    Folks have different ideas that often differ from each other, and all are trying to help.
    If it were my antenna setup here is what I would do and hope it helped.
    1. Not isolate from the mast if I isolated the feedline at the antenna. The antenna needs a counterpoise.
    2. If I isolated the mast, I would not isolate the coax at the feedpoint, but put a choke inline at 9' below the feedpoint. The antenna needs a counterpoise.
    3. I would also, actually first of all, put a choke in the feedline right at the shack end of the feedline. This helps address any noise on the coax braid from the house or that got by the first choke.
    4. Ground all the shack equipment to earth the shortest possible route.
     
    #10 HomerBB, Mar 29, 2020
    Last edited: Mar 29, 2020
  11. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    It very close to the phone line - that is a strain relief there - right where that mast, the MFJ and the standoff are all close together like that.

    upload_2020-3-29_11-59-29.png

    This is what I would call a frustrating install - too many things can go wrong...

    So then the picture was taken on the "landing" - above the 1st story (=?) that must be a flat spot up there.

    The guy in the unit with the AC-unit can use that for sitting outside with a simple folding chair...

    It's really kind of a cool if not "cozy" setup, but it's amazing they all get along.

    To reiterate what @HomerBB mentions - the mast is the counterpoise. you have a floating ground up there. The MFJ is working to keep the currents off the coax, but CANNOT fix the coax from that point, to the radio...as said before, this A99 is only half the picture, we're seeing the rest of it in siding, downspout and mast...

    The radiative effects or coupling is where the bonding issues come up - the main one being the coax thru the Balun, and the mast, running right next to the downspout - else you have very little space for RF to radiate and arrive to - as I see it.

    Everything else is reflective, radiative - but not in the ways you want it to be.
     
  12. CB590

    CB590 W9WDX Member

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    Can anyone recommend a type of snap on ferrites that are made for this. I saw Palomar makes some and then I read cheaply from eBay will work. Type 31,43?? Which ones are the correct ones?

    I'm running LMR240 and figured out I need 1/4" ones. Thinking 5 at shack wall entrance and maybe 5 up top?? With snap on ones I can move them around without degrading my coax with jumpers and such as well.

    I found these for $25 for 10 count, anything comparable but cheaper?


    F084D1E4-5EE4-47DE-BE9D-8E76BA6AAA3D.jpeg
     
  13. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    Well, chokes can only fix certain effects, but not improve performance.

    Are you sure you want the "Choke" route versus just trying to get more of all the metal you have up there, to work together?

    You may fix a noise loop, but the noise you're hearing is from this floating ground you have now.
     
  14. CB590

    CB590 W9WDX Member

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    took these just now. Top to bottom. Top roof above antenna is slate and very steep and old. The roof by section 2 of mast is slightly angled but normal angle and can be stood on (that's how I got the mast up with antenna on it, like planting a flag into section one of mast). 2 top rail and then A99.

    Phone line is dead. I may just hack that off.

    Excuse the mess

    top to bottom. That's a roll up 2/70 and my endfed antenna up there too about 2/3 way up.

    19F382C9-50E9-4167-BAFA-FACEEA7E5AAD.jpeg E24646E7-1424-44E2-B746-8A8C76B20933.jpeg F514C7A0-BD1C-4463-B7B5-D5A0A251A784.jpeg
     
  15. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    Oh wow!

    This does change the perspective and no (I'm not) - anyone here offended by that mess would only be people like the Coax cops and perhaps a Stand in or two from "Home Improvement" ...

    The ladder line just blows me away...

    I'd like to know more about your feed thru from the siding - does the "plate" screw directly thru that? That may be an injection point for noise...

    My though on this would be to make either "Choke of coax" as it comes off the mast pipe at the lead-in. OR somehow fashion a fish line setup that allows you to access coax from the inside of the mast. You fish it down the mast pipe hollow as if it were a shaft to shield the coax within the mast itself.
    • Drill a hole to fish out the coax by the lead-in "plate"

    Take the MFJ, remove it, connect the coax directly to the A99, then FEED THRU INSIDE the mast pipe - down to and off the side of the mast towards the lead-in. Do your choke where you leave the hole inside the mast.

    If THEN you need to make a breakpoint - you can install the MFJ closer to earth ground and somehow, just somehow, make the coax shield grounded there before it leaves the pipe...
     

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