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Old 01-06-2012, 08:43   #1
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HF/SSB RFI

Rats! New HF ant picking up tons of RFI, especially from reefer thermostat... 33' wire is vertically polarized so I knew I'd potentially have noise, man made and atmospheric....but this antenna, designed to replace monoband dipoles may not be workable. Any thoughts on eliminating thermostat noise? I can tolerate other sources generating from ships's power...I was willing to go with a compromise antenna in lieu of multiple dipoles...but then again.... Prefer not to insulate backstay....and no real room for an alternate backstay antenna. thoughts?
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Old 01-06-2012, 08:53   #2
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A thermostat emits bothersome RFI? I thought they just clicked a few times an hour. Bypassing its noise should be easy.

A better antenna will be more sensitive to noise unless it is somehow more directional. A better test is how well you can communicate.
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Old 01-06-2012, 09:06   #3
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The compessor contoller module for Danfoss units is notorious for showering the bands with birdies. It is not easy to suppress. One vendor sells a much more expensive contoller that has been shielded to suppress these.

There is a ham who had success quieting his own unit with capacitors and ferrite chokes. He outlines it in a post on the SSCA forum.

Chip
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Old 01-06-2012, 09:09   #4
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Thermostat source surprised me as well...seems in auto mode there must be some logic circuit active that's generating the noise...hard to have comms with the RX knocked out.... I can always turn off the reefer when SSB/ham needed,.but makes monitoring nets difficult. ant loads well....33' wire, short balanced feed line to a 4:1 balun, short 50 ohm coax run to an old AT50 tuner.
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Old 01-06-2012, 16:19   #5
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Re: HF/SSB RFI

Is this an electronic thermostat or the simple bimetalic switch type? Have you tried ferrites on the reefer power lead and thermostat wire?

Mark
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Old 01-06-2012, 18:41   #6
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It is an electronic control for compressor, I presume, causing the mischief. I searched SSCA forum as suggested and found lots of info...,seems easiest to turn off reefer at Net times! Shielding, ferrites, etc needed....not sure how effective that would be though.
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Old 01-06-2012, 18:52   #7
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Never noticed any noise from my Danfoss 12V compressor on the HF. So problems with them are not a given.

If your comms worked better before the antenna change then maybe you inadvertently changed something else. Some grounding or supply error.
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Old 01-06-2012, 20:37   #8
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Re: HF/SSB RFI

Bob,

Nice to hear you on the Waterway Net.

These types of RFI sources are often very hard to suppress. And, they often are frequency-sensitive, i.e., they cause a lot of RFI on one band but not another. For some reason, the 40 meter band seems particularly vulnerable to onboard-generated noises. I have a Blue Sea Systems digital voltmeter which causes havoc on HF...have to turn it off.

Question: why the balanced feedline? I thought you were using a random length, end-fed wire antenna with a 4:1 balun. I've used these very successfully. Antenna wire connected directly to balun (actually an un-un), radials connected to ground lug on balun, and coax leading to tuner near the radio. This works well enough so that even radios with internal tuners will work.

73,

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Old 01-06-2012, 21:34   #9
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Re: HF/SSB RFI

Quote:
Originally Posted by daddle View Post
Never noticed any noise from my Danfoss 12V compressor on the HF. So problems with them are not a given.

If your comms worked better before the antenna change then maybe you inadvertently changed something else. Some grounding or supply error.
Older Danfoss controllers don't have the problem, but newer ones (and I'm not sure when the change occurred) surely do. The medley of chirps and buzzes that they generate can propagate for a surprising distance around an anchorage. Quite annoying on ones own boat, maddening when it comes from "afar" and you can't shut it off!

Cheers,

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Old 02-06-2012, 05:26   #10
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Greetings Bill, I've enjoyed, and learned, much from your other posts and replies....thank you for this one. I was seeking to install what could be considered an end fed zepp, half wave on 7 MHz that could accept power throughout HF spectrum, with compromise. Even though I know balanced feedline not robust enough to stand the rigors of sea, thought I'd get a year or so from this....essentially 33' vertical 14 ga wire, traditional zepp feed with ladder line to a 4:1 balun, then unbalanced tuner, old AT50', then TS50. Previous dipoles weren't as susceptible, it seems, to the RFI, almost exclusively from the reefer compressor controller....although I do get some from other sources. Tnx again, nice to meet you in virtual QSO! 73 de K4RCG. Bob
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