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Old 12-14-2016, 10:37 AM   #1
ke0me
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Default RF feedback on 20 mtr

I am getting a fair amount of audio feedback on ssb on 20 meters.
However, it changes with the mic I use.

When using the handheld mic , it's is barely present, but just barely noticeable.

When I use the Heil pro set unit, with a foot switch, it's horrible.

I am assuming the long lead to the footswitch is picking up the RF, compared to the hand mic.

And only on 20 meters.

All components of station are connected to a DC ground( single lead, not really a RF ground), am using Icom 7200 to Alpha vertical with 28-30 ft of coax.

So, where to start, work on microphone circuit or coax feeding antenna ( common mode problem?)????

Suggestions please.
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Old 12-14-2016, 12:25 PM   #2
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All Electroicns has a good deal on Ferrite Beads just now...... I just bought a box full.
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Old 12-14-2016, 04:49 PM   #3
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Ferrite beads. Mix 31 if you can find it, else 75 or 77. Mix 43 is commonly available but not recommended for common-mode suppression at HF.
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Old 12-14-2016, 04:56 PM   #4
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Where are you hearing the feed back? A real earth ground would be a good ideal.
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Old 12-14-2016, 05:23 PM   #5
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I'd try toroids on the footswitch cord first, since you say that's the worst. Then the mike and feedline.

I don't agree that an earth ground is particularly important, which is good because it's very hard to get one in most shacks and all RVs. Earth grounds are useful for avoiding electrocution, but sometimes cause electrocution too. Earth grounds aren't generally very significant for RF unless your particular antenna requires one, and even then there are workarounds.

Many airplanes have HF radios, and I've never seen an airplane with a good solid earth ground.
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Old 12-14-2016, 10:56 PM   #6
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Thanks for the replies.

I'm hearing my voice feedback very loud and raspy sounding into the Heil headphones when using the footswitch.
I hear very little to no feedback when I switch to Icom handheld mic, and still have Heil headphones on.

That's why I'm suspicious of the footswitch picking up RF.

I will put some ferrites on and let u know what happens.

Tax
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Old 12-15-2016, 09:11 AM   #7
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Quote:
Originally Posted by NN5I View Post
I'd try toroids on the footswitch cord first, since you say that's the worst. Then the mike and feedline.

I don't agree that an earth ground is particularly important, which is good because it's very hard to get one in most shacks and all RVs. Earth grounds are useful for avoiding electrocution, but sometimes cause electrocution too. Earth grounds aren't generally very significant for RF unless your particular antenna requires one, and even then there are workarounds.

Many airplanes have HF radios, and I've never seen an airplane with a good solid earth ground.
The air craft is the "ground" single point. His power supplies are most likely house grounded to the B- but I do not trust house grounds for RF because they can be pretty good antennas. A 1:1 may help also but it does matter what antenna is being used.
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Old 12-15-2016, 11:06 AM   #8
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Quote:
Originally Posted by N3LYT View Post
The aircraft is the "ground" single point.
Precisely. Every station, in an ideal world, ought to have a single-point ground. My point was that this need not be, usually ought not to be, and often cannot be, an earth ground. It can just as well be a purely local ground, a common point that isn't really a ground at all, though often called one.

Earth grounds are merely a safety measure. Though it is widely believed that some antennas require earth grounds, actually I don't know of any kind of antenna at all that requires one or is improved by one. A quarter-wave vertical, for example, works better with an isolated ground plane made of wire than it ever possibly could with an earth ground. Radials work best when above ground and not connected to the soil. And so on.
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Old 12-15-2016, 12:31 PM   #9
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Here is a "Feedback" question of a different sorts.

Often when I check into a net on eithe r40 or 75,,,, I will give my call, then when I release the mic I hear my call Very clear, My voice, Echoing back? Any thoughts.
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Old 12-15-2016, 02:08 PM   #10
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Quote:
Originally Posted by wa8yxm View Post
Here is a "Feedback" question of a different sorts.

Often when I check into a net on eithe r40 or 75,,,, I will give my call, then when I release the mic I hear my call Very clear, My voice, Echoing back? Any thoughts.
You're the first to do EME on the low bands!
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