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De-noising the active magnetic receiving antenna.
pa0nhc Update 20210202 ferrites.
(Copyright) The use, copy and modification of all info on this site is only permitted for non-commercial purposes and thereby explicitly mentioning my radio amateur call sign "PA0NHC" as the original writer / designer / photographer /publisher.
 

All types of active antennas perform as good as their noise free grounding, and noise free installation at its location are.
Installing without proper grounding or ferrite chokes (Common Mode Chokes) is useless.
            Grounding.
        If no measures are taken :
RF noises induced onto the OUTside of the coaxial cable screening, will travel to the antenna unit, if they are not stopped.
At the antenna PCB they will intrude into the coax inner screen surface, and will travel back through the INside of the coax cable towards the receiver input. And will be heard.

By connecting the antenna PCB ground surface to a lowZ, noise free ground, the PCB mass plane will become low-Z.

On the outside of the coax induced common mode noise voltages will see L6 on the antenna PCB as a high value (5.000 to 10.000 Ohms) wide band SERIES RESISTOR (not an inductor !). The resulting common mode current is therefore very weak.  AND on top of that, the lowZ antenna mass surface acts as a big ratio voltage devider.

Depending on the length of the coax, standing waves could appear onto the outside of the coax screening. This can lead to repeating noise maxima at certain frequencies. By installing common mode chokes every 2.5m distance, no resonance's can occur at frequencies below 30 MHz.

See also : Common Mode Chokes
For minimal noise hinder, the ground surface of the antenna unit MUST be connected onto a noise-free grounded mast. 
Do NOT ground the coax line nor the BNC connector at the antenna.
 
The receiver will automatically be grounded for DC / mains to that same mast too, via the screening of the coax cable.
 
For best signal-to-noise ratio, the receiver and all connected equipment then may NOT be connected to any extra (mains-safety) ground.
Construct only a dedicated grounding at the antenna mast,
 
If grounding via the antenna mast is impossible, the receiver MUST be grounded for safety reasons.
BUT noises on the coax outside will then not be blocked at the antenna site. The received signal-to-Noise ratio will be worse.
Extra ferrite chokes at short distances in-between over the coax will then help suppressing noise currents.
TIP : A low-Z noise-free ground can sometimes be made, by a connection to the steel reinforcement of concrete structures.
            Coax and ferrite common mode chokes.
Use THIN coax (RG174 or RG316). These enable much more 10 turns through the hole of :
- a big ferrite clamp FairRite No. 0431176451
        or
-  a big ferrite ring FairRite No. 263162202.

Do not worry about coax losses.  
The active magnetic antenna coax circuits are designed for low VSWR, so coax losses at these low short wave frequencies are very small.

The reason for thin coax and big #31 cores is :
The power of N2
20210202.
(N) times though a ferrite hole => (N2) times serial impedance.
Simpler said :
10 times though a ferrite hole = 100x more effective than 1 time through that core hole.
10 times though a BIG ferrite hole = equal or MORE effective than shifting 100 smaller cores over that coax.
Cheaper, lighter, smaller.

Ferrite material and application.
This newer version antenna unit already contains a ferrite ring common mode choke on the PCB. This makes connecting the coax to the antenna easier.

If the coax line is long, you should put common mode chokes over the thin RG174 or RG316 coax at regular intervals.
I suggest to put every 2.5m a choke over the coax.

The only best ferrite types for common mode chokes are :
 FerroxCube mix 3S4.
or
Fair-Rite mix #31  (arrow.com)
=>> Order clamps with a size where thin coax can pass at least 10 times through the hole. <<==
CHECK for well closed clamps. Both halves should lay in flat contact to each other.
Use UV-resist black nylon straps to close the clamp and fix the coax. 

-  Install a ferrite clamp over the coax at the tuning unit.
-  Install a ferrite clamp at the receivers antenna plug.
-  Install a ferrite clamp at the receiver-output of the tuning unit.
-  Install a ferrite clamp near the receiver over the mains cable.
       OR
-  If a separate power supply is used, install a ferrite clamp near the receiver over the DC supply cable.

        20210202 :
When the coax is longer than 1/4 wavelength for the highest listening frequency (for instance more than 10m for 7MHz), you should install at least one extra clamp in-between antenna unit and tuning unit. For even longer coaxes the distance between clamps over that coax should be maximal 1/8 wavelength. Every choke needs about 1m extra coax length.

        Also very effective :
-  Burry the coax cable at least 10cm deep into the soil.
        AND / OR
-  Install ferrite clamps every 2.5 m over the coax between the antenna unit and the tuner unit. This proved to be very successful with my shortwave wideband RXloop. This seems to be overdone, but the investment could is worth it.

At your own risk.
You could disconnect any (mains-safety) ground at the receivers power supply.
This is ONLY SAFE if :
1. The antenna unit with the antenna mast is well grounded
 and
2. Your radio mains power line is equipped with an automatic ground leak current switch.