Featured: DX Engineering Mix 31 Snap-On Ferrites (set of 5) at DX Engineering.
This is an affiliate link: Hood's Finds may earn a commission from DX Engineering at no extra cost to you. We have not tested this product; the specifics below come from the product listing.
Add an amplifier to a station and RF sometimes shows up where it does not belong: in a power cable, a keying lead, a microphone line or a computer interface. Symptoms range from a hot microphone to a radio that misbehaves only at high power. Snap-on ferrites are a simple first tool for this kind of problem. DX Engineering sells Mix 31 snap-on beads as part DXE-CSB31-525-5.
What the listing says
DX Engineering lists the ferrite material as 31-mix, sold as a set of 5, and says 31-mix is optimal for HF and VHF. With an inside diameter of 0.525 in., the beads close over cable sizes such as RG-8, RG-213, LMR-400 and DXE-400MAX, as well as many power supply cables and control wires. They simply snap on, so no cutting is needed to install.
The listing describes them as acting as an RF choke when placed around a current-carrying conductor, and as a convenient, inexpensive and effective means of RF shielding, parasitic suppression and RF decoupling. It also says winding smaller wires around snap-bead cores before closing them provides a greater degree of RF choking and noise suppression. The part was previously known as DXE-CSB-525P.
How a ferrite helps
A ferrite around a cable resists RF current that flows along the outside of the cable, often called common-mode current, while the signal or DC current inside the cable passes normally. On coax, it chokes current on the outside of the shield without affecting the signal inside. On a power or control cable, it helps keep RF from riding into the equipment at either end.
Where amplifier builders use them
- DC power leads between the supply and the amplifier or radio.
- Keying and ALC cables between the radio and the amplifier.
- Coax jumpers where RF is getting onto the outside of the shield.
- Accessory cables such as USB, audio and microphone leads.
Put ferrites close to the equipment that is being affected, and add more or wind extra turns through a core if one bead is not enough.
Work methodically. Make one change at a time, test again at the same power into the same antenna, and note what helped. That way you learn which cable was actually carrying the RF instead of covering every lead in ferrite and guessing.
Know what ferrites cannot fix
Ferrites treat symptoms on cables. They do not cure a poor station ground, a badly matched antenna, or an amplifier that is unstable or oscillating. If an RF problem appears only with the amplifier in line, check the amplifier, its connections and the antenna match as well.
And a reminder whenever amplifier power is discussed: external linear amplifiers are not legal for use on CB radio. Keeping RF under control is part of running any legal amateur station well.
Where to get it
Check current price and availability: DX Engineering Mix 31 Snap-On Ferrites (set of 5) at DX Engineering.
This is an affiliate link: Hood's Finds may earn a commission from DX Engineering at no extra cost to you. More picks on the gear page.
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