What are the black thick things in the middle of antennas?

[DylanMadigan]

I see it mostly on scanner antennas but also on a couple of my high gain UHF antennas, what exactly is the black part in the middle and what does it do? Tried to google it but I can't describe it accurately enough for it.

 

[w2xq]

Loading coils: Loading coil - Wikipedia

 

[IcomIcR20]

This thread has some explanations that are much better than those I can provide :

https://forums.radioreference.com/threads/what-is-a-loading-coil.288474/

 

[Lauri-CoyoteFrostbite]

Best way to describe it in simple terms, Dylan- is its an isolator and/or coupler that separates and resonates the different frequency bands that your multibanded antenna cover's.

Typically, and in your example, it makes the lower section a quarter wavelegth antenna on UHF (~400-500 MHZ for example) that, and the upper section, coupled in, into some multiple for VHF (like 140-160 MHz) - or maybe a 3/4 wave on UHF and a quarter on VHF--- its all how the engineers constructed it.

Sometimes there is a coil in there, or in other cases its a coupling capacitor-- or both. Use a multimeter and you can get an idea..
That base section is often a collection of similar circuits, which places the antenna at a DC neutral. This circuit matches the antenna to your coax, for often these are not going to match 50 Ohm coax. If you check to see if the antnna may be "shorted out" it is-- for things like static charges- and important component in mobile antennas-- but its working as design'd, all the same......

Lauri

 

[cmdrwill]

Lauri IS correct. Also known as "phasing coil".

 

[eaf1956]

Laurie is my hero!

Sent from my SM-N960U using Tapatalk

 

[kayn1n32008]

Best way to describe it in simple terms, Dylan- is its an isolator and/or coupler that separates and resonates the different frequency bands that your multibanded antenna cover's.

Typically, and in your example, it makes the lower section a quarter wavelegth antenna on UHF (~400-500 MHZ for example) that, and the upper section, coupled in, into some multiple for VHF (like 140-160 MHz) - or maybe a 3/4 wave on UHF and a quarter on VHF--- its all how the engineers constructed it.

Sometimes there is a coil in there, or in other cases its a coupling capacitor-- or both. Use a multimeter and you can get an idea..
That base section is often a collection of similar circuits, which places the antenna at a DC neutral. This circuit matches the antenna to your coax, for often these are not going to match 50 Ohm coax. If you check to see if the antnna may be "shorted out" it is-- for things like static charges- and important component in mobile antennas-- but its working as design'd, all the same......

Lauri

As well it also can make the top and bottom elements work together to provide additional gain.


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[prcguy]

Those big black lumps on antennas are the result of disease. Its a highly contagious "Ariel Disease".

 

[cmdrwill]

Its a highly contagious "Ariel Disease".

You got that correct...... lots of that going around.

 

[RFI-EMI-GUY]

Those big black lumps on antennas are the result of disease. Its a highly contagious "Ariel Disease".

AKA: Maxwells Canker, curable with appropriate dosages of Xc pr XL.

 

[wtp]

and some are empty just to make it look better than the next guy's.

 

[6079smithw]

As well it also can make the top and bottom elements work together to provide additional gain.

It also makes a great noise when you nail a June Bug @ 80+ MPH!

 

[Lauri-CoyoteFrostbite]

.
.

OMG ! Guys !!
What can one do but smile ??

Bet by now you wished you never asked that question, hey Dylan ........................ LOL



Lauri
.
.

 

[BaoFeng_Blogger]

Dylan...

By now you should be able to figure out what those "Big Things" are in the middle...

73 to ya...

BaoFeng Blogger KN4OTS

 

[poltergeisty]

This thread has some explanations that are much better than those I can provide :

https://forums.radioreference.com/threads/what-is-a-loading-coil.288474/

Wow, totally forgot about that thread.

 

[W5lz]

Maybe a better description for those 'swoll-up' things is a 'trap', just like those things in a trap-dipole. They stop higher frequencies from seeing any more antenna beyond them. The electrical design of those traps are frequency 'sensitive' to a particular frequency and act as a closed door. "You shall not pass!" At lower frequencies they are invisible, just a plain old piece of wire.

 

[DylanMadigan]

Well thank you everyone for the information =) I didn't expect I'd be starting such a conversation

 

[K9DAK]

Maybe a better description for those 'swoll-up' things is a 'trap', just like those things in a trap-dipole. They stop higher frequencies from seeing any more antenna beyond them. The electrical design of those traps are frequency 'sensitive' to a particular frequency and act as a closed door. "You shall not pass!" At lower frequencies they are invisible, just a plain old piece of wire.

Sorry, couldn't resist... think of the higher frequencies as King Arthur...

 

[prcguy]

The lump in the picture the OP provided is more likely a 1/4 wave phasing coil that puts the bottom of the top whip in phase with the bottom of the lower whip. Its kind of like making sure both speakers in your stereo system have the + and - hooked to the right place, otherwise one speaker can be out of phase where its sucking in while the other is pushing out. Not very efficient.

Maybe a better description for those 'swoll-up' things is a 'trap', just like those things in a trap-dipole. They stop higher frequencies from seeing any more antenna beyond them. The electrical design of those traps are frequency 'sensitive' to a particular frequency and act as a closed door. "You shall not pass!" At lower frequencies they are invisible, just a plain old piece of wire.