Large RF chokes

Thread Starter

samuel.whiskers

Joined Mar 17, 2014
95
I've been after some large RF chokes, like the ones in the pic below. I've found some on ebay and at my local componenets place, but are much smaller physically, more like a large green resistor. Can someone tell me what I need to look for - do these large ones just have a higher power rating? Something else?
cheers
Lee
 

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MaxHeadRoom

Joined Jul 18, 2013
25,469
A first silver band twice the width of the other colours evidentally identifies them as chokes, from the MIL standard of marking.

Max.
 
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Papabravo

Joined Feb 24, 2006
18,806
If it has capacitors inside, it cannot be a choke. It could be a filter, but not a choke.

So does "large" refer to physical size, or some parameter of the filter.
 

alfacliff

Joined Dec 13, 2013
2,458
the picture is of a power injector, two caps to pass two signals, and two chokes (the green things) to put power onto the coax connectors on the bottom of the picture feeds dc to preamps and to satelite lna's. the chokes block the rf and the caps block the dc.
 

wayneh

Joined Sep 9, 2010
17,167
For what it's worth, it might help searching for parts if you use the keyword "inductor" instead of choke. For RF I believe you need a ferrite core but in my mind, "choke" describes the application, not the part. Curious if others disagree.
 

alfacliff

Joined Dec 13, 2013
2,458
ferite cores are used to increase the inductance of coils. not all coils have ferite, some are air core, some have brass cores that reduce the inductance. using ferite means you can get away with using less wire to wind the coil.
 

Brownout

Joined Jan 10, 2012
2,390
For what it's worth, it might help searching for parts if you use the keyword "inductor" instead of choke. For RF I believe you need a ferrite core but in my mind, "choke" describes the application, not the part. Curious if others disagree.
Don't know if this is a disagreement or not:

For years (decades) I wasn't clear about the distinction between chokes and inductors. Finally, someone on one of these forums provided the skinny. Chokes are constructed in a way to pass rather large DC currents without saturating. They are used to keep AC out of DC domains.
 

wayneh

Joined Sep 9, 2010
17,167
Chokes are constructed in a way...
I've never gotten the distinction between chokes and inductors straight either. Your comment implies that chokes really are a specialized kind of inductor. Any more information on the construction difference? I'd love to understand this.
 

MaxHeadRoom

Joined Jul 18, 2013
25,469
To me it has always implied that a choke is a form of Inductor.
More or less implies its application, as an inductor can also be used as a tuning element and other uses.
Max.
 

nsaspook

Joined Aug 27, 2009
9,991

Power supply filter example:

http://www.bourns.com/ProductLine.aspx?name=jwm_thru_hole_axial_lead_rf_chokes

Normally the word 'choke' (in electronics) is used when the inductor is used as a filter component to stop AC from flowing in a circuit with a DC supply or bias. A choke input filter also tends to reduce the peak input currents from the rectifier to the filter caps when the supply is under heavy load allowing the use of a smaller VA power transformer when compared to a capacitor filtered rectifier of the same ripple content.
 
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alfacliff

Joined Dec 13, 2013
2,458
also thee are choke coupled audio amps. with a choke in the plate circuit of the first amplifier, and capacitivly coupled to the next stage grid.
anyone ever hear of "choke modulation"? similar.
in microstrip, a choke might just be a narrow pc trace.
also, amethod of richening the mixture of gas and air for internal combustion engines.
 

Papabravo

Joined Feb 24, 2006
18,806
In RF applications, a choke has a large impedance at RF and a small impedance at DC. Thus it is suitable as an RF load, in place of a resistor in a common cathode (common emitter) amplifier.

In power applications it is placed in series with the DC path to pass DC and attenuate higher frequencies.

In my opinion a "large" RF choke would be wound on a large toroid with 14-18 AWG wire.

In tube circuits they were often wound with fine gauge wire on cardboard cores because the currents were typically very low.
http://www.bourns.com/data/global/pdfs/6300_series.pdf
 
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