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 Choke for 11 and 10m

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Matt86
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Matt86

Call Sign : 26ct2767
Posts : 226
Times Thanked : 4
Join date : 2019-06-27
QTH or Location : Swindon
Equipment Used : Yaesu ft818 , yaesu 8900r , yaesu ft950, stalker 9
Age : 34

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PostSubject: Choke for 11 and 10m   Choke for 11 and 10m Icon_minitimeMon Jul 08, 2019 11:15 pm

Has anyone used a choke either under there antenna and near the rig ?

If so was there any improvements ?

I dont really want to have many joins with 1:1 balances as a insulator. Any other ideas and will be using aircell 7 coax .

Matt
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The DB
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Posts : 16
Times Thanked : 3
Join date : 2019-06-29

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PostSubject: Re: Choke for 11 and 10m   Choke for 11 and 10m Icon_minitimeTue Jul 09, 2019 8:16 pm

I've seen some antennas that needed a choke, and others that didn't.  It depends on the antenna system.

If you add a choke and it changes your SWR readings, then you need the choke.

Also, some antennas benefit from the choke being not right at the feed point, like the a99 which works better with the choke further away from the antenna's feed point.  Nine feet (I think about 2.7 meters) is good, and it doesn't have to be exact, close is fine.

If you have an antenna with a set of full length radials, you likely don't need a choke.


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KKD3088
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PostSubject: Re: Choke for 11 and 10m   Choke for 11 and 10m Icon_minitimeSun Jul 21, 2019 4:18 am

Matt86 wrote:
Has anyone used a choke either under there antenna and near the rig ?

If so was there any improvements ?

I dont really want to have many joins with 1:1 balances as a insulator.  Any other ideas and will be using aircell 7 coax .

Matt


A common mode choke (CMC) is advisable on any half-wave or five-eighths wave antenna without ground radials directly below the feed point. It will prevent common mode currents from flowing on the OUTSIDE of the coax. RF should only exist on the center conductor and the INSIDE of the coax shield, not on the outside.

Without the CMC, undesired RF can end up back in your operating position and also cause skewing of your radiation pattern from the antenna. This has always been a problem with the IMAX-2000 and the A99.

A CMC for 27 MHz can be made easily by winding 16 turns (side by side, solenoid style) of RG-8X on a 6.5" section of 2" PVC pipe.

If using RG-8, RG-213, RG-214, or LMR-400, the dimensions will be different.
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