Post by HighMountainRadio on Jun 9, 2018 7:04:41 GMT -6
Greetings To All From High Mountain Radio !
I thought it may be a good idea to re-visit this subject mainly for the benefit of newcomers to the hobby. The sole purpose of a 'RF Choke' is to suppress or 'choke' off any RF that may be radiated from your coaxial cable transmission line.
RF (Radio Frequency) energy that may be radiated along the braided conductor of your coaxial cable transmission line is highly undesirable and will cause a myriad of unnecessary headaches ! One unwanted issue that is caused by this RF leaking out along the length of your coaxial cable is that it causes RF to be reflected back to your transmitter, and if this reflected RF is high enough, can very easily cause harm to your transmitter's RF output stage !
Additionally, this situation can very easily cause you to pull your hair out when trying to tune your antenna for minimum reflected power and maximum forward power output at the antenna ! Having this unwanted RF radiation coming back to the transmitter will drive you crazy when trying to find that perfect match ! I've encountered many individuals that ultimately blamed their antenna for this, when in fact, it was simply the fact that the proper practice of utilizing a RF choke in your feedline, positioned at the antenna feedpoint was not implemented !
This is an easily rectified situation fortunately ! You may opt to build your own, whether it is of the looped coaxial cable variety or of the ferrite sleeve type, both are 100% effective at eliminating this issue ! While both types work equally well, the ferrite type of RF choke, which utilizes 'ferrite sleeves' simply slipped over the outer insulating jacket of your coaxial cable, they also will be more costly to fabricate due to the cost of the ferrite sleeves of the proper 'MIX' type that are necessary to fabricate this type of RF choke. Usually, no matter where you choose to purchase them, most likely you will be forced to pay at least $5.00 per sleeve and ideally you should have at least 5 of them 'stacked' inline, onto your coaxial cable for proper performance. IF you can find them at $5.00 each, that amounts to $25.00 plus shipping for your base materials as well as the small added expense for a small length of the proper coaxial cable type.
Of course, winding a RF choke from a length of coaxial cable is somewhat cheaper, depending on what type of cable you choose to utilize, you could start to approach the same cost as for the ferrite type of choke.
I have included pictures of each type of RF choke for you to view for a better understanding of how they can be fabricated and installed in your antenna system. It should be also noted that not ALL antenna systems require this choke but, nonetheless, it is still good practice to utilize one regardless, consider it an 'insurance policy' to ensure that all of your transmitted power goes up to the antenna where you want it and not wasted as reflected power !
Here, you will find a very cost effective, reasonably priced ferrite type of RF choke suitable for the FM Broadcast Band that will easily handle a full 2 Kilowatts (KW) of RF output power !
If you should have any questions, please feel free to message me here on this forum and I will be most happy to assist you ! In the next couple of days I plan to post a thread here that outlines the construction methods utilized to fabricate each type of RF choke.
73... Spooky...
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