You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
The Feb 2025 Radioddity Giveaway Results are In! Click Here to see who won!

Reply to thread

Message

I like how you built this antenna model, including the tapped stub. You even matched it, although that went out the window in your second model and its common mode currents.

I can confirm that j-pole antennas tend to have a lot of CMC's, this is both from modeling and experience. A lot of people simply throw them up and assume they are fine. Most of the directions I have seen for them don't include any form of choke. If anyone decides to make one, you should be aware of this.

This is true, however, the isolated elements of a yagi are in the primary field of the antenna, while the isolated mast in the j-pole model above is not. Their will be orders of magnitude of difference in induced current in these two situations. In one case you have elements that are designed to react to the RF field of the antenna, and in the other you have an isolated element that is designed to isolate RF currents as much as possible. Sure currents will still flow on the mast in Marconi's isolated mast model above, but their will be so little current flowing on it compared to the elements on the Yagi antenna, Their simply won't be enough to make much of a difference.

The DB

<blockquote data-quote="The DB" data-source="post: 620723" data-attributes="member: 21346">I like how you built this antenna model, including the tapped stub.&nbsp; You even matched it, although that went out the window in your second model and its common mode currents.I can confirm that j-pole antennas tend to have a lot of CMC&#039;s, this is both from modeling and experience.&nbsp; A lot of people simply throw them up and assume they are fine.&nbsp; Most of the directions I have seen for them don&#039;t include any form of choke.&nbsp; If anyone decides to make one, you should be aware of this.This is true, however, the isolated elements of a yagi are in the primary field of the antenna, while the isolated mast in the j-pole model above is not.&nbsp; Their will be orders of magnitude of difference in induced current in these two situations.&nbsp; In one case you have elements that are designed to react to the RF field of the antenna, and in the other you have an isolated element that is designed to isolate RF currents as much as possible.&nbsp; Sure currents will still flow on the mast in Marconi&#039;s isolated mast model above, but their will be so little current flowing on it compared to the elements on the Yagi antenna, Their simply won&#039;t be enough to make much of a difference.<a href="http://hittman.us" target="_blank">The DB</a></blockquote>

[QUOTE="The DB, post: 620723, member: 21346"] I like how you built this antenna model, including the tapped stub. You even matched it, although that went out the window in your second model and its common mode currents. I can confirm that j-pole antennas tend to have a lot of CMC's, this is both from modeling and experience. A lot of people simply throw them up and assume they are fine. Most of the directions I have seen for them don't include any form of choke. If anyone decides to make one, you should be aware of this. This is true, however, the isolated elements of a yagi are in the primary field of the antenna, while the isolated mast in the j-pole model above is not. Their will be orders of magnitude of difference in induced current in these two situations. In one case you have elements that are designed to react to the RF field of the antenna, and in the other you have an isolated element that is designed to isolate RF currents as much as possible. Sure currents will still flow on the mast in Marconi's isolated mast model above, but their will be so little current flowing on it compared to the elements on the Yagi antenna, Their simply won't be enough to make much of a difference. [URL='http://hittman.us'][COLOR=#000000]The DB[/COLOR][/URL] [/QUOTE]

Top Bottom