[TowerTalk] Feedline (choke) question

[Rod Greene]

I don’t claim to be an engineer or tech but don’t common mode vs differential mode currents have a big part in all this?  73, Rod w7zrc


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On Wednesday, October 1, 2025, 8:48 AM, Jack Brindle via TowerTalk <towertalk at contesting.com> wrote:

Let’s take a good look at how connections are made using PL-259 connectors. For RG-213 size coax, the center conductor goes straight through the coax dielectric and into the center tube of the connector where it is soldered. The shield is cut back so that it does not contact the center conductor, the outside of the shield is then soldered to the inside of the PL-259 shell. The inside of the shield is not connected to anything, but relies on solder to connect it to the connector shield. Thus either there is no connection from the inside of the shield, where the signal is carried, to the shell and only the outer shield connects, or the two combine at the connector.

Now let’s look at the coax that was used in the choke tests. I believe these also used PL-259s with the UG-175 adapter. The center conductor is handled the same way as in the RG-213 case. There is a big difference in how the shield is handled. In this case the braid is frayed, then folded back onto the UG-175. At this point the frayed shield is soldered to the shell of the PL-259 and to the UG-175. Because of the fraying, we don’t know whether the inside or outside of the shield connects, and most likely it is a combination of the two. In other words, the two skin effect currents are again combined at the connector.

Connectors are very important in this system. They must be added to the analysis. Without them, we have to question the validity of the tests.

Did you think that re-radiation was the mechanism for the outer currents to cause problems in your system?

73,
Jack, W6FB


> On Sep 30, 2025, at 11:22 PM, Jim Brown <jim at audiosystemsgroup.com> wrote:
> 
> On 9/30/2025 2:29 PM, Jack Brindle via TowerTalk wrote:
>> No. All connectors that connect the inner and outer edges of the shield. Purely from skin effect.
> 
> I don't buy any of this, Jack. The shells and center conductors of connectors splicing two sections of line exhibit skin effect just like any other conductor. The only difference are the dimension of the shield as it goes through the connector(s).
> 
> 73, Jim K9YC
> 
> 
> 
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