Re: Topband: How to Measure Beverage Common Mode Noise
Wayne, What is more important than a little weak noise is common-mode signal. Why don't you also test to see how well you can hear any AM broadcast stations with the coax terminated? Please also tell us more about your Beverage, especially how you are feeding it (transformer, etc.) FWIW, I don't need current chokes on my 600' of 75 ohm coax (which is lying on the ground) feeding my Beverages. Some people do. 73, Mike www.w0btu.com On Tue, Jul 24, 2012 at 12:15 PM, Wayne Willenberg wewill...@gmail.comwrote: I am still working on my new Beverage antenna. ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: How to Measure Beverage Common Mode Noise
I have run about 400 ft of F6-type flooded coax from my shack to one end of my Beverage antenna. My question is: do I need to install a feedline current choke about 20 feet from the end of the Beverage antenna (the current choke would have its own separate ground. While a dummy load test for signals (as Mike says, noise is often too weak) might confirm a poor shield connection, especially if the cable is connected to normal grounds, it certainly does not test for the most common problem. There isn't any test I can think of that will properly confirm common mode sensitivity except one: Connect the antenna through a 400-600 ohm resistor to the ground terminal of the beverage matching transformer, while the antenna post of the beverage transformer is also tied to that ground, and see what you hear. Most common issues, other than defective connectors or shield connections, are caused by using auto-transformers or un-uns to match the antenna, rather than a primary-secondary isolation transformer. The shield should NEVER have a low impedance path to the beverage antenna ground. The test above tests for that defect, as well as other common mode issues. If you look at transformers, especially before I brought this issue to public attention, most feed system designs tied the shield to the antenna's ground. That was a horrible method of matching that never should have started. Unless the ground is nearly zero ohms RF resistance, the shield becomes an inevitable extension of the antenna. Yet most early articles suggested un-un's. 73 Tom ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: How to Measure Beverage Common Mode Noise
Wayne is using a DX Engineering bi-directional system. Unless DXE changed to ununs without telling anyone, he has little to worry about there. ;-) 73, Mike www.w0btu.com On Tue, Jul 24, 2012 at 1:19 PM, Tom W8JI w...@w8ji.com wrote: Most common issues, other than defective connectors or shield connections, are caused by using auto-transformers or un-uns to match the antenna, rather than a primary-secondary isolation transformer. ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: How to Measure Beverage Common Mode Noise
Wayne is using a DX Engineering bi-directional system. Unless DXE changed to ununs without telling anyone, he has little to worry about there. ;-) Yes. Cable grounds are isolated from signal grounds. That unit uses primary-secondary isolation transformers. ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
