There's about 35 Beads on a little piece of Coax inside that when stretched out to about 15 inches, they perform much better! If you don't take something apart and make it a better product, you're not a real HAM! One problem I seen was these units when taken apart, are wrapped up over the top in stuffed into this short little PVC.Not good electronics design practice. I pulled the ends apart once since they didn't use enough PVC Glue! One TIP you might consider, Sand the PVC around the ends where water can enter, if you're gonna use these outside, Silicone the Water points for humidity and moisture entering! I put them Outside and inside, on Feedlines, on DIPOLES, on LOOPS, inside the house, Keeps the RF off of the FeedLine Jackets.Įven stabilizes and reduces the noise as well, quiets the the receiver Hash. You really need to install a couple of these. My choke sits at the base of the antenna so it isn't getting tossed around. Mine does make some noise too and I am not sure why, but it doesn't seem to affect the performance. Someone mentioned some rattling inside the MFJ-915 enclosure. An impedance close to 50 Ohms showing little reactance is observed across frequency. I've swept the MFJ-915 from 1 to 30 MHz with the RigExpert and a 50 Ohm resistive load on the choke output. All is good on the other bands so I think the choking impedance is quite effective on all the bands the choke covers. No evidence of the common-mode problem, and now 10m is behaving as well. I then retuned the 15m wire element for the desired CW point and all is good. When I checked the impedance and SWR in the station they closely agreed with what I was observing at the base. Once added between the antenna and the RigExpert at the antenna base I found my 15m resonance moved up a 100 KHz, but the SWR was very nearly 1:1 at that frequency. I decided to purchase the MFJ-915 isolator and see what results I would have. They helped, but the antenna resonant frequency and SWR varied between them. I tried a couple of homemade current chokes I had made from some -43 ferrite cores and coax. That of course is not the goal or desirable. That result was indication that there was a common-mode current flowing on the transmission line. Transmission line theory with a feedline having loss indicates that shouldn't happen. However, when I checked the impedance and SWR through the feedline in the station the impedance was off by quite a bit from 50 Ohms and it was also reactive. When it came to tuning 15m my RigExpert was indicating a feed-point impedance close to 50 Ohms and an SWR of about 1.1:1 at the antenna base. That is a very time consuming task and I could write volumes about that experience alone. I have a new Hy-gain, Hy-tower 80-10m vertical I have been working to tune on each band.
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