If your new review has not been Approved after several days you can assume that it was found to not be within the product review T's&C's shown below during screening. Before adding a new product use the "Search" tool on reviews Home page to determine if that product already exists in a category.Ĥ. The delay can vary from minutes to a day or more.ģ. The delay is for new review screening and approval. There's a delay before newly submitted reviews are Approved and posted in eHam's reviews. eHam's Product Reviews are a database of ham radio related products and services personal opinions.Ģ. Overall, you can make one at a little cost, however I would say the MFJ is a benchmark!ġ. Reading between the lines of the Jerry Sevick book my version should also work on HF. Without the rod I got just 0.7 microhenry. With 17 turns I got 12 microhenry as inductance compared to 84 microhenry of the MFJ-915. The Aircell 5 is small as RG58 but is semi-rigid and keeps the shape around the ferrite rod. Two Teflon PL connectors, some "Aircell 5" cable and a ferrite rod. I have just made a Guanella 1:1 using a different approach using spare stuff I had in the drawer. On verticals I would put one unit close to the antenna and another close to the TX. I use a T2FD, which is balanced, as an inverted V and I noticed a slight change between 24-29Mhz. On unbalanced antennas the effects should be more important. On the instruction sheet I have not found any mention on which frequencies it should work. I tried it on VHF at 50Mhz band but SWR was higher, so I think this product is mainly designed for HF. This is in my opinion quite a high value and this explains why this product works remarkably also on the lower HF frequencies. Also I measured the same inductance between the two ends of inner coax. Overall mechanics seems to me very good!Įlectrically I measured 84 microHenry as inductance between one and the other of the shield. This is made up of many ferrite core beads placed on a quality coax cable. A current balun can be made however made in many ways. According to the instruction sheet it is indeed a 1:1 current balun, i.e. And there is continuity in the shield as well. The name RF-Isolator may be a bit misleading as there is no DC isolation: there is continuity from one end to the other of the inner coax. The moral of the story, you can make one at a little cost which may work however I would say the MFJ is a benchmark and I would buy two of them again!Įarlier 5-star review posted by KD7RDZI2 on With 17 turns I got 12 microhenry as inductance compared to 84 microhenry of the MFJ-915, which means that the MFJ-915 has a better "isolation". On unbalanced antennas the effects should be more important and on verticals I would put one unit close to the antenna and another close to the TX. However the specs say 1.8-30Mhz and 50 Mhz is out of the band. I tried it on VHF at 50Mhz band but SWR was higher. This is in my opinion quite a high value and this explains why this product works remarkably well also on the lower HF frequencies. Also I measured the same inductance between the two ends of center conductor. Overall mechanics seems to me very good!Įlectrically I measured 84 microHenry as inductance between one and the other end of the outer braid. A current balun can be made in many ways. I believe it could be used with active antennas with DC voltage flowing in the center conductor and in this case I would put it close to the antenna.Īccording to the instruction sheet it is indeed a 1:1 current balun, i.e. There is continuity in the shield as well and no continuity between the shield and the center conductor. There is continuity from one end to the other of the center conductor. The name RF-Isolator may be a bit misleading as there is no DC isolation.
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