5 Pack 31500 Ferrite Filter Core Material 31 Mix ID 1/2' 13mm Inner Diameter

Cleared noise

You can never have too many of these in a HAM radio room.

I needed these to address really bad AM radio static whenever I turned on a Shopsmith multi-tool in the workshop; the motor didn't even have to be running, just powered it on and you couldn't hear much but extreme static on both radios in the workshop and in the house. Either the property isn't wired correctly or these filters are useless. I tried 3 on the tool and 2 on the radio in the house and noticed no change. Then I tried all 5 on the tool and still no change. FM stations are similar, but not as bad as AM.

Works very well on the HF bands. Put as close as possible to RFI (Car fan, PS, etc). Not for UHF or VHF, just HF. 3Db per loop in core.

See title

Works well on quieting HF common mode noise in my Ham station. Good inner diameter for coax and power cables. Easy to open with out tools.

I am glad to have installed these on my ham radio coax from amp/tuner to antenna.Not sure these are Mix 31 (I'll test that with my nanoVNA ASAP), but they surely help curb some of the RFI I was having,--NN5O

I bought 2 packs of these (10 cores total). The price was very attractive for a type 31 mix ferrite of this size. I have some of identical dimensions from a well known ham radio retailer with its HQ near Akron, OH. The ones they sell are more expensive. Today I took a few hours and analyzed their choking capability vs the ones I have from the other place. I found that these consistently have several dB less attenuation across the HF band when used as a multi-turn choke. I used a VNA (Vector Network Analyzer) that I calibrated beforehand for this test. By doing a "through" calibration with my test leads and the wire I used in the chokes in the path, I was able to null out the effects of the leads and wire on the measurements. Please take a look at the image I uploaded. This is an S21 insertion loss plot of 2 turns and 4 turns (1 turn = 1 pass through the core center) for both brands. In this case, we want to choke out unwanted RF so more insertion loss is desirable. Lower numbers are better (more attenuation of the unwanted signal). These chokes were typically 3 to 5 dB less effective than the other brand. I tried several samples from both to make sure I did not have outliers. I don't have a mass spectrometer so I can't actually analyze the mix material but these are not as effective as I feel they should be if they are using a true type 31 mix material. However, they do provide some degree of choking and therefore have some degree of effectiveness. In general and on average, it seemed that an additional turn through these brought them in the vicinity of the other brand with 1 less turn. For example, 5 turns through these was more or less similar to 4 turns with the other brand. However, you may not have the cable to spare or you might not be able to fit an additional turn in them, depending on your cable diameter. I have no doubt that some of the other reviewers did get some choking from them and may have achieved what they required. However, if you are looking for maximum effectiveness and genuine type 31 mix, you may need to consider another solution. Nothing on the packaging I received overtly stated them to be type 31 mix. It did say "Mecion 5 pack 31500 ferr...". The 31500 could be interpreted to mean type 31 mix with .500" I.D. but that would only be speculation. If you have cable length to spare, you could put multiple turns through 2 or more of these and exceed the choking of the famous brand (you'd still be using more total turns). You might still save a little money, especially if you have Prime and get free shipping. The famous place charges for shipping on smaller orders. While the other brand has the same core dimensions, the outer plastic shell has an hexagonal shape. There is a seller here on Amazon selling ones that look similar to the famous brand I have, with an hexagonal plastic shell. However, I have not purchased those and have not measured them. 73 KE2D