RSGB: Useful practical skills videos - simple Balun

[@ariekleingeld6338]

Keep those video's coming!

[@DJunclepaul2nd]

Thank you for this video. As someone new to the hobby, this really helps.

[@eugengrzondziel1706]

Thank You! Could You show the next step? How to test CMRR, the common mode rejection ratio with NanoVNA?

[@ianthomsonGM0URD]

The simple choke type balun you have described can also be used as a line isolator at the transceiver end of the coax to eliminate any common mode currents on the outer of the coax. This can also help with a correct VSWR reading as SWR meters are quite susceptible to the effects of common mode currents.

[@user-bx6vu]

Ian, if I do this, will it help prevent interference into my transciever generated by overhead LED lights? What material would work best as I operate mostly on VHF/UHF. When I turn on the lights I see diagonal lines on my Yaesu FT-991A waterfall display. I don't know the frequency of the LED lights. Many thanks M7BAL

[@ianthomsonGM0URD]

@@user-bx6vu It will help a bit. I would change your LED lighting also interference could be coming in from the mains so a mains filter might help. An easy way to check is to compare noise levels when on battery power compared to mains power. At VHF and UHF use foil plus braid type low loss coax as braid only type is only about 80% screened and can pick up interference. Also keep your antenna outside of your house mains radiation local area to reduce mains interference. Lots on You Tube about reducing interference in your shack.

[@user-bx6vu]

@@ianthomsonGM0URD Thanks Ian, Unfortunately I can't change the overhead LED lights as they are the installed in the flat that I am renting and it will be a serious inconvenience :) As soon as I turn them off the interference disappears. I use a mag mount antenna which I take out on the balcony but the segment of the coax inside the flat picks up the LED interference as it's not well screened. What I can do currently is switch off the lights and use a different light when I play radio :) I will try a choke but currently not sure which ferrite mix will be best at allowing 144 MHz and block everything else. Edit: I also ordered some M&P Hyperflex 5 coax which I hope would help with better screening

[@ianthomsonGM0URD]

@@user-bx6vu Better coax should help you could also try a Watson type 2m/70cm antenna attached to the balcony. The shorter length one should be fine but your magmout one may also just be fine. 73's.

[@smellthecoffee5314]

Very helpful - thanks

[@2EOGIY]

7:14 I always thought that it's for cancellation currents within toroid.

[@M0VFC]

The turns are still passing through the core in the same direction - you're trying to reduce capacitive coupling between input and output, though I think it's more relevant at higher frequencies than lower. Rob, M0VFC

[@2EOGIY]

@@M0VFC "The turns are still passing through the core in the same direction" yes, they are but at half of the toroid faze (direction of current) is turned 180 degrees. For me, it's like half of the turns induce magnetic field within the core and the same amount of field induce a current in the cable on the other half (Lorentz force) but because the direction of current is reversed the currents cancels out itself.

[@markdunsford4377]

A 120-63 ferrite doesn’t seem to exist. (At least not on any of the many specialist ferrite and general electronic suppliers I’ve looked at. Firstly, the closest types available are 61 and 67 - no 63s in sight. Similarly, sizes seem to be based around quarters (or possibly eights) of an inch so there are 100 and 125 but no 120. Have I missed something or is that number incorrect. Also, is a 125-61 likely to have suitable characteristics or will it be radically different?

[@corvus-ch]

I am wondering how this is actually transforming a unbalanced signal to a balanced one. Both ends are directly connected to one and another. So if the unbalanced side has its shield connected to ground, the supposed to be balanced side also has a connection to ground and therefore can not be balanced. I might be missing something here. Hopefully somebody can point me into the right direction.

[@corvus-ch]

@@WECB640 I knew about RF only traveling on the surface but I have never thought about a coax shield having two surfaces. So your explanation definitly helped. Many thanks.

[@DJunclepaul2nd]

@@WECB640 as someone new to the hobby, this is very useful thanks. I was looking at making a very simple dipole as a learning experience and this certainly has helped. Now I know what to do, and why.

[@ynot6473]

the T2LT or "flowerpot" antenna uses the same principle/method.