Choke Balun - a few questions..

[USASAgencyman]

OK so I get another kit and wind a 1:1 on a ferrite doughnut, to actually feed the Windom, after a close 4:1?

I may also experiment with some clamp on chokes, (I use them on computer and even audio cables that are hooked up to wideband preamps and amps), maybe as part of that 20' drop below the antenna.

The final combination should be illuminating!

Bruce

 

[USASAgencyman]

Reading, reading...There is a lot of theory out there, and not all in agreement!

I realize for listening, I can just hook the coax to the two legs of my soon-to-be-built Windom. But the comparative performance between balun combinations should be mirrored in transmission performance, later when I get there. If I can get consistent and reliable comparisons from no skip stations.

I think my first two experiments will be; (1), 4:1 at the feed, with the Carolina style 1:1, also ferrite core, located 22 ft. below feed, with the other option, (2), being; A 4:1 up as close as I can wire it to feed point when followed immediately with the 1:1 to actually feed the antenna.

If I don't fall off the extension ladder, I might learn enough to be ready for the transceiver!

 

[prcguy]

You need a lot of clamp on ferrites to be effective at HF and most clamp on's are type 43 material better suited for VHF where type 31 is more effective at HF. You will have much better common mode choking wrapping multiple turns through a core than simply clamping several of them over the coax.

For 40m through 10m wrapping 8 turns of RG-58 size coax through an FT-240-31 core is a good start. For 80m through 10m or worse, 160m through 10m you really need to break the choke into two parts with maybe 17 turns of coax through an FT-240-43 core for the lower bands then maybe the same amount through an FT-240-52 core for the higher bands so the two different chokes are in series.

I hope to have a better test jig made up soon to measure choke baluns with a vector network analyzer. I've been curious about stacking two different types of core materials, one favoring the low bands and one favoring the high bands and wrapping just one choke made with the two different core materials to see if it retains the same wide band properties as winding them separate then connecting in series.
prcguy

 

[USASAgencyman]

I think I will save clamp-ons for another day.

The kit I was going to make for 4:1 used magnet wire or teflon sleeved wire, small and rated about 100-200W

Since you seem to be talking higher transmit power, I guess the coax windings give you more?

If you have a list of folks you send such research results to, then I would definitely enjoy your adding me,

bch {at} alltech-systems {dot} com

Thanks,
Bruce

 

[prcguy]

Coax is commonly used in a 1:1 choke balun but you could run two parallel wires instead of coax. Its mostly the core size and type that determines the power handling but the wire size and insulation voltage rating or coax size can also limit the max power. Some of my choke baluns use dual 2.4" dia cores and RG-142 coax and will handle a good 5kW through 10m.

Your 4:1 balun is also an impedance transformer, which can be made in many different ways from an actual transformer with a discreet primary and secondary, or bifilar/trifilar windings tapped and connected to give whatever impedance ratio you need.
prcguy

I think I will save clamp-ons for another day.

The kit I was going to make for 4:1 used magnet wire or teflon sleeved wire, small and rated about 100-200W

Since you seem to be talking higher transmit power, I guess the coax windings give you more?

If you have a list of folks you send such research results to, then I would definitely enjoy your adding me,

bch {at} alltech-systems {dot} com

Thanks,
Bruce

 

[USASAgencyman]

Prc guy,

I'm 66 and have gone from self employed, (my own AV+data svc/sec company), to seriously underemployed, so I want to try to make my items if possible.

Would you consider helping me with a schematic to build a dual ferrite dounut core, (for wide bandwidth, if I understand you correctly), choke for 100-200W? If I can ever afford 1000+ watts, I will at that time be able to buy the high performance parts!

Until I started looking at baluns, I thought transformers were ratio related directly by turn counts on the in v. out!

Bruce

 

[USASAgencyman]

I just had an intriguing question pop into my thoughts:

Has anyone ever experimented with an "unbalun" transformer, where the internal windings might be appropriately out of balance to feed an out of balance antenna, (off center fed)?

 

[prcguy]

I've not experimented as much with low power choke baluns except for the FB-31-1020 ferrite bead with about 5 turns of sub miniature coax through it. This is the bead that is supplied with a lot of HF mobile screwdriver antennas and they wrap about 5 turns of the motor wires through it to decouple them from the antenna. The same formula works fine for choking RF off coax.

You can't really copy the # of turns of coax from a larger choke balun and use it with a smaller core because the inductance will be much less with a smaller core and it will take more turns to achieve the same effect.

What I would recommend for your low power offset center fed dipole is the BN-43-7051 binocular core and instructions in post # 10 and use another BN-43-7051 core configured as a 1:1 with these instructions: http://www.elecraft.com/manual/E740077 BL1 1 to 1 Rev B.pdf

I've used many of the 4:1 versions but have not made a 1:1 on this core but it should give more than adequate choking over the 80-10m bands. Total cost is about $10 in cores to make the 4:1 and the 1:1. As a coincidence I'm just finishing up an 80m offset center fed dipole using the BN-43 core for an upcoming trip to Dallas, TX where I will be leaving the antenna and a complete HF station at the location so I don't have to keep dragging one with me.
prcguy

Prc guy,

I'm 66 and have gone from self employed, (my own AV+data svc/sec company), to seriously underemployed, so I want to try to make my items if possible.

Would you consider helping me with a schematic to build a dual ferrite dounut core, (for wide bandwidth, if I understand you correctly), choke for 100-200W? If I can ever afford 1000+ watts, I will at that time be able to buy the high performance parts!

Until I started looking at baluns, I thought transformers were ratio related directly by turn counts on the in v. out!

Bruce

 

[nanZor]

Has anyone ever experimented with an "unbalun" transformer, where the internal windings might be appropriately out of balance to feed an out of balance antenna, (off center fed)?

Sure - normally used with non-resonant verticals, or other non-balanced wire setups. Balanced antennas in the real world are usually not always balanced at all due to the surrounding environment, so an "UN-UN" might be a better choice.

While you are awaiting for broadband ferrites to arrive, you can cook up something old-school with air-wound balun / unun on say a 1-inch PVC pipe.

About half-way down the page this project has a nice schematic and wiring diagram of a typical pre-ferrite era 4:1 air wound:

SM2YER Goran's Homepage

Essentially, 13 bifilar wound turns on 1-inch or so pvc. Wired as shown it is a 4:1 balun.

If you want to turn it into an UN-UN, swap the center conductor and shield of the coax connector - keep the wires the same. In the case of a non-resonant vertical wired with an un-un, the shield connection side of the unun would also attach to radials. The other free wire of the coil merely goes to your antenna wire. Follow this with a good 1:1 choke.

The major problem with air-core bal / ununs, like the coax-wound "ugly" baluns, is that they are narrow-banded, and also have considerable reactance and leakage current. In this case, much capacitive reactance at 10m, which is usually problematic.

Most people overestimate the coverage. The following is a bit more reasonable.

13 bifilar turns (26 individual turns total) = 13mhz to 21mhz <--- typically overestimated as 160-10m in most articles...
18 turns = 3.5 to 7mhz <--- low band coverage
10 turns = 18 to 28mhz <-- higher band coverage, but still, capacitive reactance can be fiddly.

Still, 10m is a bit problematic with air-core, but if your application isn't too critical (perhaps an rx-only setup) then you may not notice a big difference.

So, knowing that these are narrowband devices, with some funky reactance and leakage current, there is no wonder that ferrites became so popular.

Fun to whip up on a whim to try out. Sometimes we over-engineer things depending on the application.

 

[USASAgencyman]

A long time away in a galaxy far, far ago, Big Daddy DIRNSA had a listening post that was staffed by us mils. We had the most advanced wave guide on a big tracking dish ever! I picked up the equivalent of a walkie talkie with that rig at 45k miles coming back from, (???)

That antenna had the ability to physically phase align its active elements for freq desired.

I think a switchable component at the feed of an antenna too high up to be constantly touched, might be fun to design and test. Could be multiple feed devices!

Oh, OK, I am fully waking up now, back to reality!

 

[USASAgencyman]

Too late to edit, I guess...

This switch could be activated by Wifi. Seems like a similar process could also be used for antenna switching for those with more than one.

It's probably already out there, I shall search.


ETA: Um yeah, no shortage of such!