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[W2EAF]

I'm thinking of putting up a 5 band trap dipole for 80 through 10, using 2 traps and an overall length of 108', as described in William Orr's book "Simple wire antennas". The text says to feed it with 50 ohm coax and use a balun "if desired", but doesn't specify what kind (1:1, 4:1, current, voltage?). Any help would be appreciated.

Rob W2EAF

[WB6BYU]

Certainly a 1 : 1 balun.  Since it is designed for a 50 ohm
feed, you don't want any impedance transformation.

A current balun does a much better job as a balun than
a voltage balun.

[NA6O]

Start here, and prepare to learn something: http://www.k9yc.com/2018Cookbook.pdf

Gary NA6O

[N2TO]

FYI

Bill Orr, W6SAI (SK) was one of my heroes.

Maybe Octopart can help. I buy Fair-Rite toroids through authorized resellers to ensure I'm getting the right thing.

I use 2.4" Mix 31 and Mix 43 on feed lines. Recently made feed line chokes, 12 turns Mix 31 at feed point and 12 turns Mix 43 at rig. I also do not use coax with foam dielectric for chokes. And I check spec sheet for bend radius too.

GL

https://octopart.com/

GL

73 Kevin N2TO

[W9IQ]

Type 31 ferrite is superior to type 43 for all HF choking applications. The standard part number for type 31 is Fair-Rite 2631803802.

Lately, I have found the best price at Newark.

- Glenn W9IQ

[K1KIM]

Type 31 ferrite is superior to type 43 for all HF choking applications. The standard part number for type 31 is Fair-Rite 2631803802.

Lately, I have found the best price at Newark.

- Glenn W9IQ

Compound 43 for 10M-160M UNUNS/BALUNS and compound 31 for common mode chokes correct?

[WA3SKN]

Since the antenna is designed to provide a near 50 ohm Z, using 50 ohm coax and a 1:1 balun makes sense.  However, you could feed with open wire/ladder line and a tuner in the shack with the balun at the tuner (inside?) also.
For 80-10m use the 31 core is better that the 43 core, but both can be made to work OK.

-Mike.

[WB6BYU]

A “common mode choke” is exactly the same
thing as a “1 : 1 current balun”.  For that,
type #31 is better, although #43 may be
adequate in some applications.

For transformers, #43 is better.

[KH6AQ]

A 1:1 balun (feedline current choke) having a (CM) common-mode impedance of >500 ohms will do the job. A greater CM impedance results in less coaxial cable external shield current and less choke heating. The 8 and 12 turns of RG-58 on one FT240-31 ferrite core chokes look good. 10 turns looks like it will provide >1k ohm from 80 to 10 meters. Amazon, Ebay, Mouser and others stock the ferrite core.

I used such a balun on a Diamond W8010 5-band trap dipole.

G3TXQ chokes   http://www.karinya.net/g3txq/chokes/

[N4UFO]

For 80-10m use the 31 core is better that the 43 core, but both can be made to work OK.

Everyone here keeps saying this, but if you look at G3TXQ's charts (which is what I consulted years ago) when the antenna is covering multiple bands, the #43 is 'broader in coverage' than the #31. If you are only doing 1-2 bands, then yes, #31 is better... but for 80-10m, wouldn't #43 be better... overall, I mean?

As my antennas are multi band, #43 is what I use. (Plus when I first bought a bunch of toroids at a previous QTH, #31 was less prevalent and more expensive is memory serves.) On the lower bands (160-40m), I simply used two toroids in my choke. On the higher bands (30-10m), I made two chokes, one at feedpoint, and one at shack entrance.

[N0GV]

My experience is that for a choke you can use either mix 31 or 43 but that 31 will generally perform somewhat better. For a transformer you will want to use larger cores, stacked and a lower loss mix, 43 is preferred, due to heating (losses).

A choke only has to block the portion of the reflected or induced rf current on the outside of the shield whereas a transformer carries 100% of the rf current that makes it to its load. That is the reason for the difference. If there is 200 watts reflected then the center conductor carries ~100 watts and the shield also carries ~100watts of which the majority is on the inner surface (lower impedance than the outside) hence your external shield power may be only a few tens of watts... only the external rf on the outside of the shield creates a magnetic field in the choke's ferrite.

In a transformer the forward and reflected power all go thru the magnetic field in the ferrite core....

Grover

[W2EAF]

Thanks to all for the info! And yes I'm always prepared to learn, which is why I ask questions here. I've ordered some toroids and will be experimenting with 1:1 baluns. I'll wait till my brother in law visits before putting up the antenna because his throwing arm is way better than mine!

[WB6BYU]

...I'll wait till my brother in law visits before putting up the antenna because his throwing arm is way better than mine!

Here's a simple method I use to get a rope up 50' - 60' in
a tree, and I'm certainly not an athlete by any stretch of
the imagination.

[K6JH]

What happens if you stack two different toroids, like a 31 and a 43?

[W9IQ]

What happens if you stack two different toroids, like a 31 and a 43?

From a core perspective, you end up with something that looks like an average of the two ferrite properties. In other words, worse than stacking two type 31 ferrites.

Also keep in mind that stacked cores will approximately halve the effective frequency of the common mode choke. You will generally get better results by winding two chokes, each on their own core, and then place them in series. You can use different winding counts on the two cores in order to improve the combined frequency coverage.

- Glenn W9IQ