Building a 1/1 Current (Choke) Balun

Another simple useful device: 1:1 current balun, used as a choke for RF suppression. I've built this balun following this site: http://kambing.ui.ac.id/onnopurbo/orari-diklat/teknik/balun/current%20balun,%20current%20choke,%20choke%20balun,%2050%20ohm%2011.htm

The core is an FT140-43 toroid and the winding is made of RG-174 coax cable. On antenna side I added a 10kohm - 1W resistor in parallel between cold and hot connector of the PL for static suppresion. The final result is here:

SWR with 50 ohm dummy load is 1:1 160-10 meters, on 6 meters SWR is better than 1.5:1. At this time I've not tested the balun on the air.

Building a 4/1 Current (Guanella) Balun

I need a 4/1 balun for feeding balanced antennas, such as Up-and-Outer (my preferred antenna) or M3KXZ 'no counterpoise' antenna.

I've built one following the instruction found on this link: http://www.n0ss.net/qrp_4-1_guanella-type_balun.pdf

I use a single core, FT140-43 toroid, enclosed in a little black box, using two "banana" binding posts for wire and panel female BNC for feeding.

The result:

Another photo: Box closed and added 32mm diam. clip for fishing pole locking

Very simple to build! Results: VERY VERY VERY good! I.E. North Patagonia on 15m with 2.5 W using up-and-outer antenna! See http://iz8jji.blogspot.it/2012/07/a-great-qso-un-15m-with-lu.html

I've not used this device on 80 or 160 meters but the performance expected is not so good. I've tested the balun in 6m but the performance are very poor!

Building a 9:1 Un-Un for longwire antenna

I'm always fascinated by the "magic" 9/1 un-un for longwire antennas, also called "Magnetic Longwire Balun". You build this device, connect the transceiver and a longwire antenna of almost random wire, and GO!!! No SWR on 160/10 meters, no Tuners, perfect.....OR NOT?

The background study:
If you google "Magnetic Longwire Balun" you may find a lot of experiences of many ham operators all around the world about this antenna. The cores used for Un-Un are various: ferrite sticks, FT and T Amidon toroids and even cores from old TV EAT transformers.

There is also a SWR table versus wire lenght, found somewhere in the 'net attached to manuals of commercial longwire antennas (click image to enlarge):

I suggest to look at M0UKD web site for a quick guide to build a 9/1, If you want to deep in with different cores and expected performance, read:

• G3TXQ web site contains a very good article (http://www.karinya.net/g3txq/unun/) on cores and ratio comparison for 9/1 and 4/1 un-un.

•  G8JNJ web site has a very good article (http://g8jnj.webs.com/cometcha250b.htm) on building a clone of the Diamond BB6W wideband antenna (scroll down...). The balun used is a 6/1 but there are some interesting facts and tests on various cores.

Building the 9/1 Un-Un 
My requirements was:

• 80m to 6m use
• QRP or max 100W power
• light and little for portable use

I use an Amidon toroid, a T130-6 with 9 turns trifilar using insulated stranded wire. For the box, I choose a grey PVC coupler (40 cm diam.)  and two caps. Connectors are PL female for TX and M5 screw for antenna wire.

The Un-Un have no hooks for hanging, but I arrange also two insulators made of hard white plastic (teflon?) from a chinese chopping board. The right one is for connection to Un-Un (using the third hole for hanging) and the left one is for wire end.

The SWR of Un-Un with a 470 ohm dummy load was measured and better than 1.3:1 from 3.5 to 50 MHz..
I've made several 9/1 for me and for some friends using different materials. On-air performance is sufficient, not bad for a so simple antenna.

Cores used in the Un-Un :

• Amidon toroid (T200-2, T130-6, FT140-43, FT240-43)
• Unknown Yellow-and-White toroids (I suppose are for switching power supply)
• Ferrite sticks from old AM radios

In order to chioose the core material, mind this simple facts:

• Using Amidon cores (in particular TXXX-2 and -6) the losses are relatively low and the performance of the antenna is better, but in the lower bands you may need a antenna tuner to obtain good SWR. Otherwise, if you don't like to bring ATU, try to use a "long" coax feeder (more than 10 meters)
• Using low frequency toroids or ferrite sticks the losses incrase a lot, but this lower your SWR and you don't need an ATU at all.

Another 9/1 Un-Un I made for a friend with ferrite stick

UPDATE!
Look my new "Shorted" longwire antenna