Ferrite beads for 6 meter aerial balun

[VK4WTN]

hi all just wondering if anyone knows a good supply of ferrite beads to go over LMR400uf coax to make a choke balun for a 6 meter G0KSC LFA yagi. Someone mentioned that Jaycar had cheap ferrites tht may be suitable. Would anyone know the part number and how many you would need for a 6 meter yagi
regards Wayne VK4WTN

[VK1JA]

G'day Wayne,

Not ferrite bead related, but I've built one of Justins 5el 6m LFA yagis (4.4m boom version) and I used the 'G0KSC Antenna Balun' way, ie. a 1/4 wave rod as described about mid way down this page.

http://www.g0ksc.co.uk/creatingabalun.html

It's fool proof and easy to build into the antenna, and also lets you then feed the coax straight into the boom making it nice and neat instead of having bulky ferrite beads hanging off the feed point.

[VK4WTN]

hi Jayson, I am looking at making four of the G0KSC 4.1 m boom 6M yagis and stacking them on a H frame.I was going to use the 1/4 wave balun but I was under the impression that I might still have to use ferrites as well. It would be a lot cheaper if you dont have to use the ferrites.Just wondering how you locked the sliding section on the driven element did you use a screw or hose clamps.And did you have to fiddle around with the sliding section to get your swr down. I am going to build a single yagi first and have a play with it
regards Wayne VK4WTN

[ZL1RS]

Someone mentioned that Jaycar had cheap ferrites tht may be suitable.

That may have been the Jaycar LF1260 cores as suggested at http://vk1od.net/balun/W2DU-LF1260/index.htm

...but alas they will only slide over a maximum 8mm diameter coax.

Owen's article was using RG-58 coax ... and RG-58 is typically only good for 600W at 6m. Otherwise the LF1260 appears to be a good core for 6m as the impedance peak from Owen's simulation looks like it is somewhere just above 30MHz.

73

[VK1JA]

G'day Wayne,

My understanding is that it behaves the same as a pawsey stub but you don't have to fuss around with velocity factors, therefore no need for a coax balun or ferrites = win !

For the sliding sections in my 2m LFA I used screws but found that it was fiddly to then adjust for lowest swr. So on the 6m LFA I've used stainless hose clamps, cut slots in the larger tube so the smaller tube can slide in and out easily etc. You'll find that there's a bit of excess hose clamp sticking out once you tighten it up, you can cut this off once all tuned. You could be lucky and get the swr at it's lowest first time around and use the screw method, but seems you'll be running a bay of 4 you'll want to tune each of them individually first, so I'd go the hose clamp way.

If you haven't already bought the booms, have a look at the 4.4m boom version, the extra 30cm gives a nicer pattern and will bay up nicely

I'll be super keen to see pics of your progress, a bay of 4 will be very nice. Will you be doing eme with them?

Cheers

Jayson

[VK4WTN]

Thanks Bob and Jayson. The reason for the 4.1 design was that G0KSC recommended them for stacking and they will stack at 4.1M veriical and Horizontal which makes for a nice small stack. Bob ZL1RS what balun did you use on your LFA antennas?
regards Wayne VK4WTN

[ZL3ADT]

Hi Wayne

I have built 6 metre and 2 metre LFA yagis.
The G3WOS build instructions on Justins web are helpfull.
I made the tube baluns, thats all you need and they can take the power.

I used hose clips aswell to connect the loops to elements, makes SWR tuning easy.

Ross

[ZL1RS]

Bob ZL1RS what balun did you use on your LFA antennas?

I had a handful of unspecified green coloured cores that were used for EMI suppression in switch mode power supplies that just happened to fit over the 16mm diameter 75 ohm hardline used for the phasing harness ... so I used them. Otherwise just kept the phasing lines and coax taped close to the booms and stacking mast as instructed by my VHF antenna mentor VE7BQH. More could have been done perhaps, but the results speak for themselves (to be fair, largely due to the QTH) ... and I'm an "if it ain't broken, don't fix it" sort of guy!

As for tuning, one antenna was set up temporarily and the loop ends slid in/out in equal increments until the MFJ-259 showed the desired result across the low end of the band ... then I drilled holes and riveted the joins together. The loop measurements were duplicated on the other LFA, checked to be OK with the MFJ-259, and drilled/riveted that one too. The joins were sealed up to keep the rain out ... then holes were drilled in the under side of the loop "tips" (being the lowest point with element sag) to let the water drain out that would get in anyway

There was always going to be a slight change in the SWR due to mutual coupling between the two LFAs and the phasing harness being made from 75 ohm coax rather than the "ideal" 70.7 ohms. The array is currently indicating 1.2:1 SWR across most of the bottom 300kHz of 6m. Close enough ....

73

[VK4TI]

Someone mentioned that Jaycar had cheap ferrites tht may be suitable.

That may have been the Jaycar LF1260 cores as suggested at http://vk1od.net/balun/W2DU-LF1260/index.htm

...but alas they will only slide over a maximum 8mm diameter coax.

Owen's article was using RG-58 coax ... and RG-58 is typically only good for 600W at 6m. Otherwise the LF1260 appears to be a good core for 6m as the impedance peak from Owen's simulation looks like it is somewhere just above 30MHz.

73

http://cpc.farnell.com/ does a suitable core for a much better price on a 10 day delivery , about $2.20 per core in bags of 5 delivered

[VK4WTN]

Thanks for all the feedback guys.I will enjoy playing with the LFAs over the next few months
regards Wayne VK4WTN

[VK5PO]

Tune your LFA yagis to MNINIMUM X... take out any stray capacitive and/or inductive reactance.

SWR is only half the story Wayne and Co.

Ideal and reachable figures are R = 50 (ohms) and X = 0 (reactance)

Ferrites over the feed line may help with keeping "noise" off the feed line, but there should be ZERO
stray RF if the antennae are tuned to minimal X. That will be your resonance point obviously, so the S.W.R. will be good too.

Make your "1/4 wl " tube / flat section, as described, and you will be just fine.

Any questions, just ask.


73, VK5PO, John

[VK4TL]

Palomar have the beads for RG213. Kit comes with heavy duty shrink tubing. Bought a couple of sets about three years ago and they were $18 au each then. I have them installed on my new 12 metre 4 el direct feed beam. Hope this info helps. John VK4TL

[VK4WTN]

Thanks for the info everybody. John I will pick your Brains later about the LFAs I am sure that there are a few tricks to learn
regards Wayne VK4WTN