Common-Mode Choke Balun...

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Marc, G0TOC

Thu Jul 03 2008, 04:33PM
I'm am shortly going to replace the coax to my beam with Aircell 7. Can anyone suggest what length of coax and diameter of former would make for a good common-mode choke balun?

Marc - G0TOC.
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Paul, G4CLJ
Thu Jul 03 2008, 06:01PM
Paul, G4CLJ
Registered Member #337
Joined: Wed Apr 30 2008, 03:05PM

Posts: 10
About 6 Turns 6 inch dia will do.Or you can use clamp on ferrites, ive several that you are welcome to, If you send me a message.
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Ian, G5WQ
Thu Jul 03 2008, 06:29PM
Ian, G5WQ
Registered Member #81
Joined: Sun Mar 23 2008, 07:57PM

Posts: 29
hi marc .
i allways use 3 turns of 5 to 6inch diameter at my feedpoints on 6m aerials
this is what i use on my 4 yagi 6m EME array and any other array i have built and used in the past .

to be honest you ought to increase the spec of coax you want to use , i would recommend you go up to H100 as a minimum requirement .

im not sure what aircell 7 costs but H100 is 1.40 per metre from KNIGHTS CB shop in lincs and is good quality coax that takes normal 9mm PL259 plugs or fits standard n-types as sold for RG213 cable [no need to file down centre conductor either] .

H100 is very flexible and can be used around rotators, the loss figures are ok at 50mhz .

you would lose quite a lot of RF power up a long length of aircell 7 , this coax has probably got same loss figures as mini rg8 .

if you could run to it i would say buy some ECOFLEX 15 coax for your main run to top of tower and then use some H100 around the rotator and to feedpoint , this will give you a more efficient feedline for 50mhz .

if you can find any LDF450-A heliax or even better some LDF550-A , then thats going to decrease your coax losses even more .

you should aim for less than 1.5db coax loss if at all possible or try to get under 1db for the optimal figure .

there are some differing versions of H100 type coax, ie ecoflex 10 , spyder H200 , pope 100 .

you can try W103 westflex but i dont personally like this coax because the foil screen breaks up if you bend the coax , plus the dielectric melts behind the solder joint if you apply a fair amount of heat when soldering plugs and can make the centre conductor shift off centre .

H100 has a spiral weave plus a solid tube polythene dielectric which is far more robust and is a litle more forgiving to high temp soldering of plugs .

myself i use LDF550-A , H100 , 7/8 cellflex, LMR600 , LDF450-A and FSJ450-B coax on my 6m gear .

try to use n-type plugs as much as possible , they are far better matched to 50ohms than PL259s.

if you want to work out your coax losses then just stick a power meter and dummy load at the end of your feedline, then measure what power goes in and what power comes out the other end .

find the best coax you can afford and then use it, it will repay you .

73 ian G5WQ
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Steve, G4WCS
Fri Jul 04 2008, 06:51AM
Steve, G4WCS
Registered Member #283
Joined: Fri Apr 18 2008, 11:55AM

Posts: 70
Ian , thanks for this informative reply.
I will be putting my beam up soon and will be taking your recommendations on board

EDIT just found a link to this most useful table comparing attenuation etc...



[ Edited Fri Jul 04 2008, 08:47AM ]
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Marc, G0TOC
Sun Jul 20 2008, 07:02PM
Marc, G0TOC
Registered Member #162
Joined: Fri Apr 04 2008, 11:34PM

Posts: 2
Hi Paul, apologies for the late reply, but many thanks for your advice and kind offer. I have, as an interim measure made a 6-turn common-mode choke balun using a CD spindle case as a former. However, I realise that after not too long, UV will have a damaging effect on the plastic. If your offer remains, I would like to acquire the clamp-on ferrite's that you mention in your message. Please contact me directly so that I can arrange for their collection.

Regards, Marc G0TOC.
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Paul, G4CLJ
Wed Jul 23 2008, 08:44AM
Paul, G4CLJ
Registered Member #337
Joined: Wed Apr 30 2008, 03:05PM

Posts: 10
I will put them in the post for you, Ive a shed full hi.
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