rf choke advice

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in2media
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rf choke advice

Post by in2media »

theres many of articles and advice on ugly baluns or rf chokes, but i find so many just complicate things. just watched 4 or 5 videos on youtube and feel my head is just about ready to explode.
one says 15 turns of rg213, one says 12 turns rg58, some say do 2 coils, many say 5 turns of any coax..

my question is
i want to set up my superstar 3900 and antron, ive got rg8 mini as my main run to radio from antenna, im thinking of using rg213 for the balun
would this be ok?
how many turns?
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henry
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Re: rf choke advice

Post by henry »

Hello !

5 turns 10cm diameter. (Rg213)
With the antron, its best to place the RF-choke with some distance from the feedpoint
say a feet or more...
google g3txq for accurate information

Hope it was of use !
kind regards

Henry
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kr0ne
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Re: rf choke advice

Post by kr0ne »

henry wrote:5 turns 10cm diameter. (Rg213)
I think that's pretty much the minimum bend radius of most standard RG213 cables and is less than some...

If it were me, I would use something thinner and lighter than 213 to make a choke. But have you tried it without?
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bigpimp347
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Re: rf choke advice

Post by bigpimp347 »

was always told 8 turns over a 6 inch diameter..

but why do you want to ??
we never bothered 30 years ago, or even 20 years ago, and i think even 10 years ago not many bothered..
so why all this concern about choke, and baluns and such ??

if you really needed one it would have said it from day one in the instructions....surely ??
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henry
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Re: rf choke advice

Post by henry »

HI !

20/30 years ago the RF choke certainly wasn’t that "popular".
But more things have "changed". Power for instance.
30 years ago it was really something if you were running 100 Watts
These days it’s rare to find someone who doesn’t have 100 Watts.
And perhaps that power thing is why it has become a bit more known.
As with QRO your have to prepare (or be aware) for CMC

I’m looking at it more or less like a safety belt.
You probably won’t need one....but just in case.

And there are plenty of cases where a RF choke has "helped"

Especially with "unbalanced" antennas like the EFHW (Anton 99) in high power situations.

Why bother ...well why not?
You might not have common mode currents, but just in case you do...and they are causing issues..Better be safe than sorry.

I wouldn’t go spreading around too much those other diameters/turns.
Most didn’t do they’re homework; sites like ham universe unglybalun etc are terrible.
Guys like G3TXQ on the other hand did

Kind regards,

Henry
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RadioPixie
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Re: rf choke advice

Post by RadioPixie »

I agree with Henry. Times have changed and power levels have gone up.

Also think of a lot of problems that can occur with a HF radio (including 27MHz) installation, that may stem from CMC (common mode current). SWR problems, TV/radio/hifi interference, RF feedback etc. These problems were there in the 70's and 80's but wasn't understood enough by CB'ers (and many a hamateur). Also more recent interference to CB/Ham reception increases the need to be more precise.

Antron 99 EFHW (end-fed half wave) antenna is prone to cmc, as is other antennas. One solution is the ground plane kit to reduce cmc on the coax. May be a reason behind this popular accessory?!

If you look into the theory of the EFHW, often it is recommended to have a short counterpoise. Once again for RF issues as well as matching. May be this is the reason behind the Hy Gain silver rod with the little diddy radials.

A theory I have: Another issue with the modern installation is the lack of earthing. Once a radio installation had big "boat anchors" in a shed with a direct lead to RF earth. Now equipment is smaller, less bulky, in a flat apartment up in the air with inadequate RF earthing, therefore an increase in problems. Not saying in such a situation this will occur, but simply some factors to consider.

Talking about the 80's, there was an antenna that was based on a 1/2wl centre-fed dipole made by GAP. It was a 1.5m long top section with a base loaded coil, as per regulation in them days. It had a 2.6m long bottom section (from a silver rod) and the coax from the centre went though this section. At the bottom was a 5 turn (4 to 5in diameter) coax choke (ugly balun) to reduce the cmc!! I know as I was a silly teenager at the time and bought one :oops:

Not forgetting even in the popular book of that time, "The CB Bible", it recommended using a balun on a wire dipole (inverted v??).
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Re: rf choke advice

Post by ChrisCSL »

''say a feet or more''

Earlier today, this said 'a foot'.

Is that an English foot, or the well-known Dutch foot, or 'Een Voet', not used in Holland for a hundred years or more?

Also: how have you suddenly learned how to use - and not use - the Saxon Genitive so accurately in the last 24 hours?
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mattltm
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Re: rf choke advice

Post by mattltm »

You may find this useful...

http://www.karinya.net/g3txq/chokes/
"Spooky action at a distance."
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