Bob. Your impedance is likely in the 25 ohm range, so you would need a 2:1
balun. A 4:1 likely overshot the 50 ohm mark. I'd just go with a hair pin coil
between the vertical and ground. About 10 turns and maybe 3 " diameter. Spread
coil to change match. Should get you to 1:1. Kenny K2KW
Sent from my iPhone, Kenny
> On May 30, 2015, at 12:00 PM, topband-request@contesting.com wrote:
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> Today's Topics:
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> 1. vertical balun (Bob Kupps via Topband)
> 2. Re: vertical balun (shristov)
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> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 29 May 2015 21:13:50 -0700
> From: Bob Kupps via Topband <topband@contesting.com>
> To: topband <topband@contesting.com>
> Subject: Topband: vertical balun
> Message-ID:
> <1432959230.96755.YahooMailBasic@web125001.mail.ne1.yahoo.com>
> Content-Type: text/plain; charset=us-ascii
>
> Hi we have a 30m top loaded monopole with the feed point about 2m above a
> large ground radial field. Right now we are feeding it through a 4:1 balun
> (not a unun) with 12.5 ohms on the balanced side, and the SWR is 1.4 with no
> matching network. Is this balun acting as a common mode choke? Do we even
> need a choke? Would an unun be better?
>
> Thanks 73 Bob HS0ZIA
>
>
> ------------------------------
>
> Message: 2
> Date: Sat, 30 May 2015 06:40:14 +0200
> From: shristov <shristov@ptt.rs>
> To: topband <topband@contesting.com>
> Subject: Re: Topband: vertical balun
> Message-ID: <fb2e9fb35082.55695b4e@ptt.rs>
> Content-Type: text/plain; charset=us-ascii
>
> Bob Kupps wrote:
>
>> Right now we are feeding it through a 4:1 balun (not a unun) with 12.5 ohms
>> on the
>> balanced side, and the SWR is 1.4 with no matching network.
>
>
> You should get quite a reasonable SWR with no matching at all.
> A good high-impedance common mode choke is recommended.
>
> 73,
>
> Sinisa YT1NT, VE3EA
>
>
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> End of Topband Digest, Vol 149, Issue 17
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