Bill, FWIW, I'm using 30 turns of 9913 coax close wound on a length of 8" ID
PVC tube. Works very well for me.
Jim / W6JHB
On Wednesday, Oct 2, 2013, at Wednesday, 10:04 AM, Bill Stewart wrote:
> Tnx Richard for the info.
> I've got a small collection of doorknobs and will ck to see
> if I can cobble up that much capacitance. I only run less
> than 200 watts output, so won't need any HV vacuum caps. From
> what I read, the inv L can be fed directly with 50 ohm coax, but
> no mention is made of what the swr might be. In an open field,
> made per the book, the swr might be much lower than mine. My ant.
> has a lot of tall pines close to it.
>
> I thought the "Q" of the antenna was not vry good since the SWR
> curve is vry broad.
>
> The choke you mention..is it made with coax coiled up at the feed
> point..if so, any idea how many turns & coil dia?
>
> Last night I made contacts into Minn, NY and PA, with 589 reports..
> running a Viking 2 at 100w output. Oh, and receiving seems to be
> good too...W1AW overloaded my SX-71 and other stns were cmg in
> good as well...so some success.
>
> Tnx, 73 de Bill K4JYS
>
> ----- Original Message -----
> From: "Richard Karlquist" <richard@karlquist.com>
> To: topband@contesting.com
> Sent: Tuesday, October 1, 2013 6:14:12 PM
> Subject: Re: Topband: 160m Inverted L High SWR
>
> On 2013-10-01 14:08, Bill Stewart wrote:
>> Good afternoon all,
>
>> The vert. section is
>> abt 55 ft & the rest is nearly flat horizontal. Total length is 130
>> ft/6 in. I am using a
>> 4 wire c-poise abt 9 ft high of which none are directly under the
>> horiz. section.
>> Each wire is abt 135 ft long. The min. SWR is abt 2.9:1 at 1833 khz.
>> The SWR
>
> This is exactly what you would expect. It corresponds to a drive
> impedance
> of something like 18 ohms, about right for a top loaded 55 foot
> vertical.
>
> You will need to put a shunt capacitor of about 2400 pF across your
> coax,
> and then increase the length of the L until you get the resonance to
> 1833 kHz.
>
> I currently have a top loaded 60 foot vertical and this is very similar
> to my situation. You will find that after proper matching, the
> bandwidth
> is really quite narrow, indicating reasonable efficiency.
>
> You should probably add a common mode choke at the feedpoint if you
> don't already have one.
>
> Rick N6RK
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