Topband: Toploaded vertical - SWR

[Grant Saviers]

Several suggestions, some already mentioned -

Although your swr plot shows you are in the ballpark for resonance, the 
feedpoint resistance is very low, as mentioned likely 12 to 20 ohms.  A 
transmission line transformer stepdown will help a lot.  4:1 likely the 
best choice.  If parts are hard to obtain, parallel two 50 ohm coax 
cables 1/4wl long (measured electrically, considering velocity of 
propagation)  That will make a 25 ohm matching section between 50 ohms 
and 12.5 ohms which is a better match than 50 ohms.

The swr curve is broadband which says you need a lot more radials to 
reduce ground loss.  They appear to be buried or on the ground so 20 or 
30 more will make a difference, longer than 65' if you can but more 65' 
is better than a few longer ones.

Increasing the angle of the top hat appears to be possible, so that will 
decrease the shielding of the antenna by them and improve its performance.

Grant KZ1W

On 9/19/2018 9:36 AM, Herbert Schoenbohm wrote:
> An L network with a coil in series and a 500pf variable to ground might do
> the trick. You impedance of the antenna is to low and you need to bring it
> up.  You can also try extending the top hat wires by 20' each and see what
> difference that makes.
>
> Herb, KV4FZ
>
>
>
> On Tue, Sep 18, 2018 at 5:44 PM Ashraf Chaabane <ash.kf5eyy at gmail.com>
> wrote:
>
>> Hi all,
>>
>> I just finished setting up my vertical antenna for 160 in 3V8SF
>> location. It is 17m (55 ft) long with 2 top loading wires 12m each
>> (40ft), angle to vertical about 40 deg. I added 8 radials, 20m each
>> (65ft).
>> With no shunt matching, the SWR at antenna base is 3.2 and at radio side
>> is 2.8. Is there any way I can improve the SWR further?
>>
>> Photos of the antenna along with SWR curve can be found here:
>>
>> https://drive.google.com/drive/folders/1_3FsWZI3zdi56zz0LOiKNOmfgiWeN6yG?usp=sharing
>>
>> 73 Ash 3V8SS/KF5EYY
>> www.kf5eyy.info
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