[TowerTalk] 160 vertical question (Top Hat)

[Grant Saviers]

Jim's suggested tuning method works well for me to cover the entire 
band.  I short/open 3 series capacitors all the same value and can cover 
1800 to 1975 < 1.5:1 swr.  I use a transmission line transformer before 
the caps to match the 25 ohm resonance.

Now for some propagation to EU from suffering sevens land - Redmond, 
WA.  It's Unobtainium.

Grant KZ1W

On 2/3/2018 20:59 PM, Jim Brown wrote:
> I agree with both Grant and Rick, but with this caveat.  Current is 
> greatest near the feedpoint, and an inductor at the feedpoint is right 
> at the current peak. By contrast, current is least near the end of the 
> antenna. SO -- this is an important reason why top loading is better 
> than inductive loading. BTW -- there was an excellent piece of work 
> published 3-4 years ago studying the relative effectiveness of bottom, 
> center, and top loading of mobile antennas. The study included 
> extensive measurements of field strength, which confirmed that top 
> loading was significantly better, AND that NEC failed to accurately 
> model inductive loading.  As I understand it, NEC models the inductor 
> is as a lumped component, so fails to accurately take into account 
> phase shift across it.
>
> Another technique that is often used for matching is to make the wires 
> much longer than resonant (that is, resonant around the top of the BC 
> band), so that the feedpoint Z is 50 +jX ohms (that is, inductive) on 
> 160M, and tune the capacitance out by adding a capacitor of equal 
> value in series.    NEC can easily model this.
>
> 73, Jim K9YC
>
> On 2/3/2018 7:51 PM, Grant Saviers wrote:
>> Top loading is a winner to increase antenna efficiency.  I agree that 
>> EZNEC is essential since umbrella (slanted) wires have less effect 
>> than a flat top hat and also tend to shield the antenna a bit. The 
>> model needs the segments aligned in each element.  Trig or use AutoEZ 
>> to figure that out.
>>
>> There are a couple of articles worth reading on Rudy Severns web site 
>> antennasbyn6lf.com
>>
>> This article is for top loaded verticals for the new LF bands but 
>> covers the principles well
>> http://rudys.typepad.com/files/chapter-3--1.pdf
>>
>> My T is 10' at the base elevated radials, 85' to the top, and 33' or 
>> so each side, resonates at 1820, 25 ohms.
>>
>> Grant KZ1W
>>
>>
>> On 2/3/2018 17:44 PM, Richard (Rick) Karlquist wrote:
>>> You should really model this on EZNEC.
>>> Having done this many times, I can say
>>> that the length of the vertical plus the
>>> length of one of the top wires should be
>>> about 120 feet to hit exact 1830 resonance
>>> without a loading coil.  However,
>>> there is absolutely no compelling reason why
>>> this is necessary.  A loading/matching coil
>>> is far more convenient if you keep the wire
>>> length to 25 feet.  Therefore, it should
>>> never be necessary to put it up and down a
>>> bunch of times to get it "just right".  There
>>> is no "just right" with respect to the antenna
>>> proper.  Use the taps on the coil to do the trimming
>>> to make the system just right.  This has been
>>> discussed many times on this reflector.
>>>
>>> Rick N6RK
>>>
>>> On 2/3/2018 5:20 PM, Bill via TowerTalk wrote:
>>>>
>>>> Planning on putting up a 160 vertical, but of course a 1/4 wave 
>>>> vertical is out of the question here in HI since we have a height 
>>>> limitation.
>>>>   Here's the question:  I'm putting up around 50 feet of 3 inch 
>>>> aluminum tubing  (left over from various antenna takedowns).  I 
>>>> plan on putting up on top of that around another 10 or 15 feet of 
>>>> smaller diameter stinger for a total height of around 60-65 feet.  
>>>> I obviously need to make up for the lack of height and I was 
>>>> planning on making a top hat of four wires coming down from the top 
>>>> of the antenna at around a 45 degree angle.  The problem is how 
>>>> long to make each of those wires.  My guess is around 25 feet based 
>>>> on my past experience in making Tee-topped 80 meter verticals. 
>>>> However, it is only a guess and I don't feel like yanking the 3 
>>>> inch pipe up and down a bunch of times to get it just right.
>>>>   I know some trimming will be necessary since this is not an exact 
>>>> science.  I just need an educated guess for where to start with the 
>>>> length.  Any ideas?
>>>>   Bill K4XS/KH7XS
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