I once constructed an emergency 160 meter vertical out of a 60 foot mast
made of aluminum irrigation pipe along with a top hat consisting of two
120 foot "umbrella wires" that I cut to length to make resonance at
1830. I guess you could call that a "240 foot" top hat. It of course
had a very low drive impedance that I matched with a shunt capacitor.
It worked pretty well over the limited bandwidth that was possible,
because I had it over a very effective ground screen. This sort of
thing also has a 2nd harmonic resonance in the 80 meter band, but it is
"voltage driven" meaning the drive impedance is 1000's of ohms. I have
also put that kind of antenna on the air on 80 meters using some
breadslicer air variables. Nothing mysterious about these antennas.
---
Rick Karlquist
N6RK
On 2022-12-19 09:01, john@kk9a.com wrote:
> I was also trying to understand the 300 foot top hat. I have never seen that
> even on top band. It would be easy to model to see where it's resonant.
>
> John KK9A
>
> Stan Stockton K5GO wrote:
>
> 350 feet is about 5 quarter wavelengths at 3.8 MHz. Quarter wavelength is
> about 65 feet or so. If that thing is really 350 feet long you should see
> resonance at about 700 kHz, in addition to every odd multiple of a quarter
> wavelength. Was there a typo or is this really an inverted L that is 350
> feet long?
>
> Stan, K5GO
>
> Sent from my iPhone
>
>> On Dec 19, 2022, at 2:57 AM, w5jmw at towerfarm.net wrote:
>>
>> Hello all.I have a t antenna.50ft vertical and roughly 300 ft ntip to tip
>> horizontal.I get a nice drop and resonance at abt 3.8 mhz.Is this weird
>> resonant point normal??I would think it would be lower.I have another at abt
>> 2.2 but almost a 3-1 swr..Normal ? I have used an inverted l before and
>> resonant was abt right with a 1/4 wave length..thanks..john
>
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