[TowerTalk] Good vacation antenna

[David Gilbert]

The loss is the same (probably), but the current profile at the antenna 
is different (definitely).

Dave AB7E


On 7/3/2025 4:10 PM, Wes wrote:
> I'll confess some difficulty (probably my failing) in understanding 
> your point(s).  To try and simplify the situation to something my pea 
> brain may understand, let's use a toroid at either location. Now tell 
> me what the difference is.
>
> Wes  N7WS
>
>
>
> On 7/3/2025 3:39 PM, David Gilbert wrote:
>>
>>
>> Because whatever current is left after the loss in the tuner still 
>> makes it to the antenna but doesn't have a major portion of it 
>> compressed inside the coil where it matches and also suffers loss but 
>> doesn't radiate.  Radiated RF is a function of BOTH current and 
>> length.  If it was otherwise we'd all be using parallel tuned 
>> circuits with large coils on 40m instead of aluminum tubes and wires.
>>
>> Dave   AB7E
>>
>>
>>
>>
>>
>> On 7/3/2025 2:11 PM, Wes Stewart via TowerTalk wrote:
>>>    So you move the loading coil from the base of the antenna to 
>>> inside the tuner in the radio (with some coax in between).  How does 
>>> that affect the radiation efficiency/?
>>> On Thursday, July 3, 2025 at 01:57:33 PM MST, Jim Brown 
>>> <jim at audiosystemsgroup.com> wrote:
>>>> https://www.dxengineering.com/parts/cha-ss25
>>> That looks like a great solution, Dave! I strongly suggest against a
>>> loading coil for 40M, using a tuner built into the radio instead, with
>>> or without some top loading. Loss in short lengths of decent-size coax
>>> on 40M is pretty low, even with significant mismatch. An excellent 
>>> study
>>> in QEX about ten years ago showed that inductive loading at the base
>>> greatly reduces the radiation efficiency, because it's at the current
>>> maxima! The study included the construction of multiple configurations
>>> of loading, and very rigorous measurements.
>>>
>>> 73, Jim K9YC
>>>
>
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