Topband: Broadband Inverted L

[Herbert Schoenbohm]

And in some cases where the bandwidth is clearly excessive from normal 
the closer you are may be closer to a dummy load at the end of the 
feedline...if you care to look at it that way.


Herb Schoenbohm, KV4FZ


On 11/20/2014 6:52 PM, Tom W8JI wrote:
>> A few years ago I put up a temporary 60 foot vertical over
>> my 230 foot diameter ground screen.  It was top loaded with 2
>> "umbrella" wires sloping down.  The bandwidth was MUCH
>> narrower than your 65 foot vertical.  IIRC, the 3:1 VSWR
>> bandwidth was less than 50 kHz.  The feedpoint impedance
>> was about as predicted by EZNEC over a perfect ground.
>> IE, very low.  It got out really well in contests
>> (anecdotal "data").  If you are seeing a bandwidth broad
>> as a barn door, it can probably only be explained by
>> substantial ground losses.  I understand you can't get
>> a ground like I have, do the best you can and get on
>> the air.
>
> We have to be very careful.  Bandwidth of an antenna system is not 
> just related to loss resistance. bandwidth is also related to the 
> ratio of applied energy to energy stored in and around the antenna, or 
> reactance in the loading system. Bandwidth can go all over the place 
> even without losses going opposite of what we think.
>
> For example, a 60ft vertical of #14 AWG wire over perfect ground and 
> virtually no loss can have a 3:1 bandwidth of 100 kHz when hat loaded.
>
> The same antenna coil loaded with a coil, with significant loss, could 
> be less than 20 kHz wide.
>
> There are countless cases where an antenna with wider BW has better 
> efficiency, and countless cases where they have less efficiency.
>
> 73 Tom
> _________________
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